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greglepore 01-10-2007 05:58 PM

Question for Wyd (or others) re gt35
Thinking about converting. What A/R and trim are you running?

YermanCars 01-10-2007 06:02 PM

I have a special non ball bearing turbo, that will out perform the 35r for half the price.

PM if interested.

930gt-40r 01-10-2007 07:16 PM

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?

greglepore 01-10-2007 07:33 PM

This is for a low boost setup, I'm just interested in gaining spool over my existing, somewhat obsolete, turbo. Ultimate hp isn't as important as getting some response below 3k. I'm leaning towards bb, but I could be convinced otherwise.

930gt-40r 01-10-2007 07:38 PM

I am new to ball-bearing and am waiting arrival of my 35r, I have heard many people run them and be very happy. It is defenatly an update from any of the stock replacement junk. However I have seen some nice k-27, k-29, "K-28" hybrids out there. I just dont like how porsche does not use bbs. I think they do it to stay on the safe side for longevity purposes

YermanCars 01-10-2007 08:15 PM

I have ran a custom Gt40 turbo, it sucked. Too laggy and no throttle response, but when it hit, it took off.

I was going to get a custom Gt35r, but the Guys at Precision built me
the turbo I have now. It is a custom turbo built for me by Precision turbo, I can't give out the details really. It is a 60 trim turbo w/ a t4 flange and v band clamp, but can be built w/ a t3 or t3/t4 flange on a 3.3l w/ 7:0 comp. Full spool @ 2,900 rpms and pulls all the way to red line. I made 430rwhp @ 1bar w/ a chipped motronic based system.

The turbo runs about $700, the bb option can be added.

Porschefile 01-10-2007 11:29 PM


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.

greglepore 01-11-2007 04:21 AM

Tony, thanks for the imput.

Porschefile, I'm running a low boost Protomotive setup on a 3.2. No internal mods, so I'm stuck w/ .5 bar or .7 intercooled. It currently runs an obsolete GN style turbo, which is very laggy.

930gt-40r 01-11-2007 07:27 AM

Porschefile, the only reason I am going with the 1.06 is because the motor is 9.5:1 3.4L and I really want this thing to pull to the redline (going to spin her to 7500). I dont think she will have too much problem spooling, I am hoping for 550-600 to the wheels and with the 35R that is right at the sweet spot, 22-26 psi. But you are right, I could have done the .82 or .83 housing and had a hell of a lot of bottom end. I dont know, we will just have to see when she is done, I will keep everyone posted.

YermanCars 01-11-2007 08:19 AM

Here is the turbo I had, than sold.

Notice the low a/r on the hot and cold side. The new turbo I have, has .58 and .60 ar.

Jim2 01-11-2007 09:12 AM

Question. Does GT series use conventional Turbonetics compressor and turbine configurations? They are not very forthcoming with compressor maps.

They appear to be prepackaged combinations of regular stock parts from turbonetics... mostly ball bearing of course.

WERK I 01-11-2007 09:27 AM

Bumping to subscribe to thread.
Thanks for the great info thus far guys!

I'm looking into Garretts for the 930. I currently have a K27-7006, on B&B headers, CIS, WebCam SC grind, Kokeln IC, twinplug crankfire, C2 turbo pistons/cylinders.
The 7006 is running out of breath after 4500RPM. So I'm looking for more air volume without sacrificing too much of the low end response of the 7006 around 2800RPM.

Porschefile 01-11-2007 10:18 AM


Originally posted by 930gt-40r
Porschefile, the only reason I am going with the 1.06 is because the motor is 9.5:1 3.4L and I really want this thing to pull to the redline (going to spin her to 7500). I dont think she will have too much problem spooling, I am hoping for 550-600 to the wheels and with the 35R that is right at the sweet spot, 22-26 psi. But you are right, I could have done the .82 or .83 housing and had a hell of a lot of bottom end. I dont know, we will just have to see when she is done, I will keep everyone posted.
Hmm, honestly I really don't think a 1.06 is necessary until you get somewhere above ~4.0L as with a smaller .82 on even a 3.4l, there won't be nearly enough backpressure or lack of exhaust flow on the hotside to necessitate the use of a larger hotside. Are you sticking with the 9.5:1 CR? If so, I hope you plan on using race gas! ;) If you really want flow, go with a .81 T4. A T4 hotside is quite a bit larger and will overall flow better. I'm running a .81 T4 hotside on my crappy 60-1 w/ a P-trim turbine. The 60-1 is ancient stuff, though w/ 964 cams my car pulls hard to 7k rpm. With a 35r compressor wheel and that T4 hotside, you will have more than enough flow and reduced backpressure that it will definitely pull hard to ~7.5k

