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924-76 · Joined: 05 Jun 2006 Posts: 1475 Location: Ontario, Canada

Out of curiosity, How much boost our 2.0 engine can take?
I'm interest in fact and not speculation. What is the highest boost you are running on a stock engine with intercooler?
I'm currently running 15psi on 7.5:1 compression ratio and 2664 4.10 turbo.
Anyone running higher than 15psi/1bar?
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

morghen · Joined: 21 Jan 2005 Posts: 8879 Location: Romania

Steve runs more with the K27, John as well with his supercharger setup if i'm not mistaken.
The 2L NA has also been boosted above 1bar by a few like Raceboy and Dutchpug.
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Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

I’m running 1.1-1.2bar regularly. It has been up to 1.4bar. It is not a stock motor. It’s not a case of what is it’s maximum. It depends on the build of the engine over stock.

On a bone stock motor you’ll probably blow the stock head gasket over 1.0bar based on postings here and my experience. I did twice. If you search BassGT posts he did too when turned the boost up over 1.0bar. So a new sealing and clamping system is required if you want more.

You also need to ensure your IC is capable over 1.0bar to deal with the boost heated intake temps. Post turbo heat will be well over 100deg. I've seen temps of 125deg on my datalogs with a K26 2660 6.10, but the compressor is not as efficient as a 2664. Your #4 turbine housing could also become restrictive. Most using K26 and higher boosts are running a #6 housing. Slower to spool but flows more at the top end.

Also consider sparks, advance/retard curve and fueling if turning up over 1.0bar. Its not just a case of more boost = more power if other areas are not optimised to avoid grenading the motor. One action has a reaction on another element of the system

Mittelmotor run well over 1.4bar on their GTS spec FIA Historique race cars with a capability of 400bhp. They run less bhp in race trim for reliability. It’s all mostly stock GTS spec with their digital dizzy, GTS CIS, custom K26 6.10 turbo, Cometic and ARP sealing and clamping with forged pistons. But the whole package is optimised to reach these limits

Hope that helps a bit. You can turn it up more but I would strongly advise some datalogging, AFR and knock detection equipment. Or a dyno session with a good operator to try and find the known limit for your specific motor. Its health will determine its limits versus another

PS if you have skimmed your head it is very unlikely to be as low 7.5:1 CR.
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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924-76 · Joined: 05 Jun 2006 Posts: 1475 Location: Ontario, Canada

Thank you guys,

My question is more out of curiosity, I'm not planning on pushing my engine to 2 bar just to see what will happen. I guess I should mentioned that I'm already running Cometic MLS head gasket, APR studs, AFR gauge and Dual air temp gauge for the IC.

I know the 4.10 turbo is a restriction and I have plan to solve this in the future.

The US specs engine 79-80 are 7.5:1 and 80-81 are 8.0:1 compression ratio.

Talking to some BMW guy the other week at Cars&Coffee, he mentioned that he is running between 30-35 psi of boost. I couldn't believe it. Than I though, with Porsche tradition to build everything 3 to 4 time stronger that it needed to be, how much boost our engine could handle on stock internal?

Beside blowing head gasket, anybody blew anything on their engine? Anyone ever broke a rod?
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1976 924 N/A ROW SOLD
1980 931S
1981 931 Part car RIP

morghen · Joined: 21 Jan 2005 Posts: 8879 Location: Romania

Out of one documented experience the limit of the oem rods seems to be around 450hp if tracked? Perhaps higher for street use.
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Cedric · Joined: 27 Aug 2004 Posts: 2608 Location: Sweden

Its a very general question, and depends on many things. If you have a good EFI system with knock control etc its of course much easier to safely handle more boost. And if you still run CIS, a knock detection system, Wideband, EGT is important stuff to know what you are doing and dont destroy stuff.

Boost isnt everything though as mr.carrera points out when it comes to power, Joakim.S made ca 350 hp in an engine dyno cell at only 1 bar of boost. An extreme example, but it shows the point

If you dont have any detonation and keep to sensible RPMs and a nice timing map, it will probably be very very hard to brake anything.
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1980 924 Turbo
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Fasteddie313 · Joined: 29 Sep 2013 Posts: 2596 Location: MI

Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

Assume he doesn't mean 15psi for atmospheric pressure and then + 15psi for boost = 30psi ??!! Some (uneducated) 951 owners claim that are running higher boost due to the gauge saying 1.7bar instead of 0.7 bar once atmospheric is taken in account
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1980 931 - forged pistons, Piper cam, K27/26 3257 6.10 hybrid turbo, 951 FMIC, custom intake, Mittelmotor dizzy & cam pulley, H&S exhaust, GAZ Gold, Fuch'ed, Quaife
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924-76 · Joined: 05 Jun 2006 Posts: 1475 Location: Ontario, Canada

Thank you all for the info, based on the info provided by DutchPug:

Raceboy · Joined: 01 Mar 2004 Posts: 2326 Location: Estonia, Europe

Stock headgasket and stock bolts are good for 350+ hp no problem. But blowing head gasket with stock CIS+ignition advance (and in many cases no IC) is also normal as you get mild knock (you never hear it while driving, when you hear it it is VERY strong).
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'83 924 2.6 16v Turbo, 470hp
'67 911 2.4S hotrod
'90 944 S2 Cabriolet
'78 924 Carrera GT replica
'84 928 S, sold
'91 944 S2, sold
'82 924S/931 "Gulf", sold

'84 924, turbocharged, sold.
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ideola · Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI

I have not been able to get beyond 12 PSI on the ClubSport without overfueling (8:1 AFR) and the resultant detonation using a Euro-spec DITC setup and my top mount charge cooler.

I run 12-15 PSI on the 941 depending on temp, using only the water-meth injection setup for intercooling. It still overfuels at around 10:1 at high boost, but the more primitive S1 CIS setup WITHOUT DITC seems to be better at handling higher boost than the DITC cars.

The GTRs were running well in excess of 1BAR, short bursts on close to 2BAR if I recall correctly from the Carrera GT book. So the limitation is not in the block. As others have pointed out above, it's all about spark and fuel management. CIS is the gating factor.
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Carrera RSR · Joined: 08 Jan 2010 Posts: 2309 Location: Somerset, UK

ideola · Joined: 01 Oct 2004 Posts: 15548 Location: Spring Lake MI

morghen · Joined: 21 Jan 2005 Posts: 8879 Location: Romania

I did a similar thing on my turbo.
I fitted a flow restrictor inside the signal line to the WUR to try to limit the amplitude of the signal....to make it run a bit leaner.
It actually worked for the mid-range boost but it then got too lean at high RPMs and started detonating then.
The enrichment curve does not match the engine's requirements...the only way to keep this old technology but get proper control is to do what fasteddie did, use the e-cis dizzy and program it.
This way, no need for a WUR and the enrichment curve can be tuned to perfection using CIS.
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Cedric · Joined: 27 Aug 2004 Posts: 2608 Location: Sweden

Have you seen the results on my car? Pretty much spot on AFRs with just removing the boost line to the wur, no other mods to the s2 systen.

If you dont move the intake temp sensor to the compressor outlet you will have a significantly more agressive ignition curve with the DITC after adding an IC, due ti the lower intake temps. It was on the limit for me according to the knock sensor, will have to take out some timing..
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