LS6 head on 1969 L71
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From: Anoka, MN
LS6 head on 1969 L71
The heads on my L71(427 11:1 435hp) engine are 3272990 with 1973 cast date. Would these heads allow usage of 91 non-oxiginated lead free fuel without any lead or octane additive assuming pistons are factory?
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From: Anoka, MN
Yes, 6272900…..thank you for the response, being a 1973 cast head would it have induction hardened exhaust seats and with the larger cc (106 vs 118) would it lower the compression enough so 91 octane would be good enough.
Race Director
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With the larger chamber 91 should be OK.
You don't need leaded gas.
Team Owner
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From: Southern Cal Ca
St. Jude Donor '22
rec port open chamb
highly thought of by some
A little c/r drop but you are concerned about fuel req'ts
from experience with your car or just the @11 to1 ratio.
a few things can be done to make it safe.
from
timing curves
carb jetting
cam grind
highly thought of by some
A little c/r drop but you are concerned about fuel req'ts
from experience with your car or just the @11 to1 ratio.
a few things can be done to make it safe.
from
timing curves
carb jetting
cam grind
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Joined: Apr 2023
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From: Anoka, MN
with the 118cc open chamber heads and the 7041PA pistons can the compression ratio be determined?
Does it look like it has exhaust hardened seats installed?
Dr. Detroit
Joined: Mar 2012
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From: New Braunfels Texas
It already has open chamber heads on it.......the L2308 is a 50cc open chamber dome and absolutely will not by any circumstances fit a closed chamber head......
3272990 comes back as 71-94 Open Chamber 325cc rec intake port.......which makes sense as the LS6 was available until 1994 over the counter.
The only way you are reducing compression in this engine is with new pistons.
Don't get hung up on induction hardened valve seats.......you would have to run the engine 70,000-80,000 miles to see a sunken seat.....
Assuming a 4.400 Fel Pro head gasket at .039 crush, a 4.280 bore and 3.760 stroke with a 118cc open chamber and a 50cc dome....you are at 11.9 to 1 compression.....
Jebby
3272990 comes back as 71-94 Open Chamber 325cc rec intake port.......which makes sense as the LS6 was available until 1994 over the counter.
The only way you are reducing compression in this engine is with new pistons.
Don't get hung up on induction hardened valve seats.......you would have to run the engine 70,000-80,000 miles to see a sunken seat.....
Assuming a 4.400 Fel Pro head gasket at .039 crush, a 4.280 bore and 3.760 stroke with a 118cc open chamber and a 50cc dome....you are at 11.9 to 1 compression.....
Jebby
Last edited by Jebbysan; Aug 22, 2023 at 10:46 AM.
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From: Anoka, MN
Well not exactly what i wanted to hear...........
Factory L71 has 11.0:1, it is now closer to the L88 race engine that needs 103 octane minimum.
This sucks!
What pistons would get me down to 9.5-10.0:1 CR?
Factory L71 has 11.0:1, it is now closer to the L88 race engine that needs 103 octane minimum.
This sucks!
What pistons would get me down to 9.5-10.0:1 CR?
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All LS6 heads were not aluminum, in fact most were not. The L89 option was for aluminum heads with very few on LS6. Generally accepted number I believe is 18 one year only, Corvette. While listed as available on 1970 Chevelle LS6 I don’t believe any were ever built, but someone will correct me if I’m wrong. Mostly L89 was a 427 and 396/375 option. 
Last edited by Vette5311; Aug 22, 2023 at 11:15 PM.
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From: Waterford WI
All LS6 heads were not aluminum, in fact most were not. The L89 option was for aluminum heads with very few on LS6. Generally accepted number I believe is 18 one year only, Corvette. While listed as available on 1970 Chevelle LS6 I don’t believe any were ever built, but someone will correct me if I’m wrong. Mostly L89 was a 427 and 396/375 option.