[Note from admin: this thread split off from http://ecomodder.com/forum/showthrea...-nay-9732.html ]

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I also believe in tucking the exhaust system up closer to the body and insulating it as well as possible, so that the exit velocity is higher, making more of a pressure differential across the face of the exhaust valves, even though I can't prove it. It's intuitively correct, and some science backs up the theory.

I agree with your ideas about the exhaust system. One of my future projects will be replacing my muffler with a more eficient one and tucking it up out of the air stream. The stock one hangs down quite a bit. By keeping the exhaust warmer do you mean using the header wraps that they sell for race cars. I have heard that they can contribute to pipe rusting if the pipes are not warmed up very well. (short trips)

Nah, just use insul-shield (it's basically fiberglass mat wrapped in aluminum foil) on the body of your car. Even if the pipe comes in contact with it, it won't burn.

I don't actually wrap the pipes up, other than headers if I'm using one. The best insulator is dead air, so the best way to insulate your pipes is with more pipes. This makes your pipes heavier, though, from being double walled. It will also quiet your exhaust's resonant noise, since there's a layer of dead air to vibrate, then another layer of steel, before finally making audible noise.

The last time I actually insulated one, I just made sheet metal half-moon shapes that I could follow the car's exhaust path with. Put some insul-shield above the exhaust, and put more in the half-moon, then tack the half-moon up to the floor with aluminum rivets. (Leave tabs on the metal when you cut it out and form it.)

You can do this from the firewall back, basically, on cars where the exhaust has a place to tuck into the body. (I did mine on a 4th gen Honda Civic). It gets a bit trickier when the exhaust no longer tucks into a pocket in the body, then you have to either make bigger pieces of pipe to tack to the body, or use double wall pipe.

DBL wall is pretty extreme, and probably isn't worth it's weight on a car on the street. It's nice for motorcycle headers, though.

One thing I'm not sure about, though, is the header wrap and rusting pipes. I'd assume it's correct, since that wrap will absorb moisture, salt, etc and keep it right there w/ the pipes. Since wrapped pipes are essentially a cool version of an annealing furnace, having those corrosives right next to the hot pipe is just inviting disaster.

Ways around this include aluminized, zinc plated, stainless, and straight aluminum exhaust pipe.

I have a 4th gen Civic... so is insulating the exhaust just to keep it hot and therefore velocities up, or are there other benefits? Maybe like keeping the heat from melting a coroplast belly pan? How did it work out on your car?

Wow, I didn't even know this was split off... LOL

I never tried it with a belly pan, but given the proper insulation, I'd have to say it would work just fine to keep the heat away from the coroplast, so that you'd not have to worry about melting/fires under the car.

A friend of mine suggested using fiberglass insulation batts in the R13 variety and wrapping them up with foil tape in a helix pattern (winding it around the pipe). I'm almost certain this is just too thick of insulation, but it won't add much weight to the car. You have to use the stuff that doesn't have the paper backing on it, though.

PS - use either corn starch or baby powder on your skin before handling fiberglass. It will stop it from getting into your skin and itching.

Here is about the most extreme example of consumer level heat wrapping I've seen.

NASIOC - View Single Post - exhaust wrapping procedure?

Somehow I don't think it will ever pay for itself. Might be a fun experiment though, wrapping from head to exhaust tip. The catalytic converters would light off almost instantly.

This may sound bizarre...
as I do have an old sube, wrapped from ebnd to the other by factory, and hardly a place for it tucked up into body without banging it up..
I found after welding the body, heat wrap doesn't even matter. If to speak of resonance and flow...:rolleyes:

It is more than ironinc seeing this stuff targetted on unibodies that strain. Hondas, minivans, and subarus are indeed dramatic.

As of now, I am as old school as keeping the catalyst convertor wrapped, and I hung the exhaust from something I saw on a subaru outback (they do not try to tuck in like they used to). no thoughts of it. I humored a half wrap oe stylr up front, for ice and snow piles, animals, kittens poodles and wandering pedestrians. :thumbup:

I can attest to the rust under fiberglass exhaust wraps. I't's BAD. I think Christ's double pipe is best and would actually protect the pipes from rust.

Not quite... The best insulator is no air... Double walled evacuated stainless pipes anyone?

Interestingly the Previa's header is twin wall stainless. In the sae paper they only mention weight (as opposed to cast iron) and noise as a reason for the double wall.

You and me need to meet up, build a vacuum chamber, and start selling exhausts! :P

I knew about the evacuated pipes, but I have no idea if we could make them realistically.