Plenum Design?
Turbo Mini Forums

I am building a new plenum for the new race car (not mini). I have a collection of bits and am trying to settle on a design. One thing that has come up is the positioning of the trumpets inside the plenum.

Would you:
a) Mount the trumpets in free air inside the plenum. A bit like this:


or b) Flush mount the trumpet end to the face of the plenum. A bit like this:


Explain your reasoning, please.

The plenum has a secondary set of injectors, injecting right down the trumps, if that changes anything.

Cheers

Ben

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I don't think that there is much difference to be honest.

Vizard shows a slight advantage for b) in the yellow bible, but then he was just measuring flow and there is more to it than that.

My preference is for a) as used in all my manifolds to-date. I scrapped 3 part completed plenums with a tangential exit because it flattened the pulses.

Simulations show good flow characteristics for a) :



Personally, I would make the decision based on ease of construction, provided you do not compromise runner length i.e. don't shorten the runner to accommodate b).

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."

Thanks, Paul. Pretty much what my opinion was. I like the idea of them extending into the plenum to give that extra scope for runner length in a more compact package.

http://www.twin-turbo.co.uk
http://www.hillclimbandsprint.co.uk/default.asp

A man without a project is like a like a woman without a shopping list.

I found the flow simulation and some other data of interest:

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."

Glad you raised this one, I have been thinking about the same thing recently.

Me too.

I was looking into making some carbon plenums and this was the sketch layout:



Yes, version 24. I'm currently on version 28.

Anyway, I had drawn both options in the cross section of the plenum, but moved on to another design before doing a CFD run.

If there is sufficient interest, I could do a CFD run of both options to bottom out the best flowing inlet.

Edited by Paul S on 15th Dec, 2013.

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."

All,
1st post. Have an interesting site here. I don't own a Mini, please don't hold it against me. There are not many locations of good information related to EFI'ing and Turboing of siamesed port engines. I am working on a Packard flathead straight 8 actually. My dad used to race a Austin-Healey Sprite with a 948cc when I was young.

My question is if you don't mind is, do siamese port engines respond like normal engines plenum design wise? Or do they need something different than a traditional plenum that is 1.5 times the engines displacement.

Thanks and sorry to bring back an old thread.

John R.

Not many of us are running EFi with big plenums on siamese ports and us that have haven't actually tested different plenum volumes, so do real data to go on.

There's no real technical reason why plenums for siamese ports should be any different from normal though.

My simualtions have shown that inlet runners have the most significant impact on engine performance though, particularly with the 5 port A-series.

Depends on the firing order and port arrangement on the Packard though.

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."

Paul S,

Thanks for the reply. I will research intake runner length and stay with the traditional 1.5x engine displacement. The Packard is 1-6-2-5-8-3-7-4 sort of like 2 A-series 90* off, so the 4 siamesed ports all feed cylinders that fire 180*/540* like the A-series. I do have 1 exhaust port per cylinder though.

Thanks much,
John R.

If I have found the right one using Google, that certainly seems to be a very interesting engine....

Side valve with siamese inlets and individual exhausts (as you describe) and all on the same side of the block, like an A series, which is presumably why they used siamese, not enough length down one side for all individual ports.

Firing order certainly gives the same overlap of the inlet valves so potential charge robbing but, again only if I've been looking at the correct images on Google, it looks like the side valve design gives a nice short run from the block face to the valve, possibly even shorter than the A series.

Whilst Paul rightly says the overall runner length is probably the most important issue, when it comes to the EFI side of it, my experience is the closer you can get the injector to the valve (ie, true port injection, not just somewhere back near the plenum) the easier it is to set the injection timing against RPM/load because the transit time (injector to valve) is less, wall wetting is less, etc., etc.

Plenum I aimed for 1.5, achieved 1.3 because of space limitation. But as Paul says, no real comparative data yet.

I believe Graham T's new inlet setup will have the option of a couple of plenum sizes both of which will be larger than his current one (read the other thread on his dyno comparison a while ago) so we may learn something from that.


EDIT - typo

Edited by Rod S on 10th Mar, 2018.

Schrödinger's cat - so which one am I ???

Rod S, yes that is the one. I have been doing alot of research here since the efi'ed turbo'ed A-series is probably the most analogous experience to what I am trying to do. Thanks for the comments and I will find Graham T's Dyno Comparison.

Best,
John R.

Edited by Graham T on 11th Mar, 2018.

’77 Clubman build thread
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=618189

Siamese 5 port EFI testing
http://www.turbominis.co.uk/forums/index.php?p=vt&tid=611675

Graham T,
Thanks for your reply. I assume your earlier plenum(s) were smaller volume, compared to your displacement? Does the large volume effect throttle response?

Thanks,
John