bureau13

Well, according to figures posted earlier in the thread, 10% would give a 1.5% improvement. I've seen people pay for smaller gains that that!

I'm torn on how cool it would look, actually. I do like scoops, but there's somethign to be said for the clean lines of the stock hood.

I actually do like those vents in the The Fixer's "RS" above....

jcorenman

There are two issues here: What are the air temps at at the intake (i.e. ahead of the filter), and air temps at the cylinder inlet just prior to combustion.

As John mentioned we've done a lot of monitoring of air temps just ahead of the filter, that is part of the Sharktuner Alpha-N system. We typically see quite a bit of rise (20-30C) when the car is fully hot and just sitting, with no air flow. Temps at the filter can rise to 50C, but drop right down to a few degrees above ambient when driving, even at relatively modest speeds. This is a non-issue IMO except for stop-light racing.

The factory cold-air plumbing (upstream of the throttle body) is all plastic, with low heat conductivity and little thermal mass. Providing a better source of cool air and keeping it from heating would be useful, but I don't think that is where the real issue is.

Kurt, your work focuses on the air temp into the cylinders, which is a whole different matter. Your method of getting a temp probe into the intake runner is brilliant, please forgive me if I steal that.

I've always believed that there was a lot of heating in the intake itself, the aluminum throttle, plenum and runners. There is abundant thermal mass, and terrific heat transfer capability-- exactly what you don't want, especially at slow airflows (e.g. cruising down the highway).

What surprised me about Kurt's results is how little and how slowly the temp came down after 10 min on the autobahn. The air temp at the filter would have dropped right down to ~25C so this suggests that the air was getting significantly heated by the manifold/plenum even at speed. Veeeery interesting...

Two things would be useful as a follow-up: One is to repeat the experiment with a smaller/faster temp sensor, the other would be to duplicate the intake in something with much lower thermal conductivity. I can work on the first, maybe Hans can print a manifold in nylon as an experiment?

Cheers, Jim

Alan

The pressure chart is inverted (have no idea why...?) Anyway ahead of the Rad is all negative until you go down to the nose.

Some have attempted an insulated internal air splitter from the nose duct to keep hot radiator convected air away from the intakes (obviously only effective at idle flows). Porken tried it & Jim M made it look nice & Herman K is making more. IMO this is a minimal issue except for at idle, the conducted/convected/radiated heat to the intake body is the much bigger issue

Alan

kurt_1

Jim,

I am more than happy if you find my design useful and if you can reproduce the measurement - maybe even reach down a bit further into the tube to get closer to the valves.

I did some crude experiments with a hair dryer and my resistor should register 60% of a 10 degree air temperature change within 2 -3 seconds.

I think that for the parts of the measurement with slow changes of load/flow the air temp is accurate down to a couple of degC. The exact temperature profile during the short WOT acceleration might not get fully caught.

With this results in mind I now look differently at the ubiquitous plastic intake manifolds which I used to despise as cheap crap!
_____
Kurt
90 S4 satin black metallic
928 OC Charter Member

Dictys

Can you just not replace the rubber gaskets between the air intake and the heads on a S4 with something with less thermal transfer properties? this would prevent some transfer of heat through to the intake, how much who knows.

worf928

Cp charts come from aero engineers. They make perfect sense for wings: Negative pressure is needed for lift. Lift is up.

jpitman2

I have a Suby GT (2.5L 4cyl boxer Turbo, 250HP) with a top mounted intercooler with very short air tracts. I have an OBD-II display connected that shows intake air temp live, pretty sure this is the temp that the ecu uses for fuelling and ignition control. At a steady cruise on the freeway the intake temp is reliably no more than 2C above ambient. As soon as traffic slows it rises very quickly, and I have seen it show 80C when ambient is 25C.
jp 83 Euro S AT 55k

mark kibort

on race day, the intake plennum is cold if you pull into the hot pits and check. it rises very quickly if you are not WOT!

potdog

I have made a Strosek style hood on my S4 with naca vents just in front of the air intakes / rad so air goes strait in air pipes and a power bulge at the rear of hood quite large fits between washer jets and about 24" long and only have a 75/mm hole cut in hood above the air intake and there is a difference showing on temp gauge . Could be better I think with moor metal cut out of hood ?.

Alan

Things may not work as you expected... The outside pressure is lower in front of the rad so you will actually have vents there not intakes... Venting it at the rear 'power bulge' depends where that is - if too near the cowl area that may have higher pressure and be an intake. If that vent is far enough forward (more like Matt's example - or further forward) then it could vent engine heat and would likely be the primary reason why you'd see any temp difference. However in that case I think it's also likely your HVAC will be sucking in some of that hotter air, may not be ideal.

Alan

potdog

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potdog

crap on computers have had no training just muddle through HO/HUM

Alan

Looks like those are the thumbnails not the pictures, but at least they show up.

Seems likely air will come out of the front vents (reducing airflow through the radiator at speed) and will enter the engine compartment from the rear vent assuming its at the back edge of the hood, and exit underneath.

I know it all seems counter intuitive.

Maybe tape some woollen threads to the opening edges and see what happens when you drive

Alan

potdog

Hi Alan will try the woollen thread .The exit is through a 75/mm hole under the rear bulge about in the middle of the plenum .

The Fixer

Porsche dd not vent the hood of the Daytona lightweight to look cool. All the people prior and since are doing it for gains.

Porsche wanted the lightweight to be as stock looking as possible for marketing reasons yet they really
vented that hood which is in plain view. Or could that be a special intake? It is in the high pressure location.

Anyway,
I have noticed modern cars like BMW, Rover and Jaguar to name a few are venting their engine bays as well for added efficiency.
GM vents the Corvette bays as well.

Can't all be doing it to look cool. But it does.

To test my hood vents at speed;

I could tape a short length of yarn (6") to the leading edge of the vents and see if they are sucked in or raise up.

Note my "RS" mirrors are that which the lightweight wore, but mine is almost 300 lbs. lighter.