EVO Intake discussion I had with a mechanic.

[Lil bastard]

Originally Posted by Jaxonalden

LB,
I agree with what you said except the intake air temp claim. For ambient air temp to affect the engine it would have to be pretty high, 150-200 degrees. In a naturally aspirated engine I think you will agree that the air temp in the manifold is pretty low, in some instances actually causing frost to form because of rapid expansion. I'd like to know where the temp is taken that Jaay is getting on the Scangauge tool.

Well, not really. Adiabatic heating is the result of compressing a gas - any gas, including air.

The basic numbers are that for every PSI in pressure increase, you increase the charge temp by 1°F. Now I do not have absolute values for the Boxster, but several other mid-engined cars I owned ran engine bay temps of 130°F - 150°F.

Let's say that a Boxster is driving in 90°F ambient temperatures. And, for ****************s and giggles, let's say the engine bay temp is 150°F. Now, lets assume that for the short run through the airbox that the 90°F intake air picks up an additional 8°F of heat through engine bay heat migration (I have no idea what the actual value would be, but feel these are conservative - I suspect the actual value is higher, by maybe 10° - 15°F, but for theory's sake, we need to use some value). Anyway, you would now have 98°F air entering the cylinder.

The Boxster has an 11:1 CR, meaning that you are compressing the air 11 times it's normal volume, and increasing it's temperature 11°F to 109°F, or greater than 10%.

10% is a lot when you consider that the DME is so finely calibrated to react to dynamic conditions.

Even if the addition of 11°F of heat is insufficient to actually cause, or contribute to detonation (and I'm not saying that it isn't), given the very definite parameters programmed into today's ECU's, it's entirely possible that this value alone could cause the DME to select different (read less efficient) maps to operate the timing advance, EFI duration and volume, etc.

When an ECU is forced to operate under less than ideal conditions (which is what it's optimally programmed to do), it responds by causing the engine to operate in a less than ideal state with respect to performance, emissions and/or range.

I too am not confirming or condemning the mechanic's statement(s), only pointing out that with today's modern engines, concerns about intake temps are more valid than ever and any device with the potential to increase them should be looked at very hard before blindly implementing them.

So far as any values returned by the scangauge, I suspect that they're derived from the intake temp sensor which is integral to the MAF.