924Board.org

[Joes924]

Ok I have a new cam from schnieder and Iwant to raise the compression . Was thinking on shaving the head how much 1 mm I am eventually going to rebuild and over bore and go with just rings but if going through all that work should get new pistons .
whats a over bore and shaved head going to do hp wise.

[-nick]

well the ROW engine had 9.3:1 compression and put out 125hp. compared to the highest US compression was what 8.5:1 and put out 110hp? (i think these numbers are right).

i don't think there were any other changes between the two engines other than compression. so this should give you an idea what more comp will do.

careful on shaving the head!! i don't know how much can be taken off (if any), the head is flat on the bottom and you will quickly be cutting into the valves. shaving the block is probably a safer idea (but i bigger pita).

or, i picked up a copper headgasket a while ago that can be made in any thickness. you could just use a thinner gasket instead of shaving. i'll look up the company name if you want it. they were cheaper than a stock headgasket i believe, and you'll need to replace yours if you're pulling the head off anyway.

-btw- be sure to share what cam grind you got and what you think of it when it's all together.

good luck
-nick

[larso]

I've never seen a 924 head but I think it has a small hemisphere shape in each combustion chamber correct? well the more you shave, the smaller the hemisphere gets, and the comb. chamber gets flatter, which means less flow and less turbulence, but higher compression. Higher comp pistons are good because a flatter piston is better than one with recesses in it (more pressure on a smaller surface, flat is best), but of course you've then gotta worry about valve smacking. Are euro pistons interference with 9.3 or 10.1?

[cs]

the NA head is flat, and even if there were a little room for shaving i would save it in case it had to be shaved one day to get it even. go with shaving the block. i've had mine shaved (had too, never let someone tell you they can get it true with a wet stone!). i also have the 9.3 euro pistons, they have valve pockets cast into them to keep them from colliding, but i don't know what the clearance is now with the shaved block.

[ This Message was edited by: cs on 2001-08-24 10:48 ]

[eturbo924]

The 924 NA head can not be shaved. Do not do it, it could quickly make your head junk.
The combustion chamber is in the cylinder bore on the NA cars. Shaving the head will do nothing for you. Put in 9.3 to 1 pistons and this should play well with your new cam with out getting to radical or to expensive.
Eric

[Joes924]

Thanks Eric. How much was your block shaved

CS.

[cs]

good question, wish i remembered. it was just enough to fix the block. it might say on my reciept from the machine shop, but i don't even know where those are at. what you could do if you're worried about hitting the valve is put this putty type stuff on top of your piston, torque down the head, turn the engine over (by hand of course). then when you take the head off you can see how close the valve comes to the piston. that might give you some idea as to how much you can shave off.

[Joes924]

Naa .. I think Ill just call some piston people and see about getting those pistons and talk to my machine shop and go pick up this motor and get started on a rebuild with
the pistons and cam and new stiffer springs and id like bigger valves but to spendy so
ill stop there.

[Joes924]

found ebsracing in a magezine porsche excellance sept issue wonder if they make 9.3:1 pistons for the motor. there website is
They do but there around 600.00 from Je pistons.

engine building supply co.
http://ebsracing.com



[ This Message was edited by: Joes924 on 2001-08-29 11:27 ]