Milling vs. Smaller head gasket
Thread Starter
TECH Fanatic
iTrader: (19)
Joined: Apr 2002
Posts: 1,590
Likes: 2
From: Dyess AFB, TX
Milling vs. Smaller head gasket I'm looking for around 11:1 with my LS6 heads. Now I'm deciding on whether or not I should mill or use a smaller gasket. My original choice would be to use the MLS gasket again and mill .030, or mill .015 and use a different gasket with a .040 compressed height. What would be the advantages and disadvantages with either choice?
I personally don't see a difference in either one, because either way the head is going to be the same amount closer to the block. I'm personally leaning to the .030 mill with the MLS gasket because that gasket has alot less issues it seems then the Cometics. Anyone want to talk me out of it?
I personally don't see a difference in either one, because either way the head is going to be the same amount closer to the block. I'm personally leaning to the .030 mill with the MLS gasket because that gasket has alot less issues it seems then the Cometics. Anyone want to talk me out of it?
Well, every .005 smaller gasket is worth 1cc, whereas youd have to mill .0075 off the head for that same 1cc. Thats because the gasket is the full bore size, where milling the head the actual combustion chamber area is much smaller. Running a smaller gasket also makes for a tighter quench, but you shouldnt run it any closer than .030. keep in mind your piston could come up as much as .010 out of the hole. Youll probably want to do a combination of both milling and a .040 - .045 gasket.
this thread should answer some of your question:
https://ls1tech.com/forums/advanced-engineering-tech/397179-how-critical-piston-deck-height-quench-distance-ls1.html
I would also do a combination of both mill them .018-.024 and run a .040-.045 gasket
https://ls1tech.com/forums/advanced-engineering-tech/397179-how-critical-piston-deck-height-quench-distance-ls1.html
I would also do a combination of both mill them .018-.024 and run a .040-.045 gasket
I would suggest the head gasket, to a point. A thinner head gasket will make for a tighter quench. Taking the quench down to .030 or .035 will help the fuel/air charge mix and burn more completely in addition to increasing compression. Plus the gead gasket raises compression 50% faster than milling does, so you can raise i more before running into piston to valve issues.
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
The best way to gain compression is using a thinner gasket.
As said above .040 is perhaps the thinnest for street purposes.
That would gain you ~3 cc.
Milling a head reduces its flow potential, so a head flowing let us say 300 cfm at .600 will not be flowing as much if it is milled. The more you mill, the more you loose.
As said above .040 is perhaps the thinnest for street purposes.
That would gain you ~3 cc.
Milling a head reduces its flow potential, so a head flowing let us say 300 cfm at .600 will not be flowing as much if it is milled. The more you mill, the more you loose.
Trending Topics
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
Gas Monkey Built a 6-Wheel Ferrari Testarossa With a Corvette LT4 Engine
Verdad Gallardo
7 Most Reliable High-Performance Engines GM Has Ever Built
Verdad Gallardo
Amazing '71 Camaro Restomod Is Modern Muscle Car Under the Skin
Verdad Gallardo
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
When considering something of this nature you need to first consider what will happen to the quench distance... or piston to head deck distance. Stock piston out of the hole is around .007"-.009" and the stock gasket is .054" or so leaving your "stock" quench distance ~.046. You can take this distance to around .040 on a street type application safely. You can run a tighter distance but then rod/piston expansion is more of a factor as well as some other variables. Tightening the quench distance will increase the static compression ratio but will yeild a more efficient burn cycle (increased efficientcy = more resistance to detonation).
To answer you question either is fine unless you are using boost... just keep your quench distance in the .040-.043 range to get a nice improvement with the higher compression without increasing the likelyhood of detonation. Hope this helps.
Scott
To answer you question either is fine unless you are using boost... just keep your quench distance in the .040-.043 range to get a nice improvement with the higher compression without increasing the likelyhood of detonation. Hope this helps.
Scott
Thread Starter
TECH Fanatic
iTrader: (19)
Joined: Apr 2002
Posts: 1,590
Likes: 2
From: Dyess AFB, TX
So since the stock quench is ~.046", milling .015 or using a gasket with a compressed thickness of .041", would put me at a quench distance in the mid to low .30's, correct? I'm assuming this is pretty tight and I'd start having issues here with valves kissing pistons, but plenty of other people are using the .041 gaskets without any issues, correct? Or are those gaskets used mostly on new engines with a .000" or negative piston height? If .040" is ideal, then would I only mill .006"? This seems low to me.
