.63 or .85 on 251 stroker

[gnloyalty877]

I'm currently having a 251 stroker built with ta si aluminum heads and 218/218 roller cam and i've been running a .63 housing on my 6765 with a ptc 3200. I'm wondering with the extra cubic inches am i going to need to run a .85 housing?

 

[slimtastic]

id run the .85 housing, with your combo it sounds like itll be a top end monster....

but at the same time, housings from pte are like 140 bucks, so buy both and find out with one works better

 

[Slow91z]

.85 all the way.

 

[413turbo]

i tried this yesterday. i put a brass rod about a foot out of my o2 bung, then connected a boost guage to it. a 6765 on a 231 c.i. gave me 21-22#'s of exhaust boost, where in the manifold i'm getting 19-20#'s of boost. i was told that as long as the exhaust boost wasn't alot higher than the manifold boost, i wasn't choking the motor with a small housing.

maybe someone can shed some more insight into this, and maybe you can try, if you do- post the results. i'm working on a 4.1 and was told to go with .85 also.

 

[GNDriven]

Sorry I don't have any real backpressure data to offer. however being that you only have the two choices with the 3 bolt housing, I would go with the .85 the housing upgrade isn't that expensive, and spool is not going to be an issue. If you are going to put headers on I would go to a t4 setup on that engine to really let it breath.

 

[gnloyalty877]

I thought about going t4 but i already have a really nice set of old atr stainless headers so i'll probably end up getting a .85 housing

 

[Boost231]

once you hit 2:1 on the back pressure your out of turbo

 

[413turbo]

once you hit 2:1 on the back pressure your out of turbo

i called precision, to help me interpret the data, he said the same thing. that 1:1 is ideal. and that 2:1 is overspeeding the turbo. i don't know if that means you need a new bigger exhaust housing or just a bigger turbo. looks like i'm good though, for the 6765 on a stock 231 w/3000 stall.

 

[Boost231]

i called precision, to help me interpret the data, he said the same thing. that 1:1 is ideal. and that 2:1 is overspeeding the turbo. i don't know if that means you need a new bigger exhaust housing or just a bigger turbo. looks like i'm good though, for the 6765 on a stock 231 w/3000 stall.

Going to a bigger housing once you hit the 2:1 ratio will help some. It will lower BP slightly. In may case i didn't change housing i just went to a bigger turbo.

That 6765 will be more then enough for your 231CI motor