CUT THE BULLSHIT- THE TRUTH ABOUT TURBOS! - MY TOP TEN!

Since the death of car magazines and internet forums, and the rise of YouTube videos and Facebook groups, the amount of misinformation and pure bullshit about tuning is higher than ever. It's fucking unreal what gets said and how often, and it's making me a bit disillusioned with the whole scene, but it's also made me want to clear a few things up lately, as reading pure shit constantly is doing my head in.

Probably the worst piles of bullshit I hear is about turbos, so let's clear some stuff up in ten very important points.

​Apologies for the swearing and less than sexy layout of this feature, but this is me saying what I think and explaining some stuff rather than trying to look impressive...


No1- IF YOU'VE NO EXPERIENCE ON THE SUBJECT, PLEASE, SHUT THE FUCK UP
This is the worst thing of all, not just on turbos, but everything. Seems most the people who shout the loudest with their advice are the people who know the least.

On a certain car group I'm a member of that's mostly turbo related, the two main people who reply to peoples questions seem to have zero experience and reply with complete and utter shite almost all the time, but comment so often and so confidently, to anyone who didn't know who they were, ie most people, they'd sound like people who know what they're on about.
Shit like this, on Facebook, on YouTube, and in magazines, is what's killing the scene for me most of all.

Unfortunately a lot of tuners these days will give iffy advice too, either to suit their agendas and sales, or because they're clueless on that exact subject but won't ever admit to it as they have to be seen as the all seeing gods of tuning to their customers. Fucking minefield out there.

No2- TURBO SIZING ISN'T THAT HARD-
One of the most common things I see is people (never with any experience of the turbo/engine/anything) going "OH EM GEE, THAT TURBO WILL NEVER SPOOOOL" just because it's not a fucking tiny little turbo, even if the engine is pretty big.
Don't just guess if something will spool. Either go from your past experiences or do a bit of Googling for proven results and you can make a VERY educated guess by looking at other cars and engines and turbos, even if neither are exactly what you're using.

Unless you're using a horribly specced mismatch of a turbo, or some ancient piece of shit, both of which are very rare these days in all honesty, turbos of a similar size/spec all spool similarly enough or any given size to make a very good guess on how it will work.

Wondering how a 900bhp turbo will spool on a 4ltr for example? Well about the same as a 450bhp turbo does on a 2ltr. Simple. It's not that hard. (THIS is one I see loads of with Toyota 1UZ engines- You can spool a fucking HX55 on one EASILY, but people fit turbos more suited to engines almost half the size, and wonder why they make crap power!).

Wondering how much faster a twin scroll turbo setup of any given size spools vs a single scroll one that's otherwise pretty much the same? Roughly 600-1000rpm faster in general. 2Ltr single scroll setups with ~600bhp capable turbos like GT35s and HX35s are full boost by around 4500rpm typically (seen 5000+ on GT35s with wild cams and the biggest housing though- Shite!), and proven as low as 3500rpm with a good twin scroll setup and 12cm HX35s for example.

No3- BALL BEARING TURBOS DON'T MAKE VERY MUCH DIFFERENCE TO SPOOL-
Fact. Despite being one of the most common myths. I've even posted a video of the owner of Xona Rotor saying the same thing, and he sells the fuckers. It's a mix of sales speak and bullshit that says it makes a big difference.
A Holset HX35, a Garrett GT35, and whatever other similar 600bhp turbo with similar size turbine wheels and housings spool about the same IF all else is equal. This is fact, no matter how many times pricks say one is "An old diesel truck turbo" and one is some kind of superduper thing. It's bollocks.

​In theory it helps, and it does, but by a really small amount, an amount you often can’t even feel. Wheel design, housing design, manifold design, exhaust design, cam spec, mapping, ALL SORTS, all make a way way bigger difference, ie a really noticeable difference, vs it being BB or not.

​The REAL advantage of BB turbos is they can take higher thrust loads for better reliability in extreme use. Though that's all relative to how good/bad the non-BB version would be of course- My friends GTX2860R Gen2 has massive thrust (ie in out) play and it's only done a few thousand road and dyno miles, albeit at 33psi boost.

No4- JUST BECAUSE THE TURBO IS CAPABLE OF A CERTAIN POWER DON'T MEAN YOU WILL MAKE THAT POWER...
Lots of people think this, and it ain't gonna happen. This isn't just the case with running a turbo at very low boost, but most commonly people buying, say, a 600bhp turbo, running 1.4bar or some medium amount of boost, then wondering why they've not got 600bhp (Hint- Most the time you'll be at more like 2bar or more to truly max a turbo out unless it's a very small turbo for the engine size).

