66' 427 with too much compression.. help!
01-25-2011, 10:07 AM
#1
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66' 427 with too much compression.. help!
My brother has a 66' 427 vette, 435 HP, L88 pistons .060 over, first design closed chamber, 12.9:1 compression, Performer intake.
He wants to run this car on standard pump fuel without additives
(which he now has to add). Some shops told him to stack 2 or three
head gaskets together. I suggested buying new alum heads since
he told me that his were milled and the block was decked.... although not sure how much was removed. Car also overheats in stand still
traffic with a mech. fan.... elect fan may solve this problem. Leakdown test was very good but the engine is using oil possibly from excess heat or bad valve guides & seals.
Any suggestions for a brand of heads for street use (non racing)? or
other suggestions?
He is also getting 8MPG with his 800 cfm carb/411 rear end... he would like to do a bit better if a carb switch would help.
He wants to run this car on standard pump fuel without additives
(which he now has to add). Some shops told him to stack 2 or three
head gaskets together. I suggested buying new alum heads since
he told me that his were milled and the block was decked.... although not sure how much was removed. Car also overheats in stand still
traffic with a mech. fan.... elect fan may solve this problem. Leakdown test was very good but the engine is using oil possibly from excess heat or bad valve guides & seals.
Any suggestions for a brand of heads for street use (non racing)? or
other suggestions?
He is also getting 8MPG with his 800 cfm carb/411 rear end... he would like to do a bit better if a carb switch would help.
01-25-2011, 10:16 AM
#2
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St. Jude Donor '12
Switching from closed chamber to open chamber, and iron to aluminum will help, but he is not going to get there from here. He's going to have to change pistons. IMO.
01-25-2011, 10:22 AM
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My brother has a 66' 427 vette, 435 HP, L88 pistons .060 over, first design closed chamber, 12.9:1 compression, Performer intake.
He wants to run this car on standard pump fuel without additives
(which he now has to add). Some shops told him to stack 2 or three
head gaskets together. I suggested buying new alum heads since
he told me that his were milled and the block was decked.... although not sure how much was removed. Car also overheats in stand still
traffic with a mech. fan.... elect fan may solve this problem. Leakdown test was very good but the engine is using oil possibly from excess heat or bad valve guides & seals.
Any suggestions for a brand of heads for street use (non racing)? or
other suggestions?
He is also getting 8MPG with his 800 cfm carb/411 rear end... he would like to do a bit better if a carb switch would help.
He wants to run this car on standard pump fuel without additives
(which he now has to add). Some shops told him to stack 2 or three
head gaskets together. I suggested buying new alum heads since
he told me that his were milled and the block was decked.... although not sure how much was removed. Car also overheats in stand still
traffic with a mech. fan.... elect fan may solve this problem. Leakdown test was very good but the engine is using oil possibly from excess heat or bad valve guides & seals.
Any suggestions for a brand of heads for street use (non racing)? or
other suggestions?
He is also getting 8MPG with his 800 cfm carb/411 rear end... he would like to do a bit better if a carb switch would help.
01-25-2011, 10:24 AM
#4
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Forgot I am sure a diff set of pushrods also will need a little longer one.
01-25-2011, 10:41 AM
#5
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St. Jude Donor '12
The 427 rectangle closed chamber heads are 106.8 cc's, I can't see that the 110 cc edelbrocks are going to helpthat much.. The 118 cc 69 and 70 model Chevy aluminums will knock the compression down some, but probably not enough. If he has a true 12.9 now, 2 full points is a bunch to drop, especially with the .060 overbore, and the block being decked. I'm just sayin....
