Welcome to my world, my world of turbos, tyre smoke, and tuning...
Tuning cars, driving cars, testing parts, and complaining about everything. It's my job, and a the majority of my non-work life too...
I like Holset turbos, and not in the bizarre bias or weird belief way a lot of car people like certain things, I’m not like that. I like them because, provided you can source them for the right price, they’re, in my book, and my book is pure fact and no BS or unproven info, the best overall value turbos you can buy, when you consider power, reliability, spool, initial cost, and repair costs.
The thing is, everyone knows I know Holsets well, and because of this I seem to get about 10 questions a day about them, most of which I’ve been asked 100 times before, and this has happened for years, probably over a decade now.
Having said this, I still also constantly see some right bullshit and misinformation about them from other people too, most of which are people with zero experience of them, and unfortunately these days, from certain sellers of them too.
So, to help you guys, and to hopefully reduce the massive amount of questions I get and especially to help reduce the amount of BS I see about them, I’ve decided to make a guide to Holsets and using them on your car...
(Apologies for any minor typos or grammar issues, but I've done this for you lot for free so give me a break lol)
Who are Holset anyhow?
Holset are a UK turbo manufacturer, one of the oldest and biggest on the planet, and have been owned by Cummins for a long time.
They supplied turbos to the tuning scene as far back as the 1970s, and have even supplied turbos for Formula One and Indy Car winners too, but on the whole don’t get actively involved in the aftermarket tuning scene.
The reason for this is simple- They’re a massive company and the commercial market is literally millions of times bigger and more profitable, so they generally leave the tuning scene to the smaller brands.
I personally first heard of them in the late 90s early 00s, and initially thought they were a Scandinavian turbo brand, as I purely saw Holsets fitted to big power cars in Scandinavia, cars making more power than I’d ever seen the same engines make in the UK. But no, they’re actually based in Bradford, but have factories all over the UK and in fact the world- Practically every continent has at least one Holset production facility. Holset factories I can think of off the top of my head are in the UK, USA, Brazil, India, and China, but I’m sure there’s more.
Most turbo manufacturers have worldwide production too, with Garrett having Romania, China, USA, Japan, and many more.
Most are oil cooled, isn’t that a problem?
In a word, no. Water cooling on journal bearing turbos serves zero purpose on a performance engine, and even with a BB core the purpose it serves is debatable, and almost all true race turbos with BB cores (WRC cars etc) are oil cooled only too. All water cooling is for on production cars with long gaps between oil changes is to stop the oil in the core overheating, carbonizing, and gradually blocking up the turbo oil system, when owners shut the turbo off immediately after hard use with the turbo still red hot. This is the reason turbo timers exist and why most of us already know you should at least drive the car off boost for the last minute or so before you switch off.
But they’re not ball-bearing, doesn’t that make them spool slower?
No. ‘Ball bearing helps spool’ is pure sales talk in reality. Even the owner of Xona Rotor admitted this HERE. There’s no friction regardless of bearing type with the engine running as there’s basically no contact; it’s all floating in pressurised oil. Don’t get me wrong, there is a small theoretical advantage, but this is tiny versus the actual things that affect spool on a turbo, ie wheel and housing design, not to mention all the external factors (manifolds, exhaust, mapping, etc etc) which all have a huge effect.
The main advantage is they can take higher thrust loads if all else is equal. Unfortunately, all else isn’t equal, but that’s a whole other story. Basically, don’t worry about it.
Aren’t they ‘old fashioned laggy truck turbos’? My mate said they were...
This is a sure-fire sign of someone who’s talking total shit, either because they’re talking about something they know nothing about, talking from experience of a bad setup, or, which is quite common with tuners- Talking shit about them as they sell a different brand so don’t want anyone to buy one.
Fact is, commercial turbochargers, for any given age, tend to be some of the most hi-tech on the planet, as long as whatever technology doesn't affect long term reliability and is actually a true benefit rather than a sales tactic, as efficiency and reliability is more important to the commercial industry than anyone else, and will pay a far higher price than anyone else to get the best too.
Certain things they won’t have if it’s not needed and sacrifices reliability, but generally, for their age, commercial stuff make a lot similar age tuning parts look very low tech to be honest.
Having said that, of course a typical Holset isn't THE top technology, not at all, but the good ones are right up there, and when it tends to cost 50%, sometimes 25%, of the price of others, but performs almost as well and often lasts longer, it's no surprise they're popular for people for people without unlimited budgets, who know they can spend the saved money better on other more important tuning parts.
Aren’t they all massive?
No. Holsets exist from tiny T2 size ones good for about 250bhp to giants good for about 10 times that. But as the most common applications we see are from large commercial vehicles, plus the fact most people use big ones as they want big power, and famous cars tend to be the big power big turbo ones, make the larger ones far more common than the smaller ones. In reality, it’s the middle sized ones that are most common, the REALLY big ones are rarer than the small ones!
What do the letters mean after the name?
Like, some are HX35, some are HX35W etc?
I won’t bother talking about the earlier Holsets, but for he HX and HY series, W means internal wastegate. G means water cooled (Because most commonly used on compressed natural gas fuelled engines), and V means a variable geometry turbine.
For the newest range, the HE series, W still means internal wastegate, but WG is also used. V still means VGT, but VE is also often used, which means an electronic actuator for the VGT (but it can be used with a mechanical actuator still). Some HEs are called FG, which is non-wastegated housings, but some will have nothing.
My friend has a HX35, and I have a HX35.
His works great and mine is shit, why?
This is a common one, and happens on all types of turbos, but especially Holsets, and that’s because the name is simply a VERY vague description of the turbo type, and there’s countless variations of each. If I remember right there’s over 650 variations of HX35 alone!
HX35s all tend to have similar turbine wheel sizes, but even then is a few small differences, but can have very different compressors good for over 100bhp difference in peak power, and countless different turbine housing specs, from too small for most cars to way waaaay too big.
All the name will do is give you a rough estimate on the turbo size- Buying a car just because it’s a HX35 or whatever is a massive, stupid, mistake.
