Optimal quench?
Launching!
Joined: Jul 2004
Posts: 200
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From: Gainesville, Florida
Originally Posted by NoseUp
Keep in mind, though the block is aluminum, the cylinder sleeves aren't...Where the block would expand is where the most heat resides, which is at the top of the block. The sleeves shouldn't permit much (if any) block growth. Any big shop that builds aluminum engines should know how much a block can actually grow. If there was much growth at all, I think we'd see some tighter reccomendations from the builders. I've never been given less than .035".
Also, as the engine is used, carbon builds up on both the piston tops, and chambers (quench areas as well). That can reduce your Q/H a good bit. That's probably the reason GM doesn't opt for the more effecient, tighter quench approach from the factory. With a .052 thick gasket and say .007 above deck (average), that's a .045" Q/H which leaves some room for carbon build-up (cheap gas, rich tune, ect.). Just an assumtion though...
I've been told OEMs don't go for a tight quench because they simply can't on mass produced engines. When they deck the block, their tolerance is only so good. If they deck it too low and there is piston/head contact, the block is junk. So instead they deck it a bit too high, don't make any junk blocks, but also end up with a larger quench clearance.
I agree with tighter quench engines not having alot of carbon build up in the actual quench areas because of experience and the fact that the whole reason of having a tighter quench is to move as much as possible the air/fuel into the combustion chamber to be fired and turned into energy. With the tighter quenches people are running there is less amounts of air/fuel to be burned to create the carbon build up to begin with and the amount that does happen to be burned is lighty knocked of as it does build up by the piston before it has a chance to adhere. I have torn down race engines that have been ran all season that were built with tight quenches that had carbon build up only in the combustion chambers and the corasponding areas on the piston. I also agree that the aluminum block will expand more than the iron block at the same temperature- the sleeve is iron and doesnt expand as far as the surrounding block but doesnt really go anywhere and when the engine cools off everything goes back to its original size. That is the reason the interferance fit has to be right on the sleeve because if its not enough the sleeve will loose its "grip" and move- which is not a problem if they are installed by a good machinist that pays attention to what he is doing during such a precise procedure.
When the quench distance is proper there is no combustion in that area,thats why there is no carbon there.Hypereutectic pistons like the stockers don't expand much
so they won't eat the dimention up either.Gm runs the quench where they do because
of stacked tolerances.You could have one rod,one piston,and one crank on the high side of accepable dimention and still be ok with a block on the short side.I guess someone is going to have to run one at .025 and see what happens.
so they won't eat the dimention up either.Gm runs the quench where they do because
of stacked tolerances.You could have one rod,one piston,and one crank on the high side of accepable dimention and still be ok with a block on the short side.I guess someone is going to have to run one at .025 and see what happens.
6600 rpm clutch dump of death Administrator
Joined: Dec 2001
Posts: 4,983
Likes: 13
From: Texas
Block growth is as much as .010 or more from cold to hot.
This is why when folks set the preload on their Comp-R lifters cold @ .010, the car starts to rattle when it gets warm. The preload is all gone, and the cam now has positive lash in in. Thats why minimal pre-load must be done with the motor warm.
As for quench, as stated .035 - .040 with the gasket compressed. And without the actual spec of the piston and how much in or out of the bore it is, its all a guess.
This is why when folks set the preload on their Comp-R lifters cold @ .010, the car starts to rattle when it gets warm. The preload is all gone, and the cam now has positive lash in in. Thats why minimal pre-load must be done with the motor warm.
As for quench, as stated .035 - .040 with the gasket compressed. And without the actual spec of the piston and how much in or out of the bore it is, its all a guess.
TECH Apprentice
Joined: Jan 2002
Posts: 320
Likes: 5
From: Nottingham, Notts, England, UK
Yep, I go for tight squish to push all the unburnt fuel to the centre of the chamber so it meets with the expanding flame front and speeds up burn time. So optimum quench means no carbon in the quench area. In fact you may see a piston reflection 
It also means more of the fuel in the cylinder will get burned, less waste means more power. As for quench effect, I think that does a similar thing to squish but it also cools the charge temps (hence quench) as the fuel burn is squeezed away from the pad on the piston and the pad in the head. This reduces detonation and again speeds up combustion but thats been said already.
You know your getting close to optimum if the top end rattles when cold but is quiet when hot! Happened on a tvr over here with the wrong head gaskets at any revs over 3500 rpm. Funny thing was the owner could still rev past 7 yet there was no visible damage when he fitted the right gaskets. Lucky guy or what.
I alweays found it strange that our rover v8's had quench pads in the heads and bowled pistons. Iirc the buick 300 is the same.
