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Stay with the .85 housing or go to a .63 on my PT-70

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Steve

Well-Known Member
Joined
Jun 1, 2001
Messages
1,232
I recenlty changed from a GT-6776S turbo to a PT-70 P-trim. The PT-70 has a Precision .85 housing. I have a 3400 stall which spooled the 67 great but I feel like it will be borderline for the PT-70. I am not opposed to having my converter restalled but I would rather not if I don't have to. How much spool up difference will there be between the two housings? Anyone ran both on the same car so tell the performance difference between the two. Thanks
 
No, Jack sells the Turbonetics turbos so this would not be in his area of expertise. I did talk to Limit Engineering and they said that the .85 housing would be slower spooling but its hard to qauntify how much. That's why I am asking for advice from people that have tried both on the same set up.
 
The time in my sig. is my a 70 p trim and .63 housing. I've since switched to a .85 without any improvement. Take that for what it's worth.
 
Jack sells both brands of turbos, he just prefers Turbonetics. I would call him and ask.
Bryan
 
Haven't compared them back to back but there will be a difference. A boost controller can help with the spool time. There are some options out there now, but if the instant spool of the 67 with the smaller housing is what you liked you will be a little disapointed with the .85 IMO!
 
I have compared the two, the .63 will reduce mph by 1 over the .85, but the .63 is way more fun to drive on the street!
 
Some results that I heard from customers when I was still at PTE, were anywhere from 400-500 rpms difference on the spool up times. Now, this could be a result of a bad tune (aka too rich during spool up) or a result of too tight a converter. I have run a 70 P-trim in the past, and I did have a .63 A/R housing. I was running a 3800 stall at zero psi and it spooled it up fast. When I had it upgraded to a 74Q (old school) back in 2001, it spooled up ok. IMO, the .63 A/R housing on a 70 P-trim likes a converter that will stall at 3400 at zero psi and the .85 likes a converter that will stall at 3600-3800 at zero psi on a 231-235 CI built motor.
That 400-500 rpms difference was pretty common on all the turbos that I sold, when going from .63 to .85 A/R ratios. I would normally spec a .63 A/R on all P-trim and GT-Q turbine wheel equipped turbos, if the car was going to be mainly a street driven car with limited track use, and a .85 always for a track only, all out car.
Hope this helps.

Patrick
 
Thanks! Awesome info guys. That tells me exactly what I needed to know!
 
I would normally spec a .63 A/R on all P-trim and GT-Q turbine wheel equipped turbos, if the car was going to be mainly a street driven car with limited track use, and a .85 always for a track only, all out car.

This is exactly what Dan @ PTE told me.
 
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