924Board.org

brit2514 · Joined: 21 Feb 2007 Posts: 18

hi i own a 1984 924 lux euro edition 125bhp. i also have a 924 turbo head and s2 pistons, the euro 177bhp ones (CR 8.5:1). i would like to know:
1. what problems i might get if i run without a turbo. lowering the cr is bad mine is 9.3:1. would the turbo head bring me back up ?
2. would it be better to raise compression ratio by skimming the turbo head?
3. would it be better to fit a turbo or super charger? ( if i havve to go this way)

Martijnus · Joined: 29 Dec 2006 Posts: 2019 Location: Netherlands

brit2514 · Joined: 21 Feb 2007 Posts: 18

i understand that the compression chamber is in the head on a 931 and the 924's is in the block.

i wanted to now if i use the 931 head and pistons would i get an increse in hp?

as the compression raio would be 8.5:1 with the series 2 pistons or would the head need skimming to increse the cr, and if so how much would need skimming?

or would using a turbo or supercharger be a better way to go? i was thinking about using a aton m62 superchager off of a merc?

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

the bolt pattern on the exhaust side is different between the 931 and NA heads. Even if you resolved all of the other issues, you'd have to address the exhaust manifold. I suppose you could take a turbo exhaust manifold, block off the turbo flange, and get it to work, but it wouldn't exactly be a free flowing setup. of course you could make your own manifold, but that's certainly no trivial task.
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erstwhile owner of just about every 924 variant ever made

brit2514 · Joined: 21 Feb 2007 Posts: 18

i understand that the compression chamber is in the head on a 931 and the 924's is in the block.

i wanted to now if i use the 931 head and pistons would i get an increse in hp?

as the compression raio would be 8.5:1 with the series 2 pistons or would the head need skimming to increse the cr, and if so how much would need skimming?

or would using a turbo or supercharger be a better way to go? i was thinking about using a aton m62 superchager off of a merc?

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

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

emoore924 · Joined: 13 Apr 2004 Posts: 2822

oh gawd, here we go again...

endwrench · Joined: 07 Dec 2002 Posts: 1631 Location: Victor, Montana

Like he said, he has the Euro S2 pistons to go along with the head, so we know what the compression will be, 8.5:1. Same as a 110HP US model 924. As far as I know I have yet to see ANYONE put a 931 head on an NA motor so it will be difficult to say what the power is. It will only be a guess.

With that said, the 931 head is a superior fllowing head compared to the 924 head and with the simple decking of the block .050" you wil arrive at 9.5:1 compression. With very little guessing I am sure this motor would outperform a Euro 9.3:1 NA 125HP engine. How much it would outperform is still a guess.

If you're going to turbo/supercharge it, why up the compression anyway? 8.5:1 is near perfect with boost.

BTW, if you do deck the block, watch your piston clearance. May be a problem with 931 pistons.

Todd
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'79 924NA. Rebuilt 9.5:1, MSDS header, Mega Squirt Injection, MJLJ-EDIS Ignition, 1.6L Whipple Charger and Intercooler, 10lbs Boost, 944 Trans, Custom HD Clutch.
"simsport" said....superchargers are better than turbos its official!....

Chrenan · Joined: 15 Jan 2003 Posts: 3903 Location: Canada

I hope someone finally does this, attach a 931 head to a normally aspirated 924 engine. I'd love to see the results, especially with custom pistons to get the compression ratio high. I guess decking the block gets the same result, but there is something nice about having the timing belt adjustment stock if you use custom pistons, nice and simple.
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1987 951 - M193 Version for Japan

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

I'm doin' it. The sick plan is to put the turbo on the cold side, GTR style, with intercoler and EFI. Looking for a 77-78 tub, have a spare 931 head.

MUAH-HA-HA!
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Toofah King Bad

WeiBe (1987 924S 2.5t) - 931 S3

baldwin · Posted: Thu Feb 22, 2007 4:08 pm Post subject:

CBass · Joined: 03 Nov 2002 Posts: 2807 Location: Vancouver, Canada

I don't think you'd see too much more power naturally aspirated, definately more with forced induction.

The 931 head flow better, but at 8.5:1 compression you're not going to be able to run too hot of a cam, which means you won't be able to really use it as a high rpm engine and get much extra flow out of it.

If you were to run with the 931 head and try to make power naturally aspirated you'd want a higher compression ratio and a longer duration camshaft than stock.
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'81 931 in various states of assembly

leadfoot · Posted: Thu Feb 22, 2007 6:48 pm Post subject:

with euro pistons you will get about 8.5:1 with the turbo head, exhaust manifold can be the N/A just enlarge the bolt holes in the vertical plane up/down to bolt it too the turbo head.
It might become an interferance motor or just get some of the lift taken out of the cam and add some duration to make it non - interferance... use vw pistons if you want a larger bore and more compression or some other pistons with a dish and lower compression height and stroke the crank at the same time...
You will need the intake manifold or need to construct your own and use 931 injectors or modify the injector inserts....
If your going to this trouble, make a new inlet manifold to suit a supercharger, use your turbo pistons and run 6psi without an intercooler....
Leadfoot
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1981 ROW 924 Turbo -
carbon fiber GT mish mash
LS1 conversion in progress...

morghen · Joined: 21 Jan 2005 Posts: 9102 Location: Romania

I was going to do this but i left it because i did not find the parts needed

And by the time i had all figured out i wanted to turbocharge it.
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