What to do about this turbo for my Stage II

[GNDriven]

I purchased a turbo recently that has the following specs.

Garret (new)
Compressor = Cast 76mm (large housing 5" in 3" flanged out)
Turbine = Qtrim (80mm / 68mm) 4 bolt 1.00 divided AR
Ball Bearing

I am putting this on a stage II 4.1. I am concerned about the air flow through the turbine and the backpressure it may develop.

Do I need to sale this turbo and get the larger 82 / 75mm turbine wheel? Are can I get around the high backpressure with a good flowing wastegate 60mm TIAL or something? I mean the only heat/pressure/flow the turbo will need is to get it to full boost (25 psi or so). What happens to the backpressure once the wastegate opens?

Car will be driven on the street with ET goals in the mid - low 9s.

I appreciate any education on the topic.

 

[GNDriven]

I would not mind a little less lag on the street, but at this level I really need to find a combination that does not rip the tires off.

I thought that maybe with the small exhaust housing the boost will come up at a lower rpm, therefore not hitting the tires so aggressive. Kinda like a loose converter hits the tires hard once it starts coupling and you're already at 5000 rpm, puff goes the tires.

On the other hand with the smaller housing the power will come in too hard at the lower rpm spinning the tires so a little lag is best.

What is the trade off between lag and total exhaust flow. I do not want to choke total flow, but don't want a turbo that I can' t sixty foot in the high 1.4s either.

I mean this turbo has BB, 1.00AR. It is going to spool crazy I assume.

 

[bison]

It would like a 4000 stall but shouldn't hit backpressure at the performance level you're looking for. The total boost pressure will determine how hard it hits the tires. You need to have a converter built for the boost you plan on running at the track. There will be a big variation in power between 20 psi and 25-30psi.

 

[GNDriven]

Not sure what you mean by the "turbo should not hit backpressure".

My converter is a PTC unit. Stall is appox 3500.

What I am wondering about is what will I be leaving on the table by running the small turbine housing (80inducer/68exducer) vs (82inducer/75exducer).
Does anybody have an idea if the backpressure is going to choke the performance of my 4.1stage II with this turbo, specs above? Target boost will be around 25psi.

Also, if boost pressure is going to be high running a "Qtrim" then what affect will the waste gate have on exhaust backpressure?

 

[bison]

Not sure what you mean by the "turbo should not hit backpressure".

My converter is a PTC unit. Stall is appox 3500.

What I am wondering about is what will I be leaving on the table by running the small turbine housing (80inducer/68exducer) vs (82inducer/75exducer).
Does anybody have an idea if the backpressure is going to choke the performance of my 4.1stage II with this turbo, specs above? Target boost will be around 25psi.

Also, if boost pressure is going to be high running a "Qtrim" then what affect will the waste gate have on exhaust backpressure?

When you hit backpressure you will have a hard time increasing boost and getting more power out of it. If you have 9.5:1 CR and cam installed properly you will raise the point where backpressure will hurt you. The 7080 turbo has been about 150mph in TSM trim with a 3 bolt ex housing. The 7068 supercedes the 7080. You also have a less restrictive hot side. You will start seeing some higher backpressure when you run it to 150mph but it's not going to kill it. If you went with the next step up hps wheel it would need even more stall. I'd run it and see where you are. Log backpressure so you can see if it's climbing rapidly.