O/T, plenum design non mini.
Turbo Mini Forums

Bit of an odd one really, relating to Plenum design.

A mate of mine is building a supercharged 1.8 16v Vauxhall Corsa (for hillclimbs)

He's running Jenvey 45mm Taper Throttles on it, and basically, he wants to enclose the trumpets, and have the charge air blowing into an airbox type thing.

thing is though, between us, we can't work out whether the charge air needs to be evenly distributed (ie. one pipe over each trumpet), or if he can just have it all going into the plenum at one end.

I've been looking at the inlet design on the sierra cosworth, and it seems like its just a box, with a hole in, and 4 holes out.

same goes for the skyline etc, all seem to be a single inlet.

BUT, neither the sierra nor the skyline are running ITBs, so I'm still unsure.

he's come up with this so far -



obviously with the 4 smaller pipes joining a 3" charge pipe.

but, would something like this be better?



obviously not exactly like that, but something similar.

which would be more efficient?

Cheers for the help guys, I couldn't think of anywhere with people who would know other than here.

look at R32/33 GTR skylines and nissan pulsar/sunny GTiR's they all run individual throttle bodies, plenums and boost.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

I know of a supercharged fiat twink [merc charger] that had probs with diff mixtures in cyls. but that was single throttle .
Surely with multi throttle bodies on a plenum it doesn't matter 'cos all your doing is creating pressure ?
Maybe if the blower is close to the plenum it will be an issue

the blower will be at the front of the block, the inlet is on the back, so there will be about 2 feet of pipe between them, including the IC.

we thought it might be a problem (like the fiat one) as one TB would be getting more air if he used a plenum like the second one I showed, but then, like I say, the Cosworth and Skyline ones are like that.

I can't see a way round it, but obviously, he doesn't want to build it, just for it to run wrong because of a poor plenum :S

If its all pressurised then they should all see the same pressure i would have thought. I have a mate running an xe powered corsa and the space round the back of the engine where the inlets are was quite tight to have the individual feed pipes into the plenum i would have thought would be very tight.

the 20XE is a bigblock engine though, which is why my mate isn't going with it.

the 18XE is smallblock, which gives a bit more space to play with.

20XE -



X16XE (same engine as the X18XE) -



I've been reading this - http://www.max-boost.co.uk/max-boost/cylhe...akemanifold.htm - and it seems that it needs individual pipes, or the cylinders get different AFRs.

Its all very confusing, as some people say it'll work fine with a single inlet, some reckon it'll need a tubular inlet.

the fiat had the blower next to the plenum , even with all kinds of deviders the flow to each cyl. was diff

With 2 foot of pipe and i.c you wont get direct flow to indevidual cyls.

Not that i'm an expert...

I don't think it will make a big difference, as long as the plenum is big enough, if your plenum is a bit on the small side then the inrush of air from one end is bound to upset the first cylinder by blowing across its intake, also the one at the end may not get as much air after 1,2&3 have had their fill.

basicly make the plenum big, and position the inlet so it doesn't blow across the ports, I think if there's room putting the inlet in the middle is a good idea.

check the plenums about 1/4 down this page.

http://www.rbracing-rsr.com/bmwturbos.htm

Why not try MIGWEB?

That is an interesting link above. How wise that one can critique, and yet provide zero evidence. Not saying that the comments are wrong, but that I can't see any evidence on that page suggesting anything else.

"cylinder #4 will not get the same airflow as #1"

How is that then? 1 and 4 are divorced by 360 crank degrees and a full cycle. If they were open at the same time, or even next to each other in the sequence, the statement could be believable, but still un-proven.

Sure - the picture of the lousy intake on the engine with the blue valve cover is clearly not great, but the sample others with a plenum diameter of at least three-times the cross-sectional area of the runners still get called junk... Again - ZERO evidence...

Edited by turbodave16v on 29th Oct, 2006.

Thats like saying the Rover T series turbo plenum is all wrong :-

Frankly, i think what that guy is going on about is also bollox.

Edited by Sprocket on 29th Oct, 2006.

Tom, MIG is rubbish, hardly anyone actually has technical knowledge.

