Inlet manifold designs - some science, inc cutting PB manifold up final cut done

not quite what I meant but I can see what your saying, pm me your email and I'll send you some experimental data and screen shots I have from my dissertation last year. I did them myself so you're welcome to post them.

basically I meant a diffuser within the plenum chamber.....

imagine starting at the entrance to the plenum you fitted a bell mouth then extend this back all the way until it nearly touches the back wall with a slight taper.

basically you end up with the chamber pretty much being totally filled with high pressure air so each runner/cylinder should fill evenly regardless.

as for the pulse plate part of things thats kind of a seperate missconception, pulses fron the intake dont actually bounce off anything they just reach the intake runnes bell mouth and turn round of there own valition... please dont ask why, that would involve me doing deep and meaningfull research! I didnt need it for my dissertation so after I established what happened I sidestepped the why part

 

as a side point one of the early 2000-2006ish era F1 cars used a diffused inlet infront of its radiators that constricted to a nozzle style apature on exit behind them, if you let it idle to working temperature then blew air into the front of the rad the car would move forward against the air you were blowing!

turns out because of the way the air was defused, heated (causing it to expand) then directed through a smaller nozzle shaped exit that it would actually give a genuine level of forward thrust! worth a good few mph too

 

regarding the earlier post asking why the bell mouths were at differing angles, i.e 2 facing upwards and 2 downwards, it is because the manufacturer/designer didn't want the mouths to overlap. This problem is shown in post 30.

The air needs to have a clean path into the bell mouth, the overlap would create a fair bit of an eddy where the taller bellmouth overshadows the lower mounted one.

 

I've found threads where vrsteve has put up pics of his inlet manifold, the only problem is that the pics no longer work.

 

Seems like th AGG inlet is the one to go for?

 

Nice thread, some pics from a DIY I never got around to finishing.

Yep Alan, in the context of fluid dynamics and resonance tuning the volume/dimensions/design all affect speed/swirl of incoming air whether it's plenum, runner or port but the worst seems to be TB & 1st cylinder air trajectory in aftermarket designs.

Your aiming for an "all things being equal" scenario so air and fuel mix is perfectly matched (speed/swirl/density/air-fuel mix etc). The tapered plenum body reduces the turbulence created on the end wall affecting this and one of the things that most designs don't cater for is the TB and first cylinder. If the taper angle is v steep then a better flow of air will go to the other cylinders, too shallow and it'll ingest more.

Turbulence off end wall


I tried to take into account cylinder one (this was just first rough cut) - you can see a slight curl in the taper angle into cyl one though (yellow line) standard ABF it's pretty much straight down at 90 deg, blue shows a bump from 1st template design.


Should also note that manifolds such as the VR6 24V had a vacuum operated secondary runner designed into them to change the helm freq depending on revs, these cater for both low-end and high end peak torque values by variance.

This is a pic of an old MR2T mani I had, this had a variable runner/res due to the T-VIS and plates either being open or closed (sitauted between port and main runner)


No tapered plenum but runner length variance on this German VR6SRI, also bump at TB inlet somewhat:

 

Carrying on from above and with my excellent drawing skills

quick drawing:


There are numerous ways in which to change the way incoming air is affected;
Using the tapered side off cut I did you generally break down the plenum into the cylinders
* If fabbing from sheet like this you can change the top plates to change the volume, for example the top plate can taper outwards as the side plates taper inwards..... however,
The blue bit shows that as the air tapers it is compressed and in terms of fluid dynamics this increases both the speed and density (although not by much but depending on the angles really)
Speed generally isn't that much of a factor as hundreds of litres of air will be ingested in a matter of seconds at high revs, so the taper angles increasing the density is one calc, which, as alan was enquiring, in turn can be counteracted with either runner length or matching plenum volume per cylinder/taper angle and air density.

If I was funded by, say, the Lower Saxony area in Deutchmarks, one fun R&D experiment would be testing staged air-to-water cooling within the manifold, say 4 little coolers where each red line on the pic were! (Sky's the limit but so's the pockets in R&D).

One other thing I have noticed in research is that the high taper angle of the runners (like factory mani's but not so many of aftermarket ones) seems to bring out the best results, however, port and valve design also vary and change this.

Tried to make it simple for those who get dumbfounded by the sciences, hope it helps.

 

That is terrible design and should not be used for any basis for your own designs. That will only be this shape because one it's FI, two it packages well and three it was easy to make. This would starve an NA engine of air.

 

Extra material (plenum width) before the throttle body may cause packaging issue between intake duct and the tower. May be an idea to flip it 180 degrees

 

V old pics I did, was years ago and was going to make a dozen or so different ones at the time as I was bored. I found that the runner internal diameter was well out when I hacked it up, poor casting



Yep, the VR6 SRIM is for FI, NA sucks, they're all too slow. I'll see if I can dig out some old pics of the 850i V12 I had for you.

 

So would it be a good experiment if someone cut the this plenum and welded it to PB runners to see what you get?

 

yes!! want to try it?

 

yes why not! that big lump of alli is sitting in my garage not doing much. I dont trust myself chopping it up and dont know an alli welders so let me know if you want it for experimenting. If it works you can make me one

 

arent you using it??

 

nope I will be using the 1x inlet to begin with even though it has d shape ports. I guess that will be a bit of an experiment in itself to see what effect it will have going from the d shape ports on the inlet into the oval ports on the head without port matching.

 

Random but related question - does the mk4 crossflow inlet manifold have the same spacing as the counterflow?

This is the lower half of my ABA inlet but I think it's essentially the same as a mk4. I'm wondering if this could be fitted to a counterflow?




The whole thing



(I have a couple of these spare in case you want to experiment - and pay shipping from USA )

 

Interesting suggestion. Would be a case of integrating a suitable counterflow head flange leaving the plenum design up to user requirements.

 

No. Crossflow inlet manifold is different to counter flow. Mounting stud holes, port spacing, clearance for exhaust, port shape.............

 

Indeed it would be. That is why I was suggesting thinking outside the box
It maybe a lot of work for similar benefit, if another solution for the current is already on the way.

 

Only slightly then..