Last edited by vettsplit 63; 01-25-2011 at 10:44 AM. Reason: wrd
01-25-2011, 11:53 AM
#7
Le Mans Master
The 427 rectangle closed chamber heads are 106.8 cc's, I can't see that the 110 cc edelbrocks are going to helpthat much.. The 118 cc 69 and 70 model Chevy aluminums will knock the compression down some, but probably not enough. If he has a true 12.9 now, 2 full points is a bunch to drop, especially with the .060 overbore, and the block being decked. I'm just sayin....
this of course all depends on cam duration and such and it will be tough to knock off 2 points
i think the 118 cc heads better than the oval 110's from edelbrock but ultimately a piston change would do the trick
i wonder if the op has tried a blend of say 50-50 racing and 93 first
good luck......
i really like my be cool rad also
01-25-2011, 01:10 PM
#8
Melting Slicks
You said he shaved the heads so if you "cc" them you will have a base to start from. You can then figure what it will take to get where you need.
01-25-2011, 01:27 PM
#9
Race Director
The 427 rectangle closed chamber heads are 106.8 cc's, I can't see that the 110 cc edelbrocks are going to helpthat much.. The 118 cc 69 and 70 model Chevy aluminums will knock the compression down some, but probably not enough. If he has a true 12.9 now, 2 full points is a bunch to drop, especially with the .060 overbore, and the block being decked. I'm just sayin....
01-25-2011, 01:56 PM
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The 427 rectangle closed chamber heads are 106.8 cc's, I can't see that the 110 cc edelbrocks are going to helpthat much.. The 118 cc 69 and 70 model Chevy aluminums will knock the compression down some, but probably not enough. If he has a true 12.9 now, 2 full points is a bunch to drop, especially with the .060 overbore, and the block being decked. I'm just sayin....
on the 110 my mistake on the #. But if you had the 12.9 with the open chamber that you can get from ebelbrock with a 30over size on the head gasket. The guy at summitt said it would put it to are between 10.9.1 to 11.2.1. which will be safe with 93 gas. Man have your brother call them to tech help...
01-25-2011, 07:24 PM
#11
Race Director
I forgot to mention that if his closed chamber heads are steel, just switching to aluminum heads alone, even with the same effective compression, will result in his engine being more tolerant of fuel octane.
01-25-2011, 07:25 PM
#12
Sounds like he should have bought a newer car. My vette is not my commuter car and I have 100 octane race fuel at the local gas station at 6.80/gal, and I'm happy to pay that. Premium here in Tucson is 91 octane.
Last edited by bdhulderman; 01-25-2011 at 07:36 PM.
01-25-2011, 10:00 PM
#13
Safety Car
One thing NOT to do is to stack head gaskets or use thick ones to drop the compression. You'll only drop about 1/4 point for every 0.025 inches of gasket thickness, but you'll totally trash the quench area in the combustion chamber. You'll end up with the worst of both worlds: too high compression and really big power loss from the too big quench volume. The suggested quench clearance (piston flat top to head surface) is about 0.040 to 0.045 inches for these motors.
Don't know whose pistons you're using, but there are some (Wiseco) that have millable domes. You may want to check on that, too.
Don't know whose pistons you're using, but there are some (Wiseco) that have millable domes. You may want to check on that, too.
01-25-2011, 11:53 PM
#14
Le Mans Master
One thing NOT to do is to stack head gaskets or use thick ones to drop the compression. You'll only drop about 1/4 point for every 0.025 inches of gasket thickness, but you'll totally trash the quench area in the combustion chamber. You'll end up with the worst of both worlds: too high compression and really big power loss from the too big quench volume. The suggested quench clearance (piston flat top to head surface) is about 0.040 to 0.045 inches for these motors.
Don't know whose pistons you're using, but there are some (Wiseco) that have millable domes. You may want to check on that, too.
Don't know whose pistons you're using, but there are some (Wiseco) that have millable domes. You may want to check on that, too.
Advise him to cut the pistons or get some new ones...
Cheaper than new heads too.
01-26-2011, 09:20 AM
#15
You don't mention the altitude where you drive. You can use more compression at higher altitudes.
You can't just add head gasket thickness. The quench distance is one of the most critical dimensions in an engine. It determines the turbulence in the combustion chamber. Ideally, it is zero under operating conditions. You can do the math on different heads but, in the end changing the pistons is the best course.
You say it is a 435hp engine with a performer intake? What happened to the 3x2s? If this is a hot rod engine and you are not concerned with originality you have more options.