Even if you have the EXACT same turbo, that sure as hell don't mean two engines will perform the same! Mapping and almost every aspect of engine spec will massively affect both spool and power, far more than what turbo is fitted will, and SO many engine setups have terrible setups that aren't making the most of the turbo fitted.
If your turbo is performing worse than you expect- It's almost always you or your mappers fault!
What A/R size is my Holset turbine housing?
Holset don’t use A/R, they, like Mitsubishi, KKK, Trust, and others, use cm2 to measure turbine housing size.
A/R and cm2 isn’t directly comparable, cm2 is a static measurement, A/R isn’t, but you can still get pretty close if you want to compare. On a HX35/GT35 sized turbine wheels, 12cm is generally accepted to be about 0.89 A/R, but the larger the turbo the smaller A/R any given cm2 would be the equivalent of, with 14cm generally being considered to be just A/R 0.80 on GT40/HX40/S300 sized turbine wheels, and conversely, on a tiny turbine a 6cm housing could still be the equivalent of A/R 0.80.
Because of this use your common sense, use your eyes, and do your research. A 25cm HX55 might sound like a super huge housing when you’re used to 9cm housings on HY35s, but a HX55 is practically twice the size and a 25cm housing is actually not that big.
You can use the housing sizes on other stuff as comparisons too. With most Subaru turbos using cm2, and Mitsubishi Evo ones also, you can compare those to the similar smaller Holsets.
And for bigger ones, well the famous Trust turbos used on countless big power Japanese cars used cm2 as well. The T88 34D, a 1000bhp capable unit, like an older fashioned version of a HX55, and often seen on Skylines, Supras, and RX7s, tended to be a 22cm housing, as was the 38GK version. The Trust T78, a 700bhp turbo, so HX40/HX50 size, but older fashioned, was generally 17 to 24cm housings. The Trust T67 turbo, similar to a HY35 in capability, but again, older design, also had similar housing sizes, 8cm and 10cm most commonly, but 12cm and 16cm was also used. Even Trust’s version of the TD04, good for ~300bhp, used a 8.5cm housing.
There's a common list of A/R to CM2 that goes around the internet, and it's spoken about and published by people who make out they're experts in the field, but IMO it hints at how clueless they really are, and it says this...
6 cm2 = 0.41 A/R
7 cm2 = 0.49 A/R
8 cm2 = 0.57 A/R
9 cm2 = 0.65 A/R
10 cm2 = 0.73 A/R
11 cm2 = 0.81 A/R
12 cm2 = 0.89 A/R
14 cm2 = 1.05 A/R
16 cm2 = 1.21 A/R
18 cm2 = 1.37 A/R
21 cm2 = 1.61 A/R
NO! Fuck no. As said, A/R vs CM2 totally depends on the turbine size, and the above is only about right for TD04 sort of size turbines.
In REALITY, it's more like THIS...
HE221W- 6cm- 0.47, 8cm- 0.60, 9cm- 0.68
HX35- 16cm- 0.98, 14cm- 0.90, 12cm- 0.80, 10cm- 0.65
HX40- 18cm- 1.05, 16cm- 0.92, 14cm- 0.85
HX52- 16cm- 0.85, 13cm- 0.73, 11cm- 0.60
HX55- 28cm- 1.42, 25cm- 1.26, 19cm- 0.96, 16cm- 0.78, 14cm- 0.71, 12cm- 0.62
And obviously, any turbos that are in between sizes of the above for their turbines, so HY35, HX32, whatever, you can extrapolate from there obviously...
Can I use the internal wastegate?
On a diesel, yes, no problem. On a petrol, well it’s debatable. On the smaller turbos yes, defo. But for bigger ones, personally I’d not take the risk as they’re pretty small and you could/would suffer with boost creep. But oddly I’ve seen people use them, even on HX35s and HX40s, with perfectly good success; but I’d not take the risk, just go external.
As a side note, the 'G' versions, ie the water cooled ones normally fitted to CNG fuel engines, often have a VERY large internal wastegate- They MAY be perfectly fine to use on a petrol car without boost creep, but I can't confirm. Certainly better than most!
My manifold is single scroll but the turbo is twin scroll, can I still use it?
Yes. Fitted to a twin scroll manifold will help spool, 500-1000rpm faster on average, but you can use a twin scroll manifold on a single scroll manifold no problem. BUT I’d highly recommend you port match it to suit, including smoothing off the divider so the exhaust gas isn’t hitting a flat surface, which is bad for both spool and power.
When will the turbo hit full boost?
Well I’m going to talk about this in the next section, and this is a bit of a 'how long is a piece of string' question, but peoples obsession with ‘full’ boost is wrong. Some boost and full boost can be 2000rpm+ different from each other, especially on bigger turbos, but they’re often absolutely flying long long before full boost, and boost pressure itself isn’t a pure sign of power.
On my Skyline RB20 for example, I originally had a Garrett GT2871R, and swapped to a Holset HY35 based turbo, which is good for about 150bhp more, a much bigger turbo. The GT2871 was at 15psi by 3500rpm, by then the HY35 based turbo was at about only at 8psi at the same rpm, but still pulling MUCH harder despite less boost. And while full boost (23psi or so) wasn’t until 4000rpm, it was making positive boost and accelerating nicely well under 3000rpm.
So who cares if your turbo isn't at full boost until 5500rpm if it's pulling hard as hell even at 3k? Not me!
My turbo's meant to be good for up to 600bhp, but I only got 480, that’s shit?!
That’s nothing to do with Holsets, that’s not even a turbos fault, that’s your fault for not understanding turbos and turbo sizing.
A turbo may be able to hit 600bhp maximum on the right engine, but without enough boost, or if you fit it to an engine far too big or with poor airflow, you’re not going to hit the peak numbers, possibly not by many hundreds of bhp.
This is the case with all turbos of all makes, in fact it’s worse for many such as these new Garrett turbos with tiny turbines and big compressors, so you need to know what the hell you’re doing.
The less boost you want to run for any given power, the bigger the turbo you will need.
The bigger the engine you have, the bigger the turbo, especially the turbine side, you will need for any given power.
The higher the rpm you plan to run, the more turbo you will want, more turbine especially, for any given capacity too.
