Street Car Peak Power Where Is Best

[sweepa]

from what I can gather you really seem to be more interested in the look and the plumbing than any real performance gain. have you considered just relocating the throttle body

done right it can work pretty well and look good too.

[Bsa]

Yeah I have

[rob82]

Hmmm - what GTSboy has said is correct. There is some misinformation in this thread though. Intake manifold tuning is just as critical on a turbo charged engine as it is on an aspirated engine. I have delived into manifold design quite extensively but my design has never come into fruition. I have read multiple SAE documents and have personally seen many different intake manifold designs over the years as a tuner. I can tell you that even the top manufactures get it wrong.

The best fail I witnessed was the cosworth plenum on a mazda SP23 MZR I4 2.3L. It lost power throughout the entire rpm range until 200rpm before the rev limit where it made a bee's dick more hp. The std plenum was dual runner length thermoplastic design where the cosworth was staic runner length with shorther runners and larger cross sectional area - it was never going to work.

If you want to do something difference - create a dual runner length plenum or introduce a way of dynmaically modifing the cross sectional area of the runner. Or change the material. Think outside the box!

PS - in this point in time with varaible cam control, direct injection, varaible turbine turbo's and HCCI I beleive the intake manifold is the only major part of an engines design that is yet to be exploited.

[Tony de Wonderful]

from what I can gather you really seem to be more interested in the look and the plumbing than any real performance gain. have you considered just relocating the throttle body

done right it can work pretty well and look good too.

I wouldn't do that since the OEM plenum was never designed to flow air in from the side. It is going to make cylinder 6 more likely to run lean I am afraid.

[Bsa]

Yeah thats y I didn't modify the stock intake. Thanks for all the info rob82 really got me thinking now. When I had my BMW I exterimented with the intake changing it from plastic to alloy and extended the runners and made the plenum smaller made a heap of difference with low end power which it was lacking it was the slanted 6 na. I think what your saying is correct the plenum does have a huge impact on the engine just trying to figure it out properly is the hard part. Iv drawn up 3 designs that I'll start making this week there will not be any progress photos untill completed as I kinda want to keep it to myself. Thanks everyone for the help sorry for reving a few people up sorry if I offended you.

[rob82]

Yeah thats y I didn't modify the stock intake. Thanks for all the info rob82 really got me thinking now. When I had my BMW I exterimented with the intake changing it from plastic to alloy and extended the runners and made the plenum smaller made a heap of difference with low end power which it was lacking it was the slanted 6 na. I think what your saying is correct the plenum does have a huge impact on the engine just trying to figure it out properly is the hard part. Iv drawn up 3 designs that I'll start making this week there will not be any progress photos untill completed as I kinda want to keep it to myself. Thanks everyone for the help sorry for reving a few people up sorry if I offended you.

Sorry it was a Cosworth intake manifold - not just plenum.

And to add I was also involved in tuning an XR6T with the aspirated duel inatke length manifold installed. From memory the boost was on about 400rpm ealier along with a huge increase in torque.

[Bsa]

Do you have a photo of one?

[DVS JEZ]

Dual intake with butterfly's sounds like an awesome idea, mission to make but awesome

[rob82]

Do you have a photo of one?

Not on me - its the same intake manifold ford has used on EF-BF I6 aspirated engines.

[Bsa]

I'll have a look might be a good thing on a rb

[Bsa]

Just looked on google look like it would be a hard thing to make but rewarding just have to figure out how make it work proper runner lengths all that stuff back to the drawing board. Thanks heaps mate helping a tone just thought of a great idea how to use the same sort of setup with twin tb

[GTSBoy]

A switchable Helmhotz resonator would have to be the easiest to achieve for the backyard fabricator. Much easier than trying to package 6 or 12 butterflies on a common shaft to make dual length runners happen. Trouble is, all the rules of thumb you commonly see splashed about for such plenums all have NA engines as the underlying assumption, and the density differences in a boosted engine's charge mean that all the sonic velocity and resonance tuning numbers move about - a lot - and change with boost level, which will be different on nearly every engine you sell a manifold to. So now you not only have to decide on a couple of different plenum volumes to switch between (or a couple of different runner lengths if you go down that path) but you then have to decide how and when you're going to switch between them. If you get the volumes a bit wrong, you can test on the dyno for ages trying to find a good switchover point, and come to the conclusion that it's a waste of time. But if you get them right, it will work nicely. At least for some of the engines they get put on. But now we're talking about a >$3000 manifold, not a

[Bsa]

I have a whole engineering workshop to work at. I know it won't be cheap but after doing one I can figure out how to do it faster and make it cheaper I'm not saying your wrong. I believe a can get it right one day could be a while before it happens but good things take time

[rob82]

