THIS STRANGE LOOKING INLET MANIFOLD HAS WON PIKES PEAK AND A WHOLE LOT OF RALLYCROSS EVENTS...

Since I created the StavTech YouTube Channel (Click here!) I planned to put everything on there from now on, as unlike here, there's money to be made, and I need to make a living after all, BUT some things just work better as words, so I've decided some things will be on the website regardless (plus Facebook and Instagram), so here we go...

A few weeks ago I saw a post where a bunch of retro-rallycross fans were confused about the strange 'loop the loop' inlet manifold in the above picture (by rallycross photography legend Eddi Laumanns), and were discussing what the hell it was all about.
I replied and explained exactly what it was, but I got the feeling they didn't really believe me. It was only once someone posted a clearer pic that proved I wasn't talking out of my arse that they finally seemed to accept it.
BUT the whole situation made me think it's ideal as a cool bit of tech for you lot, so here it is!

​This funky looking inlet manifold is used only on certain variations of one engine, the XU8T, which is the 16 valve turbo race engine version of the PSA (ie Peugeot + Citroen) XU series of engines that are found in countless production cars, and was first used (unless very late spec 205 T16 Evo2 Group B engines used the same? If so I've never seen one!) on the 1987 Pikes Peak 205 T16, ie this one...

It was then used the year after in the 1988 Pikes Peak winning Peugeot 405 T16, the world famous car driven by Ari Vatenen which starred in the famous 'Climb Dance' video.

In fact, here's a few pics of this inlet as fitted to the 405 T16 Pikes Peak winner...

The next time this inlet was seen on a car was in Matti Alamäki's 205 T16 E2 rallycross monster in 1989, which made well over 550bhp from it's 1760cc (I understand? Slightly less than the GrpB versions for some reason?) engine...

Soon after this it also found it's way in to Jean Luc Pailler's Citroen BX4TC rallycross monster...

And after a good few years Jean Luc Pailler pretty much swapped the engine and running gear in to the BXs replacement in the production car world too, the Xantia, where it was used for the number of years in the 1990s...

ANYHOW! Enough of the history lesson... What the FUCK is that crazy looping inlet all about then?
​Well, it's actually a lot more 'normal' than you might think...!
As crazy as it looks, all this inlet really is, is a variable length inlet manifold like a lot of production cars have these days, albeit a super trick one running two sets of individual throttle bodies, really long runners (which should have a far greater effect than typical ones), and a boost-operated (rather than rpm) switchover point.

Variable length inlet manifolds are quite common these days, used on everything from MX5s to Ferraris. As you probably know, in conventional inlet designs, longer inlet runners tend to improve low rpm performance at the expense of high rpm performance, short runners improve high rpm at the expense of low rpm performance, but a good variable length inlet should be the best of both worlds.

The common myth is that inlet length makes no difference to turbo engines, hence why it's rare to see factory turbo cars with them, but in reality it makes a difference no matter what; it's just turbos are so good at making a wide powerband, and masking flaws in an engines powerband, that they're rarely used on boosted engines.

​Rarely used or not, it doesn't take Sherlock Holmes to work out that if Peugeot, who were one of the world leaders in turbocharged motorsport at the time, used it on multiple Pikes Peak cars, including an outright winner, and then it was used for about another decade in high end rallycross, it's fair to say it had a very worthwhile effect- They didn't fit stuff for fun or just guessed at that level, that's the stupid shit road car tuners do, not them!

The main reason they fitted this inlet to these engines was to improve low rpm performance via the long runners, which has the positive side-effect of spooling the turbo faster, while also having the switch-over to short runners, shorter than most typical non adjustable inlets, for maximum high boost high rpm power.

The engines this inlet was used on were as small as 1760cc and up to only about 2.1ltr, but all made somewhere between 550 and 800bhp depending on the application; we're talking really big turbos that needed all the help they could get to spool, especially for the tight and twisty rallycross and Pikes Peak events they were used in.

So, what are we actually looking at here? Well the top-down shot of it mounted in the Citroen BX is a good one to check out... Follow the boost pipes!

The air comes from the filter (bottom right), through the Kevlar inlet pipe, and in to the turbo compressor housing (top centre). It then leaves there and enters the chargecooler (top right), then heads down to a centrally mounted plenum as part of the inlet manifold this feature is about (middle right).
​Just to the left of the central plenum are 4x individual throttles, one per cyl, but these aren't the engines main throttles, these are simply to block the short inlet runners, forcing the air to go around the long looping runners you see exiting the right hand side of the centre plenum.
​The aforementioned throttles are opened at a set boost pressure via the turbo wastegate style actuator you can see painted black on the right hand side of the inlet, near the air filter outlet.
​The engine itself also has 4x conventional throttles, one per cyl, but they're mounted VERY close to the inlet ports, and are pretty much invisible in the above shot, but you can see the the springs and rods that operate them on cam cover.

​For a MUCH clearer view of both sets of throttles, which will also easily show you how the inlet works, check this pic out...

This style of inlet isn't seen in modern motorsport anymore, mostly as modern anti-lag systems are so effective at spooling turbos, which makes setups like this a bit redundant for most race works race engines which have pretty unlimited budgets.
​
​Having said that, this style of inlet makes no noise, adds no engine stress or heat, and is purely mechanical, so for us road car based people, indeed for race car people without a works race team budget, variable length inlets do potentially have a worthwhile use on turbo cars, despite what many people think...!

Or do you (think you!) know better than Pikes Peak winners...? (Hint- You don't!)