It also means more of the fuel in the cylinder will get burned, less waste means more power. As for quench effect, I think that does a similar thing to squish but it also cools the charge temps (hence quench) as the fuel burn is squeezed away from the pad on the piston and the pad in the head. This reduces detonation and again speeds up combustion but thats been said already.You know your getting close to optimum if the top end rattles when cold but is quiet when hot! Happened on a tvr over here with the wrong head gaskets at any revs over 3500 rpm. Funny thing was the owner could still rev past 7 yet there was no visible damage when he fitted the right gaskets. Lucky guy or what.
I alweays found it strange that our rover v8's had quench pads in the heads and bowled pistons. Iirc the buick 300 is the same.
When we talk about Cometic .040" or any thickness for that matter, is that compressed thickness?
I kind of screwed up on my gasket thickness when building the motor. I was told one thing and got another and ordered Cometic .040" gaskets ahead of time. This means I have .048" quench, pistons are +.008". this is not really optimal quench right?
Dan
I kind of screwed up on my gasket thickness when building the motor. I was told one thing and got another and ordered Cometic .040" gaskets ahead of time. This means I have .048" quench, pistons are +.008". this is not really optimal quench right?
Dan
Originally Posted by Viper
DanZ28,
Don't you mean .032" quench? If you're pistons are out of the hole .008, you subtract that from the gasket. See the first post.
Don't you mean .032" quench? If you're pistons are out of the hole .008, you subtract that from the gasket. See the first post.
Dan
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TECH Apprentice
Joined: Jan 2002
Posts: 320
Likes: 5
From: Nottingham, Notts, England, UK
Hi Dan,
Maybe they were made for another chevy? I know that a while back everybody was insisting on using the older small block pin diameter which I found really frustrating as I wanted to retain stock rods and large pins. It's good everybody has caught up and now we can buy the right piston/rod parts You'll just need a thinner gasket and maybe a check on the pushrods which has been covered elsewhere quite recently.
Maybe they were made for another chevy? I know that a while back everybody was insisting on using the older small block pin diameter which I found really frustrating as I wanted to retain stock rods and large pins. It's good everybody has caught up and now we can buy the right piston/rod parts
You'll just need a thinner gasket and maybe a check on the pushrods which has been covered elsewhere quite recently. 
Every engine is different. Rods, cranks, piston, blocks, , rpms. There are too many variables to say specifically what works and what will hit.
I know what works because we have tested it. Its called Research and Development, something the average DIY guy doesnt have the money to perform unless you are more than just the DIY guy
I know what works because we have tested it. Its called Research and Development, something the average DIY guy doesnt have the money to perform unless you are more than just the DIY guy
Viper, I was confused the first time I heard +.008" as well. Just to clarify, "+" is below the deck and "-" is above the deck.
Mike, mine are below the deck because of the use of Ross pistons and Lunati connecting rods. I already use 7.350 PR's and am pretty good on the geometry of the valvetrain along with pre-load.
So I guess a .030" gasket for me is in store to set me at .038" quench. Good thing I have valve reliefs because the heads are milled .035" as well to get the CR in the 10.8 range...
Dan
Mike, mine are below the deck because of the use of Ross pistons and Lunati connecting rods. I already use 7.350 PR's and am pretty good on the geometry of the valvetrain along with pre-load.
So I guess a .030" gasket for me is in store to set me at .038" quench. Good thing I have valve reliefs because the heads are milled .035" as well to get the CR in the 10.8 range...
Dan
For anyone that is interested in a .040" headgasket- here is some useful info-
I got mine from AFR:
The AFR part # for the .040 Cometic gasket is "6846".
They sell them for $72.95 a piece.
I got mine from AFR:
The AFR part # for the .040 Cometic gasket is "6846".
They sell them for $72.95 a piece.
Originally Posted by z-ya
So Louis will you share with us what the minimum is on a stock shortblock, or are you
keeping that to yourself?
keeping that to yourself?
Last edited by RX-Ben; Jan 11, 2005 at 08:28 PM.
Originally Posted by Viper
To add, if someone searches in the future:
With .042 gasket, if piston is ____ quench will be _____:
.005-.037
.006-.036
.007-.035
.008-.034
.009-.033
.010-.032
I read of the .042" gasket here https://ls1tech.com/forums/generation-iii-internal-engine/257420-vicni-afr-205-head-only-test-take-2-a.html
but who makes it?
With .042 gasket, if piston is ____ quench will be _____:
.005-.037
.006-.036
.007-.035
.008-.034
.009-.033
.010-.032
I read of the .042" gasket here https://ls1tech.com/forums/generation-iii-internal-engine/257420-vicni-afr-205-head-only-test-take-2-a.html
but who makes it?
Tony @ AFR uses the .040" gaskets. I'm not sure which AFR test you are referring to, but in one of the dyno results threads he stated he was using the .040" gasket.
Ben
Ben
Originally Posted by mrr23
i'm not sure which one they used in the AFR test, but roger is getting me Mr Gasket head gaskets they normally use when they do heads which he told me are .042" thick. when i see them on thursday, i'll know the part number.