quench and DCR questions...
07-09-2013, 05:05 PM
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quench and DCR questions... Alright so I've been doing some reading on quench and dynamic compression ratios. I have a few questions about these subjects and how They will play into the new cam.
I've read that the optimal quench is .035-.040. Now currently I'm pretty sure its stock. The block was not decked and stock replacement head gaskets were used. When i go to have my heads re-surfaced they will likely take .010 off, correct? Running stock crank and rods so i'd guess the piston is sitting in the hole as far as a stock one.
What I want to know is, with the heads surfaced, am I safe to run the .027 thickness head gasket, i dont want ptv clearance issues? What CR ratio would that put me at? What Quench?
I've read that the optimal quench is .035-.040. Now currently I'm pretty sure its stock. The block was not decked and stock replacement head gaskets were used. When i go to have my heads re-surfaced they will likely take .010 off, correct? Running stock crank and rods so i'd guess the piston is sitting in the hole as far as a stock one.
What I want to know is, with the heads surfaced, am I safe to run the .027 thickness head gasket, i dont want ptv clearance issues? What CR ratio would that put me at? What Quench?
07-09-2013, 11:29 PM
#2
Quench will not change due to the heads being milled. It will ONLY change due to using different thickness head gaskets......and/or decking the block.
Remember.....quench is the sum distance of :
Piston crown to engine deck at top dead center + the compressed thickness of the head gasket.
Milling the heads = no effect
The effect of taking .010" from the heads will have a largely unknown effect on compression ratio without knowing to what extent the heads will be ported. And if they are.....we can't know the amount of cc's the combustion chambers will have without measuring them.
Bottom line.....you can't have an answer to this until after the heads are ported and milled......and THEN you have the combustion chambers measured.
Could you use .027" head gaskets? Most likely. It will depend, in large part, on your piston to deck distance and your cam specs as to whether you'll have valve/piston clearence issues...... The .010" milled off the heads is (IIRC) a safe amount to take off.
Sorry couldn't be of more help.....
KW
Remember.....quench is the sum distance of :
Piston crown to engine deck at top dead center + the compressed thickness of the head gasket.
Milling the heads = no effect
The effect of taking .010" from the heads will have a largely unknown effect on compression ratio without knowing to what extent the heads will be ported. And if they are.....we can't know the amount of cc's the combustion chambers will have without measuring them.
Bottom line.....you can't have an answer to this until after the heads are ported and milled......and THEN you have the combustion chambers measured.
Could you use .027" head gaskets? Most likely. It will depend, in large part, on your piston to deck distance and your cam specs as to whether you'll have valve/piston clearence issues...... The .010" milled off the heads is (IIRC) a safe amount to take off.
Sorry couldn't be of more help.....
KW
07-10-2013, 09:25 PM
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if thats cam only... holy ***** i cant wait to get this cam in ... and on a side note the heads wont be ported there just getting milled down a tad
07-10-2013, 11:27 PM
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A shaved head or block deck is usually only a few thousandths inch. The machine shop has to tell u how much they remove as if more than a few thou inch removed and the intake needs to be machined to match.
Stock chevy sb deck height is 9.025 from crank center-line. The usual ritual is to zero deck the block to 9.00" deck height and just run a 0.039" or greater compressed thickness composite head gasket - machining the intake to fit also. Since u post a 355 u could check this with a piston at TDC by measure distance from piston (along the pin axis) to a straight edge across cyl bore.
Quench height should be at least 0.030" and more like 0.035" to be safe but less than 0.060" for any quench effect.
If u need help calculating static compression just post your final head chamber volume, piston dish volume, deck height or piston to block deck distance, stroke, bore size and i will calculate it for u. BTW i don't do dynamic c.r. but i'm sure others will volunteer to help with that. U Can measure the head chamber volume with a small square piece of plexiglass and anything calibrated in milliliters - drill hole in plexi and seal with grease, get head level, fill with liquid of choice.
Good luck,
cardo
BTW u need to adjust vlv lifters correctly or u will keep trashing cams. Not trying to be a pain but hope to save u from the hard lessons i have learned.
Stock chevy sb deck height is 9.025 from crank center-line. The usual ritual is to zero deck the block to 9.00" deck height and just run a 0.039" or greater compressed thickness composite head gasket - machining the intake to fit also. Since u post a 355 u could check this with a piston at TDC by measure distance from piston (along the pin axis) to a straight edge across cyl bore.
