924Board.org

[ideola]

Bruni, there's another fallacy in your argument, I think. If I can paraphrase, what you're basically saying is this: you worked on a race team that had a reasonably large budget, so because that team didn't use phenolic on that application, the whole concept of phenolic insulators is null and void.

Here's the fallacy: in that kind of environment, i.e. race team with lots of money and R&D capabilities, I would not expect to see a 5HP gain from ANY single modification. It's called the point of diminishing returns.

But for those of us with very limited budgets modifying street cars, there certainly are opportunities to achieve 5HP gains with relatively minor mods. Granted, it's harder on the 924/931 because of the inherent limitations of the head, but it's not uncommon to see simple things like cold air intakes, freer flowing exhausts, underdrive pulleys, etc. free up as much as 20HP on stock vehicles. These are ALL well documented and tested. By extrapolation, if you took that same cone filter and put it on a race car, it would probably make performance worse due to all the other fine tuning that had already been done! So your anecdote IMO is fallacious.

I don't mean to question your experience, but I'm not sure the logic you are using to arrive at your conclusion is supportable, both in the conceptual world as well as the real world; i.e. show me documentation that refutes the IAT and dyno plots, and your argument will be more believable. But bear in mind, the comparison should be fair. Showing that phenolics make no difference on a highly tuned race car is not a fair comparison to the tests described elsewhere in this thread.

Oh, and by the way, phenolics ARE used in other forms of racing, namely in drag racing.
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[tuurbo]

[bruni]

Oh this is fun

[The basic function of the insulators is to reduce intake manifold temperatures, ]

This is the crux of the issue, I agree with this statement, to my knowledge this type of heat insulator was first used on carberated engines in-particular "V" confederated engines where the heat soak into the carburetor would evaporate the fuel in the float chamber and they worked very well, I don't think i have seen a V8 carb engine without such a spacer.

What you have to ask yourself is what effect (cooling or heating) the manifold temperature has has on the AIT. Now there are many factors that will that will affect this the 3 main ones are I believe
1 The temperature difference between the air entering the manifold and the temperature of the manifold
2 The mass or volume of air passing through the manifold
3 The surface area of the manifold

Now I had a team of engineers that did the maths for me and they said wast of time, but I had money to spend so we set up a test on the flow bench and used a heating element wrapped around a single inlet tract we stopped at 150degc with no significant reduction if flow.

You talk about the law of diminishing returns this states that you have to spend more to get less Now do you think that if I could get 5hp for $50 I would pass it by? Show me the road cars fitted with phenolic spacers, a Porsche, a BMW ? perhaps this guy with his laptop dyno knows something they don't

Now I don't really care what you spend your money on, but this is "snake oil"
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1982 931
1975 harley sportster

[tuurbo]

So are you saying, Bruni, that when used in a carburetor, the hot metal could easily heat a small amount of gas, but this kind of heating is different from an air intake manifold, where the issue is a large volume of air being heated by a relatively small amount of metal? If so, I get why theoretically it's going to be more of a challenge to cool that air charge with a manifold - a manifold is very likely not effective like an intercooler.

But to prove this case that it is snake oil, we'd need the math. Do you happen to have a guy you can email for the math, Bruni? It might be worth a peek. Or if you can dig them up, the bench results?

Sometimes negative test results are because the testing conditions need a tweak to make the right comparisons.
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1980 924 turbo, MSD, Meth. Inj, otherwise stock.

[ideola]

[tuurbo]

[!tom]

The key here is that we are dealing with heat transfer to change the temperature, rather than other methods of changing temperature (like compression).

Heat transfer involves a number of variables, like temperature difference, time, etc.

When it comes to gasoline in a carbeurator vs. air in an intake plenum, the time scales are quite different.

Although insulating the intake plenum from the head will theoretically cause a lower temperature to the intake charge, provided the IAT is lower than the temperature of the head (if higher, the head could act as a heat sink for the plenum), the difference in temperature may very well be very small as bruni points out.