HX35s and HY35s for example- Both are well proven at 600bhp on cammed 2ltr engines at 30psi+ boost. But go up to about 2.5ltr and I don’t recall seeing anyone manage more than 550bhp with one.
Honda engines that rev like fook is another example- You'd want to run a HX35 bare min on even a mild engine combo looking for barely 400bhp, purely as you've got an engine that wants to make peak power at best part of 8000rpm.
How do I find out what the spec of a Holset turbo is?
Well, that’s not easy. This is the main reason, unless you’re a geek like me who can spot a spec from a few pics, you’re better off buying from a proven specialist like Compressor Racing who gives you the detailed spec with every advert.
In more recent times more and more sellers of Holsets have cropped up to jump on the bandwagon, and to be fair some of the pure lies some say to get a sale boils my piss. Beware, massively.
As already said, there’s literally hundreds of variations of each kind of Holset, so a name means little, and even the part number won’t help much as Holset themselves won’t help you, and details of components aren’t publicly available. Dealers have a part number database, but they guard it like their lives depend on it, and even this doesn’t have details like wheel and housing sizes; more of a use as a cross reference than anything else.
The main thing you can do, aside from a general estimation from what it is, ie HX35, 40, whatever, and this is usually the most important factor as generally modern Holsets are all good wheel specs, is knowing what turbine housing size you have.
If you look just inside the turbine inlet flange, you’ll see a number, 7, 12, 25, whatever. That’s the turbine housing size in cm2. If you can’t see that number, you usually can read it on the outside as a combination of the other numbers. Usually a number printed after the main part number.
I’ve got a T4 flange Holset, but the bolt holes don’t quite line up with my T4 manifold flange?
That’s because most Holsets, in fact most OEM T4 flange turbos, use T4i or T4 International, which is almost the same, but the bolt holes are like 3mm out. I never understand why people worry about this as it takes all of 10min to elongate holes ever so slightly so it fits, and many manifolds have bolt holes big enough that you don't need to at all, but some people do get confused...
What about the VGT variable geometry turbos?
Are they any good? Can you use them on petrol engines?
Can the VGT be easily controlled?
In a word, to all of these, yes, and in fact they’re arguable the best variable geometry turbos in the world. Why are they the best? Well aside from using the usual Holset wheels etc which are great, and the fact VGT can speed up spool by as much as 1500rpm, they solve the main issue that people are wary of when it comes to variable geometry turbos- The fact they’re fragile, suffering from sticking vanes and unable to take the high exhaust temps of petrol engines.
Well Holset VGT works differently to most, as instead of a huge number of moving parts and fragile vanes, the vanes are fixed and instead the main body inside the turbine housing moves up and down to change the effective housing side.
This design change makes them far more robust than usual variable geometry turbos, to the extent it’s very rare to see the VGT system fail unless it’s due to a serious failure that’s also damaged the turbine wheel, and in these cases even a conventional turbo would have the same issues.
Does this mean they can be used on petrol engines? Well yes. It’s still rare, but has been done many times in the USA, and I’ve seen these turbos on 4G63s, 2JZs, Saab 4cyls, and even 13B rotaries. I helped build a Mercedes V8 using a Holset VGT turbo in fact, check that out HERE.
Controlling them is pretty easy too, but you’ve got a few options. There’s two kinds of Holset VGTs, ones badged as ‘V’ and ones badged as ‘VE’ but when it comes down to it things are similar. ‘V’ ones are the older style and intended from the start to be operated with an actuator. Just like most diesel actuators, they are vac actuators, but it doesn’t take a genius to change them for a pressure one, and in fact I’ve seen someone cut the top half (and half the valve!) off a cheap external wastegate, and weld it to the actuator rod, to make a very cheap but effective pressure actuator for one of these turbos that fitted all the OEM mounting brackets.
The most complex, maybe overly, but it is very clever, was the guy who used the VGT turbo on the Saab 4cyl. He used two actuators joined to a central adjuster wheel (I can’t think of a good word to explain it lo), one a vac one, one pressure, so while the pressure one opened it as normal, the vac one opened it slightly when off throttle and at a cruise, lowering cruise EGTs and increasing fuel economy- Overkill for most performance applications, but very clever!
For what it’s worth, despite using a very big VGT turbo, he had no issues spooling it mega fast and if I remember right found that he only needed to set the VGT to open by about 7psi, and beyond that it spooled super fast even with the VGT fully open.
You don’t even need an actuator, and in fact many don’t. One of the most effective ways of controlling a VGT, and is in fact a lot of OEM ECUs use this as part of the VGT control strategy, is to base it on pre-turbine backpressure. So as backpressure increases, the VGT turbine opens up to keep it in check at a sensible level. This is done in motorsport a lot too with conventional turbos, as it’s a very good idea, and something that would be done more often if cars had pressure sensors in the exhaust manifold etc. In fact you can see Ferrari doing it with their Formula One turbo engine HERE. Anyhow, this sounds complex, right? Well no, to do this is one of the most basic looking ways possible, so much so it looks like a bad idea, but done right works great, and that’s just using a spring. You simply are using a spring to hold the VGT in the fully closed position, and exhaust backpressure will, at whatever level the spring tension is, overcome the spring to push the VGT open. Of course this takes a little testing and trial and error, but it’s not tricky and we found the suitable spring rate almost straight away when we did the aforementioned VGT Mercedes AMG V8.
So, what about the ‘VE’ version? Well, the above options all work and are used, but as standard these are controlled fully electronically by a motor on the side of the turbo- E for electronic, see?
Anyhow, these electric motors, while expensive as hell to buy, work well, and while in OEM use are controlled the stock ECU, these days there’s loads of programs and hardware which allows them to be controlled easily.
BUT what if your VE hasn’t got the control box? Loads don’t. Well as said, you just use the conventional methods, it works just the same and in aftermarket use I think there’s a lot more VEs using conventional mechanical VGT control than ones using the electronics!
The only thing you need to do is weld/tap/whatever a bolt or piece of metal or whatever to the VGT arm to allow an actuator or spring to be attached to it, because as standard it’s a small toothed arm. 2min job really, easy.
