Question on plenum size in the 2.5l intakes

[cpapashley]

something I read recently started me thinking when I was looking at the 2.5l engine upper intake manifold today. Maybe someone can give me an answer.

The volume of the plenum should be around 80 per cent of the volume of the cylinders to which it is connected.

I know a 2.5 l is fairly small, but would the plenum part of the intake truly be 80% of the volume of the cylinders. It just does not look very big when I compare it to some other plenums visually that are rated as able to give 100% volumetric efficiency at peak torque.

[jrak123]

Yup it sure is, there are a lot of bends in that thing. I worked with Ford Racing on this very thing for about 6 months. But when I made a couple sheet metal intakes I made them for the full volume of the engine. This is exactly how we would dyno an engine for brake power. we would even have premiums on the exhaust as well( kind of like an expansion pipe on a 2 stroke engine).

[cpapashley]

Originally Posted by jrak123

Yup it sure is, there are a lot of bends in that thing. I worked with Ford Racing on this very thing for about 6 months. But when I made a couple sheet metal intakes I made them for the full volume of the engine. This is exactly how we would dyno an engine for brake power. we would even have premiums on the exhaust as well( kind of like an expansion pipe on a 2 stroke engine).

Wow, that is a surprise, I need to get mine off and have a good look at it sometime. must have been awesome working with Ford Racing, must have given you lots of insight into how to get the best out of an engine.

Edit: So I am here pondering on this and thinking the imrc improves velocity at lower revs, has plenty of air available in the plenum so why is it that when the imrc opens (3300 rpm for me) it is like the car all of a sudden comes to life, now when you consider that the idea is to have torque available at the lower revs I just find that I could possibly have it coming in around 2500 and the car would be much more enjoyable to drive as a daily driver (bearing in mind that mine is an auto). It honestly feels so much like a turbo that has this almighty lag until 3300rpm when it goes, it is like "oh so now it is time to go".

So I am just wondering if anyone has moved the rpm point for the imrc around, and specifically lower down the range on a 2.5l.

[Gorman]

over on CEG; Terry Haines answers your questions. He was explaining that opening the throttle fully at low rpm causes the air flow to stall or cough back. This is why I was interested in a RAM air style intake....I have had the secondary opening point moved to 3200 in the past and it is great. There is more to it than just that. The tune I had was from Bluefin and they're not letting on...G.

[cpapashley]

Originally Posted by Gorman

over on CEG; Terry Haines answers your questions. He was explaining that opening the throttle fully at low rpm causes the air flow to stall or cough back. This is why I was interested in a RAM air style intake....I have had the secondary opening point moved to 3200 in the past and it is great. There is more to it than just that. The tune I had was from Bluefin and they're not letting on...G.

Thanks for that big G, I was starting to think I would go searching specifically for this issue, seeing it was so quiet.

I am sure around 2800 would be great if you could get the fuelling right. Understand what you are saying about the ram style air intake.

Hopefully tomorrow I can finally do some intake restriction analysis, yet to get to the point of checking air intake temperatures, but I will get there.

Haven't heard of Bluefin, must do a search

Thanks again, will go reading over on ceg.

[warmonger]

Originally Posted by cpapashley

Wow, that is a surprise, I need to get mine off and have a good look at it sometime. must have been awesome working with Ford Racing, must have given you lots of insight into how to get the best out of an engine.

Edit: So I am here pondering on this and thinking the imrc improves velocity at lower revs, has plenty of air available in the plenum so why is it that when the imrc opens (3300 rpm for me) it is like the car all of a sudden comes to life, now when you consider that the idea is to have torque available at the lower revs I just find that I could possibly have it coming in around 2500 and the car would be much more enjoyable to drive as a daily driver (bearing in mind that mine is an auto). It honestly feels so much like a turbo that has this almighty lag until 3300rpm when it goes, it is like "oh so now it is time to go".

So I am just wondering if anyone has moved the rpm point for the imrc around, and specifically lower down the range on a 2.5l.

I've moved the IMRC around and there is no real benefit to it. The imrc point is based on the tuning length of the intake manifold runners.
This is a fixed length and it gives the characteristic "dual hump" in the torque curve. If you aren't convinced then you dyno and see where the intersection of the low-rpm hump and the high-rpm hump would 'theoretically cross" then you set the IMRC point right there. I've looked at it and this point has always been withing +/- 50rpm of the factory imrc point.

[cpapashley]

Originally Posted by warmonger

I've moved the IMRC around and there is no real benefit to it. The imrc point is based on the tuning length of the intake manifold runners.
This is a fixed length and it gives the characteristic "dual hump" in the torque curve. If you aren't convinced then you dyno and see where the intersection of the low-rpm hump and the high-rpm hump would 'theoretically cross" then you set the IMRC point right there. I've looked at it and this point has always been withing +/- 50rpm of the factory imrc point.

Thanks for that input. I can understand that when you have no changes to the factory setup that would be the case. But changes to intake/exhaust surely would make some differences, although like you have said it may only move very slightly.

Will probably get some dyno time when I get the emanage settled and everything running well. So might look at what you have outlined.

Thanks again.

[warmonger]

Originally Posted by cpapashley

Thanks for that input. I can understand that when you have no changes to the factory setup that would be the case. But changes to intake/exhaust surely would make some differences, although like you have said it may only move very slightly.

Will probably get some dyno time when I get the emanage settled and everything running well. So might look at what you have outlined.

Thanks again.

Changes to the intake would alter some things....unless you just mean a air filter change or something like that.
Changes to the exhaust would (99% sure) have no effect on IMRC point placement.

[cpapashley]

Originally Posted by warmonger

Changes to the intake would alter some things....unless you just mean a air filter change or something like that.
Changes to the exhaust would (99% sure) have no effect on IMRC point placement.

I know that exhaust shouldn't affect it but the difference between the oem exhaust manifold and headers is so significant and the scavenging of the spent charge is so much better (not to mention the lack of the egr filling up the intake) I would think that would mean you could make some pretty significant changes to the air/fuel mixture coming in (especially at lower engine speeds) and get some pretty significant improvements in the lower torque band.

From reading and some other threads velocity is so vital and so I understand there would not be too much to play with but it is just if the cougar imrc comes in around the 3800rpm and on my vehicle it comes in around 3300rpm then it seems with correct a/f tuning there could be some significant improvements had for specific driving styles. It is only rarely that wot is used in daily driving. (yes I know, for some reading that is a shock).

I understand what you were saying that it is a matter of looking at the two torque graphs. So I will do some more reading over on ceg this week (time permitting).

Thanks for your input warmonger. Always so appreciated.

To add in some interesting fodder on the intake system, I was having a play with vacuum readings (pressure drop) on the intake system. Seems that there is about 4-5 inches of water so far in pressure drop from the start of the intake system to the MAF. Will finish off the experiement when I get some vacuum caps to block off the holes I am drilling in the intake system .

[warmonger]

Well, the headers should provide all that you are talking about but all that does is better empty the cylinders and help pull in the intake charge. Anyway, that doesn't seem to be any issue with exhaust mods because the increased air is automatically compensated for by the MAF and injection system.
The headers seem to complement the intake system but no changes in IMRC point have been needed even with headers and high quality exhaust systems.