Got this from "Auto Math Handbook" by John Lawlor:

Amount to mill = ((new disp ratio - old disp ratio)/(new disp ratio x old disp ratio))* stroke

disp ratio = cyl vol / combustion chamber vol = 1.0 less than CR

For a stock LQ9:
Old CR=10.0, old disp ratio = 9.0, stroke = 3.622"
New CR=10.5, new disp ratio = 9.5

amt to mill to achieve 10.5:1 = ((9.5-9.0)/(9.5x9.0))*3.622 = (0.5/85.5)*3.622 = 0.021"

Anyone familiar w/ this formula? Sound Correct?

 

the math looks good and the amount to mill looks right....but wouldn't it be easier (and cheaper) to just use a thinner head gasket ??...I think FelPro makes a thinner gaket that is good for around a point of compression

 

If you are gonna get compression up and try to avoid detonation you have to keep the quench area down. First step is to use Felpro head gasket #1041 (.041" compressed). This will get your compression up to 10.30. Then if you remove approx. 2cc from the heads you will have 10.54 compression. This would be about .012" off the heads.

 

67SS509 - I couldn't have said it better myself. Well, actually I did two weeks ago when he asked a similar question (read the third post down): https://ls1tech.com/threads/showflat...31&fpart=1 Its good to know that others have the same opinions I do.

 

Will the Fel-Pro 1041 work on the LS1 5.7?

 

Richard - No I didn't forget your post (thanks as always), actually just trying to double check your recommendation before I go and have the heads cut. Really would like to understand in my head how to come up with the desired CR so I've been searching out different formulas. Started w/ this one since it was the simplest. Haven't removed the heads yet, so I don't know deck height specs (along w/ other dimensions) in order to use the more complicated formulas. Also see my next question below.

67SS509 - what is "quenched area"?

I guess my question is, how do you calc/know how much each .010" of milling will change the chamber cc's? And at what point to you start having geometry problems w/ the intake manifold, pushrods, etc.?

Support is great on this board but I have heard enough horror stories and seen alot of incorrect info being put forth as "fact", that I want to be able to come up w/ these numbers myself. Thanks for helping me be smart too...

 

Break out the geometry. Here are some specs you will need:

Bore= 101.6 mm
Stroke= 92 mm
Gasket bore= 102.616 mm
Deck Height= -.1524 mm
Stock Gasket compressed height= 1.3716 to 1.524 mm depending on gasket
Stock 317 head chamber volume= 71 cc
Felpro gasket comp height= 1.0922 mm
Felpro gasket bore= 104.14 mm

I estimate the chamber area to be 2/3 the area of the bore.

Most people say you are safe milling .030 before you get into any fitment issues, and that may be conservative.

 

Ok now that is the kind of info I'm looking for.
Where do you get your data from? Is there a GM website that goes beyond bore & stroke info? Have you done your own measurements? Maybe reverse engineer the numbers?

As for estimated chamber size & milling, GOT IT!

 

Big Tex & 67SS509 -

Tried to call More Performance Inc. looking for the Felpro #1041 but they claim FELPRO never did produce or supply them w/ the gasket. Any other sources for this gasket?

Thanks,
Gregg

 

Call Summit first then Jegs. Summit has a 10% off sale if you use the code "N54101" when you place the order. This code is good through July 31st. www.summitracing.com