Is there really a significant performance difference between 3bolt and 4bolt turbos?

[86brick]

Topic pretty much says it all....... For example on PTE's website http://www.precisionte.com/buick.php they rate the 3bolt PT70GTQ at 785hp (I'm guessing this is at the FW) and then they rate the 4bolt PT70GTQ at 850hp (again I'm guessing this is at the FW)...... I just think the HP ratings they give between the 3bolt and 4bolt turbos is way off considering Dave Bamford went 9.57 @142mph with a 3bolt PT70GTQ and keep in mind his car weighs 3560lbs (that means he has to be making about 900fwhp)..... I just don't buy the difference in HP between the 3bolt and 4bolt turbos being that major (according to PTE's website the difference is anywhere from 50-75hp)..... Anybody agree or disagree with what I said? If so please give your $.02 on this and if you can honestly answer this question please by all means do cause I'm a bit --------->

TIA

 

[86brick]

Where are the turbo gurus on this one? John Craig? Joe Lubrant? Patrick Rubio? Will anybody take a stab at answering this question

 

[fubar2.5]

Fwhp?

 

[86brick]

Originally posted by fubar2.5
Fwhp?

Flywheel Horsepower......

 

[The Radius Kid]

It's due to the larger inlet size of the 4 bolt housings[a/r's being equal].
The greater inlet size allows more unit area pushing the exhaust gases through the volute and wheel.
That means greater flow on the exhaust side.

 

[GNSCOTT]

And of course greater flow on the exhaust side means more lag. Its a trade off. With a wild set up, the exhaust housing itself becomes the restrictor on the motor. A 3 bolt is fine for someone with mildly ported heads because the heads are still the most restricive, but if your heads are outflowing the ex. housing, its time to step up to a bigger ex. housing.

 

[1badTTA]

Originally posted by 86brick
they rate the 3bolt PT70GTQ at 785hp (I'm guessing this is at the FW) and then they rate the 4bolt PT70GTQ at 850hp (again I'm guessing this is at the FW)...... I just think the HP ratings they give between the 3bolt and 4bolt turbos is way off considering Dave Bamford went 9.57 @142mph with a 3bolt PT70GTQ and keep in mind his car weighs 3560lbs (that means he has to be making about 900fwhp
TIA

OK, they also say that a 109 block won't handle more than 600hp either.

As far as horsepower ratings go for anything, they are only a rule of thumb and not gospel. Just because you are currently making 785hp with a 3 bolt pt70gtq doesn't mean that you can't possibly make any more power with the same turbo. And btw, Dave Bamford is a sick puppy for getting a 109 to live with that much power!!!!