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Originally posted by 930gt-40r
I dont know what Yerman has, but I am going with 1.06, with the "e" cover for the cold side becuase I have heard that the 4" inlet on the bigger housing is a pain in the @$$ to fit with the sheet metal. Are you going to use ball-bearing or no?
Why the 1.06? That's going to be unnecesarily laggy. A .82 T3 or .81 T4 will work just fine and still be good for lots of hp. I'm not sure what displacement you're running but, with a 3.0L+ you'd be fine with a .82 T3 or .81 T4. On a 3.0l, 3.3L or any larger combo f6 I'd personally run either a .82 T3 or .81 T4 on a 35r. A .68 T4 would work fine too. There is also a neat .78 T3 divided housing which will help it spool even more quickly, and it would be sufficiently sized. I honestly wouldn't run any smaller hotsides than what I've mentioned here. These motors generate a large enough exhaust volume that running anything smaller, while it will spool a turbo more quickly, will be sacrificing a serious amount of power. How much power do you want, at what boost level, and what kind of spool do you want?

I'd really like to see more GT series turbos on Porsches. There are some excellent improvements with these turbos over the older T series stuff. While many of the GT series turbos may have similar boost thresholds to their older T series counterparts, one of the biggest improvements is transient response. Basically, that means being able to roll on the throttle and receive nearly instantaneous boost response compared to the second or two delay it might take a T series turbo. Of course you can't necessarily do that at 1000rpm and expect it to build any boost but, you get the idea. Also, the turbos stay spooled between gear changes much better so they don't have to spool back up when engaging the next gear. The wheels are redesigned and have improved aerodynamics, so they are more efficient and will create more power compared to a similarly size T series turbo. Honestly, I think some of the benefits of the GT series might be lost on many 930's. One of the major benefits of the GT series is with the redesigned internals, the wheels are lighter AND stronger, plus the ball bearings maintain tighter tolerances. This all equates to turbos that are capable of reliably withstanding extremely high boost pressures under constant usage (like 30-40+psi, depending on the exact model). Also, some of the GT series are in their max efficiency "island" at some higher boost levels than the older T series stuff. Not too many 930 owners run anywhere near that pressure, so some of the power benefits might not be as noticeable. Most of the GT series line really starts to "wake up" above 20psi. Most of the Gt28's, Gt30's, Gt35's, etc tend to have their max efficient islands around the 20-30psi range, depending on the exact turbo (Gt28's and Gt30's are great right around ~22-25psi). In that regard, power wise, you really might not see huge differences from the T series stuff. Though, the improvements in response are still there. Anyways, that's one thing to consider. If you're just looking for power, the older T series stuff can still give you ~80-95% of the same performance unless you are running high boost pressures. Geez, sorry to type a novel! I love these turbos as you can probably tell. At the moment I'm installing a gt35r on my 951

Guys, there are some general guidelines about the Garrett GT series that are very important to follow, otherwise not doing so can lead to a significantly shorter lifespan. The GT series do not require nearly as much oil supply as an older T series turbo. Technically they shouldn't run much more than ~40psi, otherwise you can cause the turbo to start leaking oil due to excessive pressure. For most cars, that's a relatively low pressure so 9 times out of 10 you're going to need an oil restrictor. The exact size restrictor is really going to differ between cars with different motors. Also, the GT series were designed to be used with oil AND water cooling. Simply not running any water can lead to short bearing life. Some people have tried running oil through the water ports, which apparently seems to work okay and is definitely preferrable from just running the water ports dry. You can also of course add a small water tank and make a simple water supply setup for it though this might be a bit too much trouble for some people. Either way, don't simply run the coolant ports dry; at least supply them with oil. Hopefully someone that has used them on 911's more (like Wydryd) can give a bit more info into this.

Yermancars, was it by chance the plain bearing Gt4088 and not the DBB Gt4088r? I'm thinking about a Gt4088r on my 3.4l. The 4088r is quite a bit more responsive than the non ballbearing 4088. The boost threshold still isn't going to be all that low though transient response is significantly improved so the turbo will "respond" much more quickly rather than taking several seconds to spool. Judging by what I've seen of the 4088r on some ~3.0L i6's, on a 3.4l f6 it should be pretty responsive (meaning full boost ~3.8-4k) for a 700whp capable turbo. Hehe, it's tempting to me to just go all out and do a Gt42r! I personally don't mind higher boost threshold (not lag) as I love the way big turbos "hit".

Greglepore, what displacement do you have? The typical 3.3l or something different? If someone wants an ultra responsive setup for a 3.3l, a gt3076r with a .82 T3 or .81 T4 would be insanely responsive (like 1 bar below ~2.8k) and should still be good for over 350whp at 1bar. That turbo is a bit small for a 3.3l but, for those that like low-end response it would work well.
Old 01-10-2007, 10:29 PM
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