Greglepore, with a stock CR motor, I really wouldn't waste the money converting to a GT series turbo. I'm not sure what size turbo you have on your setup. Do you have a T3 or T4 exhaust flange? I'd highly recommend checking out a turbo from Precision's "SC" series Precision Turbo I believe someone was running one on Pelican and they were reporting some crazy quick spool. Anyways, Precision's SC series turbos are usually only ~$800-850 new and I believe you can even request a T4 hotside. Ultimately, you're going to be limited on total power by your CR, and I doubt if you could make much more than ~350whp.

Jim2, Garrett's GT series doesn't use anything related to Turbonetics. Turbonetics is a completely different company. Here's a link to their website. On their website they have all of the info and compressor/turbine maps you could want. ;) Most of the stuff they are using is fairly conventional. Most of the turbos have your typical T25, T3, or T4 flanges. There are some unique and cool things about them though, such as divided exhaust housings like This which help a turbo spool up more quickly. Other than that, the wheels have been redesigned using the latest stuff like advanced CFD software, so they are much more aerodynamically efficient. On top of that, I'm not sure exactly what processes they used though the GT series wheels are lighter than their equivalent T series counterparts, yet they are stronger. This equates to quicker spool and higher shaft rpm capability, meaning they can more easily withstand high boost pressures.

Frank@AMS 01-11-2007 10:38 AM

GT series turbos are made by Garret, Turbonectics does not use the GT series design.

I deal with the 35R's on a daily basis, as well as the 30, 37, and 42.

Unless you are going to use the full potential of the turbo, you can always step down a size.

930gt-40r, what type of power are you looking to put down, and I'm guessing that you want to spool around 3krpm? also what boost level will you be running?

930gt-40r 01-11-2007 03:09 PM

I dont know what Im going to put down, I do know that I just want it to be safe. I will tune it for whatever it could go to and then turn down the pressure a few pounds. I dont think much more than 550 which would be perfect with the 35r. On race gas will be a diffrent story, Ill probley get a s-load more because of the compression. I will just have to wait and see.

Frank@AMS 01-11-2007 03:17 PM

The GT35R will be maxed out right around 650 hp to the wheels however, I doubt you will be spooling at anything before 3300rpm.

930gt-40r 01-11-2007 03:28 PM

which is the equivalant to say a k-27. I cant remember my 27 spooling much before that either. Then again I havent driven a car with a k-27 in a long time.

WydRyd 01-11-2007 03:30 PM

Greg, I have a GT35R with a 0.78 A/R divided inlet housing on the GSF headers. Spool is amazing! I'm not after big top end HP, just quick street spooling ;)

For your application, I'd highly recommend a slightly smaller GT30R, rated at 500HP. That would be an awesome turbo for your application IMO, if you're specifically after a BB solution.

Frank@AMS 01-11-2007 03:39 PM


While I do agree that a GT30R would spool up sooner, Garret does not make a T4 hot side GT30R. I can most likely get one specially machined, but at the same time, the turbo would really run out of breath in the top end.

When Yermancars converted to the smaller turbo he is running now, there was a small loss in power however, it spooled up so much sooner, and the power band expanded. The car felt quite a bit faster than before, even though its down a few horsepower from the GT40.

Also, the ball bearing turbos are nice, however, you will have to run and extra oil line through the water passages.
Standard journal bearing turbos, with updated housings, are a better way to go with the air cooled boxer motor in my opinion.

930gt-40r 01-11-2007 03:40 PM

Wyd, I just thought to ask you, how do you like the protomotive/ Bosch sys. in your car? I have been thinking about my next project and concluded that I want to do a 993 to turbo conversion and that protomotive setup is is what I would want. How does it drive? Do the use the factory maps and modify the signal for map sensing?

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