A switchable Helmhotz resonator would have to be the easiest to achieve for the backyard fabricator. Much easier than trying to package 6 or 12 butterflies on a common shaft to make dual length runners happen. Trouble is, all the rules of thumb you commonly see splashed about for such plenums all have NA engines as the underlying assumption, and the density differences in a boosted engine's charge mean that all the sonic velocity and resonance tuning numbers move about - a lot - and change with boost level, which will be different on nearly every engine you sell a manifold to. So now you not only have to decide on a couple of different plenum volumes to switch between (or a couple of different runner lengths if you go down that path) but you then have to decide how and when you're going to switch between them. If you get the volumes a bit wrong, you can test on the dyno for ages trying to find a good switchover point, and come to the conclusion that it's a waste of time. But if you get them right, it will work nicely. At least for some of the engines they get put on. But now we're talking about a >$3000 manifold, not a

I think you will find that the sonic velocities at the length most runners are will have very little effect if you working from atmospheric pressure to 2bar of boost pressure. You've got to remember that air travelling in and out of an engine is close to sonic speed so with a 0.5m long runner your talking about timing multiple resonance pulses (depending upon rpm) - which essentially dulls the helmholtz effect.

I can tell you from experience in all the non OEM boosted applications I have seen on variable length manifolds I've never once had to move the rpm switch point - to my amazement!

If I were you I would be looking at designing two different runners with differing cross section area and length and then switch between the two. Use a plenum which is suitable sized to deliver an even charge across all cylinders.

BTW the best piece of varaible length intake manifolds mass produced is the FR500. I have tuned a stroked modular 4.6-5.4L V8 with one of these intakes - power difference from long runner to short runner was about 60rwkw!! Best sounding v8 I've ever tuned! BTW these intakes are magnesium and cost around $7000.

[GTSBoy]

I think you will find that the sonic velocities at the length most runners are will have very little effect if you working from atmospheric pressure to 2bar of boost pressure. You've got to remember that air travelling in and out of an engine is close to sonic speed so with a 0.5m long runner your talking about timing multiple resonance pulses (depending upon rpm) - which essentially dulls the helmholtz effect.

Actually, you're right. The sonic velocity remains constant at different boost levels (although inlet air temperature still has an effect and this is a wider range on turbo engines than on NA engines). I was convinced though that the tuning frequency of runner lengths varied with pressure. But now that I'm forced to think about it......if the sonic velocity is fixed, then the wavelengths are the same, then maybe they don't vary much with boost.

Trouble is, I have the opposite experience to you. When boosting an NA engine with variable manifold back in the late 90s, the switchover point had to be moved quite a lot to stop it killing the power when it switched at the original point. And there was little else done to the engine except an exhaust manifold and turbo. It wasn't my job, it was a friend's job, so I can't even remember what engine it was. But we spent a long time scratching heads and then working out how to change the switch point to get it working right. But this wasn't variable length runners like yours, this was a split volume plenum with valve in between.

[zebra]

The BA xr6 turbos used the same intake as the Na ones but ford removed the variable length butterflies

The latest ones use a yb cosworth esque centre feed unit with short runners

Forgot where I was going with this lol

[rob82]

Actually, you're right. The sonic velocity remains constant at different boost levels (although inlet air temperature still has an effect and this is a wider range on turbo engines than on NA engines). I was convinced though that the tuning frequency of runner lengths varied with pressure. But now that I'm forced to think about it......if the sonic velocity is fixed, then the wavelengths are the same, then maybe they don't vary much with boost.

Trouble is, I have the opposite experience to you. When boosting an NA engine with variable manifold back in the late 90s, the switchover point had to be moved quite a lot to stop it killing the power when it switched at the original point. And there was little else done to the engine except an exhaust manifold and turbo. It wasn't my job, it was a friend's job, so I can't even remember what engine it was. But we spent a long time scratching heads and then working out how to change the switch point to get it working right. But this wasn't variable length runners like yours, this was a split volume plenum with valve in between.

Yeah - the charge velocity reamins close to sonic velocity irrespective of boost level. Its really just the density of the charge that will change.

The xr6T manifold on BA/BF's is really easy to convert back to dual length by adding the valves and actuators and drilling a few holes.

[GTSBoy]

Oh, I wasn't talking about sonic velocity with any reference to the actual velocity of the air.  I was talking about it purely with reference to how the sonic velocity affects the acoustic properties, such as tuning frequencies (and hence wavelengths and hence lengths of runners to achieve the required ordered resonances).

But, on a matter brought up by you (rob), the velocity of air flowing through inlet runners has to average a lot less than sonic.  Typically for peak volumetric efficiency you aim for about 0.6 Mach at the inlet valve and/or narrowest cross section of the port - and the manifold runners are usually bigger cross section than the ports, so you'd expect the manifold velocity to not be much more than 150 m/s or so.

Edited December 5, 2011 by GTSBoy

[Roy]

Have you bothered going any further with an inlet manifold? Curious to know where you got your billet flanges from?

[Nee-san]

Did you only half read what I wrote. I understand the stock manifold is capable of the job I need but lets face it looks like shit. Forward facing looks so much neater and it improves pedal feel and maybe a bit more torque y not. Mathematics is the major factor in design your dreaming if its not. And yes a have access to getting it flow tested and all that which will be done

You do realise a centre feed plenum performs better then a front facing, even though it doesn't look as "Cool".