turbo question

[AutostradaVR4]

would it be possible/practicle to use large deisel turbos on our cars? is there any difference between turbos on gas engines and deisels?

The question was sparked when i realized my dad (diesel mechanic) has access to cummins turbodeisel turbos for very good prices...even better if i get a remanufactured one.

also, anyone know what size WRX turbos are offhand?

[2old]

No... Large diesel turbos spool slower and they wouldn't give you as much pressure given you probably are not generating enough exhaust gases to drive them properly (consequently have less boost).

Unless at WOT at 7000 RPM your Turbo cannot reach enough pressure to open your wastegate, there really isn't much point to a larger turbo.

[Dreamspawn]

Originally Posted by 2old

No... Large diesel turbos spool slower and they wouldn't give you as much pressure given you probably are not generating enough exhaust gases to drive them properly (consequently have less boost).

Unless at WOT at 7000 RPM your Turbo cannot reach enough pressure to open your wastegate, there really isn't much point to a larger turbo.

Point a larger turbo is more power so there is a point. But like you said a 30psi tubo is gonna take more exhaust gas to spool it up. You could always go supra style and small turbo to spool then taken over by a larger one but most find this impractical. I would ask around for the specs on the turbo then talk to some ppl on 3si about how much lag this would be to get boost. And the fact could you motor handle as much as that thing is gonna put out. Once again the old fashion anything is possible with money comes in hand.

[2old]

What I was trying to say is, unless you find that the turbo cannot achieve the level of boost you are trying for going to a larger turbo would not net you more power.

A cummins turbodiesel is a pretty big engine and does not require a lot of boost (IE the blades on the spindle are not that aggressive). It is designed for a lot of air volume and not really high PSI.

I can't say for sure unless you have the efficiency graphs, but I sincerely doubt it would be worth using on a 3.0L engine.

[talskinyguy]

What? Its not about the amount of boost, its about the amount of air. A bigger turbo makes more power at the same PSI.

The cummins engines don't require a lot of boost? 21psi is stock. I'm running around 35psi, and there are people running upwards of 150psi, if thats not a lot I don't know what is.

Yes they will work, but it depends on what cummins engines you are taking turbos off of. And I would suggest going the single turbo route unless you are aiming for 800+hp.

I think you need to give more info as far as what turbos you are looking at with what exhaust housings. Im assuming you mean the turbos off the 5.9 engine that goes in a lot of things. The HY-35w and the HX-35w

[2old]

Is he talking about the "small" cummins diesel in a pickup or the "large" cummins diesel in a semi?

I didn't realize that there were diesel mechanics that specialized in non-heavy duty applications...

And Turbo efficiency is a curve dependent on the volume at various pressures. This is related to vein design. You CAN plunk any turbo on any engine but you are trying to maximize the turbo efficiency to decrease the about of backpressure generated at any particular boost.

If you were to do it properly you would choose the amount of air you want to flow at a particular pressure and choose the most efficient Turbo at that pressure. Not just bolt a bigger turbo on.

That said your right, if he was talking about the 5.9 cummins turbo it would fall within the spec if he increase his car's boost to around 18+ PSI for a single turbo... Unless the cummins is a twin turbo as well... I don't know I am not familiar enough with the engine...

[2old]

Originally Posted by talskinyguy

What? Its not about the amount of boost, its about the amount of air. A bigger turbo makes more power at the same PSI.

I will admit I did not know that a cummins turbo did 21 psi but this statement really bugs me.

An engine will only take up a certain amount of air at a certain pressure... If you try and "cram" more air into it the PSI on the intake side will go up. You cannot get more power for a certain PSI... You can flatten the hp curve by being able to apply that PSI earlier but that is why you want the most efficent turbo for you chosen PSI and CFM.

Also big turbos take more exhaust "mass" to move... If you don't have the exhaust it's a little like trying to run a hoover dam turbine off a mountain stream... There is point where the returns diminish enough to actually reduce the usable power.

[2old]

Oh and before I get flamed for the "drag racer" thing... Got back to my comment on the wastegate. You have to change the BOV and wastegate trigger pressures to make more effective use of a larger turbo.

[talskinyguy]

Originally Posted by 2old

An engine will only take up a certain amount of air at a certain pressure... If you try and "cram" more air into it the PSI on the intake side will go up. You cannot get more power for a certain PSI...

This statement is completely wrong. The reason a bigger turbo will allow the engine to ingest more air at the same PSI is due to backpressure.

If the turbine wheel was the same size on every turbo you would be correct that the only way to get more air into an engine is to up the boost, however if you put a bigger turbo on the engine the backpressure drops on the exhaust side and most air will flow into and out of the engine at the same PSI. More air = more power.

[2old]

I agree with the decrease in backpressure...

But the amount of backpressure is not directly proportional to the size of the turbo. It's actually a curve based on the efficiency of the turbo at that CFM and PSI.

Saying a bigger turbo will have less backpressure is too generic a statement... If will have less backpressure if you current turbo is undersized for the CFM and PSI you are trying to achieve. If it's too big it won't produce the target PSI early enough in the rpm range to be useful.

[AutostradaVR4]

well, you guys kinda jumped uver my head a bit here, its clear you both know much more than i do about the subject. lots of good info for sure.

turbo size...he works for the county, and he works on anything from pickups to semi-sized dump trucks and plow trucks, so i have options with the size.

[talskinyguy]

Originally Posted by 2old

If it's too big it won't produce the target PSI early enough in the rpm range to be useful.

This is entirely subjective and depends completely on the intended use of the car and how built the motor is. But as I said, I would go with a single turbo unless you are looking for 800+hp. Guys are running the stock turbos off cummins engines on DSM's so there is no reason they cant be used.

[Stealthee]

Originally Posted by talskinyguy

This is entirely subjective and depends completely on the intended use of the car and how built the motor is. But as I said, I would go with a single turbo unless you are looking for 800+hp. Guys are running the stock turbos off cummins engines on DSM's so there is no reason they cant be used.

Oh reeally? Hmmmmm I got connections with a diesel performance place. I might have to look into thatt for the TSI.