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Forte500
 
Join Date: Jun 2010
Location: Greenwich
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Question GT35R turbo for 3.4L?

Looking for recommendation on Garrett GT35 (or other) for my 3.4L, EFI Porsche 930 motor...

Engine was newly built with all the good stuff: 8:1 compression, 3.2 intake, Motec ECU, 996 Cams and custom headers (w/T4 flange), and LARGE SPA Turbo (don't ask..). Car has G50 tranny.

With current set-up boost doesn't kick in until 4000+ RPM and pulls HARD to max boost at 6500. I would like more torque/power at lower RPM's w/o restricting too much air flow at upper end.

Can someone tell me their experience with the Garrett GT35 (or equivalent)? Boost kick-in RPM? Reliability? Compressor/Turbine size used?


Much appreciated..

Frank

Old 10-25-2011, 07:45 PM
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A gt35r with a 0.82 hot housing will get you max boost AT LEAST 1k rpm quicker without a doubt, and have plenty of puff up top too. Perhaps even try the new gen GTX-R with the 11 blade impellers.
Old 10-26-2011, 06:18 PM
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Forte500
 
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911TT33....thanks for reply. Quickly a few... should I consider lower in A/R (.60ish)? Do you know if oil cooling only will damage the turbo? Will T4 (I have T4) vs. T3 flange impact spool significantly?

Hopefully - I can this can be close to "drop-in" install.

Much appreciated!!

Frank
Old 10-26-2011, 07:29 PM
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A 0.63 hot side is too small and will choke the motor.

If this is a street car, leaving a GT turbo oil cooled is fine. If you are taking to the track, then consider a water cooling solution too for longevity. You could even run oil through the water ports too. Seen that done too.

If you want a drop in install, stick to a T3 turbine housing, otherwise you will need to modify your headers with a T4 flange. Not worth the expense IMHO.

Also, get one with a 3" compressor inlet to make intake plumbing easier too.

For exhaust discharge, I'm a huge fan of V-Band flanges... Makes R&R so much easier!

Last edited by 911TT33; 10-26-2011 at 11:12 PM..
Old 10-26-2011, 11:10 PM
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Forte500
 
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Thanks!

ps. I have T4 flange and V-band discharge (see pic) - so agreed.
Old 10-27-2011, 03:24 AM
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Twin .63's on the other hand will let it boost into oblivion....63 is what is on my motor.
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Old 10-27-2011, 03:26 AM
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Quote:
Originally Posted by Reaper930 View Post
Twin .63's on the other hand will let it boost into oblivion....63 is what is on my motor.
Lol, but twins is not exactly a drop in upgrade now is it?

Forte500, you will also need to modify that oil drip tank with a new oil inlet flange. It's not the same as the KKK flange I believe. Worth getting some measurements of that flange to confirm

How much power are you looking for?

Will you track this car, or is it purely to terrorize the streets?

Last edited by 911TT33; 10-27-2011 at 01:35 PM..
Old 10-27-2011, 01:29 PM
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Forte500
 
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This is strictly a street car to terrorize all the hedgefund guys in my area who "suddenly" thought it was cool to have a fast car..lol

Seriously, I would like an honest 400 RWH (.9 bar max) with better response off the line and some decent legs at the top. With a G50, Motec and 8:1 compression - this car should respond nicely and be reliable.

I hear the GT35 is best of both worlds, although some old-schoolers/tuners preach a hybrid K27 or Tial is a better option. My current SPA turbo (leftover from another build) seems better suited for racing (i.e. high revs). Not practical for the street.

What's your set-up?

ps. thanks for quick response....helpful
Old 10-27-2011, 07:07 PM
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I ran a single GT35R for years.... Loved it! The tinkerer in me wanted to try something different, so I'm in the process of doing a twin turbo conversion. It's a loooong slippery slope when you go down this route. In hindsight, I should have stayed with the single GT setup and just enjoyed terrorizing ricers and bikies

Why limit boost to 0.9 bar? If you have fully programmable engine management and an efficient intercooler, no reason why you can't run more boost... Within safety limits that is

I use to run 1.2 bar in my car for years before taking it off the road for the TT conversion

Last edited by 911TT33; 10-27-2011 at 08:30 PM..
Old 10-27-2011, 08:09 PM
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Chain fence eating turbo
 
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4000RPM in 4th or 1st?
Old 10-28-2011, 09:47 AM
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Quote:
Originally Posted by 911TT33 View Post
I ran a single GT35R for years.... Loved it! The tinkerer in me wanted to try something different, so I'm in the process of doing a twin turbo conversion. It's a loooong slippery slope when you go down this route. In hindsight, I should have stayed with the single GT setup and just enjoyed terrorizing ricers and bikies

Why limit boost to 0.9 bar? If you have fully programmable engine management and an efficient intercooler, no reason why you can't run more boost... Within safety limits that is

I use to run 1.2 bar in my car for years before taking it off the road for the TT conversion
At 8 to 1 compression, is it safe to run more than 0.9 bar on pump gas? Even with fuel injection and ignition timing control the dynamic compression ratio is getting up there for an air cooled engine.
just my thoughts...
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Old 10-28-2011, 10:27 AM
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Quote:
Originally Posted by fredmeister View Post
At 8 to 1 compression, is it safe to run more than 0.9 bar on pump gas? Even with fuel injection and ignition timing control the dynamic compression ratio is getting up there for an air cooled engine.
just my thoughts...
That's why I said "within safety limits". Keep an eye on A/F ratios and EGT temps when tuning for more boost. Don't just increase blindly without knowing what these readings are like.

