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Joes924Racer · Posted: Fri Feb 14, 2003 12:26 pm Post subject: Decking block.

Should I have 2 mm off the deck or slightly less Im thinken
just slighlty less.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

gohim · Joined: 02 Nov 2002 Posts: 4459 Location: Rialto, CA

You can't take that much off without screwing up the cam timing.

And where are you going to find the gas with the compression that high?

On top of that, I suspect that you would be turning your engine into an interference type engine.

Porsche makes thick head gaskets available specifically to make up for lost deck height when it is necessary to cut the block or head. So, I suspect that what you are considering would be a bad idea.

Joes924Racer · Posted: Fri Feb 14, 2003 1:27 pm Post subject:

yea 8,5 to1 is stock I only want to go to 9.5 so 2mm is to much for the timing I have a dial a cam sprocket though I dont know where to get a belt it might be to small
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Richard · Joined: 04 Nov 2002 Posts: 617 Location: Pacific N.W.

I think it would make more sense to find a thin copper head gasket. That way, you could always go back to stock. There are lots of sealants and tricks (like head studs instead of bolts) that will give you a good seal without O ringing the head. But hey, if you're gonna pull the engine anyway, get it O ringed! www.scegaskets.com has 924 gaskets as thin as .032". Not sure what this would give you in compression ratio, but this is .81 mm. Might bring you up to 9.0:1, but to tired to do the math. Don't forget to find out when the pistons hits the valves. Ouch. [/url]

OR_Sunset · Joined: 04 Jan 2003 Posts: 312 Location: Veneta, OR

Have heard of a 924 running around 10:1, and it was definitely quite a project. They put custom pistons in at 9.5:1, I don't know how much off the deck, and had a cam custom made and timed to compensate for the INTERFERENCE nature of the engine. Some kind of super thin re-inforced head gasket as well.

Pretty cool if you have access to 107 octane gas and can afford to replace bent valves every time the timing goes awry. Maybe upgrade to a sprocket driven timing chain with adjustable sprocket and run a propane mix.

Forgive my ignorance, but what exactly does running super high compression get you in terms of performance... like in terms of HP per 0.1:1 CR???

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2745 Location: Sydney, Australia

from what I've read the relationship between cr and hp is very hard to predict or describe mathematically. On a graph it's like a 45 degree line to about 9.5 - 10.0 : 1 then it flattens out.

If you can control detonation then higher cr = higher power because of greater volumetric efficiency but as for how much power ??
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

Joes924Racer · Posted: Sat Feb 15, 2003 2:26 pm Post subject:

I just would like the cp to be like I had a set of euro pistons ..the thin gasket is good

Ill check into that ..No way am I going to O-ring. Theres a good article here about a motor they built in a 79 a long time ago..

Im ready to take apart a motor I got from the european car clinic
here its a complete motor.. Ill clean it up and put it on the stand
and I dont know Ill keep you all posted. Who do I talk to about
recurving a dizzy.

http://www.geocities.com/the_924_site/IndianRed.htm
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

Richard · Joined: 04 Nov 2002 Posts: 617 Location: Pacific N.W.

Start calling distributor rebuild shops.

Peter_in_AU · Joined: 29 Jul 2001 Posts: 2745 Location: Sydney, Australia

O-ringing is not a great idea unless you're building a drag motor and have a very large budget. An o-ring will stop you blowing $40 head gaskets, instead what happens is that you blow holes in $200 pistons and bend $200 rods when something goes wrong and you get to rebuild the entire engine.

The head gasket is a safety fuse, if you're blowing them then something is wrong. Granted, the head clamping on the 924 and 944 is very poor but that should be fixed properly with studs.
_________________
1979 924 (Gone to a better place)
1974 Lotus 7 S4 "Big Valve" Twin-cam (waiting)
1982 924 (As featured on Wikipedia)

Learn to love your multimeter and may the search be with you

-nick · Joined: 16 Nov 2002 Posts: 2699 Location: Cambridge, MA

if you use the copper gaskets you _have to_ o-ring. even with studs it will leak.

Joe, i wouldn't worry about timing changes from 2mm off the block. is anyone really saying that the timing belt stays the exact same length over the hundred degree temp changes in the engine bay?? plus that's what your adjustable cam sprocket is for.

i really doubt this is going to give you an interference engine too. especially if you're just shooting for 9.3:1 or so. i think it's a fine alternative to trying to find euro pistons.

-nick

jpab924 · Posted: Sun Feb 16, 2003 9:54 am Post subject:

Someone fill me in on an adjustable cam sprocket. On how it works and how to adjust it. I have an idea what it is used for....but I want to be sure.....I`m thinking it compensates for any machine work that is done to the block or head. What does it exactly do? I can be stupid at times.

Joes924Racer · Posted: Sun Feb 16, 2003 12:09 pm Post subject:

Well sorry your going to get stupider cause Im not explaining a thing to ya and your a mechanic.

_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

simsport · Joined: 06 Nov 2002 Posts: 573 Location: UK Warrington

I ran a N/A engine with 40thou off the block. This was a Euro spec 9.3:1 motor. I had ignition management but know of other folks who kept the std setup and used pump fuel (97 octane).
I had no det problems and the car made more torque although peak bhp was only up a little.
Cheers
Simon
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Blown is always best!

Joes924Racer · Posted: Tue Feb 18, 2003 10:50 am Post subject:

Sorry Jpab I was only being silly the advantage of the adjustable cam sprocket is that it allows you to move your power peak to where you want it. This allows you to tune your camshaft to your engine; it helps you get the greatest power gains exactly where you want them. Advancing the timing improves low-end torque and helps reduce the rough idle that some performance cams produce. Retarding the timing improves top end performance. The adjustable cam sprocket can be used on any 4 CYL engine.
_________________
1979 porsche 924 Na
1980 porsche Turbo 931GT Replica
Have u ever driven a turbo.

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

Joe, I did this exact same thing (shaved .050" off the block) in order to bring my compression up to 9.5 to 1. So far no problems but I haven't had a chance to run it much as I am now having tranny problems. This does not make for an interfernce engine. I checked it out on the stand before finishing assembly. I also computed the timing difference. This mod retards the timing 1.5°. Not much but should be corrected with offset key or adjustable sprocket as you have. I say go for it!

Todd