(and my mate wanted to keep the engine under wraps to the Vauxhall people for now)

So general concensus is it'll be fine whatever the plenum looks like?

I thought that may be the case, because of some of the ones I've looked at.

The RS500 plenum - i believe - as something like 1/2" thicker than the stock cosworth unit, and also had an entry at the middle bottom of the plenum.

Thay way i see it is - if you have enough volume inside the plenum, then it won't matter where you make the entry. The nay-sayers are those that likely haven't even made a plenum in their life, preffering to stick with "Izal" zorsts, or "phase whippy-doo" upgrades. :)

cool, I'll just get him to make it as large as space allows then :)

cheers for the help everyone.

I've been pondering much the same question and having read as much as i can find then the only answer is as you say a single plenum with intake at one end.
Mine will be a 2L XE with Jenvey TB's.

Rich

Here for the craic..

Supercharged Arden powered

double post

Edited by Richspec on 29th Oct, 2006.

Here for the craic..

Supercharged Arden powered

he came up with this, which unfortunately was too big, the bonnet would have caught it



and the latest plan, which seems to look as if it would work -



judging by his name for that last file, that'll be the one which makes it.

would that last oen not be better if all teh runners extended up to the plenum? surely theres space? i know your not going to get any charge robbing but given both runners merge into a single runner the same ID (as far as i can see) then go to teh plenum you may get one cylinder messing slightly with the one next to it? why not have 4 runners going up to a much bigger plenum then have that inlet pipe going into the side of it? the 90 degree bend in that big white pipe occupies alot of space that could easily be made plenum. then as TD points out such a big pelnum will take care of any charge delivery problems.

I'v never designed a plenum myself, jsut going by my gut feeling on the matter.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.

yeah, i think you might be right on the smaller pipes, and i told him to make the plenum bigger too, so there's more air for low down.

good spot :)

But then we are back to the log type plenums that are stated to not work.

So your point is?

Note that if its for port injection, the inlet to the plenum does not matter where it is. If its for carb or TBi then everything needs to be as equal as possible.

so which would be best out of the last 2 designs? the tubular jobbie?

Just had a good look at the RBR plenum for their K1200 turbo kit
Really like the idea of the integral radiused velocity stacks , these will sort you out !

Edited by carl talbot on 29th Oct, 2006.

Something that I 'think' needs to be considered is the firing order - and the fact there IS an overlap between the valves closing and opening...
Say it's 1-3-4-2, then that last picture will be drawing air in through both the siamesed intakes at the overlap point. Now, I can't say for sure - but I'm pretty sure this should be avoided if at all possible.

I also 'feel' that the larger plenum volume (not including the runners) - I mean the area DIRECTLY behind the runners - needs to be sufficiently large that it can (in theory) fill two cycles-worth of engine capacity. i.e. two cylinders worth of volume, to dampen out any effects of the pulsing from the opening and closing valves.

I guess you could argue that that should be in each 'half' of the plenum aswell (ie for cylinders 3&4 and 2&1), but I'm not so sure that is neccesary; because for there to be a set boost right above a valve that is about to open, the pressure must also be the same right at the furthest corner of the plenum away from the valve in question???

I seem to recall Corky Bell stated 1.3 times the engine capacity - I'm struggling to fully understand how that figure was generated though

I'd definately think that a plenum volume (not including runners) of 0.5 times the engine capacity as a minimum is a target.

I'm basic this on nothing other than applying stuff I learnt at college / uni / general engineering however. LOL!

Edited by turbodave16v on 29th Oct, 2006.

I'm going to go back to the first idea with this pic lol.



that was built buy the company another mate of mine works for, and has ITBs, and a centrifugal charger on it, running through a non tapered, log type inlet.

and it runs fine, makes 220bhp @ the wheels!!! and 200lb/ft.

according to the engine builder at the company, that inlet works as well as any other they could think of.

looks simple to make too.

maybe it IS that simple after all

i recognise that car :) .. if your lookin over designs for that engine have a look here:- they managed to fit long induction legnth, and a big plenum into a tiny space. they done sumat similar for a one off boosted application, but you get the idea.

Edited by evolotion on 29th Oct, 2006.

turbo 16v k-series 11.9@118.9 :)

Denis O'Brien.