Final thing worth noting with these VGTs are most the HE341VEs and HE351VEs use a funny turbine inlet flange, rectangle, but longer than a typical T3 one etc. That would normally be a pain in the arse, but they’re so commonly used in the USA that companies make and sell the flange, like THESE FOLK...
Also, if you want a sexy billet HE341VE (basically a billet VGT HX35), they’re available HERE.
'Hybrid' or 'Custom' Holsets-
To be honest, hybrid turbos made from Holsets are pretty rare, especially as the big draw of Holsets is they’re so good, and well-priced, as standard, so there’s not a lot of need to make hybrids.
Having said that, they do exist and tend to be pretty good.
I’m very sceptical of hybrids that don’t even use a Holset compressor wheel, as the big advantage of Holsets tends to be they make big power for any given compressor inducer size vs many other turbos, so changing to a bigger wheel of another brand may not be the advantage it looks, no matter how shiny and billet it may be.
One of the most common hybrids is a HX35/40, so a HX35 turbine side and bigger HX40 compressor. This is pretty easy to make as many HX35 and HX40 parts are all interchangeable, so you simply fit the correct spec (not all are compatible, but that's another story) HX35 turbine wheel and housing to a HX40 and job done. I was surprised to find from a friend’s car running one he lost around 700rpm spool versus a straight HX35 though. Holset themselves make what is really a HX35/40 with most (not all!) versions of the HE351 being just that.
Some of the best hybrids, in my eyes anyhow, are the ones that don’t mess with Holsets wheel combinations and just change housings to more useful ones. Things like the Bullseye Power ones that made HX35s direct fit to Mitsubishi 4G63 engines, Tim’s Turbo ones allowing them to direct fit Porsche 944s, and things like the Compressor Racing RS341 are good and well proven examples of this.
This is a weird subject, as people get really confused about something that’s not complex at all.
I see a LOT of turbos people legit think are genuine Holsets, despite not having a single Holset marking on them at all- That’s clearly not real. The exception to this of course is hybrid turbos using non-standard housings of course, but you should know that.
At the same time, I see a LOT of people where people question if it’s a real Holset, despite being covered in Holset markings etc. Don’t get me wrong, it’s ‘possible’ for fake ones to be covered in real branding, but in my experience of messing with, using, buying, and selling Holsets for over 15 years now, if it looks like a real Holset, it’s highly likely it is. The exception to this, well I don’t know for sure, but I’m sceptical, is Chinese sellers of what looks like legit Holsets. They may be real, some of Holsets biggest production facilities are in China, but I don’t like to take the risk when I can source them closer to home- Personally I won’t buy a Holset direct from China no matter how real it looks.
Who’s safe to buy off?
I think this can be summed up with “Any well proven company”. In the UK the Holset specialist seller from an aftermarket tuning point of view has always been Compressor Racing, they've been around for years, supplied thousands of Holset turbos to people.
On the other end of the scale, I have still been stung buying what was meant to be 'good used' ones from a certain Polish eBay seller who often has a lot of Holsets listed- In reality it was a badly worn one sprayed with silver paint to not look too shit in the pics. Mad thing is, he's still out there selling painted up old junk, and for barely cheaper than new ones either. Seems madness buying that shiz just to try and save a few quid.
Lately I've seen a few other overseas sellers promoting their Holset sales with some proper shady stuff. Half truths and flat out lies. And it's working too. Boils my piss...
What about the unusual flanges some Holsets have?
Quite a lot of Holsets have v-band compressor outlets and while most have v-band turbine outlets so easy to sort by just buying a v-band off eBay or anywhere, The Holset HX2* and HE2** series have 4 and 5 bolt outlets that look like Garrett T/GT/GTX2* outlets, but aren’t quite. And a few turbos, the HE341VE/HE351VE especially, have an unusual turbine inlet flange too.
A lot of people make a big deal about this, but in reality it’s very basic, and in the grand scheme of fitting a custom turbo setup to your engine, it’s even less of a big deal. Holsets are incredibly common in tuning, especially in the USA, so all parts are available.
For the 4/5bolt turbine outlets mentioned- You’ll find various sellers advertising the OEM outlets for pretty low cost, but generally these aren’t exactly high flowing and may well not suit your engine bay layout. You’ll also find various sellers (non-UK but that doesn’t matter these days) selling the plain flange, which is a way better idea as it allows you to knock up a custom downpipe to suit your car perfectly. But these days, with engineering shops and CNC machines on every street corner (ok not really, but they’re not uncommon), getting a custom flange made up locally isn’t exactly tricky either.
For the compressor outlet flanges- Again you can just buy the adapters from various places all over the world, even from Cummins UK you can buy them for about £65, but in all honestly most don’t bother. Many simply spend 10min with a Dremel or similar machining the v-band lip down to just be a small lip for a conventional silicone hose and Jubilee clip. And the other option, and to be honest what’s done on most turbo setups even if the turbo does have a normal hose fitment outlet, is just get whatever suits you welded on to the compressor outlet. Removing the housing is a 5min job, welding the perfect outlet for you on to the housing is a 10min job for a TIG welder, and getting this right no matter what turbo you have is usually better than having a compromised setup just to use the stock outlet.
Finally, while I've already covered this earlier in the feature, the turbine inlet flange- Almost all Holset are just the usual T2, T3, T4, and T6 flange, though many T4s are T4i, which basically means 2 of the 4 bolts are literally half a hole, ie a few mm, further out. Many manifolds have big enough bolt holes to take this in to account, but it’s literally a few mins with a grinder or similar to oval two of the holes slightly, so no big deal either way.
The most common turbine inlet flange issue is for the very common and popular HE341VE/HE351VE turbos. These use a rectangle flange, but it’s neither T3 or T4, but thankfully as they’re so common and popular in the aftermarket, plenty of companies in the USA sell these flanges, and even adapters to go from T3 or T4 direct to this flange.
There’s a huge range of Holset turbos out there, countless ones over the decades, and there are many hundreds, sometimes well over 500, variations of each version, but here’s the general lowdown on each kind…
The HX/HY series-
By far the most common type of Holset you’ll come across, and the equivalent of Garrett GT series, though in some respects actually more advanced and more capable.
