| There's a few closet manual tranny TT Zers out there who have purposely swapped their turbos out for auto tranny stock turbos to get a little quicker spool due to the lower A/R ratio of the exhaust side. Stock MT turbos are around .63, the AT turbos are around .48 or .49 on the exhaust side. you'll get "less efficiency" at higher RPMs --higher meaning, maybe around 6500 rpm. Then you read Corky Bells book and get all confused about what he's saying because he's talking about high speeds and huge HP gains. A low A/R ratio turbo is probably not a good way to go if you want to go 150 MPH for hours, and also, get 600 hp. Corky will tell you this, and you'll go buy some huge monster of a turbo that's a dissapointment for real world driving. So, the folks bent on world domination thru absolute max HP numbers will try to tell you to not use smaller A/R ratio turbos. But if you do, you'll smoke them off the line and in 60' times, every time :-) What is your application? That's what I asked myself. I was going to go this route ( some mere AT stock turbos) till I stumbled upon a local set of Skylines I could buy for cheap (but adapt to fit for alot of $$ and time and effort). They have a .49 A/R ratio as well, and spool very quickly, and can do a bit more boost than stock safely (but not much more).
I do, however get higher EGTs. My probe is before the turbo. I have heard JWT will build you a set of Sport 500s that have A/T exhaust housings, and therefore the quicker spool. 10 PSI and an NA rear end result in some wheelspin for me!! A TT rear end would damper this some and result in a good track-able useful first and second gear. I can burst between cars in traffic and zoom from 40-60 or 60-80 way quicker than any of my pals' Sport 500 boost-controlled cars. while my NA rear-end helps here, they always remark how quickly my turbos spool. we all have DPs and exhausts and JWT ECUs and controllers--very similar setups. Look into this.
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