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Discussion Starter #1
I currently have an On3 ball bearing 76mm with .96 a/r hotside on my 284ci forged 2v 4.6, 5-speed street car, turned up to 20-23psi. It makes nice power up top but it could use a little help in the spool department, LOL. I had a 70mm with .68 a/r on it before and it was much better spooling obviously but I switched it out because I figured it was 'done' at the 590rwhp/630rwtq I made when it was at around 20psi. I now make around 650rwhp at the same 20psi boost level and as much as 680 at 23psi.

I was considering throwing a .68 or .81 exhaust housing on my BB 76mm. I want to help spool as much as possible without affecting breathing once it's moving some air. I am tempted to try the .68 to see how it works.

Thoughts?
 

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Are you on E85 or 93 + straight meth? What's your comp ratio to be able to crank it to 23psi?

I think a .81 would help spool but not choke it out too much.
 

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My buddy makes 625rwhp with billet 62, .68ar on his 2v. I personaly made over 650rwhp with a .68 ar on a billet 67 on my 3v. My new Comp CT4-7068 I just ordered I went with .68 and going to be running 20-22psi.
 

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Discussion Starter #5
My buddy makes 625rwhp with billet 62, .68ar on his 2v. I personaly made over 650rwhp with a .68 ar on a billet 67 on my 3v. My new Comp CT4-7668 I jsut ordered I went with .68 and going to be running 20-22psi.
Thanks. Sounds like you like small exhaust housings. :) I think I will try the .68. Not the end of the world if I have to go bigger.

I see 23lbs on the street in 3rd gear by about 4200rpm with my .96 a/r.
 

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Yeah my results are limited to billet wheel turbos which flow around 20% more and spool around 1000 rpms sooner already comapred to the same size cast turbo. So im sure it would be a a little different from setup to setup. The 4.6 can make good power on the smaller ar without it being a restriction in general though. Also the turbine wheel size plays a role in this as well, the bigger the wheel the more axial flow anyway so the ar can be smaller to promote low end/ low load velocity with no noticable effect on power production up top.
 

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did you have any problems getting it to fit? I cant seem to get mine to fit between the rad and the front cover.
can you post a pic?
 
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