These days this issue is coming about thanks too all these tiny but very flashy turbos with funky compressor wheels rated at big power but still running teeny tiny turbine wheels and housings (ie a huge mis-match for most engines, and more sutied to twins on insane power GTRs etc). Things like the smaller Garrett GTXs and so on are big ones for this, as they might be rated at whatever power, but they're not gonna do that aside from on a pretty tiny engine, or as twin turbos on a medium size engine (Such as twins on a Nissan GT-R V6 or Toyota V8), as they've not got the turbine flow to max out on larger capacity engines. Ever notice the truly powerful engines have actual big turbos with big turbines? Yes, that’s because you need it.

What goes in has to come out of an engine, and while better designed wheels help, size is still king.
Take the Garrett GTX2871R rated at 560bhp, or even the new G25-660 turbo rated at 660bhp. They both have tiny 54mm turbine wheels, smaller than a stock little CT12B off a 1JZ VVTi. I don't care how fancy a turbine wheel is, with that size, you're either not going to max out one of them on anything but sub-2ltr engine at mega boost, or your pre-turbine backpressure will be astronomical.

​You'd not make even half of many of these turbos rated power if you was daft enough to fit one to a larger engine, as it's as much about turbine flow as compressor.
Even looking at Garrett's own turbine maps shows it's no magic- The GTX2871R turbine with the biggest housing flows about 21lb/min, the G25-660 one with the biggest housing flow about 24lb/min. Both less than a GT30R turbine does with the biggest housing at 26lb/min, despite the GT30R rated at a good 100bhp less.

So even IF you make the power, you'll be making it with a far less happy/healthy/reliable engine than if you did with a bigger or 'older' turbo that had a bigger turbine wheel.​

No5- TURBINE SIZE IS KEY-
While little turbine wheels and housings help spool, and are fine on suitably small engines, what goes in has to come out, and the smaller the turbine wheel and/or housing, the less can come out, which means less power per psi boost, and less engine reliability.

When chosen right, this is just a trade-off, you just give up a bit of power for a bit of spool, with no reliability issues, and still ballpark correct power.
In fact if going for the maximum power and torque but fastest possible spool, you can build an engine like they would a rallycross engine, that's been specced to handle big boost and big backpressure from a relatively small turbine side with no issues and be loving life. Unfortunately most engines aren't specced like that.

But more often than not these days, people think running the tiniest housings and wheels they can find for any turbo they think can do the power they're after is the right thing to do with no bad consequences, as they have zero understanding that turbine flow matters. Because of this the result is often way too small, so they often struggle to make the power they do, and even more often have reliability issues due to the massive pre-turbine backpressure.

Pre-turbine backpressure is the no1 killer of turbo engines (behind shit mappers!), and both killers are pretty invisible to most, and other stuff gets blamed for the problems.
The less turbine flow you have, the harder time your engine has to stay alive. Heat issues and far less resistance to det, are the biggest problems, problems which people tend to first realise when they're shitting out head gaskets and pistons a lot, or needing to run race fuel when other similar engines with bigger turbines don't...

There's plenty of examples where there's two similar engines, running similar power, but one is highly strung and less reliable than the other, just as it runs a smaller turbine side in an attempt to get faster spool.

Unless you've specced the engine to suit, it's simply not worth trying to gain a tiny bit of spool considering what you give up just to get that.

And remember the basics- The bigger the capacity, the bigger the turbine flow needs to be for any given power. What will make 600bhp on a 1.8ltr might have a turbine side too small to even make 400 on a 3ltr...

No6- LAG VS BOOST THRESHOLD-
What most people call 'Lag' isn't lag, it's just not being in the boost threshold.

The rpm where your turbo can't make boost, that's being out the boost threshold.

Lag is your turbo response when within the boost threshold.

You put your foot down at 2000rpm and it don't come on full boost until 4000rpm isn't lag, that's being out the boost threshold.

You put your foot down at 4000rpm and any delay then is LAG.

But how much 'lag' is there on even slightly modern turbos when truly within the boost threshold? Even fucking big ones? Some vs being naturally aspirated, but in real world terms, very little, not enough to win or lose a race unless you're rallying.

Even something like a Holset HX35 on a 2ltr with a single scroll manifold (Bad idea btw when twin scroll often spools it 1000rpm faster). Boost threshold would be fairly high, full boost not until 4.5k, but do you think there's any real delay between planting your foot to the floor and fucking off down the road like a rocket when you're within the boost threshold (ie 4.5k+)? No. Pretty much zero, even for things like drifting etc.

No7- BOOST = TORQUE.
If you're grip limited or haven't got the strongest engine or transmission out there, torque can do more harm than good, BUT if that's not an issue, torque is always fun! Despite this, a lot of people seem to be confused why they haven't got lots of it despite having lots of power.

