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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,142
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Running a turbo without the intercooler connected
Reading the webs in its' infinite misinformation cesspool, do you think you can overrev or overspeed a turbo if the intercooler is NOT connected venting to the atmosphere?
99% of the web says 'yes', but I found a turbo engineer who states otherwise. He states there is still resistance of air on the compressor side into the atmosphere and is not a problem as the engine is not producing enough exhaust airflow due to the lower HP output, essentially. I also have blown off hoses many times under full boogy without grenading a turbo yet. What are your thoughts? Why I ask, is I plan on massively revamping the intercooler piping on my custom Treadstone unit on a Carrera 3.4, but I want to continue to drive the car if needed as this may take weeks. I thought of hooking direct without the IC and not getting into the throttle, but that probably would not be wise.
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Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR, 993SS cams, Borg-Warner S366 turbo @ 1.2-1.5 bar, Treadstone full bay IC, 70mm TB, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MicroSquirt AMP'd w/GM smart coilpack, Bilstein coilovers, Tramont replica Speedlines (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel |
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10-08-2025, 08:46 AM
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Registered
Join Date: Jul 2008
Location: Central Washington State
Posts: 4,403
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Unless I misunderstand your question, well of course you can't run at all without the intercooler connected to the intake, for CIS anyway, unless you rig up some sort of MacGyver plumbing.
Isn't the issue that if you don't vent out the boost pressure - or recirculate it- when shifting gears, you get all this back pressure against the turbo and it stalls the spin?
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, B&B intercooler, stock 3LDZ. Last edited by mark houghton; 10-08-2025 at 12:58 PM.. |
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10-08-2025, 12:28 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,142
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Yeah Mark, I am EFI. Carrera 3.2 with a turbo, so no CIS.
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Cory - turbo'd '87 C3.2 Guards/Blk, 3.4, 7.5:1 CR, 993SS cams, Borg-Warner S366 turbo @ 1.2-1.5 bar, Treadstone full bay IC, 70mm TB, TiAL F46 WG, HKS 1 1/2" BOV, twin 044 pumps, MicroSquirt AMP'd w/GM smart coilpack, Bilstein coilovers, Tramont replica Speedlines (285's rr, 225's frt), Big Reds frt, 993 rr., tower brace, MOMO wheel |
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10-08-2025, 01:44 PM
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Registered
Join Date: Jul 2008
Location: Central Washington State
Posts: 4,403
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Quote:
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Mark H. 1987 930, GP White, Wevo shifter, Borla exhaust, B&B intercooler, stock 3LDZ. |
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10-08-2025, 03:49 PM
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Registered
Join Date: Nov 2017
Location: Qatar
Posts: 638
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If that was true then I should have replaced every turbo when I had a slipped out hose during a full boost blast. which I did endless times and will still do it.
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-1977 911S Coupe, Mahle 3.4, single GTX3584 turbo, - G50 5 speed trans, Haltech 2500 engine management. -1987 Carrera Coupe. -2013 Carrera S PDK Coupe, factory Aero Kit. My DD. -1987 928S4. |
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10-08-2025, 11:12 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,142
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Quote:
I think it’s more than likely ok to run them unconnected. |
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10-10-2025, 04:28 AM
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Ingenieur
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You can and you will overspeed the turbo. You won’t see any particular effect though. The shaft and bearing system is designed to remain relatively stable to at least 150% of design speed. Event that level it may only cause a slight wheel rub.
The turbine wheel burst speed is also very high, and the HCF limit is also very high. The aluminum compressor wheel burst speed is also at least 150% of the design speed. The problem for the compressor wheel is LCF. You will eat up a bunch of LCF life with a big overspeed, but this is not visible. These old aircooled engines are running at pressure ratios that are not high enough to make LCF a very big problem though. I don’t think it likely that anybody would experience a failure from running a short test without the intercooler. |
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10-10-2025, 04:53 PM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,142
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10-17-2025, 04:10 PM
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Happiest when Tinkering
Join Date: Jun 2007
Location: Missouri
Posts: 4,623
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I frequently pop my up pipes particularly at the throttle body that is why I now have a tube bead tool because I am doing this at 7 psi I can only imagine when I start bumping up the boost. I have had no ill effects so far.
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" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go! 76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3 76 Blazer also restored by me |
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10-19-2025, 08:05 AM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,142
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10-19-2025, 11:18 AM
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Happiest when Tinkering
Join Date: Jun 2007
Location: Missouri
Posts: 4,623
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Quote:
__________________
" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go! 76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3 76 Blazer also restored by me |
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10-19-2025, 11:33 AM
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Chain fence eating turbo
Join Date: Dec 2008
Location: Austin, TX
Posts: 9,142
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10-19-2025, 12:39 PM
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Happiest when Tinkering
Join Date: Jun 2007
Location: Missouri
Posts: 4,623
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Quote:
__________________
" Porsche there is no substitute" I always liked that saying. Air cooled is the only way to go! 76 911 C.R.A.P. Gruppe #2 BIG time TURBO C.R.A.P. Bitz EFI/EDIS Now MegaSquirt 3 76 Blazer also restored by me |
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10-19-2025, 01:04 PM
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