NZ951

Yeah some idea, but I want to scienfitically determine it based on distance and resonance travel time. So when the intake valve closes and pressure resonates off the plenum, the length means the valve is open on a return "stroke"... I am not sure when that is though, I know it travels at the speed of sound though, but not the time between valve cycles at say 4500rpm.

RobNL

NZ951, I think most literature you've read about plenum size and runner lengths is for N/A engines. For those engines harmonics is much more important because it's one of the few way to improve air speed and the total amount of air that is sucked/pushed into the engine. I believe Porsche even uses variable runner lengths on the later N/A 911's to improve harmonics throughout the entire rpm-range.

For Turbo engines it's less important because you've a turbo charger that's pushing the air into the cylinders. You still have to avoid restrictions and improve airspeed, for example by tapering the runners.

If you looking for setup, similar to JME:


and still want to taper the runners to 40mm you need something like 48-50mm TB's.

BTW, now that you've read Corky's book, based on which of his statements you would say the intake manifolds of LR or SFR are poorly made?

Skunk Workz

The turbo doesn't push air in...it gives the engine an amount of air that's denser than one amosphere to ingest... if it's tuned to recieve it. You still need proper intake/exhaust tuning to get the most out of it. Or else you could just make the port flow a ton and all would be good and well...that's not the case,not for NA engines,and neither for turboed ones.

Dave E

The speed sound travels in the intake runner will vary somewhat with density, I don't know the equation but at 1 atm absolute at sea level we get 1100ft/sec. (if I remember my physics at all). At 2 bar (14.5 psig) in the manifold I suspect the rate sound is traveling from the closed intake valve back to the plenum and then back to the opening intake valve will be faster.

J Chen

Hi RobNL,

Yes I personally do think that the LR intake is a compromise.
With the TB at the inlet of the plenum, the volume becomes
much more critical in acheiving equal flow as well as good
throttle response. Also the runner lenght is too short for producing
good low end torque.

NZ951

Rob,

I think the runner length is too short on the LR design, and will rob torque (excuse the pun). I just did a search and someone dyno tested a loss of 15 ftq. Which is in line with the thinking of J Chen and I and others. The plenum is hard to comment on, I dont know the volume of it, nor can I see any taper in the runners, it may be there but I cant tell. As for the JME design, I think it should be symetrical, but cant because of the oil filler / AOS tube.

RobNL

Andrew,

I find your statements a bit to vague. First of all to what rpm-range was that car optimized? Any dynosheets including list of other modifications to show? Are the tests done on the same day/dyno. Especially with the intake manifold it's the total package that counts. You can't put a high rpm intake manifold on a low end torque configuration.

Hell, the European car project car with the new turbo produced less power and torque at a certain rpm-range than it did with the stock turbo. Does that mean that those new turbos suck (figuratively speaking)? No because from a certain point they gain a lot more than they've lost at the beginning.

If I've read your arguments correctly, would you say that the SFR intake manifold is even worse?

About the JME intake, can you tell me why the intake manifold must be symetrical? If so, the F1 cars should have an awfull big problem. The AOS can't be the reason. For that amount of money JME would have solved that issue. Aren't most JME-engines dry-sumped anyway?

evil 944t

ALL JME engines I've seen where all dry sump. Not to say they all are, just the 5 I've seen

NZ951

I dont know the rpm range... how would I? PM the guy, do a search you will find it. A symetrical design has a greater chance at equalised flow, pretty obvious really.