Make sure the fan clutch, radiator and radiator seals are in good shape. The car will stay cool with the stock cooling system but it has to be in proper working order. 45yr old radiators with thick mineral deposits don't work like they did when Beatles fans were young....
You can't just add head gasket thickness. The quench distance is one of the most critical dimensions in an engine. It determines the turbulence in the combustion chamber. Ideally, it is zero under operating conditions. You can do the math on different heads but, in the end changing the pistons is the best course.
You say it is a 435hp engine with a performer intake? What happened to the 3x2s? If this is a hot rod engine and you are not concerned with originality you have more options.
Make sure the fan clutch, radiator and radiator seals are in good shape. The car will stay cool with the stock cooling system but it has to be in proper working order. 45yr old radiators with thick mineral deposits don't work like they did when Beatles fans were young....
My brother has a 66' 427 vette, 435 HP, L88 pistons .060 over, first design closed chamber, 12.9:1 compression, Performer intake.
He wants to run this car on standard pump fuel without additives
(which he now has to add). Some shops told him to stack 2 or three
head gaskets together. I suggested buying new alum heads since
he told me that his were milled and the block was decked.... although not sure how much was removed. Car also overheats in stand still
traffic with a mech. fan.... elect fan may solve this problem. Leakdown test was very good but the engine is using oil possibly from excess heat or bad valve guides & seals.
Any suggestions for a brand of heads for street use (non racing)? or
other suggestions?
He is also getting 8MPG with his 800 cfm carb/411 rear end... he would like to do a bit better if a carb switch would help.
He wants to run this car on standard pump fuel without additives
(which he now has to add). Some shops told him to stack 2 or three
head gaskets together. I suggested buying new alum heads since
he told me that his were milled and the block was decked.... although not sure how much was removed. Car also overheats in stand still
traffic with a mech. fan.... elect fan may solve this problem. Leakdown test was very good but the engine is using oil possibly from excess heat or bad valve guides & seals.
Any suggestions for a brand of heads for street use (non racing)? or
other suggestions?
He is also getting 8MPG with his 800 cfm carb/411 rear end... he would like to do a bit better if a carb switch would help.
01-26-2011, 02:12 PM
#16
Advanced
Installing a cam with a lot of overlap will also do a lot for avoiding detonation at low RPMs too. The overlap will bleed off the compression a bit at the lower RPMs. It will also reduce the effective engine vacuum for your power brakes - usually not enough to be an issue.
01-26-2011, 06:07 PM
#17
Racer
too much compression
i also have 66 coupe with big small block 350 in it. it has been
bored .030 over. i am running AFR aluminum heads and a roller
rocker and a roller comp cams thumper cam.
i am making around 450 hp. i also had a lot of problems with pinging and detonation because i was running jahns aluminum domed top
pistons that were rated at 11;1 compression.
my engine would always ping and detonate when running on the street
with using 91 octane gas.
my only choices to eliminate the detonation was to either change
my pistons which of course a great big expense or run 110 racing
fuel.
i did run 110 racing fuel for about a year and it did eliminate all my
detonation and pinging but it just got to be too expensive every
week buying gallons of 110 racing fuel.
so i had to make a decision on what i wanted to do.
rather than tearing the motor apart and putting in flat top pistons
i chose to put thicker head gaskets on.
i am now a very happy camper as i eliminated all detonation and ping
and can run premium gas without adding racing fuel.
before i put the new head gaskets on i tried backing down my timing
and it did help a little but i lost all my power.
now i still have all my power and no pinging. its wonderful to drive
and i can just pull into a gas station and fill up with 91 octane.
by changing the head gaskets i knocked my compression down 1/2
point from 11.1 down to 10 1/2 to 1.
it really makes a difference and i did not lose any power or
have any quench problems.
the head gaskets were a little pricey at $200 but was better than
me grinding the domes off of the tops of my pistons.
when u order your head gaskets make sure you order SCE copper
head gaskets from summit. they are .093 thick and will absolutely
get the job done for you. it worked for me.