And, sorry ideola, but from what I saw from the quote you posed last page, it appears to me to talk about the plenum temperature, not the temperature of the air inside.

As has been pointed out before, the design of the intake plenum would make for a pretty crappy intercooler, which implies it will make for a pretty crappy interheater, which is your concern.

I'm quite positive the spacers will do what they claim to do, if their claim is that by fiting them you will have colder intake temperatures. However, if your intercooler drops the temperature by 20 degrees, and these spacers cause a further 0.2 degree drop, is it really worth it? I think that is the point bruni is trying to debate. In fact, benefits of fitting them may be outweighed by the necessary restrictions in flow due to the extra gasket that is necessary to use them.

It seems to me that there are many important reasons why these insulating spacers may be used on an intake plenum. Some that come to the top of my head are to keep a carbeurator cool (not applicable here), and to reduce heat-soak on an IAT (Intake Air Temperature) sensor (not applicable on a stock 924/931, but may be applicable to some custom jobs guys are doing around here). It seems as though a side benefit to those applications is a lower intake air temperature. However, this may only be a side benefit, and this reduction in temperature may very well not be enough to justify the very little complexity increase in having these spacers.

Clearly, reliable data is necessary. I, as are others, am skeptical of the dyno plots. I'd like to know just how much heat is transfered to the air when going through an intake in real-world applications. I'm sure it's far less than there would be to fuel in a carb, or its impacts on readings from an IAT sensor.

By all means, I'm sure there's a reduction in temperature. But is there a point? When the topic was first brought up, I too thought it would be a no-brainer. But further thought has me wondering if it is worth it in and of itself.
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78 924 NA

[bruni]

Eureka
I hate being negative so I'm going to post 5 ways to get a minimum +5hp for less than £50
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1982 931
1975 harley sportster

[Min]

[bruni]

I think you will find that is a cost issue it is a chev after all To be serious the plastic manifolds have a fantastic surface finnish on the inside and can be held to tighter tolerances than aluminum manifolds and require little or no machining, however I think Ford have had big problems with plastic manifolds
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1982 931
1975 harley sportster

[ideola]

I used to work for a company (Hayes Lemmerz International) that manufactures the injection molded manifolds for MANY cars, domestic, European, and Japanese. The main purpose of injection molding is weight savings and overall lower cost of production, has nothing really to do with performance. Remember, OEM cars are not built for performance, they are built for fuel economy, especially with modern fuel efficiency requirements.
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[morghen]

the manufacturers might also choose not to use phenolic for the gaskets because of cost...but serious race cars should have them....do they ?
I dont think that there is anything that is not common knowledge about engine tuning...those times are over since the 80's.
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924 Carrera 1.0bar == grin factor. 10/10;
932 K27 - WIP
http://www.cardomain.com/ride/3181205

[bruni]

I have worked for several manufacturers and manufacturer supported race and rally teams over the last 25 years, many had their own engine departments and others subcontracted to some of the best engine builders in UK Europe and Scandinavia, I can't recall any of them using any type of insulators.

One last thought for you to ponder on, if the the inlet manifold is so good at transferring heat to the air rushing into the engine how come it does not feel cold (on a N/A) you would think it would drop to the temperature of the air entering the filter

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1982 931
1975 harley sportster

[ideola]

A radiator radiates heat and still feels hot to the touch.
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ideola's garage
Unique Products, Used Parts, Group Buys & Downloads for the Porsche 924, 944 and 928
Visit our CarDomain site

[bruni]

your missing the point, the outside of a radiator is pretty close to the temperature of the fluid running through it, why is the manifold not close to the temp of the air running through it? it is because the surface area of the inside of the manifold is so small in relation to the volume of air flowing through, even the smallest top mounted intercooler has a surface area 100s of times greater that the the inlet manifold.
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1982 931
1975 harley sportster