Engine Squench Question??
Thread Starter
Melting Slicks
Joined: Apr 2005
Posts: 3,113
Likes: 4
Engine Squench Question??
So i started to assemle the 327 chevy corvette block and the pistons stick up about .015 to .020 above the deck. The gasket i have is .039 thick. If there isnt any interference with the heads will i be ok running these gaskets since the engine will only have a .019" squench?? I think technically it is suppose to be around .030-.035 from the advice i have received on this forum
Thanks
Thanks
Racer
Joined: Jun 2003
Posts: 290
Likes: 1
From: Torrington Ct
So i started to assemle the 327 chevy corvette block and the pistons stick up about .015 to .020 above the deck. The gasket i have is .039 thick. If there isnt any interference with the heads will i be ok running these gaskets since the engine will only have a .019" squench?? I think technically it is suppose to be around .030-.035 from the advice i have received on this forum
Thanks
Thanks
Le Mans Master
Joined: Apr 2001
Posts: 5,441
Likes: 1,255
From: Sarver Pa
2021 C1 of the Year Finalist - Modified
Hey, wait a minute ! You sure you are not checking it with piston rock ? You need to measure that right at the wrist pin centerline. Either that or someone decked the heck out of it.
Burning Brakes
Joined: Oct 2005
Posts: 1,000
Likes: 99
From: Captain Cook Hawaii
If you are assembling this engine; please buy the book on How to Rebuild the Small-Block Chevrolet by Larry Atherton and Larry Schreib.
Please refer to chapter 7 pre-assembly, page 106. You must grasp and calculate the relationship of your piston to deck height with the head and valvetrain that you are using, to establish the optimum gasket thickness along with calculating your compression ratio. This book and this forum will answer all of your questions. No guesswork!
brgds
rene
Please refer to chapter 7 pre-assembly, page 106. You must grasp and calculate the relationship of your piston to deck height with the head and valvetrain that you are using, to establish the optimum gasket thickness along with calculating your compression ratio. This book and this forum will answer all of your questions. No guesswork!
brgds
rene
Thread Starter
Melting Slicks
Joined: Apr 2005
Posts: 3,113
Likes: 4
I dont have that one, but a lot of others.
I've been reading up online and it appears that my feeler gauge method should give me an accurate measurement considering that the piston tops are sticking up past the deck. If they were down inside the bores i would need to use another method, but they are not.
Yes the block has been decked to hell and back. Long long story that i really dont feel like typing again.
If my measurements are correct i will need a thick head gasket.
I'm getting a measurement of .030 at the top of the piston and .025 at the bottom-wow!
So, i assume i will need around a .060 head gasket.
After i get this all figured out should i use
a. copper
http://store.summitracing.com/partde...=FOG-909364175
or
b. http://store.summitracing.com/partde...t=FPP-1144-061
The copper units are less expensive.
I've been reading up online and it appears that my feeler gauge method should give me an accurate measurement considering that the piston tops are sticking up past the deck. If they were down inside the bores i would need to use another method, but they are not.
Yes the block has been decked to hell and back. Long long story that i really dont feel like typing again.
If my measurements are correct i will need a thick head gasket.
I'm getting a measurement of .030 at the top of the piston and .025 at the bottom-wow!
So, i assume i will need around a .060 head gasket.
After i get this all figured out should i use
a. copper
http://store.summitracing.com/partde...=FOG-909364175
or
b. http://store.summitracing.com/partde...t=FPP-1144-061
The copper units are less expensive.
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Melting Slicks
Joined: Nov 2002
Posts: 2,460
Likes: 5
From: Wheaton IL
What will a .060 gasket do to your compression ratio? Did you recalc your compression ratio with this new piston/deck height?
If you're going to do it, I think you might need to enter -.030 into the calculator. As a point of reference, my piston/deck height was from .042 to .032 IN THE HOLE.
A quick calc tells me your heads combustion chamber volume should be closer to 70 than 60. I don't remember what you're going to run but it shouldn't be stock double humps unless they have had some work done to them.
Brian
If you're going to do it, I think you might need to enter -.030 into the calculator. As a point of reference, my piston/deck height was from .042 to .032 IN THE HOLE.
A quick calc tells me your heads combustion chamber volume should be closer to 70 than 60. I don't remember what you're going to run but it shouldn't be stock double humps unless they have had some work done to them.
Brian
Burning Brakes
Joined: Oct 2006
Posts: 797
Likes: 11
So i started to assemle the 327 chevy corvette block and the pistons stick up about .015 to .020 above the deck. The gasket i have is .039 thick. If there isnt any interference with the heads will i be ok running these gaskets since the engine will only have a .019" squench?? I think technically it is suppose to be around .030-.035 from the advice i have received on this forum
Thanks
Thanks
Le Mans Master
Joined: Apr 2001
Posts: 5,441
Likes: 1,255
From: Sarver Pa
2021 C1 of the Year Finalist - Modified
You see the straight line at the valve relief pockets? That's where you should be measuring deck height. You SHOULD be using a depth mike, but will be close with feelers guage. The proper way to fix this is to cut the tops of the pistons. BUT, you can get away with a thicker head gasket. It's also a good idea to check your valve to piston clearance.
