Reducing the underhood temperatures

At my first auto-x I noticed that the underhood stuff got really hot. Duh, idled five minutes, ran car hard for nearly two minutes, idle again for five... repeat for four runs. I set to work at reducing the underhood temps.

First for $34, I purchased header exhaust wrap - it works for exhaust "manifolds" as well, just not as nicely. I wrapped from the heat shield gasket to about one foot past the oxygen sensor.
I then found some foil backed furnace exhaust insulation and wrapped all the intake plumbing from the fender wall to the throttle body and fastened it down using heat reflective aluminum tape.
I also wrapped the radiator hoses with a heat shield so the radiator is the only place heat from the coolant is dissipated and not right next to the intake.

Intake cool = more HP, exhaust hot = better scavenging and less backpressure from cool gas slowing down towards tailpipe, and underhood temps greatly reduced!
After a long session of in-town driving I could touch the hood w/o burning myself and the intake air box was substantially cooler (even next to radiator hose and alternator) than it was during similar driving without the insulation.
Put my hand at the exhaust pipe and exhaust gas is hot (burn-hand-hot) immediately, it used to come out cool with condensation initially, taking five minutes to heat up.

Instead of purchasing a cat-back exhaust for $5-600 I went to Meineke and had them bend pipe with no muffler that I could bolt on for race days and use all stock hangers and dimensions (to remain B-stock!) yet get the great exhaust rip and more high-end HP. This cost me a mere $120. It could be done for less if you were to bend your own pipe using a rental pipe bender. Next on my list is possibly intake manifold polishing and BL/SS for my ride... M3 shifter ordered, in Friday, race Sunday. All told under $160 for cat-back exhaust and cool air intake!

Further information:

For the exhaust I used Cool It-Thermo Tec header wrap. I struggled to cover as much of the upper manifold as possible however due to it's rounded shape and not having any center passes the wrapping isn't that substantial. However, I continued down past the oxygen sensor wrapping both pipes together. I fabricated my own ties using binding wire and as of now, everything is still holding up after 4 months or 5K miles. The only difference I've noticed so far is the temps under the hood are much lower especially around the manifold(DUH!). So the stuff does insulate!

For the intake I used 6 or 8" furnace exhaust insulation. Foil backed with fiber glass glued to it. I sliced it down one side and covered from the throttle body to the plumbing connecting the airbox the the duct leading outside. This works because after staging my car for ten minutes twice and running twice at each autocross, I reach under and feel that the air box is more or less outside temp opposed to much hotter...i.e. compared to the surface temp of the fuse box the airbox was substantially cooler and cooler than the airbox had been prior to insulating it.

This is my personal testimonial, no dyno tests to back it up...but since the project took under an hour for both intake and exhaust and cost less than 50 bucks, I figure it was worth it...because cool air makes more HP...that's a fact.

Daniel David Ayd