HX20- According to Holset literature, the compressor, at least the biggest version, is good for 275bhp, making it similar to a Mitsubishi TD04, a turbo it shares a lot of components with. HX20s are very rare though, and I honestly don’t recall seeing one in my life to be honest, on an OEM or tuned engine...!
HX25- Again, this shares many parts with the Mitsubishi TD04 series, albeit bigger compressor and turbine wheels than the HX20, and is capable of around 290bhp. Usually internal wastegate, T2 flange, and often with a ported anti-surge inlet, it’s a good and very compact turbo, but rarely used in tuning still to be honest. You can consider all of these HX2* series turbos higher spec versions of Mitsubishi TD04s, and can use them accordingly. HX25s spool fast even on 1.6ltr engines, for example.
HX27- The biggest and most commonly used of the HX2* series, again very compact and T2 flange, it’s pretty much the equivalent of a Garrett GT28RS, and spools very very quickly even on 1.8ltr engines. Good for roughly 350bhp, it lives in the shadow of the more popular HE221W, which while slightly more powerful, is a similar turbo.
Check out the vid below of one fitted to a 1.8 20VT engine in a Mk2 Golf- It seriously moves for a little turbo!
HOLSET HX27 at 20psi- Mk2 Golf GTI
HY30- Honestly, I'm unsure about these, as they are very very rare, one of the very few I’ve never seen in person. They’re likely good for ~350bhp or a touch more on the right engine, as HYs normally have the HX version compressor and smaller turbine side, somewhere between HX27 and HX30, so it could well be a great turbo. Pics I’ve seen seem to show HY30s as T2 flange, but I’ve never seen one in person to be honest.
HX30- Quick spooling and compact T3 flange turbo. About the size of a Garrett T3, but certainly more capable and advanced than them. Good for up to 460bhp for at least one version according to Holset, but most versions you see available I'd personally say are capable of more like 360bhp or less. They are all T3 flange on the ones I’ve seen, from single scroll 6cm to twin scroll 12cm housing versions. They’ve often got an anti-surge compressor inlet, but not always, and there’s at least three different compressor wheel sizes that I’ve seen. Very fast spooling, I’ve seen 9cm versions spooling as fast as T28s on 2ltr engines, and making more torque for any given boost pressure too, though most don't make much more than about 350bhp.
Bigger turbine wheel than a HX27 or HE221 but generally capable of same sort of power levels.
Here's a YouTube video of a Golf GTI claiming 380 from a HX30, and it certainly doesn't look slow...
Golf GTI HX30 380BHP
HX32- Very rare turbos, but very good, and capable of up to about 500bhp, limited by turbine flow. These are in essence Holset built HX30/HX35 hybrids, as they use a HX30 turbine wheel and a HX35 compressor wheel, albeit often the smaller versions of the HX35 compressor. They come in various forms, from 12cm twin scroll housings to 6cm single scroll and everything in between. They’re almost all T3 flange but some T2 as well. Spool is very fast, somewhere between a HX30 and HY35, and while these have always been considered somewhat of a holy grail ideal turbo for tuned cars, they’re that rare that I’ve not seen a huge amount of results; mostly people saying they’re very impressed with theirs!
Here's some HX32 Videos below...
RB20DET with a HX32 in a C32 Laurel doing a pretty badass burnout
In-car hillclimb action with awesome turbo sounds of the above RB20 Laurel
Astra VXR with 12cm HX32 vs Supercharged Civic Type-R
Astra VXR with 12cm HX32 vs 371bhp Astra VXR
HY35- This is one of my favourites of the Holset range, proven good for as much as 600bhp on big boost well specced 2ltr and under engines, seen as much as 540bhp at 1.5bar on fairly stock 1JZs, and very fast spooling for a turbo capable of this much power too- People have seen full boost by just 3000rpm on well mapped and well set up 2.5ltr engines.
In the USA these are most commonly found with a 9cm single scroll T3 housing, and in the UK/Europe mostly found with a 10cm single scroll T3 housing, but in the grand scheme of things 9-10 makes very little difference either way.
Compressor wheel wise, they’re basically the 7blade HY35 compressor side almost always. Turbine wheel size, it’s half way between the HX30/HX32 turbine wheel and the HX35 turbine wheel.
The now pretty famous Compressor Racing RS341 is, for all intents and purposes, a HY35 variation, and as a comparison, I had a GT2871R on a RB20, and swapped to an RS341. The 2871 spooled faster, made 15psi at the same rpm the 341 made 7psi, BUT it didn’t matter, as despite about half the boost pressure, the 341 made the car pull noticeably harder, and once boost was at the same level it was like night and day; massively more power. So yeah, while these spool fast, with bigger turbos there’s a lot more to performance than simply what boost pressure it hits at what rpm.
HYs have become pretty thin on the ground lately, but they’re still out there.
Oh, and a 7cm T2 flange HY35 exists too, albeit damn rare. These have slightly smaller compressor and turbine wheels than the normal HYs, in fact it’s surprising it’s not called a HX32, but that’s the huge variation with Holsets for you.
Check out these HY35 YouTube videos below...
2.8ltr Saab V6 with a HY35 making 480@wheels (so well over 500 fly) on stock internals.
My old RB20 R32 Skyline with a Compressor Racing RS341 running 1.5bar...
FWD Mk2 Golf road car, 1.8 20V running a HY35- 10.4sec quarter mile at 135mph!- Likely 550bhp+
HX35- This is the best known and most common Holset on the tuning scene, and the equivalent to a GT3582R, with almost identical wheel sizes in fact. Spec for spec, same housing sizes, they actually seem to spool better- Have you seen a GT35 hit 25psi by 3500rpm on a 2ltr? I haven’t at least, but plenty of twin scroll HX35 setups have.
There’s an insane amount of variations of HX35s, 650 plus at last count. There are compressor inducer diameter sizes down to about 50mm (I’ve heard of smaller, but no proof), which would lower its power potential, but the most common ones, and the ones to go for, are the 54mm inducer 7 blade compressor, and the 56mm 8 blade inducer, both proven at 600bhp. There are rare 6 blade versions too, which theoretically should flow more for any given inducer diameter, and billet versions too, but seen no data that they’re capable of more.
Most have 82mm compressor exducer, but many later spec ones have a 76mm exducer, but it’s unlikely to affect peak power and seen no proof either way.
