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Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

I'm considering whether to put a slightly stiffer wastegate spring in my 931 and I'm curious as to whether others here have done the same. My thinking is that the euro spec 924 turbo ran with 10psi which likely accounts for the 20 extra horses under the hood. Assuming I always run 93 octane fuel do you think the US spec engine could handle the 10 psi?

BTW I'm interested in intercooling the engine but it seems to be quite a difficult task on the 931, no space, long pipe runs... will probably add lag.

Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

If engine is healthy, no problems. But it might be much easier just to use manual boost control on the wastegate line than change the spring.
_________________
'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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Cedric · Joined: 27 Aug 2004 Posts: 2810 Location: Sweden

Whats the CR on the us cars ?
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924guy · Posted: Sun Oct 14, 2007 7:52 am Post subject:

ive run up to 17 psi on regular basis without any issues.running above that without an inter cooler can greatly reduce the life of your power train (but it will handle 24 psi for a bit, do not go past 25 though!)

id definitely just go with a boost controller. its far easier to install, and better to be able to crank up the boost, rather than keep it down. swapping to a higher rated spring, you will have to fight it to keep it from over boosting.

early 931s were between 7.5 and 8.0 cr, later were 8.0 to 8.5 cr
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78 924
82 931 SE "smokey"
99' VehiCross
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morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

i think that S1 US cars have 7.5:1 CR, S2 has 8:1 and euro S2 has 8.5:1 CR.

i can feel a huge difference when driving my non intercooled turbo during day or night....during day it feels slow and slugish; because of the heat the DITC sets the advance way back and the engine problably produces 140HPmax but when its cold outside....its 177 and rubber smoking baby !

so...i would not rise the boost until a decent intercooler is added...i will not rise the boost until i get a decent intercooling setup.
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elitejaso · Joined: 24 Jul 2007 Posts: 143 Location: Melbourne

Just keep in mind that by raising the boost you are putting more strain on the engine hence shortening the life of your engine

I'd also be interested to know how effective the 951 intercoolers are with these cars (without increasing the boost). For example hp gains

johnathan1 · Joined: 08 Oct 2007 Posts: 308 Location: Downey, Ca

I am guessing our cars have no factory-set fuel cutoff point? I know with my Supra turbo, factory fuel-cut is set around 12psi, so you don't damage the engine.

If you plan of raising the boost at all, make sure you use a wideband o2 sensor to make sure your AFR's are staying in the acceptable range...you don't want to blow your engine/melt pistons, etc...Intercooler would also greatly help reduce this risk, as well as allowing you to maintain the same power all the way to redline.

Also, an electronic boost controller would be the best way to go to increase the boost...but a manual controller will do the job just as well. Make sure you have some way to monitor boost pressure as well.
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-1977 924, 4-Spd...Gone
-1987 Toyota Supra Turbo, Pearl White, BPU, 300RWHP @ 10psi.
-1989 Mercedes-Benz 300SEL

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morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

dunno about the fuel cut thing...once i gave it a pedal to the metal start and i got the wheels spining a lot and when the tach needle got to the red part the engine simply died for a few miliseconds until the tach went down to 5000 RPM...then it worked nicely.

And no..i dont have a fuel pump relay with a rev limiter..i just have a 12V relay for the pump relay.
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924guy · Posted: Mon Oct 15, 2007 7:18 am Post subject:

engine cut off at the boost switch is 25psi on the 931.. i
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Eric
78 924
82 931 SE "smokey"
99' VehiCross
Y2K Honda Insight
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Maybe924 · Joined: 14 Aug 2007 Posts: 412 Location: New London, CT

Of course I'd need to find a Euro wastegate spring to do this anyway. I've been searching on the net without luck. Anyone know of a source for 924 wastegate springs? Alternatively will an tial spring work? I'm having trouble finding out much tech info on the subject. BTW I'm starting to think a liquid to air intercooler mounted in the battery tray might be the best intercooler solution for this car... any thoughts?

Rasta Monsta · Joined: 12 Jul 2006 Posts: 11733 Location: PacNW

1.0 BAR spring for sale. . .cheep!
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WeiBe (1987 924S 2.5t) - 931 S3

9xx · Joined: 18 Jun 2006 Posts: 627 Location: Jarvenpaa, Finland

I installed Accuboost boost controller a few days ago and on saturday morning I got a chance to drive my 931 with 1.0 bar of charge pressure.

I didn't want this much boost but when I was tuning it (controller), I visited 1.0 bar a few times but only for a moment. For those brief moments I was driving a seriously fast car! It was freezing weather outside and I was running on Shell 99 oct gas. No pinging at all but then again, I didn't dare to push it really. But was it fast? YES.

Now I got it working better. It is now boosting 0,75 bar steadily. It's a bit more than stock but with freezing autumn weather it should be ok. I got to get that water injection running soon...
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All gone: 931 '82 Alpine White, original option "220" G31 with LSD + 3 x 944

ideola · Joined: 01 Oct 2004 Posts: 15550 Location: Spring Lake MI

morghen · Joined: 21 Jan 2005 Posts: 9095 Location: Romania

ok what the hell now...i've got the engine cut off on me when the needle went over to the red part of the tacho.....so...if i dont have a relay rpm limiter...how the hell did it go to 27psi ? thats 1.7 BAR...i'm in a bit of a blurr here..anyone got any theories?
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Raceboy · Joined: 01 Mar 2004 Posts: 2327 Location: Estonia, Europe

I'm running 0.92 bar on STOCK 924 NA engine with 9.3:1 compression ratio for about half a year now and had about 10 drag events, two top speed contests and few track days with it. Whatta hell are you talking about???
Is it fast? Hell yeah, 13.97 s quarter mile time proves it.

These engines are strong, but keeping them healthy requires maintaining proper air fule ratios and timing.

Get a wideband, intercooler and enjoy your car.
_________________
'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.
http://www.facebook.com/vemsporsche