The tech agent at summit was very knowledgeable and told me that
would solve my problem of detonation. he was right on the money.
he stated that 11 or over was to much compression for pump gas.
he said 10 1/2 or less compression was perfect on pum gas with
no detonation problems. i was a little skeptical about believing him
as i was very frustrated because of everything i tried nothing seemed
to work. but this really works great . i recommend it highly.
good luck
bored .030 over. i am running AFR aluminum heads and a roller
rocker and a roller comp cams thumper cam.
i am making around 450 hp. i also had a lot of problems with pinging and detonation because i was running jahns aluminum domed top
pistons that were rated at 11;1 compression.
my engine would always ping and detonate when running on the street
with using 91 octane gas.
my only choices to eliminate the detonation was to either change
my pistons which of course a great big expense or run 110 racing
fuel.
i did run 110 racing fuel for about a year and it did eliminate all my
detonation and pinging but it just got to be too expensive every
week buying gallons of 110 racing fuel.
so i had to make a decision on what i wanted to do.
rather than tearing the motor apart and putting in flat top pistons
i chose to put thicker head gaskets on.
i am now a very happy camper as i eliminated all detonation and ping
and can run premium gas without adding racing fuel.
before i put the new head gaskets on i tried backing down my timing
and it did help a little but i lost all my power.
now i still have all my power and no pinging. its wonderful to drive
and i can just pull into a gas station and fill up with 91 octane.
by changing the head gaskets i knocked my compression down 1/2
point from 11.1 down to 10 1/2 to 1.
it really makes a difference and i did not lose any power or
have any quench problems.
the head gaskets were a little pricey at $200 but was better than
me grinding the domes off of the tops of my pistons.
when u order your head gaskets make sure you order SCE copper
head gaskets from summit. they are .093 thick and will absolutely
get the job done for you. it worked for me.
The tech agent at summit was very knowledgeable and told me that
would solve my problem of detonation. he was right on the money.
he stated that 11 or over was to much compression for pump gas.
he said 10 1/2 or less compression was perfect on pum gas with
no detonation problems. i was a little skeptical about believing him
as i was very frustrated because of everything i tried nothing seemed
to work. but this really works great . i recommend it highly.
good luck
01-26-2011, 08:59 PM
#18
i also have 66 coupe with big small block 350 in it. it has been
bored .030 over. i am running AFR aluminum heads and a roller
rocker and a roller comp cams thumper cam.
i am making around 450 hp. i also had a lot of problems with pinging and detonation because i was running jahns aluminum domed top
pistons that were rated at 11;1 compression.
my engine would always ping and detonate when running on the street
with using 91 octane gas.
my only choices to eliminate the detonation was to either change
my pistons which of course a great big expense or run 110 racing
fuel.
i did run 110 racing fuel for about a year and it did eliminate all my
detonation and pinging but it just got to be too expensive every
week buying gallons of 110 racing fuel.
so i had to make a decision on what i wanted to do.
rather than tearing the motor apart and putting in flat top pistons
i chose to put thicker head gaskets on.
i am now a very happy camper as i eliminated all detonation and ping
and can run premium gas without adding racing fuel.
before i put the new head gaskets on i tried backing down my timing
and it did help a little but i lost all my power.
now i still have all my power and no pinging. its wonderful to drive
and i can just pull into a gas station and fill up with 91 octane.
by changing the head gaskets i knocked my compression down 1/2
point from 11.1 down to 10 1/2 to 1.
it really makes a difference and i did not lose any power or
have any quench problems.
the head gaskets were a little pricey at $200 but was better than
me grinding the domes off of the tops of my pistons.
when u order your head gaskets make sure you order SCE copper
head gaskets from summit. they are .093 thick and will absolutely
get the job done for you. it worked for me.
