Help understanding Dynamic CR, quench and piston fly-cut
Help understanding Dynamic CR, quench and piston fly-cut Hello everybody.. I'm finishing up gathering parts for my engine build and need some help understanding these things:
1) Should I consider anything about SCR as long as I'm at 8.5:1 DCR ? that means can I safely run a 13.5:1 SCR LS3 with a DCR of 8.7:1 ?
2) Can I run below 0.030" quench ? like 9.0 DCR and 0.020" quench ?
3) Does anybody know how much cc would I lose if I fly-cut the pistons 0.100" on both intake and exhaust valves ?
Thanks a lot..
1) Should I consider anything about SCR as long as I'm at 8.5:1 DCR ? that means can I safely run a 13.5:1 SCR LS3 with a DCR of 8.7:1 ?
2) Can I run below 0.030" quench ? like 9.0 DCR and 0.020" quench ?
3) Does anybody know how much cc would I lose if I fly-cut the pistons 0.100" on both intake and exhaust valves ?
Thanks a lot..
.035 is the generally accepted rule of thumb for quench volume. Dynamic compression ratio and quench play little to no role on each other. The main reason for the .035 quench rule is piston/rod expansion. You may have .020 with the engine cold, but once it warms up, you can about bet one over rev and your going to be replacing a lot of ****.
Hello everybody.. I'm finishing up gathering parts for my engine build and need some help understanding these things:
1) Should I consider anything about SCR as long as I'm at 8.5:1 DCR ? that means can I safely run a 13.5:1 SCR LS3 with a DCR of 8.7:1 ?
2) Can I run below 0.030" quench ? like 9.0 DCR and 0.020" quench ?
3) Does anybody know how much cc would I lose if I fly-cut the pistons 0.100" on both intake and exhaust valves ?
Thanks a lot..
1) Should I consider anything about SCR as long as I'm at 8.5:1 DCR ? that means can I safely run a 13.5:1 SCR LS3 with a DCR of 8.7:1 ?
2) Can I run below 0.030" quench ? like 9.0 DCR and 0.020" quench ?
3) Does anybody know how much cc would I lose if I fly-cut the pistons 0.100" on both intake and exhaust valves ?
Thanks a lot..
2) .035" - .040" is safe. Less than that and you're really risking the pistons meeting the cylinder heads.
3) Depends on the diameter of the flycut and valve angle as well, then find someone who can do the math. I find it easier to flycut a practice piston, fill with clay and scrap the top off flat, then measure the volume by dropping the pieces into a burette.
Please correct me if I'm wrong.
I really like your method of measuring the pistons. Thanks for sharing..
1) Personally, I don't put much thought into DCR. Get the SCR where it should be, pick the cam for your intended RPM range, and worry about the more important details.
2) .035" - .040" is safe. Less than that and you're really risking the pistons meeting the cylinder heads.
3) Depends on the diameter of the flycut and valve angle as well, then find someone who can do the math. I find it easier to flycut a practice piston, fill with clay and scrap the top off flat, then measure the volume by dropping the pieces into a burette.
2) .035" - .040" is safe. Less than that and you're really risking the pistons meeting the cylinder heads.
3) Depends on the diameter of the flycut and valve angle as well, then find someone who can do the math. I find it easier to flycut a practice piston, fill with clay and scrap the top off flat, then measure the volume by dropping the pieces into a burette.
funny, I dont give any thought to static compression. I set the DCR I want for the fuel used, pick the cam off the heads and the static compression just comes out to whatever it may be when its all together.
Overall, static compression doesnt mean ****, and dynamic is the only thing that has any impact on an engine. Case it point as above a 13.5 SCR with 8.7 DCR. You dont have a 13.5:1 motor, you have a 8.7:1 motor in all reality.
You need to run about a .035-038 quench, measure the piston out of the hole and order the appropriate gasket from there. As long as the cam you want fits figure out the head CC you need to acheive the DCR with your IVC event. get your heads as close to that CC as you can and run it
BTW I cut my stock pistons .12x and they came out to around 1.8cc each if I recall
Last edited by Grr; Jan 14, 2013 at 08:01 PM.
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Verdad Gallardo BTW.. How much chamber cc can I mill down the L92 heads without affecting head flow and\or strength ? Intake alignment isn't an issue .
I know older ls1 241 heads can be milled up to 0.100 with no problems with strength but how about these L92s ?
And can I mill the block deck 0.010" and let the pistons come out 0.016" instead of buying a .040" gaskit ?
I know older ls1 241 heads can be milled up to 0.100 with no problems with strength but how about these L92s ?
And can I mill the block deck 0.010" and let the pistons come out 0.016" instead of buying a .040" gaskit ?
Last edited by Spice Red_SS; Jan 14, 2013 at 08:24 PM.
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A great write up on fly cutting in case you go that route.
http://forums.corvetteforum.com/c6-t...mpression.html
http://forums.corvetteforum.com/c6-t...mpression.html
A new L92 head(s) isn't really wallet friendly. Car has LS3 with cnc ported heads and ported intake and 4.10 rear gears so I'm sure some higher static compression along with a custom cam that is the biggest will yield more power than the biggest custom cam with 70cc chambers.
Anywas they can be safely cut .050 without affecting there stringth. I plan on cutting them .0100 but want to make sure they are not gonna crack or something.
Milling heads professionals please chime in.
Already figured that out but thanks 
Intake valve closing point is what determines DCR. Thank you.
Anywas they can be safely cut .050 without affecting there stringth. I plan on cutting them .0100 but want to make sure they are not gonna crack or something.
Milling heads professionals please chime in.
A great write up on fly cutting in case you go that route.
http://forums.corvetteforum.com/c6-t...mpression.html
http://forums.corvetteforum.com/c6-t...mpression.html
Intake valve closing point is what determines DCR. Thank you.
