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BoxxerSix BoxxerSix is offline
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Join Date: Jun 2006
Location: Ballston Spa, NY
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Originally Posted by Lukesportsman View Post

Since we have your attention and obviously you have a knowledge base, what would you like in a responsive GT garret setup in TT format on a 3.3/3.2?
I wish I was in an area where I had more Porsche customers. You guys are fun to chat/work with This is hard to answer, not in the physics of it, but rather how biased I am towards responsiveness and of course the numerous variables that go into such a setup. Personally, I'd rather run slightly larger turbochargers(compressor wheels) at lower PR's to get the same flow rate as smaller wheels at large PR's. The trade off is a lower charge temp for more lag, but it's good for the motor and longevity vs all out spooling performance.

However set my petpeevs aside and with throttle response in mind and a priority here, for a low level(300-400 crank) build with some great offline performance a biturbo setup using GT2554R's .64a/r would work real nice. You'd get that power at moderate pressure ratios and efficiency. GT2554R is comparable to a well ported K04, yet still flows a bit more, and more efficiently at that. I've personally yet to try the 82 housings in this sort of application, but I haven't had the 64's choke out yet when kept within the compressors' range. 82 would most definitely carry you out well past 6500rpm at the trade off of seeing oh 1-1.2 bar around 3500est. GT2560r's work well in a 420-550 crank range, again .64 a/r turbine for low/midrage. Garrett claims ~325hp from a 2560R, but that's right close to the surge limits of the compressor. The key to using small spools in a twin setup to get power is GOOD intercooling(efficiency and deign).

As a side note, anything above that and you're into 28xxR territory. 2854r's are nice, but once in this family I'd go straight to a 2860r at the least. Keeping in mind though, this is for mid boost(1.2 bar) and response. If it were my car, I'd use the 2871R's, but again I like a little lag. Keeps me on my toes while driving. I'd also use free float housings with external gates where possible to avoid creep/spike issues with the smaller internal gates found on the 25/28 series. This however, is outside the realm of what you're asking so I won't go too far on it.

The GT 25 family is one not utilized much in the performance field as most people are accustomed to the GT2860r or RS in search of big power vs streetability, but they're a perfect turbo for those who are not looking for much more than 500 at moderate boost levels. They can achieve more, but then you're back to overspeeding and cramming hot air at stupid PR's for such small turbos.

I've built a GT25 biturbo setup for a moderately built 3.3 965 engine with TEC3R EFI, 2560r .82 a/r's but it ended up in a sand rail and not the appropriate Turbo chassis(idiot!) I'm currently working on a 3.3L biturbo setup using 2871r's for my own kit car, but it's a subaru EG33 liquid cooled engine from an SVX. Not P-car comparable really so I don't know how well those number will match up to this field here.

I'll take a picture of a Ko3 turbine at my shop on Monday to show you how small they really are. I'll post it next to a 2860R turbine for comparison..
Adam Hennessy
Old 11-03-2007, 06:49 PM
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