Compression Ratio, Too High...Too Low ??? Options

[2-OH!]

Ok folks,

We just finished rebuilding the motor...94mm pistons and cylinders to match...71mm stroke...but old 1.7 case...CC'd the heads and come up with 44 cc's per cylinder...

Do the calculations and we come out with 1971 cc's...Great !!!

But, The problem is the compression ratio is now 10.64 to 1...

The question of the day:
Should I take the cylinders and heads back off and shim them to get a little relief...Probably not going to get much...Might knock it down to 10 or 9.75 (if I'm lucky)...

DO NOT want this thing to clatter and diesel on me when I get it back together...

OK, let me have it...What are your thoughts ???

2-OH!

[Jake Raby]

Ok, How the hell did you get a 44cc chamber?? Are these 1.7 heads? To take a 2.0 head, or a 1.8 to 44cc requires a ton of flycut, on a 2.0 head you'll break through the exhaust stud holes closest to the chambers at less than 51cc most of the time!

Now, if the heads have been machined this deep you have bigger issues as the va;ve deck has been dropped so far that you'll more than likely collide valves into pistons!

How did you determine that you had 44cc? Do you have pics of the chambers?

BTW_ adding a gross amount of shim to lower the CR has negative effects on the quench... This also lowers the engine's efficiency mandating a ton of extra timing advance to be used. I have seen engines have bigger issues with detonation and tempewrature with a ton of deck and lower CR than they did at much higher CR and better quench. Quench= efficiency and efficiency is the name of the game.

ONCE AGAIN, HOW THE HELL DID YOU END UP WITH A 44CC CHAMBER?
If you do have this chamber volume pull off the heads and sell them to a racer, or have them partially hemi cut to add some volume which would also be a half assed way of completing the task..