Runner length
Turbo Mini Forums

Even without a plenum, you have a reflection. You have a discontinuity which will induce a reflection. You can think of it as a plenum with infinite volume.

If there was no reflection, trumpet and runner lengths in ITB setups would make no difference which is not the case.

Jean

http://www.jbperf.com/

Jean is correct, doesn't make any difference whether you have a plenum or not.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

ok. So what effect does the plenum have then? Do you put a value in for the distance from the bell mouth to the plenum 'wall'?

It seems that my short runners will not so much loose power as not gain it. if you see what I mean.

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

The plenum creates a sort of shock absorber for the waves created by the action of the valves. The effect of the positive wave moving from a port at high velocity to a plenum at low velocity is to promote a reflected negative pressure wave back to the valve.

Interestingly, on the exhaust side, a positive pressure wave hitting the turbo nozzle causes the reflection of a positive wave back to the valve.

The distance of the bellmouth to the plenum wall has no impact on wave generation. I would just make sure that the curtain wall area is twice the runner area, as a general guide.

Your short runners will gain power, but at around 8000rpm upwards.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Fastest 998 mini in the world? 13.05 1/4 mile 106mph

www.twin-turbo.co.uk

hence my new cam.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

MioaoW!!!

fuckig belt...

what i'm going to do is see where the new cam makes peak, then make some manifold extentions that move the whole plenum forward, just means i'll have to leave the bonnet off.

Useful page from the book showing how the waves act:



This shows how the reflected wave is generated. Note the positive waves are travelling against the direction of the gas flow.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

http://www.peter-burgess.com/flugelhorn.html

If something is worth doing, it's worth doing half of.

Thanks John.

Another one:

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Sorry Paul for dropping a bit of inane twitter into your thread but I thought this sort of shows your theory in practice.

EDIT: Although it being on an exaggerated comedy scale.

Edited by John on 18th Feb, 2011.

If something is worth doing, it's worth doing half of.

bit of time travel here but how did all this turn out some of the plots and pictures are missing

thinking about trying this out they are 34mm id and its about 700mm but can be shortened to about 500mm approx 100 each leg on the bend






TB somewhere close to the cooler inlet not sure if that will mess things up being the core adding to the volume

edit yess it just fits under the bonnet and at that length its clear of the firewall its actual less than the carb setup i had there

Edited by Turbo This.. on 16th Apr, 2017.

Runner length will determine the shape of your torque curve and ultimatley your maximum power.

Too short and you lose bottom end torque and if they are too long it will limit your top end.

At 34mm bore and 500mm long you are a bit too long. 300-400mm is optimum for a 5 port. For a high revver and peak torque at 6000rpm, 300mm is just right.

400mm would be good for low revving torquey engine with a small turbo.

It depends on the rest of the engine: head, cam, exhaust and the turbine side of the turbo. If I put 500mm runners on my 998, the induction pulses would be working against filling the cylinders before the turbo kicked in.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

ok far to long sounds like 350-400 from head face to plenum is where i need to be?

its 1098 based so would like to keep it to about 6k rpm but prefer it to be more low-mid rpm with loads of torque due to the 2.95FD and SC CR box
202 head 33/27 opened at the push rods blended around the guides and seats
kent 274 cam 1.3 rockers
10.5 to 1
think ill splash out on a GT2052 not sure yet but it wont be the metro t3 that ive been using that's for sure
going to do a LCB side mount type ex manifold to try match the intake for the better VE

target for me is a nice grunty engine that's a blast on the street i feel like id be happy with 150-170 as i think the mini will never be fast compared to most other stuff that gets around
now that ive gotten involved with bikes everything is now slow
so its more of a smiles per mile car now its been parked up for to long and it just need to be back moving

its not that im wanting to or trying to re invent the wheel here its just that for me at least its not easy to find and put the information together to be a simple list of parts and sizes etc
i get that you guys have hard to find out whats a waste of time and what works well together

Based on the Engleman/Helmholtz formula which seems to be substantiated by simulations, a 500mm runner at 34mm bore will induce a peak VE/Torque at about 4000rpm.

If you use the GT2052, then that is unlikley to spool up before 4k, so it is far from ideal.

There is a big problem with getting runners between 300mm and 500mm as you are finding out. I've managed to get 300mm in by putting the plenum right up under the scuttle.

With a 6k limit, I would use a smaller turbo.

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

big turbo and a big cam for a 1098 IMO, are yopu going to go large bore at some point?

Saul Bellow - "A great deal of intelligence can be invested in ignorance when the need for illusion is deep."
Stephen Hawking - "The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge."

Ah!

ignore me then!

ok i was wondering why i couldn't see the gt 15 and gt 17 turbos on there page guess they just didn't sell them so culled them for a single and renamed it as the 2052

so i mainly just want a new modern turbo for the little 1098 that with the 274 and keeping it below the 6krpm im really wanting that low-mid range grunt side of things i think id be happy to dump some top end to gain low/mid range

that said i was messing with the runners and goofing around for a good part of the weekend and ive got it down to like 425 430mm or so from head face to trumpet yea i had a go at some kind of shape that i hope is better than just a raw tube sticking into the plenum or a 90 degree runner to plenum wall angle the main part of it is 15 degrees with a few steps to round it over with about a 6mm radius donno it was more just goofing around on the lathe than anything as i was anoyed about the runner and the radius of bends that i got they really need to be shorter radi and i think i could get it where it should be on the firewall side

anyway im prepared to spend for a new properly sized turbo just not sure whats out there as i dont really know how much cfm and stuff the thing will flow to look at maps nether do i know what is relistic for the low rpm tourqe monster im looking for here so maby it needs a tinny turbo that is all aouta puff at like 4500rpm? but boost from like 1500?

hell i donno at this point but given 425-430mm @ 34 ID runners and the low rpm grunt i want ill need a kinda small turbo maby 1548? but i cant really fint them new from a genuine source ?

not really sure on injector size but i guess that is dependent on how the turbo flows? i think some guys use like 600-700cc per runner? so on E thats about 840-980cc given about a 40% insincere in volume ive found some long/extended nose one that i think i could poke down into the head a little ways or at least get them flush to the head maby that could help with avalible time to spray so reduse the injector needed i donno i guess ill just have to try some and see what the dutty is and go smaller or bigger maby end up with some spare injectors that arnt right

big turbo big cam thought the 1098s don't like the rpms due to lack of journal over lap and 3 main bearings not to mention the piston speed

ive got a 1098 crank that was in the car for like two years that admittly reved the snot outa when it was na and its cracked like 3/4 the way around where the thrust is it runs around the jurnal and then up the web this is the one from back when i had clutch shudder haha it was the crank bend aouta shape and the throw out running all squeiff

id love to go big bore but they are hard to get here in aus for a good price that i know of and all my stuff is 998 or 1098