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Old 12-22-2011, 11:31 AM
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Hyd roller vs Hyd flat tappet for sbc

Been reading like crazy the past month and thought I've decided on lunati's "268" cam "Basic Operating RPM Range:1,800-6,200
Intake Duration at 050 inch Lift:227
Exhaust Duration at 050 inch Lift:233
Duration at 050 inch Lift:227 int./233 exh.
Advertised Intake Duration:268
Advertised Exhaust Duration:276
Advertised Duration:268 int./276 exh.
Intake Valve Lift with Factory Rocker Arm Ratio:0.489 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio:0.504 in.
Valve Lift with Factory Rocker Arm Ratio:0.489 int./0.504 exh.
Lobe Separation (degrees):110" but I have the opportunity now to pick up comps "276" Hyd roller Basic Operating RPM Range
1,900-5,600
Intake Duration at 050 inch Lift
224
Exhaust Duration at 050 inch Lift
230
Duration at 050 inch Lift
224 int./230 exh.
Advertised Intake Duration
276
Advertised Exhaust Duration
282
Advertised Duration
276 int./282 exh.
Intake Valve Lift with Factory Rocker Arm Ratio
0.502 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio
0.510 in.
Valve Lift with Factory Rocker Arm Ratio
0.502 int./0.510 exh.
Lobe Separation (degrees)
110

My goal is to run high 12's (12.99999 is ok with me) my platform is a 64 chevelle SS with a gm goodwrench 350 stock bottom end eddy performer rpm heads rpm intake Holley 750 vac secondaries backed by a th350 with a shift kit 2k ish stall 3:73 12 bolt posi. I would like to keep the p/b

What do you guys think about the cam choices? Am I totally off base here for my application?

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Old 12-22-2011, 11:36 AM
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And the heads are 185 intake 64cc chamber with eddys .38 head gasket
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Old 12-22-2011, 12:48 PM
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What is the static compression ratio of the motor?
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Old 12-23-2011, 02:17 AM
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Hey tech inspector I've read a lot of your posts and was hoping you'd chime in, I'm fairly new to this but using a couple calculators online I was getting a DR and SR in the mid 5's with the 64cc heads .38 gasket stock deck and piston volume and using the 39.5 ABDC from lunati's cam card... I hope I'm making a mistake because that doesn't sound right to me...
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Old 12-23-2011, 02:55 AM
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4.00" Bore X 3.48 Stroke.
64cc Head, 4VR 3.160" X .080" 13cc Dish Piston.
.025" Deck Ht., .038" Gasket, .063" Quench. = 8.97Cr
With .028" Gasket, .053 Quench = 9.15Cr

This is the usual Piston used in several GM Crates.
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Old 12-23-2011, 10:22 AM
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Thanks SSedan now that ive gotten some sleep and have some coffee on board I noticed on my numbers I was missing a "0" in front of my .38 headgasket haha
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Old 12-23-2011, 11:02 AM
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Quote:
Originally Posted by SSedan64
4.00" Bore X 3.48 Stroke.
64cc Head, 4VR 3.160" X .080" 13cc Dish Piston.
.025" Deck Ht., .038" Gasket, .063" Quench. = 8.97Cr
With .028" Gasket, .053 Quench = 9.15Cr

This is the usual Piston used in several GM Crates.
Thank you SSedan64. Using 9.00:1 SCR and closing the intake at 39.5 degrees ABDC yields a 7.73:1 DCR. Depends on how you look at it, but you have either too little SCR or too much cam.

A motor with 9.00:1 SCR will make good cylinder pressure with a cam that closes the intake at somewhere between.....
15 degrees ABDC @0.050" tappet lift = 8.62:1 DCR
20 degrees ABDC @0.050" tappet lift = 8.48:1 DCR
25 degrees ABDC @0.050" tappet lift = 8.32:1 DCR
30 degrees ABDC @0.050" tappet lift = 8.14:1 DCR
35 degrees ABDC @0.050" tappet lift = 7.93:1 DCR

A cam that closes the intake at 39.5 degrees ABDC @0.050" tappet lift would work this way with these static compression ratios....
10.00:1 SCR, 8.58:1 DCR
9.80:1 SCR, 8.41:1 DCR
9.60:1 SCR, 8.24:1 DCR
9.40:1 SCR, 8.07:1 DCR
9.20:1 SCR, 7.90:1 DCR


SJSS, let me help you a little with numbers....
.38 is three hundred and eighty thousandths, or about 3/8ths of an inch.
.038 is thirty eight thousandths of an inch.
.0038 is thirty eight ten thousandths of an inch
To be technically correct, you need to put a zero in front of the decimal point if there is no whole number involved, like this....
0.038" thirty eight thousandths of an inch
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