The answer is mostly boost. The biggest thing to make high torque numbers is boost pressure, and many cars, especially at 1bar or less, even the smallest fastest spooling turbos, can feel almost like a powerful N/A engine with most the power up top and fairly low torque, but the identical engine with another half a bar of boost can feel like a totally different engine with ridiculous amounts of low and midrange torque.

The lower the rpm you can make boost, the bigger the torque numbers tend to be for any given boost level, but the more low down torque you have, the harder it tends to be on engine internals, especially conrods, so it's a double edged sword in some ways!

Good example of boost giving torque and transforming how and engine feels was the old 13B rotary in my RX7. It was a large street port engine running a fairly small HKS T04E. At 0.8bar, despite being full boost by 3000rpm, wasn't really "fast" until at least 5.5k when the ports really came in to their own, then it screamed up to 8k; feeling much like a tuned N/A engine. At 1.5bar though, despite peak power not feeling much different up at 8k, it was a rocket ship with a ton of torque right from 3k to the limiter now. It was tons more fun at 1.5bar and easier to drive faster, but if I didn't have the massive grip to cope with it, it would've been slower to be honest, but still, more fun...!
I like boost!

No8- LEARN TO CHANGE FUCKING GEAR-
Unless you've made a tragic and totally mismatched engine or gearing setup, there is pretty much zero excuse to be caught off boost unless you have no idea how to fucking drive and change gear.

Putting your foot down at low rpm then blaming the turbo for you not going fast is fucking lame. No, it's your fault for being at low rpm. Your fucking fault. Even if you got a tiny turbo, you'd be going a lot faster if you had the sense to be at a higher rpm.
Even if you got a standard turbo on a petrol car that is on boost by 2500rpm, you'd accelerate a lot faster if you made sure you was in the right gear so you was already at 5k+. I've got an Impreza at the moment, 2ltr, and a tiny little TD04 that even 1.6s spool easiy. Yes it spools at low rpm, but to do fast I'd still drop a gear or two from cruising rpm so I'm at at least 5k to accelerate as hard as I can, as I'm not stupid.

You could have a GT25 or a GT35 on your 2ltr, and while the GT25 will be faster at 3k, it will still be slow, and but would be FAR faster at 5k. But the GT35 will be FAR faster at 5k regardless.

God help you if you drive a highly strung N/A engine- Any engine even approaching 100bhp per litre, even with fancy variable valve timing to help low down power, the real powerband starts at at least 6000rpm on non-turbo lumps, and by then even fucking massive turbos are at full boost.

You ever wonder why so many 'fast' cars look so average when the owners give them some beans? It's because people are fucking useless and don't understand how to change gear, that's why! Most owners are a waste of a good car...

No9- WHAT YOU GIVE UP LOW DOWN, YOU USUALLY GAIN UP TOP, SOMETIMES MORE! -
People fucking obsess over low rpm performance, and think a bigger turbo gives a smaller powerband, so would don't want to run one as they think it won't have a decent power band, but on modern engines, that actually rev, this is usually bollocks, and it's often the opposite.

Most modern turbo engines safely rev to around 7500rpm, some 1000rpm more, and even the lowest safe revvers these days are no more than 1000rpm less.

But, despite this, most modern turbo engines make peak power at least 1000rpm lower than their safe rev limit, so there's room for more if you can make it worth it...

A typical fairly small turbo engine making like 150bhp per litre, so a 300bhp 2ltr etc, makes good power from 3000-3500rpm and peaks out 6000-6500rpm. So you've usually got a 3000-3500rpm power band.

A typical bigger turbo engine, say 250bhp per litre, so a 500bhp 2ltr etc, makes good power from about 4000rpm, but tends to pull hard with no let up until 7500-8000rpm. So you've got a 3500-4000rpm power band, ie the same or fucking BIGGER, not smaller.

Even if you only pulled hard to 7k, and in all honesty you've probably done something badly to have an engine that spools that late but dies out that soon, you've still got the same size powerband as a smaller turbo, just higher in the rev range, and you also happen to have 100-200bhp more!

You can make a fucking mess of things, with small downpipes, shit manifolds, badly matched turbos, stupid cam specs, and so on, and make a powerband smaller than it needs to be, but these days you'd have to fuck things up good and proper to make a powerband much smaller with a larger turbo unless you go to a REALLY fucking big turbo.

If things are specced and built right, you can have a fucking big powerband. Even with some 600-650bhp turbos, on 2ltr engines, with good overall specs, good twin scroll setups etc, you see cars making big power from 3500rpm all the way to 8000rpm, that's a massive power band, way bigger than any factory turbo engine, but while also having about TWICE the bhp per litre of even the hottest factory turbo engines these days.