The tech agent at summit was very knowledgeable and told me that
would solve my problem of detonation. he was right on the money.
he stated that 11 or over was to much compression for pump gas.
he said 10 1/2 or less compression was perfect on pum gas with
no detonation problems. i was a little skeptical about believing him
as i was very frustrated because of everything i tried nothing seemed
to work. but this really works great . i recommend it highly.
good luck
bored .030 over. i am running AFR aluminum heads and a roller
rocker and a roller comp cams thumper cam.
i am making around 450 hp. i also had a lot of problems with pinging and detonation because i was running jahns aluminum domed top
pistons that were rated at 11;1 compression.
my engine would always ping and detonate when running on the street
with using 91 octane gas.
my only choices to eliminate the detonation was to either change
my pistons which of course a great big expense or run 110 racing
fuel.
i did run 110 racing fuel for about a year and it did eliminate all my
detonation and pinging but it just got to be too expensive every
week buying gallons of 110 racing fuel.
so i had to make a decision on what i wanted to do.
rather than tearing the motor apart and putting in flat top pistons
i chose to put thicker head gaskets on.
i am now a very happy camper as i eliminated all detonation and ping
and can run premium gas without adding racing fuel.
before i put the new head gaskets on i tried backing down my timing
and it did help a little but i lost all my power.
now i still have all my power and no pinging. its wonderful to drive
and i can just pull into a gas station and fill up with 91 octane.
by changing the head gaskets i knocked my compression down 1/2
point from 11.1 down to 10 1/2 to 1.
it really makes a difference and i did not lose any power or
have any quench problems.
the head gaskets were a little pricey at $200 but was better than
me grinding the domes off of the tops of my pistons.
when u order your head gaskets make sure you order SCE copper
head gaskets from summit. they are .093 thick and will absolutely
get the job done for you. it worked for me.
The tech agent at summit was very knowledgeable and told me that
would solve my problem of detonation. he was right on the money.
he stated that 11 or over was to much compression for pump gas.
he said 10 1/2 or less compression was perfect on pum gas with
no detonation problems. i was a little skeptical about believing him
as i was very frustrated because of everything i tried nothing seemed
to work. but this really works great . i recommend it highly.
good luck
01-26-2011, 11:58 PM
#19
Race Director
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I've done these a few times. If the pistons are the old TRW style ones they have solid domes and can be milled. The last one we did we took 10cc off the domes and then rebalanced it all. The heads were open chambers and when all was done we got it down to just under 11.0 and it does fine on 93 octane.
The note about the overlap bleeding compression is an oft repeated misunderstanding of what actually happens in the motor. If you think about it, overlap occurs when both valves are open between the exhaust and intake strokes. There is no compression happening at that point when both valves are open, so altering overlap will have no effect on compression. The reason people follow along with this is due to the fact that most cams end up with pretty big lobes (duration wise) sometimes and unless you move the Lobe separation angle a lot, you just naturally end up with more overlap from the larger lobes. What is really happening is the larger intake lobe is keeping the intake valve open longer at the end of the stroke and there is less mixture to compress as the piston rises. That's why detonation chances become less.
JIM
The note about the overlap bleeding compression is an oft repeated misunderstanding of what actually happens in the motor. If you think about it, overlap occurs when both valves are open between the exhaust and intake strokes. There is no compression happening at that point when both valves are open, so altering overlap will have no effect on compression. The reason people follow along with this is due to the fact that most cams end up with pretty big lobes (duration wise) sometimes and unless you move the Lobe separation angle a lot, you just naturally end up with more overlap from the larger lobes. What is really happening is the larger intake lobe is keeping the intake valve open longer at the end of the stroke and there is less mixture to compress as the piston rises. That's why detonation chances become less.
JIM
01-27-2011, 07:37 AM
#20
Melting Slicks
With no other changes, I went from Iron to Al. heads on my 327.
Ping was gone even with the timing set for optimum ( 64 cc with factory "11-1" pistons. Measured CR of 10.25). One question that I have. Do Al. heads make the same noise as iron when it pings. Is that ringing of the iron just not made with al.?
Ping was gone even with the timing set for optimum ( 64 cc with factory "11-1" pistons. Measured CR of 10.25). One question that I have. Do Al. heads make the same noise as iron when it pings. Is that ringing of the iron just not made with al.?