There’s a wide variety of turbine housings out there, but the best known one in performance terms is the 12cm one, though I’ve seen 6cm undivided T4, 8cm and 10cm divided T3, and many more. Generally 11cm to 16cm housings suit the majority of applications, with 11-12cm best for 2.5ltr and smaller engines, and 14-16cm best for larger engines. The oddball small ones, 8cm, 10cm, are great for spool of course, but don’t expect to be getting 500bhp+ from them, partly as the turbine won’t flow as much, but also because they tend to come with smaller compressor wheels too.
I’ve personally never seen a HX35 hit 600bhp on larger than 2ltr engines, but seen it on 2ltr and smaller engines many times, with the 4G63s in the USA hitting it most commonly, at 30-35psi. The most I’ve seen from 2.5-2.8s with HX35s is around 550bhp, and a little less on even larger engines.
Spool-wise, a 12cm on a 2ltr with a twin scroll manifold is well proven to see 25psi+ by around 3500rpm, which is fantastic for a turbo of this size. Using a single scroll manifold and a 2ltr I’ve seen more like 1000rpm slower spool, 4500rpm, but still no lag between gearchanges, and some, just not ‘full’, boost long before then. On 2.5ltr engines, the 12cm housing even with a single scroll manifold tends to be full boost by around 3500rpm.
Just to be confusing, there's a few 'HX35s' out there that aren't! They'd normally be called HX32s or HY35s really, but for some reason Holset called them HX35s! They had 35 sized compressors, but tiny HX30 sized turbines and 6cm or so turbine housings, often T4 flange. Awesome turbos, but not really HX35s!
This is a good YouTube video that shows spool with a twin scroll manifold and a 12cm housing on a well set up 2ltr engine-
HX35 on Mitsubishi 4G63 engine spool
HX38- “Oooh, a HX35/40 hybrid” I hear you say. Yes, but unfortunately the wrong way around! This, on every one I've ever seen, is basically a HX35 compressor side and the bigger HX40 turbine wheel. Pointless/useless for tuned cars unless you want low power for your capacity. Avoid.
HX/HY40V- I’ve seen these called both HX and HY40s despite the same basic spec, but this is the VGT version of the HX40. Generally tends to be T4 flange, and pretty much the typical HX40 spec, just VGT.
I’ve seen very little info on this turbo, BUT going by the video below, it has no issues spooling up even on an ancient spec 2.4ltr diesel engine, in fact this is cool as fuck!
Mk1 Ford Transit 2.4 diesel running Holset HY40V!
Effectively like the slightly bigger brother of the HX35. Good for up to 700bhp with the 60mm compressor inducer, though there are smaller compressors on many HX40s you see, with the 58mm is most common, and still good for 650odd. They come in T3 and T4 flanges, 14cm T3 is the smallest generally available housing, 16cm relatively rare but more common. Not a big step up in wheel sizes to the HX35, and the overall turbo size is pretty much identical too, so they're a good way of going another 100bhp over what a 35 can do without big changes to your setup.
Some badass engines run HX40s, as these videos show...
Audi TTRS engine race buggy making 700bhp with a HX40
BMW 4ltr V8 making 550bhp at the wheels at 0.9bar with a HX40
HX50- HX50s come in a very wide variety of wheel sizes, from only slightly over 700bhp capable, to some just as big as the biggest HX55 wheels; pretty much 1000bhp capable units. They have a variety of turbine wheels too, most somewhere between HX40 and HX55, but some being pretty much full HX55 size, making them essentially HX55 turbos albeit in a much more compact frame- HX50s are externally only about 2/3 the size of a HX55, making fitment easier.
The hardest thing with HX50s is finding them with small turbine housings. 17cm and 19cm housings are the smallest I remember seeing, but they’re rare, and around 25cm is the most common size. For a larger engine, 3ltr+, or a very high revving engine like a Honda, these big housings aren’t an issue, and a 25cm housing is still a quick spooling turbo on a 4ltr engine, but it does make it tricky to find quick spool housings if you’ve a smaller capacity engine.
My friend is running a HX50 67mm with a 25cm turbine housing on his half-bridge 13B Mazda RX7, and it's making 600bhp at relatively low boost with a powerband as good or better than similar cars on the same dyno with turbos that cost 3 times as much...
Check out some HX50 videos...
Honda Civic with B18 engine making over 920bhp on a HX50!
Toyota GT86 running a 4ltr 1UZ engine and a Holset HX50 at 15psi- Smoke machine!
HX52- Like a giant sized HX32 or HY35, the HX52 has the big boy HX55 sized compressor wheel, usually 65/66mm inducer, but a much smaller turbine wheel, smaller than many HX50 ones in fact, making for a very fast spooling turbo for its size.
In fact it's so fast spooling it's became popular on 1.8-2ltr FWD drag cars!
Unlike HX50s, HX52s always come with a small turbine housing, usually T4 flange, with 16cm the biggest most common size, 13cm being another and usually internal wastegate, and 11cm being the smallest and rarest; though I know of at least two variations of the 11cm housing, one T4i flange and one a weird flange. They take up more space than a HX50 as they have HX55 size compressor housings, despite much smaller turbine housings. Considering they’re good for the best part of 1000bhp when pushed hard on the right engine they spool fantastically well too- On a 2.9ltr, using a single scroll manifold, and the 16cm housing, 15psi comes at just 3750rpm- With a good twin scroll setup you’d likely take at least 500rpm off that, and then there’s the option of the smaller housings…!
I'd have no issue at all running one on even a 2.5ltr drift car, in fact I really wanna.
To make things even more confusing, in the last year or so of the HX naming scheme, Holset decided to badge HX52s as HX55s, despite having the small 70mm exducer turbine wheel and 11-16cm housings. So that's worth keeping an eye out for.
There's quite a few cool HX52 videos out there, and here's my pick...
HX52 16cm spool on a 2.9ltr VR6 engine and a single scroll log manifold.
HX52 16cm making 800bhp on a basic spec 2ltr 4G64 and cast manifold!
