Turbo A/R Discussion

You won't notice a big difference until you try to max the turbo out. When you see these 800+whp cars on 6xmm turbos they have the large a/r housings on the exhaust.

I have a .65 on my open scroll 60-1 and it spools great. 15 psi spring in the wastegate right now and it holds steady. After I finish the harness for the new management system i will up the boost and see how well she responds at higher boost / power levels. Also changing from ported stock manifolds to tubular manifolds when they are finished. My car always goes thru big changes in a weekend because i drive it everyday lol.

i have tried a couple of different turbo combinations and A/R

The GT35 (journal bearing copy) with 0.82 open scroll and log manifolds was lazy until 3500rpm then ran like a demon at 20psi and showed no signs of dropping off, the manifold pressure at 20psi spun the gauge needle right around until it read zero again. Those manifolds then failed, the turbo failed the journal bearing and bent the shaft. It was probably more the cheap turbo but I can see that turbo with perhaps a divided 0.82 would have been a really good match.

can also understand what flawlez is saying about not needing a huge A/R

My car runs Tube headers, Schneider cam and ported heads with a hybrid turbo i built out of leftovers. Its a GT35R compressor wheel on T04S front cover (machined to match) with your typical mild stage 3 turbine wheel and bored out stock housing. You would think its not a great combonation with a massive compressor wheel on the small turbine but this thing really moves.

at 13psi my RB25det heavy duty clutch slips at anything over 5500rpm and it shows no sign of being any less punchy than the old Journal bearing GT35R.

Yes the hot side is probally holding back power and no it hasn't been on the dyno but its a properly matched system all there way through and its breathing very well on a surprisingly small stock turbine housing.

To anybody thinking of experimenting with their turbine housing sizes Setup a manifold pressure guage , wrap a thin copper tube around a pieces of 1" stock a bunch of times and plumb it into the turbine housing and run it to a boost gauge.

Somebody with tube headers and a well matched perhaps a ball bearing turbo should in theory be able to achieve a higher boost pressure than manifold pressure.

I know this is super late to reply but still helpful for those who may search in the future. My .63 housing is an open. Precision doesn't produce a divided housing on T3 frames. On a T4 I would have opted for something like a .82 divided.