ZZ454 Increasing compression ratio question
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ZZ454 Increasing compression ratio question
When it is slow at work, you get to thinking........did some calculations and you've got to remove .035 from somewhere, to get it up to 10.5-1 from the stock 9.6-1 compression ratio without swapping pistons or heads.
So the question becomes.....
1) Is there a thinner head gasket with a lower compressed height that would be just as durable as the thicker stock part, that can be used to accomplish some of that .035 reduction ?
2) Or would you just mill the head .035 accordingly assuming there is enough meat to do so ? And there should be plenty.
All of this is on the assumption that the stock dished pistons would have plently of valve clearance with the stock, or even a mildy upgraded HR cam.....and as I think they easily would clear, since you've got it apart to do this, you just clay it up anyways to be safe.
With the 110 cc heads having 10.5-1 it will give you more HP with a better cam and you'd still be pump gas friendly with this simple mod. We've got 94 octane up here which I don't wanna waste on lower compression if I do this.......
Thoughts ?
So the question becomes.....
1) Is there a thinner head gasket with a lower compressed height that would be just as durable as the thicker stock part, that can be used to accomplish some of that .035 reduction ?
2) Or would you just mill the head .035 accordingly assuming there is enough meat to do so ? And there should be plenty.
All of this is on the assumption that the stock dished pistons would have plently of valve clearance with the stock, or even a mildy upgraded HR cam.....and as I think they easily would clear, since you've got it apart to do this, you just clay it up anyways to be safe.
With the 110 cc heads having 10.5-1 it will give you more HP with a better cam and you'd still be pump gas friendly with this simple mod. We've got 94 octane up here which I don't wanna waste on lower compression if I do this.......
Thoughts ?
Last edited by 10caipirinhas; Nov 21, 2009 at 04:40 PM.
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Whack the heads. Edelbrock makes those aluminum heads and sell a 100cc version of them.
Then use a .015 Cometic gasket.
Then put a decent cam in it and have some fun!
JIM
Then use a .015 Cometic gasket.
Then put a decent cam in it and have some fun!
JIM
Last edited by 427Hotrod; Nov 22, 2009 at 03:42 PM.
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From: Millington Illinois
St. Jude Donor '08-'09
-.035 off the heads yield different cc reduction than -.035 off the block and gasket.
With Jim. Take as much as you can with the gasket and mill the rest out of the heads. Watch the Cometic. You need a super smooth surface for them but they are really good gaskets and available in custom bore and thickness.
With Jim. Take as much as you can with the gasket and mill the rest out of the heads. Watch the Cometic. You need a super smooth surface for them but they are really good gaskets and available in custom bore and thickness.
Le Mans Master
Joined: Nov 2008
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From: columbus oh
i would think if you boosted the cr with the stock roller zz cam you would get pre ignition unless you killed back your total advance..9.5 -1 is about max with a 211 dur. @ 50 off....at 10-1 you would need 220 min. at 50 off...remember the 454ho was around 8.5 with the same stick..jmo...
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Thanks for the replies everyone. Amazing board.
Stock compressed gasket thickness is .040 IIRC so with the suggested Cometic gasket I'd only have to take .010 off the heads, which should be a no brainer.........never heard of Cometic, but looks very interesting from what I briefly read on their site.
I want to keep the bigger 110 cc chambers so I can't swap heads for smaller ones, as I need to use these with the higher compression and extra duration, for more power on the gas we've got (94 octane)........and say around a 230 intake and 240 exhaust duration @ .050 cam but with overall lift similar to the stock piece.....subject to valve clearance. There is a name for the particular "effect" that allows this to occur and it escapes me at the moment.
I figure I can get around 525 HP +/- and not have to pay the price.
Stock compressed gasket thickness is .040 IIRC so with the suggested Cometic gasket I'd only have to take .010 off the heads, which should be a no brainer.........never heard of Cometic, but looks very interesting from what I briefly read on their site.
I want to keep the bigger 110 cc chambers so I can't swap heads for smaller ones, as I need to use these with the higher compression and extra duration, for more power on the gas we've got (94 octane)........and say around a 230 intake and 240 exhaust duration @ .050 cam but with overall lift similar to the stock piece.....subject to valve clearance. There is a name for the particular "effect" that allows this to occur and it escapes me at the moment.
I figure I can get around 525 HP +/- and not have to pay the price.
Last edited by 10caipirinhas; Nov 22, 2009 at 01:01 AM.
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Not suggesting to swap heads. The GM performance heads are made by Edelbrock and Edelbrock sells a similar version already milled to 100cc. So what I'm suggesting is that there is a lot of room to mill those heads that you currently have.
Your pistons are likely .020" or so down below the deck at TDC...so that drastically affects final compression. Shoot for .035-.045 TOTAL clearance between the piston and the head including deck height AND gasket. If the block was *zero decked* then the .040" gasket would be fine.
Don't limit yourself on lift. Lift has very little to do with PV clearance because the piston is a long way from the valve when it reaches max lift. Duration, LSA and ICL of the cam determine piston to valve clearance more than anything. I wouldn't put anything less than .600" lift in there. Just double check your springs and retainer clearances etc on the heads.
JIM
Your pistons are likely .020" or so down below the deck at TDC...so that drastically affects final compression. Shoot for .035-.045 TOTAL clearance between the piston and the head including deck height AND gasket. If the block was *zero decked* then the .040" gasket would be fine.