HX52 16cm on a M50 BMW engine sounding pretty damn awesome
HX52 on a SR20DET making 800bhp at the hubs
HX55- This is the equivalent of a Garrett GT42 or BorgWarner 9180, the HX55 is capable of around the 1000bhp mark when pushed hard, though I’ve seen a couple of people claim 50-100bhp more than that. Housing wise, the smallest you commonly see is a 19cm internally gated housing, and then there is 22cm and 25cm non-wastegated housings also quite commonly found, and while most are T6 flange, T4 versions exist.
Most HX55s have v-bands holding both the compressor and turbine housings on, but there’s a less common version with a bolt-on turbine housing, which I’ve seen 22cm and 25cm T4 flange housings for.
For their size they’re impressive bits of kit, and on 4ltr engines like 1UZs they make serious power from just 3500rpm on even with the biggest 25cm housing, which is well impressive for a turbo good for 4 figure power numbers!
To make things even more confusing, in the last year or so of the HX naming scheme, Holset decided to badge HX52s as HX55s, despite having the small 70mm exducer turbine wheel and housing. So that's worth keeping an eye out for.
Check out these HX55 videos below-
833bhp at just 1.5bar from a HX55 on a BMW M50 engine in a stunning E36 BMW
950bhp HX55'd 2JZ Soarer
R33 Skyline drift car running a stock bottom end 1UZ and a Holset HX55 25cm. 640bhp at the wheels at just 1.3bar, 600nm torque by just 3800rpm
HX/HY55V- As with almost all V/VE Holsets, the HX/HY55V is basically just the VGT version of the HX55, with identical wheel sizes and so on. They’re usually T4 flange, with some HY55 versions coming with a twin scroll inlet, despite the housing not actually being twin scroll.
This is the turbo we used when we built the 'boot mount turbo' E55 AMG I helped create for Compressor Racing a few years ago. Despite being mounted 12ft away from the engine, with the exhaust going through restrictive silencers pre-turbo, no heat wrapping, and loads more things that slow spool down massively, it was on full boost by under 3500rpm, which nobody would've imagined for such a huge turbo mounted in the boot if we didn't prove it!
Click here for the video of the rear mount turbo E55 AMG.
These beasts, while many only physically a little larger in external diameter to the HX55, are rated at up to 1260bhp by Holset, and with tuned cars out there running them and making anything from 900 to over 1200bhp, they're certainly not wrong.
Some of these I've had dealings with had directly interchangeable parts with HX55s, enabling hybrids much in the same was a HX35-HX40 hybrids, but I don't think that is the case for all of them.
Rather than waffling on, check out these YouTube clips...
Audi 5cyl making over 1200bhp with a Holset HX60!
RX7 making 900bhp at the wheels with a HX60
Volvo 850 making 950bhp on the dyno with a HX60
In car acceleration with the above Volvo 850- Insanely fast!
HX80- Usually found on medium size fishing boats and similar as an OEM turbo to their giant engines, most HX80s are practically dustbin lid sized units, but slightly smaller units that almost resemble (the still huge!) HX60s, and HX80s have been seen on 1600bhp+ drag 2JZs, 5ltr+ V8s, and even 6ltr diesels giving full boost by around 3000rpm, they’re surprisingly usable considering their huge size!
This Supra on Speedhunters is rocking one of the more 'normal' looking HX80s...
HX82- The big daddy. Basically a HX80 with an even bigger compressor, and just like the 80 it’s most popular in the extreme tractor pulling crowd. The HX82 is physically about the largest ‘normal’ turbo out there of any brand, as bigger things like found on trains and ships and similar might be turbochargers but they tend to be hugely heavy and bulky, and barely resemble turbos as we know them.
This giant size means they’re not only popular in tractor pulling, but have recently became the turbo to have for certain drag racing series where a single turbo allows a 200kg less minimum weight limit vs twin turbos, leading to world famous drag racers such as Larry Larson, Birdman, and Shawn Wilhoit, all going for heavily modified HX82 based turbos for their drag cars, and looking to make around 3000bhp!
HX83- This is an odd one, and while I don’t know a huge amount about it. The ones I’ve seen have been a giant version of a HX38. What I mean by that is they had no bigger compressor than a HX82 or even HX80, but an even bigger turbine side. Many I saw even had cast iron compressor housings, so would weigh a ton. I don’t recall ever seeing a HX83 in a tuned application, and if they’re all like the above ones I’ve seen, I’m not surprised.
HX85- I honestly don’t know much about these aside from they’ve got a very limited range of applications even as OEM, and they look much like the HX83 where the turbine looks huge without a particularly big compressor, 51cm turbine housings etc, making them unlikely to be chosen for any aftermarket use. The fact I’ve seen these for sale by tractor pull guys for far cheaper than HX80s, but also never seen one used on any tuned vehicle, even a tractor puller, suggests they’re probably to be avoided.
The Holset HE Series turbos
The HE series is the successor to the HX series, and while in the most part are the same basic turbos with either minor changes, or simply renamed, some versions have cool new technology fitted to them.
The main problem with the HE series is it makes the already vague HX naming system even vaguer!
In earlier HE series it was less of a problem, as the first digit was the general frame size, and the second was the general compressor size, so a HE211 and HE221 was the same basic size, but the compressor especially on the 221, was bigger. There’s a few examples of this on bigger ones, mostly VGT ones, where the compressor is fairly small for the turbine size, HE531 for example, but again, the numbers help signify that.
Unfortunately the newer HE turbos, things get super vague with turbos good for hundreds of horsepower different, all having the same name. HE200 covers all the small frame T2 flange turbos. HE300 covers everything from sub 400bhp to 600bhp+. What was HX30/HX32/HX35/HY35 and some HX40 turbos. HE400s cover what would’ve once been HX40s and maybe some of the smaller HX50s. HE500s are the biggest variety, as they not only cover all the HX5* range, but HX60s too, which are beasts!
But while names mean less than ever, the turbos are better than ever, and the HE series are all as good as the HXs, or better. Good times!
The Holset HE221W is probably the first of the HE turbos to become known in the tuning scene, and not surprising too, as it’s one of the best T2 flange turbos out there, a hugely efficient turbo for its size.
