How we drop intake air temp 40+deg.

[Brad Roberts]

Compared to a Z06 Vette, the Boxster's and Cayman's have a HORRIBLE intake air temp issue!!

The issue: the engine heat is trapped in the "box" called the engine compartment. Intake air temps on a 996/997/GT3/Turbo are way way lower!! They have clean air flow moving about in the engine compartment (think rear wing/spoiler)

How do we *help* kill off some of this heat being ingested into the engine??

We wrap the airbox and air intake tubes in heat reflective gold foil!! We also wrap the intake!!

Took about 4 hours to wrap this 987 air box for a race car we are building.

[pothole]

What are the numbers for this then? How much does the temp drop with the foil?

My uninformed George Dubbya Gut tells me the plastic box doesn't conduct heat terribly well and the airflow will be significant at the high revs where this actually matters and the air is being drawn directly from outside so.....

[Brad Roberts]

We regularly see temps 60+ degrees higher than ambient.

We measure/data log with the mass air flow meter that mounts just a couple of inches away from the round opening you see.

Use the gold foil? and the air intake temps drop.

The air box is just one part. We wrap the intake also (but this is not logged) so.. the mass airflow sensor is reading the air coming through the air box/snorkel.

The intake absorbs a LOT more heat do to the block being 6-8 inches below it.

[Brad Roberts]

I've worked on these in the past.. GM engineers told me about an entire team of people dedicated to air intake temp control on the Corvettes. They asked me about the Porsches.. I didn't know the answer.. then I data logged the info and got back to them. They told me what they do to get the intake temp as close as they can to ambient. I was not able to achieve ambient in the Boxster or Caymans.

I was told this 10+ years ago now.. This isn't the first air box I have done.

[j.fro]

I moved my filter and box out of the engine bay. Since I don't have a top or sound deadening, I was able to put the filter where the "tunnel" used to be and build a box around it.

[j.fro]

I moved my filter and box out of the engine bay. Since I don't have a top or sound deadening, I was able to put the filter where the "tunnel" used to be and build a box around it.

[Brad Roberts]

Good job!!

I had some good idea's on different air box system, but the owner of the car poo-poo'd the idea.

Funny part? I suggested to him we take air from both sides (2 years ago) The new 981's take air from both sides.. LOL

[mikefocke]

Given that the air intake is taken from the side of the car well above the heated pavement and passes relatively quickly through the intake I would have thought that there would be little heat transfer.

How were the measurements taken to confirm the effectiveness of this approach?

[Ian c]

You are ghinking about it the wrong way ...
the heat transfer is not from warm air going in , but from the heat of the engine transferring out ...

[jb92563]

Thats a good point Ian, its radiant heat therefore blowing air into the engine compartment would not have a huge effect, and so the foil is supposed to reflect the "radiation" and prevent the walls of the airbox from getting as hot.

What about those muffler heat tapes/blankets, those are also designed to prevent heat absorbtion and can further insulate the airbox.

I suppose a combination of all these things including more air blowing out the "conventive" heat as well in the engine compartment should all help.

[Ian c]

Exhaust wrap would work but weighs a lot more than gold foil

[sb01box]

I believe that wrapping the plastic does reduce the absorption of radiated heat and therefore the increase in the plastic body temperature will be less.
google plastic for auto and got DuPont zitel PA66 is one of such plastic.
can't find thermal conductivity nor thermal emission (absorption) coefficient.
as a norm, plastics do not have strong thermal conductivity and emission/absorption.
so i'm wondering how much of an influence does the manifold have.

[Topless]

I gotta go with Mike on this. I need to see some before and after hard data because it goes against what I understand about radiant heat transfer.

For comparison, 40 degrees is the equivalent heat rise across a highly efficient copper heat exchanger inside a 400,000 BTU gas fired water heater with 1,500 degree F. flames lapping at the copper coils. Water velocity is also spread out and slowed down to maximize contact time and heat rise. That is a very different environment than a Boxster intake.

My initial engineering thoughts:

- The plastic box and intake are poor conductors of heat.
- Intake air velocity is pretty high so not much heat-absorbing contact time.
- High velocity air is a relatively poor conductor of radiant heat.

Best guess: Little if any measurable intake radiant heat rise. This is easily tested with a temp probe at the intake grill for ambient and another just ahead of the throttle body. Compare results.

[mikefocke]

Well of course I may be wrong

But given that the air outside is liable to be lots less hot than the air inside the engine compartment and given that the air is passing quickly through the intake plumbing which should keep the plastic cool (except after the car has just been shut off when the radiated heat would not be countered by the incoming cooled air until the car had been running for a while) ...

I still am curious how you measured it as 40 degrees cooler after wrapping? Under what conditions were the measurements taken (was the engine compartment cover shut, how long had the engine been running and were the measurement taken with airflow going on because the car was moving)? And where were the measurement points?

I'm the resident skeptic and old enough to remember "trust but verify".

[The Radium King]

temp sensor is part #17 on the parts diagram here:

http://c782366.r66.cf2.rackcdn.com/107-10.gif

perhaps the air filter heat soaks - lots of opportunity to heat the air as it passes through the filter.

I read on another forum where a guy put ram air side vents on his boxster (you know, scoopy vents). from what I could calculate you need to be going 150 mph or so before you get the benefit of 'ram air' - forward velocity forcing air into the intake faster than the engine can suck it in - so I thought they were useless. what he noted, however, was that the ram air intake cooled the intake air charge considerably. I guess the reduced diameter of the of the intake caused a venturi and cooling effect. so, what is of more benefit - less work to draw the air in given larger diameter intake, or forcing the engine to accelerate/decelerate the air to cool the intake charge with a constriction in the intake?

[jaykay]

Maybe a little of both....well it's really only a vèlocity stack but at least it keeps me from going deaf at 4 to 5.5K

[The Radium King]

cool, you modified the snorkel?

the more I think about it, the more I think that the air filter might be the culprit. relative to the rest of the intake tract, the air passes through the filter slowly. that would give the filter the opportunity to heat up from radiant engine heat and, in turn, heat the air as it passes through the fine filter element. I bet that oil on the aftermarket air filters gets even warmer. solution is, as posted previously, to locate the filter outside of the engine bay like jfro, or actually in the rear quarter like the bgb/fabspeed unit for caymans.

[jaykay]

Yes, cut off and shaped the end with plastic weld...then lots of hand finishing

The opening area size is a little larger than three inch diameter. Who knows if this the right philosophy. I just could not put the stock size opening in there...

It would be would be great to get some before and after temps with various changes. I can measure my configuration once my OBD2 issues are resolved

I originally had a foiled up intake duct (3.25) but it got chewed up going in the engine bay so I scrapped the foil.

Yes I will eventually go 987 box but need the garage space to do it....think I will be rotating the engine down at the front for this so I don't ruin one box or the other.