Don't limit yourself on lift. Lift has very little to do with PV clearance because the piston is a long way from the valve when it reaches max lift. Duration, LSA and ICL of the cam determine piston to valve clearance more than anything. I wouldn't put anything less than .600" lift in there. Just double check your springs and retainer clearances etc on the heads.
JIM
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From: Alberta
OK gotcha........thanks for the FU.......
I am not looking to spin over 6,000 and want this thing to make it 50K miles in 5 years of hard DD use before it gets torn down for a refresher.......you think spring pressures, cam/valve train wear, etc, will be OK over that period with .600+ lift or so........?
I am not looking to spin over 6,000 and want this thing to make it 50K miles in 5 years of hard DD use before it gets torn down for a refresher.......you think spring pressures, cam/valve train wear, etc, will be OK over that period with .600+ lift or so........?
Le Mans Master
Joined: Nov 2008
Posts: 5,691
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From: columbus oh
OK gotcha........thanks for the FU.......
I am not looking to spin over 6,000 and want this thing to make it 50K miles in 5 years of hard DD use before it gets torn down for a refresher.......you think spring pressures, cam/valve train wear, etc, will be OK over that period with .600+ lift or so........?
I am not looking to spin over 6,000 and want this thing to make it 50K miles in 5 years of hard DD use before it gets torn down for a refresher.......you think spring pressures, cam/valve train wear, etc, will be OK over that period with .600+ lift or so........?
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From: Alberta
Gonna use a 3.70 or 4.11 rear end with a TKO600 and the appropriate internal ratios.
Don't think you'd get valve float @ <6,000 rpm if using a complete cam kit and any other of the recommended matching pieces to accomodate the design RPM. Here's what I was thinking.
http://www.compcams.com/Cam_Specs/Ca...?csid=584&sb=2
or
http://www.compcams.com/Cam_Specs/Ca...?csid=583&sb=2
Don't think you'd get valve float @ <6,000 rpm if using a complete cam kit and any other of the recommended matching pieces to accomodate the design RPM. Here's what I was thinking.
http://www.compcams.com/Cam_Specs/Ca...?csid=584&sb=2
or
http://www.compcams.com/Cam_Specs/Ca...?csid=583&sb=2
Racer
Joined: Oct 2009
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From: San Antonio TX
-.035 off the heads yield different cc reduction than -.035 off the block and gasket. With Jim. Take as much as you can with the gasket and mill the rest out of the heads. Watch the Cometic. You need a super smooth surface for them but they are really good gaskets and available in custom bore and thickness.
With Jim. Take as much as you can with the gasket and mill the rest out of the heads. Watch the Cometic. You need a super smooth surface for them but they are really good gaskets and available in custom bore and thickness.Read directions on the COMETICS ...they are a " Multi-Layer " style...the ones I have stated to coat EVERY LAYER with a sealant , I used the Red spray Permatex gasket sealant between each layer and allowed the sealant to set before bolting them up ..
Running Aluminium heads & Steel Block
They have held up in my Race Boat for 6yrs now ...454 -8/71 @ 22#boost on 8:75-1 static Compression
prepped correctly ,you should not have any worries about using the Cometics
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
Read directions on the COMETICS ...they are a " Multi-Layer " style...the ones I have stated to coat EVERY LAYER with a sealant , I used the Red spray Permatex gasket sealant between each layer and allowed the sealant to set before bolting them up ..
Running Aluminium heads & Steel Block
They have held up in my Race Boat for 6yrs now ...454 -8/71 @ 22#boost on 8:75-1 static Compression
prepped correctly ,you should not have any worries about using the Cometics
Running Aluminium heads & Steel Block
They have held up in my Race Boat for 6yrs now ...454 -8/71 @ 22#boost on 8:75-1 static Compression
prepped correctly ,you should not have any worries about using the Cometics
Read the directions.This is from Cometic's website:
Why does Cometic recommend MLS gaskets to be installed dry?
Cometic Multi-Layer Steel (MLS) head gaskets go on dry because they are coated with a sealant. Each MLS head gasket is coated with a .001" thick viton rubber that is bonded to the outer stainless steel layers. Adding an additional sealer can hinder the performance of an MLS head gasket.
So is this:
What surface finish is required to us an MLS head gasket?
A surface finish of 50 RA (roughness average) or finer, is recommended for a proper gasket seal. Anything rougher may conflict with the gasket design.
50RA is almost a mirror finish. A lot of factory blocks and or heads do not meet this surface finish requirements. A lot of decking and milling equipment will not leave a smooth enough finish. You need both checked and/or resurfaced on modern higher end equipment to use these. If the surfaces are right they are one of the best gaskets available.
Here is some more info. http://www.cometic.com/faq.aspx#q2
Last edited by 63mako; Nov 26, 2009 at 10:21 PM.
Instructor
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You might want to measure your heads chambers before jumping in. Lots of those are coming in with 114cc+ chambers, plus GM's math tends to suck so ~9.2:1 is usually the true compression. IMO cutting the heads down to 100cc is the way to go but you might have to cut your intake to match the new angle.
Racer
Joined: Oct 2009
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From: San Antonio TX
63 Mako
Thanks for the update on Cometics
I Definately don't want to steer someone in the wrong direction /
I had mine custom ordered and they came with a slip of paper stating to use sealant .
Its been quite awhile since I ordered mine
Thanks for the update on Cometics
I Definately don't want to steer someone in the wrong direction /
I had mine custom ordered and they came with a slip of paper stating to use sealant .
Its been quite awhile since I ordered mine
Race Director
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From: Millington Illinois
St. Jude Donor '08-'09
If I remember correctly they used to not have the rubber coating.
