924Board.org

[Vince Ponz]

For all that are interested I tend to believe them.

www.Autospeed.com/cms/A_110474/article.html?populararticle
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"Never let them see you sweat"
77.5 924 modified track car
79 931 Euro stock
88 924S SE
87 911 Targa stock

[ideola]

Vince, this is the same article that we've been debating about over in the performance upgrades forum for the last several days. Note that it was originally published in 2000.

The issues that are up for debate:

• The intake temp claims are somewhat deceptive because the article discusses the temperature of the intake manifold itself, NOT the intake air temperature.
  
• The objectivity of the author is in question because he works for a company that manufactures these spacers
  
• The dyno numbers provided are simulated by software, not actual dyno numbers
  
• The before-and-after speed results are questionable because they were not measured on the same day under the same set of circumstances...the test was not conducted very scientifically
  
• The author makes a somewhat dubious claim by saying "During its residence in the intake manifold casting, the air charge picks up unwanted heat from the manifold". After debating at length on this and consulting with other performance experts here in Detroit, I am beginning to doubt this claim.

I am going to write an email to Autospeed to see if we can get a response back from the author or the magazine editors.
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erstwhile owner of just about every 924 variant ever made

[!tom]

[ideola]

[!tom]

I can't answer that question definitively, because for one, it can't, and for two, I don't know enough about the subject to know how much is significant.

However, I would intuitively expect a temperature change in the applications we're talking about (that is, a forced induction environment where the air in the intake tract is well above ambient) of on the order of a degree or two (I'd guess less than 3, but I wouldn't be surprised if it were less than 1), which is in the realm of it really doesn't matter. Think of the difference in ambient air temperature at the intake to the entire system in every day circumstances

As I opined earlier, there would probably be a bigger negative impact of the air flow passing over an extra gasket discontinuity than you'd see with the intake air temperature change. Think of how much MORE the intake charge will heat up when it is passing over the intake valve, or in the intake port in the head, due to the even higher temperature of those components than the intake manifold, especially once they are insulated from the intake manifold which will dissapate heat on both its inner and outer surfaces.

Again, I'm sure the air picks up some heat from the intake manifold, and it would follow it would pick up less heat from an insulated on than a non-insulated one. But, I also expect it's too small to matter.

Again, this is just arm-chair physics -- I don't even have an envelope out to scribble on the back of, so take it for what its worth.
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78 924 NA
5-lug

[Martijnus]

fun thing I didn't want to mention in the other thread.

I've seen rolls royce engines and many other engines (from 70years ago) which had the intake manifold running past the exhaust manifold, just to heat the mixture.

The effect is a much more homogenous mixture and thus a smoother running engine.

On the other hand, 'our' theory says to pack as much air (hence cold air) in the cylinders as possible.

A bit contradictory, but I still believe a hot mixture makes your engine run better in some cases (I guess it's depending on compression ratio etc etc).

Anyway, what I mean to say... sometimes the obvious (or currently supposed) isn't always the best. (take that ockam's razor!)
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"Rule: Turbo's make torque, and torque makes fun." (C. Bell)

924 "50-jahre", 1981.
MSII/extra, LPG, ITB's, 5lug.
To be turbo'ed in a while.
Killed her at the Nurburgring, Porscheless at the moment

[!tom]

The beater I commute in during the winter runs coolant through the intake manifold. The carb sits on a plastic spacer on the intake manifold, so it is insulated somewhat.

Is this to prevent the carb from icing? I have no idea. Does it help warm the car up quicker? Discussions here would suggest not much, so I really can't answer why. It also came with a baffle to draw air into the intake from over the exhaust manifold for winter driving. This sounds more like carb heat to me.

Clearly they weren't all that concerned about getting the coldest possible air into the engine. But, it ain't got forced induction either.
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78 924 NA
5-lug

[!tom]

[ideola]

Again, the point being on a stock factory delivered motor, the goal is to produce the most reliable, trouble free, fuel efficient, cleanest burning car without too great a compromise to performance. Performance and fuel efficiency are usually trade-offs...in other words, optimum settings for performance rarely result in optimum efficiency...and vice versa.

The point being, I could care less about reliable cold starts, fuel efficiency or clean burning on the race car. I want the most power possible. So looking at what a factory car did regarding induction is seldom illuminating, especially if it is normally aspired.

It seems like the only way we're going to get to the bottom of this is to make up a spacer and run our own tests. I may just go back to my original plan, which was to order up some material and make my own spacer using a jigsaw. Problem is, I won't have a fully configured car suitable for A-B testing (with an IAT sensor, NOT an infrared pyrometer measuring the manifold's temp) for probably close to a year.

We shall see. To be continued.
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erstwhile owner of just about every 924 variant ever made

[tuurbo]

[ideola]

tuurbo, I will definitely be running at least one IAT on the UWB project. I'd do this on the 941 over the winter, except that I'm not planning to convert to engine management, and consequently the extra expense involved in rigging up IATs for monitoring would just be a costly and silly distraction from the UWB project. So if I ever get around to it, it will be when the UWB is built and ready for dyno time. Which may not be until late summer next year.
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erstwhile owner of just about every 924 variant ever made

[bruni]

[ideola]

[bruni]

I think for the average street car you are correct, however if you have the option of anti lag or launch control programed into your ECU it really is worthwhile. Using a total loss cooling spray does lack some finesse I agree, however it can be quite effective at pulling down the AIT
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1982 931
1975 harley sportster

[ideola]