Increasing compression ratio

[mgnewbie]

Can someone please share their experience in increasing compression ratio on their B's? I am considering milling the head and using a thinner head gasket to increase the compression ration on my 80B from 8:1 to 9 to 10 :1 since I will be installing a higher lift and a wee bit warmer cam. I already have tube headers, and now in the process of rebuilding a set of SU's.

 

[billspohn]

A far better way is to change pistons.

If you do shave the head that much you will ruin rocker geometry and will need to get shorter pushrods, or your guides won't last long.

 

[MikeP]

Not to mention if it doesn't work out to your satisfaction you'll probaby need to source a new head to go back since you can't reliably add thickness.

 

[Hap Waldrop]

Most of the replacement piston for the later 18V engine are 8.8 to 1, so thats a good start, if that has been done then somewhere between .020"-.040" will get you to the mid 9s, anbd thats way too sutle of a change to induce any of the stuff Bill talked about, I do it all the time with the motors I build. Bottom line you need to do the math, deck height, piston dish, combustion CC, head gasket thickness (stay with the Payen headgasket) etc., But here's what I would not do, is shave a bunch off a head to put back on tired engine with stock 8.0 to 1 pistons, if you go that route then you're stuck with 8.0 to 1 piston from now on. Everyhting I build for the street is 9.0 to 1 or above, I keep my street engines to a max of 10.0 to 1 or below.

 

[mgnewbie]

That makes a lot of good sense. higher volume pistons plus some milling so that you have option to change to other pistons if needed later.

Since I am not planning to rebuild my engine(yet), I will consider taking off 0.02" to 0.04" the next time I remove the head to check the valves and service the head. That should get me near 9:1 ratio...

Hal, thanks for your advice!

 

[davester]

Uhoh! I think you are doomed now. You are never going to get that '67 'B if you don't stop thinking about this stuff. Button that thing back up and put it on the market pronto!

 

[mgnewbie]

Dave, You're right! It's a sickness...