Turbochargers and heat

[BenG]

Ok....I was driving home today, and I was thinking about turbo charging. Why does an engine bay with a turbo get hotter than an engine bay without? I mean, the same exhaust gas has to flow out of the same header and down the same down pipe. The only difference is that there is a impeller in the path of the exhaust. And why do you need "high temp" ceramic coating on the inside of your exhaust plumbing when you run a turbo? Doesn't the gas leave the engine at the same temp as an N/A engine?

So I guess the main question I have is "WHY do turbo engine run hotter than N/A engines?" and the accompanying question is "DO turbo engines run hotter than N/A engines?"

I know, I'm probably asking some idiot questions, but I couldn't really figure it out...I think I've forgotten to factor something really basic into my thoughts....

[Nick]

you feed more air/fuel mixture in there, so you make more fire, also the air coming out of the turbocharger is pretty hot from being compressed (i've heard as high as 200 degrees)

that's my shot at it

[Xevuhtess77]

and just the pure speed of the turbo spinning, the friction causes heat.

[BenG]

OH YEA! more fire! haha..forgot about that part...but in that case, wouldn't a larger engine be hotter than a smaller engine? say a 2.5L 4cyl vs a 1.8L 4 cyl? more air and more fire, right?

[alltrac165]

The exhaust temps tend to be higher due to the higher intake temps. Even with an aftercooler, the intake air is not back down to ambient. Hotter in, hotter out. Also, since the exhaust is being forced to work on the way out, it's under quite a bit of pressure. Since it stays under pressure, it can't cool as fast as NA exhaust can. Any gas that goes from high pressure to low pressure will lose heat. It's the reverse of compressing it, which gains heat. Speaking of pressure, since you are forcing much more air in the cylinder, it's similar to increasing the cr by a good margin, which is another heat builder. These all conspire to make the turbine cry in agony and your engine bay feel like a convection oven. There may be more to it, but that's my understanding of it.

[Morpheus]

I hear the turbos themselves get pretty hot. I've heard they spin at 100,000 rpms+.

[white90dx]

Originally posted by Xevuhtess77
and just the pure speed of the turbo spinning, the friction causes heat.

The spinning of the turbo has absolutely nothing to do with the extra heat in the engine...

Originally posted by Morpheus
I hear the turbos themselves get pretty hot. I've heard they spin at 100,000 rpms+.

Yes, most turbos spin over 100k rpm... Turbos get hot not because of the spinning, but because of the fact that exhaust is traveling through them...

The exhaust coming out of a turbocharged engine is under very high pressure (when the car is under boost) do to the restriction of the turbocharger. This raises the temperature of the exhaust (a 'normal' pressure ratio for a turbo car is around 2:1, so for every 1psi of boost on the intake, there is an extra 2psi of back pressure in the exhaust. Imagine my WRX running about 15psi boost on the intake - that's 30psi in the exhaust) That, coupled with the fact that many turbo cars are run 'closer to the limit' brings out the high exhaust gas temperatures...

A turbo engine also is 'hotter' just because more power = more heat. It all depends on what you meant by the original question...

-Charlie

(notice, two turbo cars below)

[MRQtwinturbo]

on those dog days of summer....when its 30+ celcius out.....the car feels so sluggish.....i hardly go into boost under those conditions......but come nite time with cooler nite air.....she runs so strong......heat is such a big factor when it comes to making power.....

[Morpheus]

You need a big 'ol IC with water sprayer.

[MRQtwinturbo]

Originally posted by Morpheus
You need a big 'ol IC with water sprayer.

i have an upgraded greddy unit.....working on making a custom water sprayer for it....i'm not dumb enough to not upgrade my IC...i'd love to have a FMIC but mid eng design does not allow me....the one downside of my car....

[zoni]

just go insane and in piping all the way to the front under the chassis... yeah its more air space to fill with pressurized air, which means more lag, but it will give you a front mount! haha

[rollhard]

Originally posted by MRQturbo
i have an upgraded greddy unit.....working on making a custom water sprayer for it....i'm not dumb enough to not upgrade my IC...i'd love to have a FMIC but mid eng design does not allow me....the one downside of my car....

you can try using the pivot sprayer which is pretty cheap ($139 average) or the nitrous express ntercooler chiller works well. youlll have to maodify it a little but the difference is def noticeable.

[alltrac165]

Originally posted by MRQturbo
i have an upgraded greddy unit.....working on making a custom water sprayer for it....i'm not dumb enough to not upgrade my IC...i'd love to have a FMIC but mid eng design does not allow me....the one downside of my car....

Another idea I've seen on rally cars is to use a W/A aftercooler with the water heat exchanger up front, or in one case it was between the wing and the body, with the aftercooler close to the engine.

[turbobrick]

I once had a turbo and the exhaust as far down as I could see glowing like an ember even with an intercooler

[turbobrick]

I once had a turbo and the exhaust as far down as I could see glowing like an ember even with an intercooler