billindenver

I spent several years in R&D engineering at chrysler. In that time I learned that just because it looks like it SHOULD work, does not mean it will. Intakes seem like a straight forward design but there is a lot going on in there, especially on a forced induction car. I've had little exposure to LR's engineering, but the little I've had has not been good. I would hesitate before I trusted his team over the engineers at Porsche. I'm not saying improvements can't be made, but I am saying it is not as easy as it looks. My 951, with 23 psi of boost on a head down bone stock engine has been putting out a lot of power for 180k miles....with the stock manifold. At PCA races my car hangs with GT1 cars on the straights (bye bye in the corners)...so the power is definitely there and I find it difficult to follow how the stock manifold is so terrible. To each his own, but I've not seen many cars with this many miles on the stock engine still sporting under 5% leakdown. I just don't see where the problem is.

Bigger is better is often true (displacement, turbos, etc) but Porsche engineers knew what they were doing. Have a little faith.

Bill
89 GT-3s

Landjet

From what I was told and read the stock intake is lean on the #3 cylinder while the other cylinders flow equal amounts. The LR intake according to there website was designed to flow all cylinders the same and they say they have the flow numbers to show. Is this not the case?

TRWright

billindenver

Lean? Then how are so many 951's going so many miles with a lean cylinder? At 16psi mine put out 320hp at the rear wheels in it current form...I then pumped it up to 23psi. Where the dyno would say its at now is anyone's guess. That was 80k miles ago...much of that on the track. Leakdown is still great, so someone is going to have to show me some kind of proof that the stock manifold runs lean on any of the cylinders. That is just sales pitch, pure and simple. Remember, that testing is much like statistics....set the test up the right way and you can make it say anything you want. A flow bench does not answer all questions, it doesn't have valves opening on one end and a turbo pushed by exhaust at the other....it only has air...and that air is not the same as the intake in action.

Again, I'm not saying there are no improvements to make...but different is not always better. Based on my car and several friends...I do not believe the lean #3 sales pitch....it just isn't happening in the field. The intake doesn't know how much power the engine is putting out, all it knows is how much air is being shoved through it. There are plenty of cars putting out far more power than mine, but not a lot going far past 23psi...and mine has no problem with that air flow....stock.

Bill

special tool

I have 5000 miles wiith an EGT on EACH cylinder.
The stock manifold is balanced.

What anyone hears from typical Porsche speculators doesn't matter, if you want the facts, remember what I said.

RolexNJ

Laust Pedersen

Also with 4 EGT’s I was about to chime in with the same message. I too observe no meaningful difference between the 4 EGT temperatures at any rpm.

A flow bench does static measurements, while real life flow depends on resonance charging of the runners, so claiming imbalance based on flow bench measurements only should raise a flag about the reason for the claim or the competence of the person making the claim.

If the goal is to make power at higher rpm, then it would make sense to consider shortening the runners.

Laust

Landjet

Thanks guys this is nice stuff to know since I have yet to put EGT on each port to find out for my self.

Bill you have a 944T running in GT3s? Did you run Pueblo a few weeks back? I will be running mine at the Hallett Club Race for the first time in a few weeks are you going to make that race? Like to see the car if so.

Duke

The length of the runners are of significant importance when to decide where you want to make power. No, make that extremely important.

Although I find the typical statement "I trust Porsche know what they did" hilarious.

Yeah they knew exactly what they were doing! But when altering cams, heads, turbos etc. there isn't much left of Porsche's strategy for that engine.

If you want to make power past 6500 rpm (or more like 6000 rpm..) you should consider a different intake.

A good tips is to never forget the "system"-approach. Every part in the engine must work together, because they act together. If you change one part, another part that was optimal before might be the very opposite.

That said, on a stock engine the stock manifold is probably the best compromise. On a modded engine with different VE, probably not.

Laust Pedersen

Now that we are on the subject it may be very informative to take a look at the graph posted here from the SAE magazine “Automotive Engineering”.
This is the 3D graphical results of a simulation showing the volumetric efficiency as a function of intake and exhaust runner lengths. I don’t know the details of the simulation, such as which engine and for which rpm it is valid, but some valuable observations can be made anyway, namely:

1. The intake and exhaust runner lengths are not independent variables, so changing for example the exhaust runner length will affect the optimum length of the intake runner.
2. Changing either or both runner lengths by a factor of 2 (up or down) only affects the VE “only” by about 10% (i.e. a soft function).
3. I think it is a fair assumption that the graph also works for varying the rpm, so for example if the graph is valid for 3000 rpm, the exhaust runner is 600 mm long and the inlet runner is 200 mm long then doubling the rpm will be equivalent to halving the runner lengths (essentially "walking" diagonally on the surface as a function of rpm with fixed runner lengths).

Laust

95ONE

seems like some have lost the point. Honda puts EXCELLENT engineering in their cars. It doesn't mean it can't be IMPROVED on. Not saying they did a bad job so it needs to be changed. I think alot of us. At least ME. are saying that theres room for more horsepower. Isn't there always? Nothing more.

special tool

we realize this - laust and I are saying that tthe factory manifold does not flow unevenly.
certainly we can make one to flow MORE, or Tim can, I can't.

Rogue_Ant

How about just shortining the stock intake? Anyone tried that before?


Rogue

95ONE

Actually S.T. that wasn't directed at you at all! I was trying to be general and not point directly at billindenver, but I guess I should have. Your point was something I LOVE to see on forums. Internet myths always get out of hand and Its great when someone knowledgable and respected on any Forum stands up and straightens it out. I seriously wasn't sure about the un-even intake thing until I read your post eagerly. I've pretty much appreciated all your honesty and Straight forward approach since I've signed on. Can't stand a$$ kissing, but I like to give credit where credit is due and make sure you know my post was not in response to yours.

Rogue_Ant

Blah, looking at it I don't see a decent way of shortening the runners...


Rogue