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Discussion Starter #1
For the people that went from stock turbo to a larger turbo was there any loss in off the line performance? Did the car become slower down low and then start to pull much harder with a less linear or smoother power band? Going to buy a redline shortly and not sure if I want to change out the stock turbo or just make some modifications and tune it.
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You will always loose some power down low with a larger turbo, but what you lose in low rpm you make up in higher rpm. There are a few turbo's that are just a bit bigger than stock so the loss isn't that noticeable. Get a tune for the stock turbo and once you're bored of it look into bigger ones.
 

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Shabby described it correctly - bigger turbo = more peak power but slower response (more lag). You have to strike a balance that pleases you. Some owners go for the BIG turbo and then brag about the power they are getting up in an rpm range they probably don't use all that much. From my point of view, the sweet spot was a stock K04 machined to take a larger impeller. I have almost no noticeable increase in lag (these cars are very good that way) but very significantly increased power.

Maybe someone that went bigger than I did can chip in with their comments.

BTW, you can get around 375 at the crank with suitable other modifications, but that's about it.
 
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From my point of view, the sweet spot was a stock K04 machined to take a larger impeller
I have a "big wheel" turbo. What I understand as the primary benefit is pushing more air at higher RPMs. Unfortunately, at least on my car with my tuner, we had to dial back boost at higher RPMs to deal with knock. We put the same kit on my buddy's GXP and after re-tune he netted a 15HP gain (mine wasn't dyno tested before or after).

So despite the advertising the contrary, the real-world benefit of the K04 big wheel upgrades doesn't seem to be very much, at least where 92 octane is the best available pump fuel.
 

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Tune will have a lot to do with it. Mine works very well - custom Trifecta tune.

Also see this thread with dyno results on this turbo

 

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Tune will have a lot to do with it. Mine works very well - custom Trifecta tune.
Dave at PAW tuned mine, and we got the turbos there. Wester tuned the GXP.

RPM claims another 50~ whp
Subjective butt-dyno says that's about right on my first logging drive. There was a big kick in the higher RPM band. But knock was detected and it got dialed back quite a lot to prevent.
 

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I don't recommend going with the big wheel turbo due to back pressure issue. With the Z54 the torque will come on about 3500 rpm. If you pull out normal to fully engaged the clutch and then floor it, it reacts pretty much like the Ko4 until it kicks and the car goes sideways without the nannies on. It keeps full torque until it hits the redline at 7300. I have been told that others go to 8000 rpm with full build. The power will be delayed to about 1000 rpm later.
 

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I don't recommend going with the big wheel turbo due to back pressure issue. With the Z54 the torque will come on about 3500 rpm. If you pull out normal to fully engaged the clutch and then floor it, it reacts pretty much like the Ko4 until it kicks and the car goes sideways without the nannies on. It keeps full torque until it hits the redline at 7300. I have been told that others go to 8000 rpm with full build. The power will be delayed to about 1000 rpm later.
Z54? Link?

Sent from my SM-G998U using Tapatalk
 

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The only option ZZP lists on their web site as Kappa-compatible is the stock K04. This could just be a housekeeping issue, but caveat emptor.
 

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So you don't want more then 375hp. Get an IC, HFC, piping, 3BAR MAPs, CAI and then have your car dyno tuned. I'm pushing about 330hp and I don't have a HFC or IC. The tuner that did my car at ZZP said if I would have had the HFC and IC, I could have seen 360hp easily. But I had too much knock. He was very careful. He would run my car up to 35mph in 4th gear, hold it there for about 2 minutes, then do the pull. He adjusted my cooling fan to come on at 182 and 100% full at 190 degrees to keep things cool.
 

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Discussion Starter #20
Interesting points of view on this. Really to me seems to come down to a possible tuning issue and possibly heat. During the dyno or tuning runs did anyone log IAT's before the knock started? The car I am looking at has low mileage but is an 08 so it is old. Was going to pull the turbo anyway to check it and then figured just a bigger wheel up grade would be fine. Still am leaning in that direction assuming it is available. Don't see any listing for it on DDM though Werks and RPM still have it listed.
 
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