16v manifold lengths
Turbo Mini Forums

right, new here and wasnt sure wether i should put it in the fuel injection (cos i think it will include that aswell) area or here but here it lay

right im just kinda planning what kinda stuff i need when i eventualy get to building my supercharged 16v.
problems im thinking about are manifold lenghs, throttle bodies, injector positioning and plenum chamber widths
reading the hilliers fundimentials of motorvehicles its saying somthing like the point at which torque is moved is devermined by the distance from the valve centre to the throttle butterly.
the jenvy throttle bodies i was thinking of getting utilise a weber bolt flange and intigrate a injector position just after the throttle bodie, and the grand thickness of 35mm.
problems im thinking of are fitting into the front (but not so bothered cos i can always go for a clubman front) and if the fuel mix will still be effective, i then had the idea that because its going to utlise forced induction it wont truly matter about manifold lenghs as there will be positive pressure passing through and no need for the oscilation of the air

also the plenum chamber is there a minimum width that should be used or can it be wafer thin if possible. is there any specific internal design that should be used so allow even air flow accross all cylinders

any help apreciated guys

Thanks David.

David.

There are many numbers stated for plenum size. But im going by the figure of 1.3 X CC so for a 1275 you'd want a plenum of around 1650cc ish. Alot of people seem to be using smaller plenums withouts any problems though, its all going to be limited by space thats left to squeez one in.

I think the main point is to have a plenum big enough to not cause any restriction to the air flow, and not starve the cylinder furthest away from the plenum inlet.

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1/4mile in 13.2sec @ 111 terminal on 15psi

thinking if maybe put the plenum feed to the centre, maybe triangulated outward aswell might make sure it doesnt starve the end cyl's
for a 1430 i roughly need a 2litre plenum :S quite big i think, i *think* i read about still using ram pipes on the inside of the plenum aswell, would this also be the way to go?

David.

From a theory point of view, if you have a higher residual pressure (boost) the velocity of pressure waves is quicker, so using a calculation which takes into account of density for the speed (haven't got one on the tip of my tongue) if you want to retain a tuned inlet to respond to the same rev characteristics, you have to reduce the length so that the resonant frequency is the same. So, having got that out the way, just so you get no nasty lumps in your power band, you're going to want the plenum design to be as anechoic as possible, you don't want any pressure waves in there at all. I reckon a good idea is to use a hemispherical end and pipe for the main "bit". 1.3x cc sounds ok.

If you're going for a blown engine on a Bimmer, have you thought about using the LT inlet cam and the RS exhaust. It's sort of like the Avonbar Ph2 for a K head!!!! Even though the head flows brilliantly, I think it's under exhausted a tad, particularly under boost conditions.

Anyway. Enough late night waffle. I've got a mini to fix tomorrow.

Bugger off, I'm getting there.

Hi,
Welcome
Take a look around there's plenty of pics and text to go with them.
Alot of people seem to be using the BM bodies and fabbing a plenum to go on to them.
The BM bodies are made for the job, and cheaper too :)
Middle feed would be a good idea for distibution, but probably impossible in a mini!
I think the theory is to taper the plenum down toward the furthest cylinder, take a look at the supercharged imp thread
Cheers,
Gavin :)

Edited by Bat on 23rd Oct, 2007.

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Normally you want with individual throttle bodies the largest airbox you can fit in the engine bay. This help throttle respons and keeps the reductions in the system the smallest. Bikes use airboxes with a volume of 10l. Also BMW use on the M3 and M5 very large airboxes.
The only force induction cars with itb I can remeber is the Skyline (not sure) and the Nissan Sunny GTI-R. Dont know what their volumes are (in airbox terms)

i had a look in the imp project, giving me ideas about plenum design, did a wee search and came up on a skyline forum and i knicked a piccy from there

aparently it comes from a M3 but i dont exactly know, i would like to do similar to that design as 1. will fit better into the mini and 2. looks like it will perform better

David.

hiya.

as for forced induction..theory is all good but it does not apply to forced induction..and well but unless you build a really bad distributing manifold i don't think it makes all that much difference for FI.

I posted a wee little bit of origami in a thread that would probably be okayisch for both available space and distribution and will fold from one sheet of alloy (steel will do too).

but it you would just use a airbox like the S54 pictures above. loose the rampipes just use short inlet donuts with a radius of 0.5 times the port diameter.
then not fit a huge plenum but the flattest you can get away with. The lehman style used in the blown imp project would be a good one i reckon. if you have a flat plenum you can put the injectors facing straight down the ports. having the injector in front of the butterfly is reported to work well.

as for NA. I have the lenghts calculated (pipemax) for both exhaust and intakes, i will look them up.

predicted power output for a na 16v 1330 with a 7800 rpm limit is 132 isch
bhp. assuming a 102% ve based on the k 1100lt factory specs.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

thanks for the reply, do you perhaps have a link to the thread you posted the origami in?
iv started noticing cars which seem to run the conicle (cls style) plenum

David.

purely for packaging i have considered losing the throttle bodies as well as the original injector mounts and fitting something in the shape i folded.

the original turbo esprit ran a double plenum as well (like the lehman tapered one but just two boxes linked by two channels i seem to remember.



the intake lenghts for the aforementioned NA 16v 1330 @7800 rpm:
- Induction System Tuned Lengths in inches- ( Cylinder Head Port + Manifold Runner )
1st Harmonic= 33.105 (usually this Length is never used)
2nd Harmonic= 18.789 (some Sprint Engines and Factory OEM's w/Injectors)
3rd Harmonic= 13.118 (ProStock or Comp SheetMetal Intake)
4th Harmonic= 10.325 (Single-plane Intakes , less Torque)
5th Harmonic= 8.377 (Torque is reduced, even though Tuned Length)
6th Harmonic= 7.048 (Torque is reduced, even though Tuned Length)
7th Harmonic= 6.082 (Torque is greatly reduced, even though Tuned Length)
8th Harmonic= 5.350 (Torque is greatly reduced, even though Tuned Length)
Note> 2nd and 3rd Harmonics typically create the most Peak Torque
4th Harmonic is used to package Induction System underneath Hood.

the original bmw setup is prety near this btw..zem germanz..

the origami link:
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=179552.

