Exhaust heat and turbos

[RobAWD]

To get off on the right foot here let me just say I have been reading posts on this great site for around a year now. A friend of mine has a 90 awd that got me into DSM's, I do most of the work on his car for him(Im very tech savvy).
but anyway let me get to the point,

In general turbo concepts the heat/velocity of the exhaust is what spools a turbine, as from what I have seen a great deal on numerous pages online.

key being the velocity, right?

I got a =gasp= 'chevy high performance' mag today(yeah I like anything thats fast and has at least 2 wheels) and there is a new turbo system for a 4th gen camaro lt1.

But the turbo is at the BACK of the car, very far from the exhaust heat and velocity I have come to think that is so very important in spooling a turbo.

I dont understand how this is possible from exhaust gasses that have cooled considerably from the way to the back of the car. The turbo sits right behind the rear axle, I suggest you go out and take a look at the system yourself. Dyno graphs and good pics are all there to prove it!


any thoughts for a dsm?


btw, the company is squires turbo systems(not a plug or any of that bs, just to let people know what the hell I am talking about =)

 

[dsm10sec]

Turbo magazine also had an article on this with a different car. They said turbo spool wasn't an issue. They didn't even use an intercooler because the piping cooled it off enough.

 

[anconover]

i saw some about it, didnt read much, but i dont know why youd want to do it really. Def not for ease, because its goin to create more bullshit and longer lines.

 

[NDgsx]

Quite possibly the stupidest turbo design ever. You get to run oil lines all the way back there, and it would require a scavenging pump.
I know they do this on the f-bodies to space, but I'm sure there would be a way to put a twin screw blower in there and have a much better performing system.

 

[dsm10sec]

i dont know why youd want to do it really

Maybe to have a stealth system? If you raced for money I'm sure you wouldn't want someone knowing what you had.

 

[Tongboy]

the reason they do it like that is completly for space in the engine bay, if you've ever poped the hood to one of those you would understand why, they are damn cramped!

the amount of cooling that happens isn't that great, nor is the velocity loss, the only thing I say would happen a lot is lots of turbo lag becuase there is just so much piping. as well as what happens when you start splashing water up on that insanely hot turbo in the rain or even in a puddle?

in an engine bay such as ours (or anyone that has enough room) there is no sense putting it back there. the less boost piping the better

another portlander

 

[dsm10sec]

the reason they do it like that is completly for space in the engine bay

You can't speak for EVERY SINGLE person that has one.

 

[Tongboy]

You can't speak for EVERY SINGLE person that has one.

of course not but that is what the majority of people are doing it like that for. if there was room in the engine bay it would be far more cost effective as well as better performance for the same turbo with less piping but there isn't any room in those engine bays

 

[pboglio]

For a given exhaust mass flow rate and fixed turbine nozzle dia, a higher temperature means a lower gas density. Low density & same mass flow rate physically means a higher velocity, there is no other way around it. This high velocity is a double edged sword, it spools the turbine wheel up to max speed but also means the turbine nozzle hits choke flow earlier due too flow drag. If you have a cooler exhaust temperature your gas density is higher, for the same mass flow rate your gas velocity is lower. This means SLOWER spoolup but less exhaust backpressure at a higher rpm band. You'll also hit choke flow higher into the rpm band. Where the slower velocity might hurt is in resistance to exhaust backflow. The point is COOLER exhaust temps after the combustion chamber means LESS backpressure and MORE available engine power. A racing car would care less, they would run a HUGE A/R anyway and use the high exhaust gas velocity for improved resistance to exhaust reversion.

Looks like in that turbo setup they have the capacity too run a nice optimized length header too. I bet total engine backpressure is less in that setup than your standard turbo setup. Aside from the extra pump required for turbo oil drainback, and the stupid pipe intercooler idea, there is no physics stating that this thing would make LESS horsepower than any other standard turbosetup. I don't like the potential loss of spool but otherwise I see no physics showing that it would make less power, perhaps even a bit more.

Remember, a turbo car only needs enough pressure in the exhaust manifold to rapidly spool the turbo and maintain enough driving force to power the compressor, anymore than needed is BAD and could cost you up to 100 ft-lbs of torque in the extreme near redline.

 

[Defiant]

I still think it's an astoundingly stupid idea, and I'm no more clear on "why?" now than when we first discussed it:

http://www.dsmtuners.com/forums/showthread.php?t=158199&page=2&pp=25