Le Mans Master
Joined: Apr 2005
Posts: 6,363
Likes: 429
From: Seattle Area WA
You can lay steel machinist rule on edge across the top of the piston where "Pop" said to measure and take your readings with your feeler gauge.
With the deck cut to sh*t, and I recall the heads being milled too, the .060" Fel Pros will help get your head to intake geometry back where it belongs, hopefully allowing you to get a good intake gasket seal. If not, then you are looking at milling your intake to fit. Granted, milling off the piston tops is the "correct" way to fix it but the thicker gasket will be fine.
As stated, really check your valve clearance to those pistons with some clay since you are using a higher lift roller. You are going to have to use a solid roller lifter or open one of those hydraulics up and shim it so it doesn't compress.
This greatly explains why your first pistons were cut so much, to get them into the block. With the measurements you have given, your block has been decked .055"-.060", I'm surprised you were even able to get the intake to seal to the heads very well.
With the deck cut to sh*t, and I recall the heads being milled too, the .060" Fel Pros will help get your head to intake geometry back where it belongs, hopefully allowing you to get a good intake gasket seal. If not, then you are looking at milling your intake to fit. Granted, milling off the piston tops is the "correct" way to fix it but the thicker gasket will be fine.
As stated, really check your valve clearance to those pistons with some clay since you are using a higher lift roller. You are going to have to use a solid roller lifter or open one of those hydraulics up and shim it so it doesn't compress.
This greatly explains why your first pistons were cut so much, to get them into the block. With the measurements you have given, your block has been decked .055"-.060", I'm surprised you were even able to get the intake to seal to the heads very well.
Last edited by Scott Marzahl; May 2, 2008 at 08:27 PM.
Burning Brakes
Joined: Oct 2005
Posts: 1,000
Likes: 99
From: Captain Cook Hawaii
Felpro used to have spacers; I think they were called Head Savers. They would restore deck to head quench ability if the block was decked and the heads were milled. Do your math. Lots of options.
As Scott mentioned; intake manifold may also require proper adjustment.
brgds
rene
As Scott mentioned; intake manifold may also require proper adjustment.
brgds
rene
Thread Starter
Melting Slicks
Joined: Apr 2005
Posts: 3,113
Likes: 4
These copper gaskets will give me a space of .034.
Should i go with them instead of spacers and gaskets.
If i have to use spacers then i will need 2 gaskets per side which will equal a higher chance of blowing a head gasket etc.
These look nice, but i am not sure what this means-can someone explain
Notes: Gasket hads valve reliefs, 4.365 inch diameter relief position.
Thanks
http://store.summitracing.com/partde...=FOG-909364175
Should i go with them instead of spacers and gaskets.
If i have to use spacers then i will need 2 gaskets per side which will equal a higher chance of blowing a head gasket etc.
These look nice, but i am not sure what this means-can someone explain
Notes: Gasket hads valve reliefs, 4.365 inch diameter relief position.
Thanks
http://store.summitracing.com/partde...=FOG-909364175
Burning Brakes
Joined: Aug 2001
Posts: 1,104
Likes: 1
From: Frederick Md
These copper gaskets will give me a space of .034.
Should i go with them instead of spacers and gaskets.
If i have to use spacers then i will need 2 gaskets per side which will equal a higher chance of blowing a head gasket etc.
These look nice, but i am not sure what this means-can someone explain
Notes: Gasket hads valve reliefs, 4.365 inch diameter relief position.
Thanks
http://store.summitracing.com/partde...=FOG-909364175
Should i go with them instead of spacers and gaskets.
If i have to use spacers then i will need 2 gaskets per side which will equal a higher chance of blowing a head gasket etc.
These look nice, but i am not sure what this means-can someone explain
Notes: Gasket hads valve reliefs, 4.365 inch diameter relief position.
Thanks
http://store.summitracing.com/partde...=FOG-909364175
Thread Starter
Melting Slicks
Joined: Apr 2005
Posts: 3,113
Likes: 4
The cam has .492 lift on the exhaust and intake-218 duration on both and 112 lobe seperation.
I am using these pistons
http://store.summitracing.com/partde...0&autoview=sku
I will definately test the piston to valve clearance with clay.
These are the same pistons used in this article. I purchased these since they have larger reliefs and only have two valve reliefs rather than the 4.
http://www.rodandcustommagazine.com/...ine/index.html
Thanks
I am using these pistons
http://store.summitracing.com/partde...0&autoview=sku
I will definately test the piston to valve clearance with clay.
These are the same pistons used in this article. I purchased these since they have larger reliefs and only have two valve reliefs rather than the 4.
http://www.rodandcustommagazine.com/...ine/index.html
Thanks
Safety Car
Joined: Feb 2006
Posts: 4,142
Likes: 704
Thread Starter
Melting Slicks
Joined: Apr 2005
Posts: 3,113
Likes: 4
Thread Starter
Melting Slicks
Joined: Apr 2005
Posts: 3,113
Likes: 4
When i calculate the compression ratio with
at
4.06 bore
4.175 diameter .064 thick head gasket
3.25 stroke
67cc heads
-5 cc pistons
piston to deck heigth .03 above the deck
i get a 9.6:1 compression ratio
at
4.06 bore
4.175 diameter .064 thick head gasket
3.25 stroke
67cc heads
-5 cc pistons
piston to deck heigth .03 above the deck
i get a 9.6:1 compression ratio
