my thoughts on testing were...

install spare manifold, with sensors installed
measure ambient temperature
with the car warm, go drive the hell out of the thing on a particular route, and then go do it on the highway as well (for high and low load comparison)
record the variance in temps and find an average

allow the car to cool.
then reinstall the manifold with the spacer under it, measure ambient, and warm the car up again, then do the same routes.

then compare the variance points along with the averages and post those here!

 

A dyno would be better. Open road testing is too subject to variables, like ambient temp, traffic, etc.

 

Let me first start out by saying that I am a Mechanical Engineer.

The increase in runner length does not disrupt helmholtz resonance, it changes the rpm at which you see the supercharging effect.

As for the benefits, colder air is denser air. On a different 4 cylinder engine with shorter runners than the 944's, I did a before and after comparison and dynoed an 8 whp and 13 ft-lbs gain with the only addition being a phenolic intake manifold spacer. The run-to-run loss reduction from heat soak was even greater than 8 whp. This was a 3/16" spacer with a modern fuel injection system. I read your 924.org thread and you talked of using 1/4". That thickness is not necessary.

Ideola I see that you were a proponent of these spacers until you spoke with your friend at MRT. He stated that the manifold would eventually equalize to the temp of the engine bay, which would be the same with the spacer installed as without, and that seemed to be the basis of his theory that these do not work. This is simply untrue, and a simple hand test is all that is needed to verify. I've recorded, on the dyno (not on a moving car), a reduction of close to 60 degrees F difference between manifold temp and cylinder head temp. This is due to a number of reasons. One is the fact that the intake charge is cooling the manifold as it enters. Since the manifold is not as hot to begin with, because it does not have the cylinder head transferring heat to it, the amount of heat removed by the intake charge is low. Also, any venturi effect in the intake system will lower the charge temp well below ambient. This happens usually at the throttle plate, which, guess what, leads right into the manifold.

 

now this is interesting

 

That's a nice gain and the guys with M45, M62, and M90 superchargers are experiencing similar results where it comes to IAT temperatures.
In the world of tuning the Iat's are very important for spark advance and how much you can increase timing with the iat's being lower.
This in turn should yield some extra horses which is what is being revealed with the phenolic spacers used in forced induction applications.

I would think that even in n/a apps, the iat's are going to be affected so that tuning can be done to add some spark timing for a bit more power without the dreaded detonation.

Good thread so far with some interesting views on how this is going to have an effect on our cars.
It's possible that with our older cars that tuning won't be coming into play with ignition advance as much as most OBDII setups in the newer cars that we probably drive too.

 

As far as everything reaching equilibrium, I think this would take forever. My manifold never has been as hot as the rest of the engine bay after a drive or a track session. I can grab onto the runners.

 

As I said, I'm not an engineer ;-) just relaying the information I've collected from a variety of sources.

Trust me guys, I want this to work...given the interest over on 924board when I surfaced the topic, I really want it to work.

I think until someone comes up with hardcore IAT differentials (as opposed to the anecdotal information posted so far), the skeptic in me (and many others, I suspect) will remain. One of these days, maybe I'll get around to testing one on my 931. So many projects, so little time!

 

In hind sight of reading this earlier, I'm not sure if you noticed that alot of car manufacturers are now using plastic intake manifolds which are impervious (to some degree) to underhood temperatures and heat soak.
Maybe this would answer your above post about performance and efficiency with new vehicles.

 

when i come up with some more money i would be willing to do dyno runs.

 

i was thinking about that yesterday after i thought that not even porsche factory or ferrari factory use phenolics, because they dont need to :]

 

Injection molded plastic manifolds are much much cheaper to produce than cast aluminum manifolds. My guess is that the plastic material allows for better fine tuning of the runners with less imperfections. The turbo charged 2.0l SAAB 9-3 also uses an aluminum intake manifold w/out a spacer.

 

Maybe we could come up with a repeatable test regimen that could be agreed upon by all, and tested on different platforms...V2Rocket has a 944 NA mule, I'd love to do a test on one of my 931's, and it would be great to test a 951 as well. If we had three independent results from three different platforms that all had similar outcomes, that might be enough to draw some conclusions.

944CS posted some interesting observations, but there are a couple of challenges to overcome: first, it's purely anecdotal; second, there's no mention of regimen or environmentals that went into the test, so it's not verifiable or repeatable; and third, there's no way to know if the results were from a reduction and IAT or increasing the runner length.

Mind you, I'm not doubting the outcome, what I'm suggesting is that lacking a documented test regimen and the associated data, there's no way to know conclusively what contributed to the noted changes. For example, as noted above, simply increasing the runner length could have an impact on where peak power occurs...so having juxtaposed dyno plots would be tremendously useful, vs. just stating an observed figure. Plotting observed IATs on the dyno chart is what is really needed. I know that's an expensive proposition, and I for one don't have the budget to do dyno runs...but man, it sure would put a lot ambiguity to rest...

 

your concerns are valid. if anyone has suggestions for testing conditions please let me know. i think personally that a high-load situation (carving corners on a mountain or whatnot) and a low-load situation (cruising on the highway) would be good as those are the extremes of most people's driving.

i can make a 931 spacer provided i have the manifold flange pattern. can you tell me if the 931 flange is the same as a 924 2.0L? if so i can get that easily, there is a 78 924 at my local parts yard.

 

One of the reasons is because most manifolds these days are plastic - it does not hold heat like aluminum. Plus, manufacturers have cheaper ways at getting to their power and fuel consumption targets. It would cost more than $10 per spacer, even for a giant manufacturer.

If you look at the very high end cars, however, where the accountants have less of an impact on the final product, you will see the R&D and money spent on the engineering ideals. For instance, the intake manifold on the Bently twin turbo engines has a special heat rejection coating on the INSIDE of the aluminum manifold.

When it come down to it, for the manufacturers it is a cost/benefit analysis that wipes out the phenolic spacers for use with aluminum manifolds.

 

No, the 924 and 931 intakes are not the same. However, I have spares of both sets of gaskets. I'll send you a PM.