rob the .81 4 bolt will not spool the same as a 62 with a small buick 3bolt ex housing
I can get the turbo in any configuration I want, that's why I'm asking the questions that I am.
It is a custom order turbo that will be built to whatever specs I give them.
I read the sticky; 3 or 4 bolt
3-bolt good,
Direct bolt on replacement for all 86-87 Turbo Buicks and TTAs. Largest bolt on 3-bolt turbo available without having to change around a lot of stuff is a PT76 GT-Q. Uses the factory style downpipe flange for stock downpipe, Terry Houston style, or external wastegate mounted onto the downpipe style. Factory heat shield will fit over even the PT76 GT-Q.
3 -bolt bad,
Limited flow capabilities once you start looking to make over 975 fwhp. GT-Q is currently the largest turbine wheel option available. Back pressure can become an issue when trying to hit the elusive 975 fwhp mark. Wastegate hole will need to be ported if wanting to run high hp and high boost levels with a standard Internal wastegate style downpipe, in order to maintain boost control. To anyone that knows how to recognize turbos, the larger 70 series turbos would frighten most.
4-bolt style
PT88 Stage II setup with external wastegate and V-band style downpipe.
GT42 series turbo on Stage II with external wastegate and v-band style downpipe.
4-bolt good,
Tremendous flow capability when using the T4 Tangential style turbine housing. Significantly out flows the 3-bolt T3 style housing on 800+ hp applications. Less back pressure at high boost than the 3-bolt. Turbo selection and hp capabilities far exceed the currently available 3-bolt turbos. You can get a GT4788 with a T4 style turbine housing that will support close to 1300 fwhp.
4-bolt bad,
Requires the use of an external wastegate that will need to be mounted either onto the crossover pipe, or off the up-pipe from the header. Requires specific headers or at least a 3 to 4 bolt adapter flange. Will not work with internally wastegated downpipes. Requires a different style v-band clamped downpipe. If you go larger than a PT76 GT-S, you will need custom air intake piping as most turbos larger than the PT76 have 5" inlets. Higher than 4000 stall converters are required to properly spool up non ball bearing turbos larger than a GT4276, even no Stage II applications. Factory heat shield will not work and on larger Medium framed turbos, and will typically scare the poop out of most on lookers.
I guess the three bolt which is often called the buick housing on the board will give me the results I'm looking for, but was wondering if the T3 would be better as I can mount any style turbo I want because I can fab up whatever I need.
I use the precision 6466BB as an example of what I'm looking to achieve from what I've read in the 6466BB thread.
Mid ten capable at around 20/22 lbs. of boost and nines in the 30lb. range.
I won't go with that turbo because of price and bearing failure issues in the BB lineup along with cost to repair when there is a problem. And now that garrett is longer associated with them that brand is off limits for me.
I would live with a little lag down low as I know that the BB turbos can be bigger than what I run now as they spool faster and I also run a 3,500 stall so I was thinking that I could run the 6767, but I could go 6765 or smaller if that would net me the results I'm looking for.
I'm also running an ext. gate so that's one of the reasons I'm considering the T3 over three bolt. I wouldn't be using the internal gate but I guess I could see if the 3 bolt could be made without the internal gate and still go that route for ease of installation as long as performance was the same between the two housings.
