Ok, I'm putting a series 4 turbo engine into an 85 gsl-se. I have both a spare series 4 turbo/manifold and a series 5 turbo/manifold. I'm debating on which one to send to BNR for a stage 2 upgrade.

From what I've been told, the series 4 wastegate can be machined much bigger than the series 5 and would be able to better control boost creep than a machined series 5. ( I know stock series 5 wastegates are superior in stock form, but were talking about a HUGE port job with new flapper in s4 compared to ported series 5).

Also, I believe the series 4 turbo will leave a little more clearance between the idler arm and turbo, series 5 less clearance.

Now benefits to the series 5 turbo/mani from what I've been told is that is has a fully divided manifold which will reduce turbo lag (and the wastegate design in STOCK form compared to STOCK ser 4 is better). Will the quicker spool of the series 5 be benneficial even with a 3 inch exhaust or would I be ok with the series 4 (twin scroll removed BTW).

Thanks for the input guys, I'm left scratching my head on this one.

 

Bryan likes the series 4 because the he says he can port the hell out of the intake....

I have a BNR s4 stage III... because I have an s4....

The s5's make more power cause its a different turbo in stock form.. but bBryan is replacing the internals anyway...

as to the wastegate.... the series 4 gets machined to 35MM, and I have NO problems with boost creep. I don't think he's able to do as well with the series5 because of the two ports in the wastegate..

I'd call Bryan and talk to him directly about it, he'll give you the straight shot about it.

If i were you... Id send bryan the sries 4 and sell the series 5 to recoup some of the costs cause you can't get dirt for a stock series 4

With my stage 3 and a streetported s4 (intake only) motor.. I hit full boost at about 3750.. I think it would be better had I given it a monster exhuast port job as well, but i was running out of time and didn't have the template. I haven't dynoed it yet, but i ran 118 in the 1/4 mile.....

 

Either way, BNR's turbo upgrades should have the wastegate passages ported sufficiently enough to not allow boost creep. You should send whichever turbo whose manifold is in better shape (the one with less mileage or less cracks in the turbo manifold).

 

Oh trust me, the wastegates are ported!