Keeping Intake cold and exhaust hot? 1

I have heard of some racers using insulation materials on both on air intake and exhaust headers to improve peformance. By keeping intake air cooler - more air? And by keeping exhaust system hot - air exits more quickly? Can anyone here confirm this? Has anyone ever done dyno tests on systems which have insulated intake and exhuast systems? I'm thinking benefits can only be realized when car has warmed up and is hot?

 

[aorangi]

A cooler intake air is denser and so more fuel can be burned for the same volume of air. More power results and the thermal load on the engine is reduced - or at least not much increased under higher BMEP and power. That’s the purpose of intercoolers on supercharged and turbocharged engines, but a naturally aspirated engine will also benefit from cooler intake air.

Keeping the exhaust hot will be useful only with an exhaust turbine, because the turbine power depends of the exhaust mass flow, pressure and temperature. Usually the exhaust turbine is coupled to a centrifugal compressor to form a turbocharger. Under high load and revs, the power of the turbine is in excess of the compressor requirement, especially with a gasoline engine, so that there's a waste gate which diverts a part of the exhaust gas to by-pass the turbine. But at low revs, the power of the turbine is insufficient to provide an adequate boost pressure, so any increase of the exhaust temperature will help.

Cheers
Aorangi

 

[GregLocock]

The other advantage of keeping the exhaust hot is that it should reduce the engine bay temperature, which is a non trivial feat even with a standard engine. Cheers

Greg Locock

 

[davidh729]

Does keeping the exhaust hot in any way contribute to the thermodynamic efficiency, or is the temperature difference in that equation the temperaturee of the combustion chamber vs. the ambient?

Dave

 

[GregLocock]

If you haven't got a turbo I can't see any direct efficiency gain in keeping the exhaust hot, in fact you actually lose a bit since the extra volume of the hot gas will create more back pressure for a given exhaust sytem.

The temperature of heat rejection, which I think is what you are referring to, needs to be as low as possible for maximum efficiency doesn't it? it would be the temperature at which expansion finishes, either way.

Cheers

Greg Locock

 

[waqahmad]

when u are letting hot gases to excape the engine at high temperatures, u are actually letting useful energy which can be converted to work to go waste. In this case how can u expect of any efficiency gains!
by putting a turbine in the path of the exhaust gases and extracting the useful energy out of them, yes u can actually increse efficiency.


waqahmad

 

By increasing the exhaust temerature you can create more HP in that you are increasing the exhaust gas temperature which if running a tuned exhaust system could move the torque spike, generated by the tuned length of the exhaust runner, up higher in your RPM band giving you an increase in HP. It could also potentially move it down also. Who knows??

 

[Reijitsu]

you want the intaken air to be cold because it is more dense, and more dense air equal more HP. when exiting, the air needs to be hot because if it is cold, the dense cold air will talk longer for the engine to push out. that is the main reason why you should use the right sized piping for your application.

 

[carnage]

i think greg hit the main reson why many people insulate the exahust, to keep the engine bay cool. This is especially important when stuffing a very large motor in a very small engine bay.

 

[mrmopartech]

Header rap and thermo plankets for the exhaust system works to help in reducing the under the hood temps and by using ceramic coated headers or manifolds help too.To gain a better fuel charge,use a reverse rotation water pump to cool the heads first and keep the block warm.This means that you will land up with more feul getting to the cylinder and producing more power while keeping the block warm and reducing friction.

 

[tannguyen]

For intake air temperature, by sheer thermodynamic fundamentals (See Otto cycle) alone, increases efficiency.

For dyno testing...many companies who make manufacture and sell intakes, when they show the dyno plot of horsepower gains, they usually show the best run, the earlier runs, before heat from the engine compartment comes into play.

I remember Weapon-R trying to market a "short ram" intake at newcelica.org, claiming it's just as effective as an Injen CAI. They tested with the hood open (for obvious reasons) and they threw out the data due to heat soak (for obvious reasons).

 

[butelja]

Could one of the advantages (aside from manufacturing flexibility and cost) of the plastic intake manifolds that are so common now be reduced heat transfer to the intake charge?

 

[TheBlacksmith]

If my memory serves me, and I am getting older, on the generation 4 Corvettes (iteration prior to the current model), someone produced a plastic intake manifold for the engine that was claimed to be a bolt on 20 hp gain, due to isolating the intake charge from the oil heat in the lifter valley. I also believe Chevrolet adopted the plastic manifold as standard one or two years later.

Blacksmith

 

[hpfreak]

Plastic intakes are good for a 2-3% gain over an identical aluminum intake for two reasons. 1) They don't transfer as much heat to the intake charge. 2) The surface finish is much better than cast Al.

One way to improve the heat problem with al intakes is the thermal isolator gaskets available for some of the more common engines. Real simple and real cheap, but should help by slowing down heat transfer from the cylinder head.

 

[mrmopartech]

One of the old drag racing tips we used to do is keep a cooler full of ice and water and put bath towels in it and remove them and ring them out a small amount and place them on the intake manifold before a run.The difference is felt right away.By doing this you see how much heat is transfered to the intake runners and causes the fuel to evaporate in such a sort distance even at 8500rpm,scott