When does an 83mm turbine wheel become the restriction on a S400?

[GOT-Torque]

Everyone throws around numbers for flow ratings of a turbo (speaking about the compressor flow ratings in lbs/min). What about the turbine side flow ratings?

What is a standard 83mm turb wheel found on most S400's rated at? At what point do you need to go bigger? And how can you tell you need to go bigger? I assume by drive pressure readings...?

Last question, which would make more power? An overdriven 83mm wheel using an ext. gate to bypass the extra drive pressure or a larger turb wheel making use of the extra exhaust flow?

 

[RonA]

I ran a 75/83/1.1 primary for a while. With a 64/71/.8 on top I had about 78psi of drive pressure at 67 lbs of boost(no gate in hotpipe). It was one of my favorite combinations because it made good power(711) towed very well, and had a nice broad power band.

I've never seen BW turbine maps, but if you go to the atp turbo site, you can compare a gt42(83mm) to a gt47(around 93mm) to get a rough comparison.

 

[smokinrod]

why stop there ? ED custom cuts housing and or wheels to fit the 87 or the 96 if that is what your looking for

 

[NickTF]

Last question, which would make more power? An overdriven 83mm wheel using an ext. gate to bypass the extra drive pressure or a larger turb wheel making use of the extra exhaust flow?

If drive is there to run it I'd say the larger turbine wheel would make more power, there's more area for the gasses to push against. Just my guess.

 

[JasonCzerak]

If drive is there to run it I'd say the larger turbine wheel would make more power, there's more area for the gasses to push against. Just my guess.

yeah, but you can only spin the compressor side so fast.. So wouldn't you need to get a bigger compressor wheel that will need more force that's required from the bigger turbine wheel to make use of the extras gasses?

 

[RonA]

I tried the same setup with an 87 wheel and it wasn't all that great. Tiny gain on top with a big loss on the bottom. The 75/83/1.1 charger is really user friendly.

 

[zstroken]

I think last I checked you could get a turbine housing cut for around $100 if your just wanting the 87x80 turbine. I would probably jump up a turbine size if you think you can still get it lit, and stay on it. A ppump with a stick should have no trouble with a 1.0 housing.

 

[NickTF]

yeah, but you can only spin the compressor side so fast.. So wouldn't you need to get a bigger compressor wheel that will need more force that's required from the bigger turbine wheel to make use of the extras gasses?

I think there's too many unknowns to say for sure or make a general statement. The larger turbine wheel will be able to generate more power to turn the compressor wheel and shaft so long as there's enough drive to warrant it's size, I think we all have that basic concept down. If not, maybe such as in RonA's case, then the costs of the bigger wheel will outweigh the benefits which in his case were too much increase in turbo lag vs. very little gain higher in the rpm band.

 

[GOT-Torque]

For the sake of discussion:

3.0"+ compressor wheel, running as a single in a ppumped manual trans sled pulling truck... Not really concerned with where it spools, can be north of 3000 rpm.

Ron, what you stated makes sense and I kind of expected that, unfortunately pulling a sled limits your useable window of rpm such that the slight gain at the top end may be worth the huge loss under the rest of the curve.

 

[zstroken]

If you want it to spool north of 3000 then go for the larger turbine housings.
You won't like the drive pressure readings you see on the rpm range your probably gonna run.

 

[GOT-Torque]

You won't like the drive pressure readings you see on the rpm range your probably gonna run.

Which gets back to one of my original questions, would I be better off to install my ED wastegate and keep the tight turbine or swap to a bigger turbine wheel and housing.

I just think running a 83mm turbine wheel and tight housing and bypassing a bunch of exhaust to keep drive pressure in check is wasting alot of hp potential...

 

[zstroken]

Which gets back to one of my original questions, would I be better off to install my ED wastegate and keep the tight turbine or swap to a bigger turbine wheel and housing.

I just think running a 83mm turbine wheel and tight housing and bypassing a bunch of exhaust to keep drive pressure in check is wasting alot of hp potential...

Two many variables.
Do you have enough HP to keep the truck going and not drop down int he rpm? If you do then stay with the larger housing.
If you don't have the HP and your truck will get pulled down, then you may need the smaller housing and run the gate.
Lots of it will depend on the sleds/tracks/driving style/how well your truck hooks up.