Alright Ive come up with another idea that has possibilities. What if you injected a small amount of water into the exhaust right after the head right when the exhaust gases leave? If I remember when the exhaust cools and gets denser it takes up less space so you normaly use smaller piping towards the end to keep the flow up. So if you used this water injection to cool the exhaust stream right when it enters the mannifold you could in theory run smaller piping so that at low rpm you keep Tq and up high it doesnt overflow itself, might also keep underhood temps down. One thing of note I do remember people saying keeping the heat in the exhaust is good for power, hence ceramic and other coatings. Alright, discussion time!?

Yes, you want the exhaust to be hot coming right out of the engine. The biggest flaw here though, is that anything that you rigged up to spray water into the manifold would melt. Also, water hitting 1500 degree temperatures really wouldn't do anything anyway.

yea, you don't want to cool down the exhaust. having cooler exhaust in the pipes means you have denser exhaust, AKA more mass in your exhaust system. this increased mass is nothing but a burden to the engine. it's the same reason why you don't want to have a 3" exhaust piping on a nt engine. the flow will be so slow that the exhaust gases will cool down significantly before they are vented into the atmosphere, so they will be more dense, and hence more exhaust mass exists for the engine to push out.

The heat and hot exhaust gasses carry a great amount of energy, if you cool it down there is less energy to push the exhaust gases along. It's not a matter of density or of activity, you want the exhaust hot and moving, coold it down and it slows down.



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What about when the water does melt? The water vapor might go back into the head, or it might make alot of pressure in the manifold..

~Tacoman

density is mass over volume, in other words density is more of a ratio increasing density would mean increasing the amount of gas in exhaust path since the piping size won't change per quantity of exhaust.

think of a pot of water. when it boils the water becomes gaseous and begins to turn to steam. when it does this it floats up. adding heat gives it the energy to move. exhaust systems work the same way. you just have a motor creating pressure to push it out. having the hot exhaust temperature means the volume of gas is easier to move. if you wanted to use smaller piping you would be better off trying to make the exhaust hotter. you would still lose top end power though. it may just be better to make the exhaust hotter without changing pipe size. since it has alot of thermal energy and the motor is pushing it out heating it up would increase how much it wanted to move and make it easier to push out.

otherwise you would be correct. cooling would decrease the amount of space the exhaust would take in the piping and you could reduce the piping size. like intercoolers cool the charge so they're dense enough to make a gain in power.

that's my $.02

ALright replies to each post:
EZ- If you use smaller pipes there is no added mass, as the denser charge is held in a proportionally smaller piping, unless you can change the laws of mass it cant just appear because it gets colder and the water does add mass but just a wee bit.
Michael 97- Cooler does equal slower in a same sized pipe, but as stated earlier running a correct sized piping bournolli's effect would take over and create that nice low pressure and speed the gases up to normal spec. Is energy really lost here, not like the water vapor is leaving the exhaust stream, the energy is just being shared between the gases and a newly added substance. There should be enough sharing that the actual pressure drops enough from the gases that a smaller pipe could be run
Tacoman- I'snt water already melted :wary just playin. Also I dont see how the water would get back into the head at over 5000rpm's
Amish- Slightly confused are you agreeing or dissagreeing, or both?? ALso going along with the hotter theme here, could you run hotter at low rpms(run lean, use good coatings, hotter plugs) then run cooler when needed higher up(run a little rich if needed and put that phenolic spacer to use) would that work in the same basic principal?
Brent