Quench height should be at least 0.030" and more like 0.035" to be safe but less than 0.060" for any quench effect.
If u need help calculating static compression just post your final head chamber volume, piston dish volume, deck height or piston to block deck distance, stroke, bore size and i will calculate it for u. BTW i don't do dynamic c.r. but i'm sure others will volunteer to help with that. U Can measure the head chamber volume with a small square piece of plexiglass and anything calibrated in milliliters - drill hole in plexi and seal with grease, get head level, fill with liquid of choice.
Good luck,
cardo
BTW u need to adjust vlv lifters correctly or u will keep trashing cams. Not trying to be a pain but hope to save u from the hard lessons i have learned.
07-11-2013, 07:43 PM
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A shaved head or block deck is usually only a few thousandths inch. The machine shop has to tell u how much they remove as if more than a few thou inch removed and the intake needs to be machined to match.
Stock chevy sb deck height is 9.025 from crank center-line. The usual ritual is to zero deck the block to 9.00" deck height and just run a 0.039" or greater compressed thickness composite head gasket - machining the intake to fit also. Since u post a 355 u could check this with a piston at TDC by measure distance from piston (along the pin axis) to a straight edge across cyl bore.
Quench height should be at least 0.030" and more like 0.035" to be safe but less than 0.060" for any quench effect.
If u need help calculating static compression just post your final head chamber volume, piston dish volume, deck height or piston to block deck distance, stroke, bore size and i will calculate it for u. BTW i don't do dynamic c.r. but i'm sure others will volunteer to help with that. U Can measure the head chamber volume with a small square piece of plexiglass and anything calibrated in milliliters - drill hole in plexi and seal with grease, get head level, fill with liquid of choice.
Good luck,
cardo
BTW u need to adjust vlv lifters correctly or u will keep trashing cams. Not trying to be a pain but hope to save u from the hard lessons i have learned.
Stock chevy sb deck height is 9.025 from crank center-line. The usual ritual is to zero deck the block to 9.00" deck height and just run a 0.039" or greater compressed thickness composite head gasket - machining the intake to fit also. Since u post a 355 u could check this with a piston at TDC by measure distance from piston (along the pin axis) to a straight edge across cyl bore.
Quench height should be at least 0.030" and more like 0.035" to be safe but less than 0.060" for any quench effect.
If u need help calculating static compression just post your final head chamber volume, piston dish volume, deck height or piston to block deck distance, stroke, bore size and i will calculate it for u. BTW i don't do dynamic c.r. but i'm sure others will volunteer to help with that. U Can measure the head chamber volume with a small square piece of plexiglass and anything calibrated in milliliters - drill hole in plexi and seal with grease, get head level, fill with liquid of choice.
Good luck,
cardo
BTW u need to adjust vlv lifters correctly or u will keep trashing cams. Not trying to be a pain but hope to save u from the hard lessons i have learned.
Alright, thank you sir, for the info. So, when I have the heads milled I need to send in the intake to? As for the trashed cam, im not so sure thats what it is, I'm just looking for an excuse to get a bigger cam lol .... if the cam is trashed im not sure how my valve adjustment is killing it cause im doing it correctly per shbox's directions, and i am pretty confident that i understand zero lash and can easily find it.
07-11-2013, 10:23 PM
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Ya know i need to get out'a this thread. My apologies for inter-fearing as i read u have a 355" motor revealing previous machine work and suggested u check the actual deck height but that doesn't seem to be something u will even consider. That and taking a look at the old cam for condition of lobes - any apparent destruction showing cause/results of your previous lifter adjust problem - what got u to replace the cam. U are welcome to adjust the lifters anyway u care to and i will no longer get involved. I see nothing now in encouraging u and had only hoped to help u.
For intake milling once u know how much was taken off the heads u can PM me or look into D. Vizards "How to ... Max HP on a Budget" or John Lingenfelters How to ... small block chevy" books for a chart on intake/block/head milling.
Good luck,
cardo
For intake milling once u know how much was taken off the heads u can PM me or look into D. Vizards "How to ... Max HP on a Budget" or John Lingenfelters How to ... small block chevy" books for a chart on intake/block/head milling.
Good luck,
cardo
