building an alloy plenum

[t5 pete]

Since seeing Rob's thread on his plenum it's gave me the itch to start sourcing parts for the 240 first off tho I understand you need to get the volume of the chamber to the same or above the ltr of the engine? and runners regarding length I've searched the net but not come up with any decent info or at least any in layman's terms just a shot are sweet answer.
The ltr of the engine is 2.3 looking at other plenums people just seem to make them to any size some 2ltr engines have huge chambers then others like cosworth tiny ones.
Any Info would be much appreciated

[claymore]

Short runners will give you more at the top end, like mine, long runners will give you more bottom end torque.

[LiamT4]

Short runners will give you more at the top end, like mine, long runners will give you more bottom end torque.

It says the opposite on this site Colin (near the middle of the page)

http://www.enginelabs.com/engine-tec...ake-manifolds/

[t5 pete]

Lol this is the problem there's just so much conflicting info but most I've read it that longer runners give more low and mid range tourque and short runner higher top end power read a really good article from jaguar designing their manifold which said what I've just wrote.

[LiamT4]

I've found plenty of info on a site called physicsforums.......................too much though lol

[t5 pete]

Mine field or what I'm currently looking at a plenum of 3.5 ltrs then just need to source some bell mouths

[jamesy12345]

A bit of basic BS here fella

http://www.sdsefi.com/techinta.htm

"Short runners are good for high rpm torque as in a racing situation. Long runners are more applicable for street use at lower rpms."

as Colin said

[claymore]

Mine wouldn't rev to 9000rpm on the standard manifold, but with my manifold it has an extra power band from 7000 to 9000 rpm, you can here it on some of the incar footage at prescott

[claymore]

standard 850 t5 manifold looks quite short runners, but when you unfold then (virtually) they're quite long

[smithy]

Short runners more top end long runners more bottom end

[classicswede]

To a fair extent you want to match teh runner length to the cam. As short cam wants long runners and a longer duration cam will normally want long runners. The engine stroke length also has an effect on what length runners are going to be more ideal. The space available in the engine bay is going to be your biggest restrication and limitation.

I have not seen any side by side comparisions for the Volvo engine with different legth runners not even on Swedish sites

[stribo]

My Cougar, well all Cougar and Mondeo V6s had different length inlets on the manifold, at up to 4500 rpm, only the long pipes were open, after 4500 rpm butterflies in the manifold opened the short ones as well. Take from that what you will, but I tied the butterflies open, so it was running both all the time, I also had the quickest Cougar from 0-60 on the forum.

[MoleT-5R]

standard 850 t5 manifold looks quite short runners, but when you unfold then (virtually) they're quite long

so the later p1 v70 onwards (me7) manifolds should give gains at top end then as they look to have shorter runners compared to the older style 850 type

[oblark]

so the later p1 v70 onwards (me7) manifolds should give gains at top end then as they look to have shorter runners compared to the older style 850 type

The ME7 inlet manifold is one of the worse manifolds to use, the plenum chamber is to small, the air has to travel in two directions and not all the runners are straight. I've only found this out after doing research for my plenum chamber.

[t5 pete]

The ME7 inlet manifold is one of the worse manifolds to use, the plenum chamber is to small, the air has to travel in two directions and not all the runners are straight. I've only found this out after doing research for my plenum chamber.

Did you work on any theroy regarding the size of your chamber or was it just a case make it to fit and then you worked out the ltr

[960kg]

It says the opposite on this site Colin (near the middle of the page)

http://www.enginelabs.com/engine-tec...ake-manifolds/

This LINK is great reading and is correct to all my knowledge of tuning manifolds!

Mine wouldn't rev to 9000rpm on the standard manifold, but with my manifold it has an extra power band from 7000 to 9000 rpm, you can here it on some of the incar footage at prescott

For you to make this statement about being opposite to the correct length of runner you must of altered something else at the same time and not only the manifold to make it run better!

To a fair extent you want to match teh runner length to the cam. As short cam wants long runners and a longer duration cam will normally want long runners. The engine stroke length also has an effect on what length runners are going to be more ideal. The space available in the engine bay is going to be your biggest restrication and limitation.

I have not seen any side by side comparisions for the Volvo engine with different legth runners not even on Swedish sites

This members logic is the correct one as other things effect the runner length for performance.

The cam timing has to be altered to suit a particular length of runner so as not to give bogging down performance.

Ok so look at the first pic. a standard T5 manifold ......in anybody`s terms those are Long runners which is partly why the motor does a fast 150mph.

Now look at the second pic. as it`s an ME7 manifold and has already said the design to some is crap .....so why does the later T5 still do a fast 150mph?

Simples:... `cos it has VVT which alters the cam timing to suit the manifold.

You can all go around in circles all day wandering which is best but until you understand the logic no where will be arrived at...only posts saying opposite to others answers!

