Coreyc619

as in, on a stock LS6 shortblock where the avg piston is .007 out of the hole and running a .040 gasket to get the so called "ideal quench" of .035ish,what am i going to gain?... just stave off some detonation? or is there more to the story? or is sticking with the .053 (maybe that number is wrong?) MLS gaskets and leaving .01 of quench on the table really that big of a deal? just curious what i would gain/lose here.. like if anybody has any facts associated with this particular question. i'd like to take every available advantage possible within reason. im a pretty meticulous person and dont mind doing the work.

my dumbass paid pat g to spec me a cam and THEN decided to mill my heads . LOL. typical me. anyhow so im tryin to get all this figured out... what exactly im gonna do, bc the original cam he speced me isnt gonna work now, too tight. whatever. regardless, im interested in raising my CR

Adrenaline_Z

The ideal quench would be 0, but that's not happening because rods like to
stretch, and parts expand while heating.

0.035" - 0.045" is about right for a street engine with specific part material
found in our LS engines and RPM range.

If you leave 0.001" on the table, you're not missing much. If you start increasing
qunech by 0.01" (> 0.045") you run the risk of detonating and losing some of the
chamber efficiency when combustion takes place.

Adjusting static compression ratios with quench height is the wrong way to
approach the build; you should tweak the chamber cc ideally (milling, quench
area).

I just posted a link in Advanced Tech about this very same topic.
Here is a good article to browse through:

http://racingarticles.com/article_racing-10.html

Mike@ZMS

iTrader: (10)

As was stated above, your not going to gain much, if anything without possibly inducing more problems that could be catastrophic in the end.

If your running ~.045 quench, then you are pretty much right where you should be. Now if your talking about building a motor with a specific racing purpose in mind, then reducing the quench through milling of the heads and reworking the chambers would be the proper way to go about things. Then obviously spec'ing the cam as a final step once all the numbers and math has been done.

Coreyc619

im not adjusting static CR through changing the quench?? (as in, thats not my method of doing so, but more like a consequence) but the two are definitely related. if i bring the head closer to the piston via a thinner gasket i am going to change CR. so i'm trying to figure out the proper mixture of both (gasket thickness, and material removal) to reach my particular goal, and figure out if i need fancy head gaskets or if im not really missing out on much. sounds like a waste of time.

mike.. how is milling the heads going to affect quench? (isnt it the space between the piston and the flat portion of the combustion chamber? if so how is milling the head going to change it? seems more like gasket thickness, deck height, compression height aka wrist pin location would dictate it, not milling) im more concerned about keeping the piston off the head. and yea, this by far isnt my first rodeo - the cam thing was just a dumbass mistake as in i changed directions for the immediate future of my car. i had boost in the back of my mind sometime soon, but got real with myself and realized thats several years down the line. so i might as well go ahead and raise my CR now to get the most out of my current setup.

Adrenaline_Z

Yes, of course. I'm a little confused by your asking about the quench height
and your final closing statement of:

If you are asking about the benefits of a tighter quench and using the chamber/piston
to regulate the SCR, then my answer applies. This is the ideal scenario
for you, and you will benefit by using a thinner gasket to arrive at the
final SCR value.

If you need to raise compression, you can mill the heads if the valve clearances
allow.

Depending on how much you need, you can phase the cam (advance it),
or spec. new valve events to close the intake valve sooner. This will increase
the DCR value which yields a similar result.

The only downside of advancing the cam, and an earlier IVC is shifting the torque
peak, and power peak lower (generally) ... which might be opposite of what you
and the engine want.


The short answer is yes, you are sacrificing power and performance with 0.010"
increase in quench @ 0.053"

The_Rizzle

iTrader: (4)

The quench comes from the thinner gasket.

As for ideal quench gap, you have to remember the block material as well. An aluminum block will expand slightly more when hot, and adds a couple thou extra clearance. Not much by any means, but it can be the difference b/w hitting when cold and perfect hot.