[mn_vette]

Does anybody know how much the Q-trim turbine will flow before it starts really getting choked up. I'm using a .96 A/R.

The reason that I'm asking is because I'm having trouble making boost. If I am cruising on the highway and down shift the turbo will spool right up to whatever the boost controller is set at, but will loose boost with rpm. If I'm at the drag strip and have my foot through all the gears the boost will not go over 8psi. It sounds like the turbo is getting choked off.

I'm running a T-76, Q-trim .96 a/r, Racegate with a black spring, custom turbo kit for a 383ci corvette. I'm using a ball and spring manual boost controller.

Any kind of advice that you guys might have would be helpful.

Thanks!

[Deeds Performance]

Originally Posted by mn_vette

Does anybody know how much the Q-trim turbine will flow before it starts really getting choked up. I'm using a .96 A/R.

The reason that I'm asking is because I'm having trouble making boost. If I am cruising on the highway and down shift the turbo will spool right up to whatever the boost controller is set at, but will loose boost with rpm. If I'm at the drag strip and have my foot through all the gears the boost will not go over 8psi. It sounds like the turbo is getting choked off.

I'm running a T-76, Q-trim .96 a/r, Racegate with a black spring, custom turbo kit for a 383ci corvette. I'm using a ball and spring manual boost controller.

Any kind of advice that you guys might have would be helpful.

Thanks!

Have you meassured the back pressure to boost psi? That turbine wheel will support 900 plus hp range but if the back pressure is to high that goes out the window.

[mn_vette]

No I havne't mesured back pressure. There isn't an easy way to tap my piping by the turbo. And the car is now put away for the winter so I won't be able to play with it till spring.

Assuming I do have a lot of back pressure, what would I do to get rid of it?

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Originally Posted by mn_vette

No I havne't mesured back pressure. There isn't an easy way to tap my piping by the turbo. And the car is now put away for the winter so I won't be able to play with it till spring.

Assuming I do have a lot of back pressure, what would I do to get rid of it?

Can you tap the turbine housing in front of the inlet flange? If it is too high then you would need to go up in housing or change turbo to a midframe turbo. The midframe turbos uses a 76mm turbo vs. the 71mm turbo that you are running now.

[mn_vette]

I'm pretty well stuck with this size turbo. My space is EXTREMELY limited. How much would it help to go to an S-trim turbine?

So what exactly causes this excessive backpressure? Too much exhaust gasses? The gasses not moving fast enough?

Here's my engine bay.

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Originally Posted by mn_vette

I'm pretty well stuck with this size turbo. My space is EXTREMELY limited. How much would it help to go to an S-trim turbine?

So what exactly causes this excessive backpressure? Too much exhaust gasses? The gasses not moving fast enough?

Here's my engine bay.

Wow...you werent joking! I would say to tap the manifold near the wastegate so that you can get some sort of reading. The S trim is the largest in that turbo frame without going to a different turbo manufacture.

[mn_vette]

Would it help to get an electronic boost controller that actually holds the wastegate closed?

Or is the back pressure not actually opening the wastegate?

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Originally Posted by mn_vette

Would it help to get an electronic boost controller that actually holds the wastegate closed?

Or is the back pressure not actually opening the wastegate?

It?s the back pressure. In a prefect world you would want something close to 1:1 on boost vs. backpressure. I think yours is kind of high.

[mn_vette]

So what actually causes back pressure? I'm an engineer so feel free to get technical.

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Originally Posted by mn_vette

So what actually causes back pressure? I'm an engineer so feel free to get technical.

Mainly it is a restriction that is causing the backpressure whether it is the muffler or the turbo itself. Intern it can also cause damage to the motor too. Here is a link that I found that might give you some more details..

http://superchevy.com/technical/engi...exh/index.html