P trim 70 with a Garrett .63 housing


Certifiable Member
Quick Question

I have a PT70 Ptrim while I love how this thing spools with the garret housing, but it just seems like the exhaust flow is hitting a brick wall

Anyone else ever used the garrett housing on a Turbo this big? wht did you find?

it seems the exhaust flow is restricted, i can hear the exhaust gasses rushing into the 3" downpipe, might be normal, I have nothing to compare it to.

the hissing sound is incredibly loud, and there are no boost leaks..

Ok , does it build boost pretty well? Or is it pretty laggy? What stll convertor do you have and any motor work?
The only true way to really tell if it is a restriction or if it's hurting your performance, would be to install a back pressure gauge before the inlet of the turbine housing. If you are running that turbo very hard with the Garrett .63 A/R turbine housing (IE: 26-32psi) then I can assure you that the back pressure is getting way up there, if not already surpassed the normally acceptable level. Eventho you love the quick spool up, you could be leaving as much as 30-50 flywheel hp on the table up top where it counts.
Remember, when using a back pressure gauge, the general rule of thumb is no more than a 2:1 ratio. Meaning, for every 1 psi of intake boost pressure, you don't want to go over 2psi of back pressure.

Example would be if you had 30psi of boost on your boost gauge, and you have 60psi of back pressure on the back pressure gauge. At that point, these items need to be addressed. The compressor wheel or turbine wheel needs to be upgraded, the turbine housing needs to be stepped up in A/R ratio, downpipe size and or exhaust diameter or type of muffler needs to be changed, or a cam shaft change. Now, people have made power by exceeding this general rule of thumb with regards to back pressure, but they are running the risk of over speeding the rotating assembly of the turbo, which can and will lead to Catastrophic Failure of the turbo, or even cause internal engine damage or header failures. Back in the day, before the advent of dual ball bearing turbos, people used the Garrett .63 housing that was machined to work with the P-trim turbine wheel, mainly because their converter was not right for the size of the turbo they were running. Typically after trying the PTE .63 and .85 A/R housings. It's a whole lot easier and cheaper to swap turbine housings then it is to swap converters and or have it restalled.
Hope some of this helps.

Great info Patrick, Thanks for the reply

I was thinking exactly what you said. I'm leaving a lot on the table running this quick spooling garrett housing.

I am Running a fairly stout engine, fully race ported irons, fully ported intake, big valves, forged pistons .030, billet mains, pollished and shot peened crank and rods, 204-214 cam, 62mm throttle body, mease sheet metal plenum, ESP front mount, Alky injected, Trans plus with Extender extreme,72 Seimans injectors, 4" maf pipe, LS1 MAF, Houston down pipe with Hooker exhaust, currently tuned @ 23 psi.

So I think I'm pushing the Turbo hard, What A/R housing should I use, my convertor stall is around 3700

Uhhh, yeah, you have enough converter too properly spool the PTE .85 A/R housing. With the extent of your build up, (which is as serious as you can get on a 30 over 109 setup without aluminum heads or a roller cam) it wouldn't surprise me if you picked up 50-60 hp just by changing the housing on 25-28psi.
The part number you want is a THB5-76 with the hardware. And don't forget to port the wastegate hole for whatever downpipe setup you have.
Even if you went with the .63 PTE, your spool up probably wouldn't change more than 200 rpms. And you would probably pick up another 20-30 with the .63 PTE. The .85 would be around 400 rpms, but you would still be able to foot brake very nicely. Just make sure you retune the setup once you change the housing, cause I'd be willing to bet you will need to add some fuel.
The .63 A/R part number is THB3-76. If it were me, I'd do the .85 and be done with it.
Hope this helps.

When you say you feel your car is hitting a brick wall you mean it does not seem any faster when you increase the boost? I have a Te-45a 66mm with a .63 housing and when I turn up the boost I can tell its making more power.

What your current time and MPH?