My forged pistons...

[earlbrown]

.040" is as tight as you want to shoot for on a normal hot build. Any closer than that and rod stretch, and piston rock become issues.  That's assuming you're not loose in the bore to start with.  Once you get past .060" you're pretty much out of the zone and lost the benefits of having quench.

As you can see, there's not a lot of quench area with 8445 heads. This pic is with a 3.995" 4.1 bore and there's still very little exposed deck meat.

[larrym]

Thanks earl! I have measured and as far as I can tell my pistons are .007 inside the hole
with a .035 compressed RJC gasket I should be at .042 going to pull the motor over the winter and put in the new short block so I'm ready for spring.


My buddy just finished a motor and he ended up .007 outside the hole....
with the stock gasket he has pretty close to the same quench and his motor works pretty well.

[good2win22]

Quench!  no one talks about quench these days!    But, if you want to minimize detonation you need to.  Funny, I run about 9.3-1 compression on both of my cars.  The car with the stock cam has no problem running 26 psi so maybe quench is important?  I have hit 30 on the other car with the 210 cam without detonation.  Of course, it can be hard to have detonation when spraying alky so I cannot stay for sure.

At one time, I ran a 221/221 flat tappet with that compression.  It needed a bit more stall that the 2600 converter, but when it hit 5000 rpm, the exhaust sounded like a 390 Ford with a good cam and steel packs.  Felt like it downshifted.  Almost as good a sound as a P-51 making a fly by 

Any way, I love compression.  I hate cars with loose converters that don't want move when you ease down on the pedal

I do. With our combustion chambers there's VERY little deck area hanging into the bore, but I'll still take it.  Anything that can mix up the mixture and/or blow out detonation, I'm a fan of.   ...not to mention the free point of compression you get from having it.


Good2win22, this is the one I use for static compression.   My domes are -22cc's.

http://users.erols.com/srweiss/calccr.htm


and this is the one that really matters....

http://www.wallaceracing.com/dynamic-cr.php


Playing with this one will illuminate just how you need to raise compression to offset running big ass cams.

Thanks Earl!

[earlbrown]

Thanks earl! I have measured and as far as I can tell my pistons are .007 inside the hole

When you measure, there's two ways to do it. Once is to take a reading above the wristpin.

The better way i to take a reading 90* from the pin and rock the piston back and forth. That will give you a low number, a high number, and a spread.  The more piston rock you have, the greater the spread will be.