I prefer a lower C/R and more boost... The rush is so addictive!
Old 10-28-2011, 01:13 PM
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The K27 hybrids and high flows will easily support 400WHP and drop your boost 1000+rpm. They also bolt on and use the OEM oiling system.
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Old 10-28-2011, 07:47 PM
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Forte500
 
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Again, nothing to compare to but before I change turbos my tuner is advising me to try .9Bar spring (now that motor is broken in) and see if spool up improves (theory the .5Bar is opening prematurely).....anyone know if this "significantly" improves spool/response??

With the G50, I don't get any boost in 1st until 4000RPM and by then it's time to shift. I watched the car closely during my morning drive and would say I hit the full boost (.5Bar) by 5200RPM in 2nd and 3rd gear....




p.s. Because of the high compression I will likely not exceed a .9 Bar spring, as well as install boost cut-off connected to Motec...in case of boost creep.
Old 10-29-2011, 11:38 AM
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What type of waste gate are you running? OEM Porsche or aftermarket?

I highly recommend upgrading to a Tial waste gate for accurate boost regulation. You may have a faulty waste gate or vacuum leak somewhere

0.5 bar @ 5200 is shocking!
Old 10-29-2011, 01:45 PM
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Frank,
What's the A/R on your current turbo?
If you're trying to avoid swapping turbos and modifying your exhaust manifold, you may give some thought to swapping a lower a/r turbine wheel in your existing turbo to see if that gives you the powerband you're looking for.

On swapping the wastegate spring - you may see a small improvement in spool, but I'd be surprised if it were more than a hundred or two rpms. Based on your comments, what I think you're after is a lower boost threshold, which should remain the same with just a spring change.

All things constant, you impact boost threshold with smaller ID exhaust manifold runners, smaller turbine A/R, less pressure drop from your intercooler... tuning can also have an impact on spool.

If you don't mind tossing the large turbo out, I'm a big fan of the ball bearing 35R. I drove a friend's 3.6L 964T a few weeks ago who had an upgraded KKK turbo... roughly the same output as my car, but came on boost noticeably later.
Best,
John

Quote:
Originally Posted by forte500 View Post
Again, nothing to compare to but before I change turbos my tuner is advising me to try .9Bar spring (now that motor is broken in) and see if spool up improves (theory the .5Bar is opening prematurely).....anyone know if this "significantly" improves spool/response??

With the G50, I don't get any boost in 1st until 4000RPM and by then it's time to shift. I watched the car closely during my morning drive and would say I hit the full boost (.5Bar) by 5200RPM in 2nd and 3rd gear....




p.s. Because of the high compression I will likely not exceed a .9 Bar spring, as well as install boost cut-off connected to Motec...in case of boost creep.
Old 10-29-2011, 01:58 PM
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The turbo you have now must be way too big. Properly modified highflow K27 turbos are at 1bar by 2700rpm with the typical mods needed to produce 400+WHP. If boosting later than that something needs tweaked.
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Old 10-29-2011, 02:39 PM
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His headers have been built with a T4 flange, and his exhaust already has a V-Band flange.

To go to a K27, he'd have to rework his exhaust system back to a T3 flange and 4 bolt exhaust flange.

It'd be cheaper to drop in the 35R and just modify the drip tank flange to suit.

I've run a k27-7200, k27hf, and gt35R. In my personal experience with all those, I found the 35R to offer the best performance. Even a 30R would meet his 400RWHP goals and deliver very fast spool for street
Old 10-29-2011, 03:58 PM
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Does anyone have any documented evidence that the GT spools faster than the K27?
I always read that some people feel it does.
Then I see Brian say he has not seen this to be the case.
I listen to what all you guys say. I have great respect for Brians knowledge.
Surely after all this time someone has done a documented test.
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Old 10-29-2011, 04:02 PM
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Forte500
 
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Keep in mind I have a 3.4L, carerra intake, 3.2 heads and as 911TT33 mentioned custom headers with T4 flange...wastegate is rebuilt/stock.....the current turbo has .96 A/R with 4" inlet and larger 70mm? compressor. Tyring to get best of both worlds (off-the-line kick w/o chocking the engine at top -end)

I tried to have the turbine housing swapped as JBurer suggested, but nothing was available for a SPA turbo (this came with the unfinished build I took on). I did have EverGreen turbo lighten up the shaft a bit - minor difference in perf.

I am leaning toward the GT35....my expecation is with a GT35 (and .9 Bar spring) I should be able to feel some boost in 1st gear (coming on at 2500RPM) and be able to easily break the tires free. Does this sound reasonable?

Thanks all!

Old 10-29-2011, 05:49 PM
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