This sort of shit is especially good on Honda engines that love a good rev. When N/A they don't really come alive until 6k+, but rev to 8k+, but provided you can drive you still won't ever fall out the power band. Even a fucking gigantic turbo is on full boost by time the N/A car is in the powerband anyhow, so even with insane, really fucking insane power, with a huge turbo, you'll still have a bigger powerband than stock...

No10- YOU DON'T 'GET WHAT YOU PAY FOR'
Turbos are all kinds of prices, from sub £200 eBay specials to £2000 swanky ones, and everything in between. But is a £2000 ten times better than a £200 one? Or even a £1000 twice as good as a £500 one? Personally, I'd say no.

Cheapy eBay ones, well that's where it's real a gamble. Personally I think a lot of these under-perform as the typical type of person that runs one is a clueless cheapskate so the car is an unreliable underperforming piece of shit in general due to the mistakes and lack of care/knowledge from the owner, rather than the turbo being truly shite, but still, it's a gamble and not one I've ever made personally yet.

Another thing you see for a couple hundred quid, is used and sometimes new turbos off trucks and so on. This is FINE if you know exactly what the fuck you looking at, but most people don't. People see "HX35" or "GT40" or "T4" and think it will be ideal for them, not realising there's a 1000 variations of almost every turbo type on the planet, and 90% of them are not suitable for you.
The vast majority of turbos, even ones on some of the more powerful tuned engines on the planet, are actually commercial/diesel based, but that sure as shit don't make them all suitable! Most big OEM commercial/diesel turbos will have far too big a turbine housing to be much good for the fairly small engines we tune, so a random purchase just because it's called a HX35 or whatever could well be a total waste of money unless you know what you're buying.

For somewhere between 400 and 600 you can often get brand new GOOD/CORRECT spec Holset or BorgWarner turbos from a specialist who knows about these turbos. Personally, for my budget and needs, this is what I go for, and what I feel is the best value for money.
Are they the very best turbos on the planet? No, of course not,  if money was no object I'd have some swanky as fuck £1500 Precision or GTX or EFR or whatever. But for 99% of us money is an object, and from experience, comparable size for size on wheels and housings, both either twin or single scroll, the performance difference between a decent Holset or Borg and a swanky one for 2 to 3 times the price, is pretty minimal.
More importantly however, and the money saved on the turbo can be spent elsewhere (better manifolds, exhaust, cams, mapping, whatever) to make the performance better than any turbo alone will.
If you have the cash to make everything on the car perfect, and can afford spending big bucks possibly yearly when you need to replace a broken turbo, fuck yeah I'd get the expensive one as it's a little bit better, but spending loads on a turbo but then having pretty average/crap spec other bits as you've not got the budget for it all, is fucking stupid IMO.

And now, top dollar turbos. Yes, they are the best, defo, but they're also expensive to buy and fix, often most of the cost of buying a new one, so you need to be able to afford it short and long term. Top dollar turbos tend to not be no more reliable, arguably less sometimes- What you're paying for is performance rather than longevity, so make sure you can afford the upkeep.

A good example of a lot of the things I've talked about in this feature was the RB20 engine build I did in my R32 Skyline.
Back when I did that everyone said RB20s were shit, unreliable, didn't spool turbos, even shitty little ones that barely make 300bhp, didn't make power, etc etc.
​
Anyhow, long story short, this good choice of parts, good choice of what to spend my fairly low budget on, and good turbo sizing, made for a RB20 that was making positive boost by under 3000rpm, full boost by 4000rpm, pulled hard to 8000rpm limiter, and made 470bhp at just 1.5bar on pump fuel, and would've easily made 550 with more boost- Which it was capable of with no det, if only I didn't have shit coils at the time of mapping that missed occasionally above 1.5 (we tried at up to 2bar). Totally reliable even with years and years of hard use too.

So faster spool, more power, wider powerband, and more reliable, than 99% of RB20s, especially back then, with 3 times the budget and running flashy turbos, and the difference was simply buying/picking/making the right bits.
​If I'd have had the budget for even flashier turbos and stuff it would've been even better, but this shows you better off with a correct overall spec than the usual totally random guesswork spec with a 1500quid turbo bolted to it like most.

Here's a YouTube video on the whole build if you give a shit...​​

So yeah, I think that covers most the typical turbo bullshit I keep reading and seeing on YouTube. Hope you liked it, make sure everyone you know in to tuning sees this too, and hopefully some bullshit might stop getting said so often.

Plenty more things people should shut the fuck up about, so there may be more of these soon...

​Stav