A replacement for the HX27 with newer (and slightly bigger) wheel designs, it’s proven capable of up to about 380bhp but fast spool even on sub-1.6ltr engines; in fact I’ve seen them used as twin turbos on a 700bhp 2JZ- It’s a great little turbo. It spools like a little TD04, with 7psi+ by 2500rpm or less on a 2ltr engine, but unlike most small turbos, is still efficient at big boost- It’s still on the compressor map at 3bar!
Even on a 2ltr Cosworth rally car using the tiny 34mm rally inlet restrictor that slows spool and reduces boost, it was capable of hitting full boost 750rpm faster than the original Garrett T3 (which is also capable of far less peak power). Not only that, but the engine made well over 400lb/ft at just 25psi boost, way more than other turbos make at the same boost, showing how efficient they are.
Common myth was they all had billet wheels, but that’s just not true, most don't in fact, and the cast wheel versions are to all intents and purposes just as good. Usually has a 6cm or 7cm turbine housing.
The HE211W is a slightly smaller version, the compressor map shows it’s capable of 32lb/min, ie about 320bhp, and seen them hit 25psi by 3000rpm and less even on a little 1.6ltr diesel. Most the ones I’ve seen have a 5cm turbine housing.
The HE200, well that’s generally one of the two above specs, usually are 211 spec, but could be either. Often the 211 version doesn’t have an anti-surge inlet, the 221 always does, but even that isn’t a sure way to tell, as the smaller ones do sometimes- I’ve owned anti-surge billet HE200s which had the 211 size wheels. They can come with billet or cast compressor wheels, and unlike the 221/211, don’t always come T2 flange; sometimes they’re all kinds of odd shapes!
There’s also a VGT version of these, which looks very promising for small capacity TDIs!
Here's a HE221W compressor map and some data from a HE221W on a 34mm restrictor Cosworth rally engine.
Here's a HE211W compressr map and a dyno graph from a old VW 1.6ltr turbo diesel in a Mk1 Golf running a HE211W...
One of the rarest, but if/when they get more popular, from the one I’ve seen at least, one of the best. These come in various specs, and are a middle ground that seems to replace the HX30, which no longer really has a purpose when the smaller HE221 can make more power! I’ve only personally owned one, and it was 11cm T3 twin scroll with compressor wheel specs I’d say were good for around 450-500bhp but with very fast spool. Quite like a HX32 or HY35, but far more compact, no bigger than HX30 size, but far more capable.
Others I’ve heard of certainly had smaller compressors, but still seemed like 400bhp+ capable turbos. One for the future I think!
This covers everything from (I think?) HX30 equivalent units, and certainly HX32/HY35 equivalents (Sometimes known HE341 or HE351, but some 341s are purely HX35 wheel size), and HX35/40 hybrid equivalents (Sometimes also known as HE351), but mostly they are the ever popular HX35 size.
Most have nothing drastically different in wheel design from the HX versions, though some have the same size but better designed wheels, and more have billet compressor than the HX versions do.
As with all HE's, the newest ones tend to just be called HE300WG or HE300FG, so you literally can't use the name for much, and you need to know the specs! In recent months I've seen HE300s that were basically HY35 turbines and big billet HX40 compressors, but also straight up normal HX35 spec turbos also called HE300s. Cheers Holset!
There are VGT versions of the above, the ones with V/VG/VE at the end, and as ever, they’re a similar design, just a VGT turbine housing. Generally the VEs perform to the same peak power levels as the non VGT versions, but they spool much sooner, up to 1500rpm sooner.
HOLSET HE400 SERIES-
These are basically the successor to the HX40 series, but some, like all the HE turbos, have upgrades that make them closer in power capability to the next size up turbos in some versions.
HX40s seemed to max out at 60mm inducer compressors, but seen slightly larger on HE400s.
All the turbine wheels I've seen so far are normal HX40 sizes, but some have even higher flowing wheel designs, which is nice.
As ever, most are normal HX40 spec, but that's no bad thing as the HX series turbos are still up there with the best of them even today.
HOLSET HE500 SERIES-
As with the others, these come in conventional and VGT form, and cover what was HX50s, HX52s, HX55s, and HX60s. Most commonly I’ve seen HX55 equivalent ones, but they have all kinds of unusual specs, from some turbofan style compressor wheels with heavily curved blades to others with REALLY big compressors, which make them more like HX55/HX60 hybrids!
HX55s always tended to be 67mm inducer maximum, but some of the HE500s I've seen have 73mm and even 76mm inducer compressor wheels capable of WELL over 1000bhp! Even the 67mm HX55s used to be able to be pushed to 1000, so these should be good for a whole lot more, hundreds...
These are basically the artist formally known as HX80/HX82. Big! The one below has a billet wheel and what is a fucking TINY housing for such a big turbo, just 22cm! Could be amazing if you can find one in the right spec...
H/HC/HT and ‘other/classic’ Holsets
There are a LOT of older Holset turbos out there, right back to things from the 1970s that look like antiques, and most of them are zero use to you.
I’m no expert on these as they’re old-skool and I tend to stick to the HXs and HEs, but I know a bit about some of them that are a little use to some of you.
HTs are reverse rotation turbos, ie spin the other way, and I’m not really sure if they’re meant to be the equivalent of the HX series or the older HC series, but I know they’re not meant to be quite as capable for their size as the HX series.
Probably the most use to tuned car owners, mostly as they’re still seen fairly often, are the H1 turbos. H1Cs are very similar in spec and performance to the HX35, with the ‘big’ H1C in particular being basically a HX35, but even the ‘small’ version (smaller compressor wheel) is meant to be good for well over 400bhp.
The H1E is like an older version of the HX40, and again comes in varying wheel sizes. The small version isn’t great as it has pretty much a HX35 sized compressor, but the ‘big’ H1Es are practically HX40s in all but name.
The turbine housings on the H1C is a direct swap for HX35s, and the H1E for HX40 ones.
The others I’m not going to bother going in to as I don’t know enough about them and you’ll rarely see any other good ones suitable for anything other than maybe tractor pull stuff to be honest!
Hi, I'm Stav...
You may or may not have heard of me, but I've spent the last 15 years working full-time in the tuning scene, and the last decade or so writing for various car magazines.