[t5 pete]

This LINK is great reading and is correct to all my knowledge of tuning manifolds!



For you to make this statement about being opposite to the correct length of runner you must of altered something else at the same time and not only the manifold to make it run better!



This members logic is the correct one as other things effect the runner length for performance.

The cam timing has to be altered to suit a particular length of runner so as not to give bogging down performance.

Ok so look at the first pic. a standard T5 manifold ......in anybody`s terms those are Long runners which is partly why the motor does a fast 150mph.

Now look at the second pic. as it`s an ME7 manifold and has already said the design to some is crap .....so why does the later T5 still do a fast 150mph?

Simples:... `cos it has VVT which alters the cam timing to suit the manifold.

You can all go around in circles all day wandering which is best but until you understand the logic no where will be arrived at...only posts saying opposite to others answers!

In regards to the last comment regarding understanding the logic do you understand the logic and a principle of what is needed regarding building the plenum as I do not know and would like to.
I would roughly estimate 80 to 90 percent of what I have read stated that the longer runner give the better low down power and tourque.
If you do have good knoledge on this I would be great full if you can expand on it and info on what is needed regarding volume and length.

[960kg]

In regards to the last comment regarding understanding the logic do you understand the logic and a principle of what is needed regarding building the plenum as I do not know and would like to.
I would roughly estimate 80 to 90 percent of what I have read stated that the longer runner give the better low down power and tourque.
If you do have good knoledge on this I would be great full if you can expand on it and info on what is needed regarding volume and length.

Because these type of threads turn into real arguments and abuse the best thing to do is read this link about Husseins motor. Somewhere around page 60 to 70 he goes into detail why he fitted and why he removed it and also mentions altering the cam timing when he removed it back to his normal!

Smithys shape plenum is the ideal on Oblarks thread so have a look....i cannot say actual lengths but can only say that the homework has already been done these others because of the room available between engine and the slam panel.

I have copied my post over to here so i don`t have to rewrite and this explains the difference and why the length of the runners matter:

I think it is good to have varying discussion so why remove posts as they are still to do with Plenums on performance motors as this is what this forum is about!

There are not many that have been there with actual tuning methods and my apprenticeship was at Brands in the `60`s, as i have said before whatever is useful to an N/A engine also useful for the turbo as it is all about airflow....whether boosted or not.

The plenum has to be tapered at the furthest end so to equalise more or give the last cylinder in line a chance of the same air pressure as the forced or ambient air is pushed up the plenum it will still compress at the narrow end more that at the larger end and so will cover the space quicker to the last cylinder to balance out the amount to each cylinder.

You can see the bolt up line on that Cosworth engine Plenum as that too is tapered inside but is rectangular outside. The inside technology is the important thing.

We used to call them inlet trumpets but the but the later term seems to be "runners" which the ends of (bellmouth) inside the plenum should still be tuned because of the vortices around them.......the longer they are the higher top speed because when the air enters the runner the air waves accelerate faster down a longer tube and the higher the speed of the air will be when entering the combustible space thus packing more charge for a higher top speed.

With shorter runners the opposite is the effect as the charge will then be slower down the tubes but as the boost is nearer the combustion chamber the motor will accelerate quicker as it gets it`s charge quicker.

One thing on the turbo motor will be where to put exactly the boost vacuum pipe for best performance as even though the boost supplied may be 15psi but in the plenum it will vary because of it`s shape and delivery?

Of course this is not the all and be all as the cam timing amongst others effects things also but then as you know this is why some other motors are faster as they have done there homework!

Just trying to help and not hinder...Lol

One thing that has been overlooked is the fact that the runners MUST be tuned on the end of them as a bellmouth is on a carb. for example. The air around these runners causes vortices which must be the correct shape and flow etc. to travel down the runner.

If still not understanding why the length of runners just think why did motorbike companies bolt the carb directly on the barrel .....it was to give max. acceleration while the larger cubic capacity gave the power for top speed.

[claymore]

I can certainly find just as much info that contradicts the above post, I calculated my plenum capacity to be 2.6ltrs which as far as I'm concerned works for me, I was deliberately tuning for low torque to protect the rods, but I don't really know what I'm doing, I've never won any races or rallies in the 30 years I've built and raced cars.

[t5 pete]

Thank you for that im just currently reading his thread it is very interesting one thing he did point out it the improvement of low end power on the stock manifold and then felt it was running out of steam high up well to quote
Makes sense, for you, with the shorter runners you'd be losing bottom end. There is no doubt the stock runners, which are around 13", are useless for good top end breathing. I felt an immediate difference the first time I put it on. Finally have all the welding & port issues resolved, so I'm looking forward to getting mine back on the car.

Ill shortly put a picture up of the plenum im looking at as I do like the design and being cast not so prone to cracks as Hussein had problems with his plate design.