cylinder head and rocker arm Q
03-19-2008, 06:52 PM
#1
6th Gear
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cylinder head and rocker arm Q
Hello everyone, new to the board. I have a '81 vette. My question is, the '81 motor has a low mile stock bottom end with a pair of summit performance cast iron heads 67cc, intake runner 165cc. 2.02 intake, 1.6exhaust. Max spring lift .520.
What compression ratio does this give me? Also, what kind of rockers can I go with, do I need self-aligning or can I use 1.5 stamped steel. The new heads do not have guideplates. The rest of the motor has a performer intake, mallorey ign., 600cfm carb, lunati 292-480/480 109 LSA bracket master II, hooker sidemounts, etc..
What compression ratio does this give me? Also, what kind of rockers can I go with, do I need self-aligning or can I use 1.5 stamped steel. The new heads do not have guideplates. The rest of the motor has a performer intake, mallorey ign., 600cfm carb, lunati 292-480/480 109 LSA bracket master II, hooker sidemounts, etc..
03-19-2008, 08:04 PM
#2
Assuming your bore is standard 4.00, stroke 3.48, assuming a 12cc
dished piston, assuming the pistons are .025 below the deck, assuming
a factory .018 thick steel shim gasket 67cc head chamber.
compression is 9.16. assuming all the above is true but someone has
slapped on a .041 thick gasket compression is 8.74.
Your cam has 230 at .050 duration, even if you have 9.16 compression
its to low for that much cam. If you have a flat top piston your Ok.
Standard piston may have more dish not sure could be more like 16cc.
16cc dish piston with .018 thick gasket, comp. 8.80.
16cc dish piston with .041 thick gasket, comp. 8.42
dished piston, assuming the pistons are .025 below the deck, assuming
a factory .018 thick steel shim gasket 67cc head chamber.
compression is 9.16. assuming all the above is true but someone has
slapped on a .041 thick gasket compression is 8.74.
Your cam has 230 at .050 duration, even if you have 9.16 compression
its to low for that much cam. If you have a flat top piston your Ok.
Standard piston may have more dish not sure could be more like 16cc.
16cc dish piston with .018 thick gasket, comp. 8.80.
16cc dish piston with .041 thick gasket, comp. 8.42
Last edited by Little Mouse; 03-19-2008 at 08:32 PM.
03-19-2008, 08:31 PM
#3
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Assuming your bore is standard 4.00, stroke 3.48, assuming a 12cc
dished piston, assuming the pistons are .025 below the deck, assuming
a factory .018 thick steel shim gasket 67cc head chamber.
compression is 9.16. assuming all the above is true but someone has
slapped on a .041 thick gasket compression is 8.74.
Your cam has 230 at .050 duration, even if you have 9.16 compression
its to low for that much cam.
Standard piston may have more dish not sure could be more like 16cc.
16cc dish piston with .018 thick gasket, comp. 8.80.
16cc dish piston with .041 thick gasket, comp. 8.42
dished piston, assuming the pistons are .025 below the deck, assuming
a factory .018 thick steel shim gasket 67cc head chamber.
compression is 9.16. assuming all the above is true but someone has
slapped on a .041 thick gasket compression is 8.74.
Your cam has 230 at .050 duration, even if you have 9.16 compression
its to low for that much cam.
Standard piston may have more dish not sure could be more like 16cc.
16cc dish piston with .018 thick gasket, comp. 8.80.
16cc dish piston with .041 thick gasket, comp. 8.42
03-19-2008, 09:06 PM
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What options do I have in order to get the max compression on this stock bottom end motor without touching the bottom end i.e pistons. gaskets, heads? . I have the origional heads as well. the origional compression is 8.2:1
03-20-2008, 01:30 AM
#5
if you could come up with 10.0 compression. Suggest you use a lower
duration cam.
Last edited by Little Mouse; 03-20-2008 at 02:55 AM.
03-20-2008, 10:54 AM
#6
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AFAIK ... for 81 C3 w/ 350 ... only 350 is low-performance, low-compression w/ dish pistons & 76cc heads.
Given any sbc350 w/ stock bore & stroke ... swapping from OE 76cc heads ... to 67cc heads ... & if ALL other variables remain same ... static compression will increase approx 0.71.
Seems advertized GM quotes for later C3 compression are often higher than actual ... a claimed 8.2 often closer to 7.7 - 7.8. Believe that or not ... true or false ... present scr < 9:1 regardless.
Agree w/ LM ... That's too much street cam for your compression.
Get a smaller cam or more compression or both ... w/ proper gasket, a pr of L98/ZZ4 heads (58cc) will bump scr up approx another 0.6. ... still not a real good street match w/ that cam.
Given any sbc350 w/ stock bore & stroke ... swapping from OE 76cc heads ... to 67cc heads ... & if ALL other variables remain same ... static compression will increase approx 0.71.
Seems advertized GM quotes for later C3 compression are often higher than actual ... a claimed 8.2 often closer to 7.7 - 7.8. Believe that or not ... true or false ... present scr < 9:1 regardless.
Agree w/ LM ... That's too much street cam for your compression.
Get a smaller cam or more compression or both ... w/ proper gasket, a pr of L98/ZZ4 heads (58cc) will bump scr up approx another 0.6. ... still not a real good street match w/ that cam.