Edited by Sir Yun on 30th Oct, 2007.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

ah exelent, tis what iv been thinkign of doing, shape wise...i might have got my friend whos at uni to design me a plenum then using fluid dynamics make sure flows near enough similar across the lot. if not im hoping to start uni next year in which case ill do it myself.
unis gona mean i can use all there equipment to design my own stuff :p and then in the end hand it in as my project...aaaah good plans!

just thinking, is there any internal shaping needed to be done? on the imp project seems his 2 seperate shapes were connected by a slot will it be ok being made from only one piece. the air would be allowed to flow around any point when it enters unlike the slotted box on the imp project

Edited by mini93 on 30th Oct, 2007.

David.

just don't over engineer it. there are numerous plenums around for turbo's that look bad but work just fine.

the idea is getting the packaging right while not building something stupid.

the box i folded would probably work fine as is.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

18" intake length that wouldn't fit under the bonnet, would it?

it does not have to be straight and it is measured from the valve.

the original BMW setup uses about 12 inches of intake lenght.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

18" from valve centre to butterly? or injector or somthing else completly

David.

I assume from engine valve till intake mounth (air horn) in the plenum

yes

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

thanks alot for the reply guys!! given me a good insight into what to design, now time to go get myself a piece of string and work out how far out the front of the car its gona be :S

David.

i'll see if I can put some sketches up.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/

exelent.

just in the prediciment of throttle bodies now, id like some jenveys, there are different length ones but tbh im not sure what the difference is, is it simply just throttle butterly positioned further away from the valve, how ever as im making my own manifold it doesnt matter which length i get.
TB, bore size might be a pain to figure but oh well ill get reading some books!

David.

the question would be NA or turbo??

for turbo i would do it a bit different and leave the whole tuned lenght idea and just use a single TB and short 'donut plate' manifold with injectors mounted through the front of the plenum directly above the ports.

the TB is just a butterfly and can be sourced from many cars in a wrecking yard for minimum cost.

you don't need rampipes inside a plenum and IMHO these mostly create more problems as in a mini you have limited space anyway.

for multiple TB's just use the bmw items.. but spacing will be tight and will need a totaly different manifold.

OK the next bit is NOT from me but by Larry Widmer of Energy Dynamics and the man knows airflow (he used to work for general dynamics and now runs endyn).

[i]
The "air duct" should have 25% more area than the throttle body, and rather abruptly make the transition into the throttle body with an "ideal" inlet radius which will net zero loss. The formula for designing the radius is R/D=.5, where R is the theoretical radius you're seeking, and D is the diameter of the throttle body. Using this formula's radius combined with the 25% increase in area in front of the throttle body allows the lower velocity air flow in the inlet "tube" to exert considerable pressure on the throttle body which is highly desirable from a power standpoint.

For your inlet tube use a constant 3" ID tube, and build a radiused connection for the throttle body as I described the other evening. Use the formula R/D=.5 , where D is the diameter of the max.ID of the throttle body, should give you a theoretical entry radius of about 1.3". So if you make a drawing of the side view of the throttle body, the ID is 2.90", now set a compass to 1.3" and place the point 1.3" away from the TB and swing an arc. Repeat for the other side, and you'll see the correct shape or radius to build.

On our turbo engines, we do keep the velocities relatively high prior to reaching the throttle body. The type throttle body is a factor here, as is driving application. If the engine is going to be run continuously at full throttle, and you have either a butterfly, or slide throttle, the velocity can remain high, and then after passing through the throttle body you want to slow it by expansion in the plenum. If part throttle performance is a concern, such as a road course as opposed to an oval or drag application, we expand the area about 30% when package space allows. This slows the flow and lessens vectoring by the butterfly or slide, and the amount of turbulence is greatly reduced in the plenum chamber.
Regardless of application (n/a, Turbo, Blower, etc.) the plenum needs to supply each intake runner with the same amount of air (distribution), and the air, even under pressure should represent a smooth "atmosphere" for feeding the ports.
We stopped using air horns in plenums back in the early '80's, and the same "ideal radius formula" is what works best. It will automatically dictate the space from the entry to the inside plenum wall. They'll look like half donuts around each runner entry.
One other note on manifold design and this is universal. If you assume that the manifold runner is an extension of the intake port, you will ideally want the distance from runner entry to valve seat to be equal on all "sides". So if you measure the length of the "roof" of the port/runner, it should equal the measurement taken on the "floor" and "short turn radius". The rational here is one of surface friction and corresponding boundary layer thickness and speed. If the distances are "different", the air fuel mixture will shear in the port, and the increased random turbulence will not only cause flow rates and mixture homogeneity to suffer, but the pumping losses go way up, further decreasing productive output.

Edited by Sir Yun on 8th Nov, 2007.

That sir, is not rust, it is the progressive mass reduction system

http://aseriesmodifications.wordpress.com/