924Board.org

[Paul T.]

I seem to remember that Vaughn mentioned once that a 931 head gasket will fit on a 924 N/A motor and up the compression slightly, is this true? And, if it is, about how much will it boost compression by? Then, where can I get one? Thanks Gentlemen!

[bacook]

I just got a 931 gasket from the local Porsche dealer for $69, with the PCA discount.

[larso]

germanparts.com has them for $67 i believe.

you get half of a point of compression.

i dunno maybe 3-5HP

[cs]

a half a point, you mean like .5, that seems like a lot for a head gasket

[dwak]

Strange that the 931 head gasket would raise compression when the pistons lower the compression.

[Joes924]

Thats a big job but its better than hooken up a 5 hp lawn mower engine for the extra go
guess if your doin head work then its the thing to do. Right

[Vince Ponz]

Hey no fooling around. Has anybody done this and is there a gain? Downside. I am rebuilding my motor and ordered a head gasket but can change it. Do all the holes line up?
I don't want to break a brand new rebuild.

help and go into detail.
Thanks

[AppleBit]

Vince-

You want to keep your size the same otherwise you will have cam timing off....

but if you already want to work around that...

Yes, the thinner gasket will work-- I kept the stock thickness... but everyone else that went in on an order of copper head gaskets went for super thin.... Still does not make it an interference engine from this.... but yes, it does get everything a little closer...

- Jon


_________________
Classic British Sports Car Restoration v6 + v8 Engine Conversion Swaps

Porsche 924 Wide Body LS1 Corvette 500 Horsepower Engine

[larso]

The 931 head gaskets, even though they are thinner, are supposed to be stronger than NA gaskets

I think copper ones are "unblowable".

There was some info about copper that was a disadvantage....i think there was some info about it conducting heat better, but also that it could warp your head easier or something...cuz its metal rather than asbestos or whatever is in those OEM gaskets.

[924_fan]

I understand that valve timing is thrown off when an ohv engine (with its cam in the block) has its deck height changed; however, I thought that the overhead cam design precluded this from happening. As long as the timing marks are set as to factory settings.

[cs]

i don't think it would throw the valve timing off, just adjust the tensioner pulley to take up the slack.

[924 turbo]

It does throw valve timing off. And it's not a matter of slack. Remember that the belt is a fixed length. When you mill the head, the distance from the cam pulley centerline to the crank pulley centerline changes. The teeth are spaced apart so that at the original distance, when the engine is at TDC, the cam is also at TDC. If you shorten this distance, you throw the cam off by a few degrees. You can use an offset key on the camshaft to remedy this.

[Vince Ponz]

Okay, so you all confused me more than I car to know about. I will have a mild cam put in and the valves made bigger and if it works put on the 931 gasket. Please tell me if it will work or not. I will be getting the parts within the week from my Porsche dealer and can change it.
Let me know +s and -s.
Thanks

[larso]

It will throw the valve timing off a weee bit.

Listen, when your engine heats up, your belt expands.
Your valve timing changes then too! It's really no big deal.

YOu will lose a little wee bit of low end power, and a wee bit of high end power when your engin is cold or hot too!

[larso]

it will retard the timing slightly ponz.

Your belt tension will also change your valve timing slightly, a loose belt will advance the timing a lil, and a tight belt will retard it (assuming clockwise rotation looking directly at the cam sprocket from front of car, on hondas it goes the other way i think)