Originally Posted by BADFNZ
So since the stock quench is ~.046", milling .015 or using a gasket with a compressed thickness of .041", would put me at a quench distance in the mid to low .30's, correct? I'm assuming this is pretty tight and I'd start having issues here with valves kissing pistons, but plenty of other people are using the .041 gaskets without any issues, correct? Or are those gaskets used mostly on new engines with a .000" or negative piston height? If .040" is ideal, then would I only mill .006"? This seems low to me.
The article is for Gen I engines but will give you what you need. Only your compressed head gasket thickness and piston deck height will change the quench distance. One thing I didn't mention is that milling can help improve the burn cycle because it "shrinks" the actual head chamber. Look through that link i posted. Hope it helps.
Thread Starter
TECH Fanatic
iTrader: (19)
Joined: Apr 2002
Posts: 1,590
Likes: 2
From: Dyess AFB, TX
Originally Posted by kpforce1
Milling does not affect the quench distance... look through this tech article I wrote... it will help you understand what it is and what affects it: http://forums.corvetteforum.com/show...19&forum_id=48
The article is for Gen I engines but will give you what you need. Only your compressed head gasket thickness and piston deck height will change the quench distance. One thing I didn't mention is that milling can help improve the burn cycle because it "shrinks" the actual head chamber. Look through that link i posted. Hope it helps.
The article is for Gen I engines but will give you what you need. Only your compressed head gasket thickness and piston deck height will change the quench distance. One thing I didn't mention is that milling can help improve the burn cycle because it "shrinks" the actual head chamber. Look through that link i posted. Hope it helps.
So when applying it to LSX engines, it seems that if the ideal quench is ~.040" and we're already at .046", would a head gasket slightly smaller than stock work best, such as one with a .048" compressed thickness for example? If this is so, how are people getting away with using a .040" gasket without running into any problems? Sorry for so many questions.
fwiw, I chose to mill .035 and use a .045 gasket, running 241's.
this was with mahle pistons w/4cc valve reliefs. could have milled less with a thinner gasket - but that would have brought quench down ever furhter - and its a street car/daily driver so i chose the thicker gasket.
this was with mahle pistons w/4cc valve reliefs. could have milled less with a thinner gasket - but that would have brought quench down ever furhter - and its a street car/daily driver so i chose the thicker gasket.
I'm glad the write up helped... Remember that the LSx typ engine was developed to be a more efficient performance engine (hence the tighter quench over the Gen I and II's). You can run tighter quench distance on LSx type engines (~.034") or any engine for that matter you just have to be aware of what is involved. Sure people are running some pretty short gaskets and they are hopefully (but not likely) aware of the risks. Most people don't fully understand what "quench distance" is. When running tighter distances the block deck, head deck, and piston height all need to be checked closely because you have less room for deck height imperfections. Piston to valve clearances must also be examined more closely.
Don't get me wrong here... I'm not saying you cant run a certain quench distance, you can run what ever quench distance you want because it is your engine. I'm just pointing out importaint info I've found through my own experience as well as many other profound engine enthusists. Just be aware there is a higher risk of something going wrong within the tighter tolerances. At least you are now armed with more information on the topic to help you figure out what is best for your application.
Don't get me wrong here... I'm not saying you cant run a certain quench distance, you can run what ever quench distance you want because it is your engine. I'm just pointing out importaint info I've found through my own experience as well as many other profound engine enthusists. Just be aware there is a higher risk of something going wrong within the tighter tolerances. At least you are now armed with more information on the topic to help you figure out what is best for your application.
Since search was broken, im gonna threadjack off to a quick tangent... Whats the most you can mill before running into problems with the intake? I seem to remember .050 being the magic number. Im aware of the other consequences of milling.
Originally Posted by GuitsBoy
Since search was broken, im gonna threadjack off to a quick tangent... Whats the most you can mill before running into problems with the intake? I seem to remember .050 being the magic number. Im aware of the other consequences of milling.
