Heads
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
small chambers are that heads only really positive feature. a point of compression gets you 4% power increase from 7 to 9. 3% 9 to 10 and less than that with higher CRs. if you own them and they are in good shape is one thing. if you are shopping for heads, look aftermarket.
Dr. Detroit
Joined: Mar 2012
Posts: 10,095
Likes: 4,025
From: New Braunfels Texas
small chambers are that heads only really positive feature. a point of compression gets you 4% power increase from 7 to 9. 3% 9 to 10 and less than that with higher CRs. if you own them and they are in good shape is one thing. if you are shopping for heads, look aftermarket.
100% correct.
Jebby
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
small chambers are that heads only really positive feature. a point of compression gets you 4% power increase from 7 to 9. 3% 9 to 10 and less than that with higher CRs. if you own them and they are in good shape is one thing. if you are shopping for heads, look aftermarket.
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
I should addend... when I was looking anyways, i needed aluminum. There were iron heads out there, but a cheap, decent, aluminum sub-60cc head never quite presented itself to me. I tried to find some old LT1 or LT4 heads too, not sure if that would work. Didn't find any anyways.
Le Mans Master
Joined: Mar 2004
Posts: 7,465
Likes: 1,485
From: Little Rock AR
It might be good to know what the OP is trying to accomplish. Lots of heads out there. Small chambers, milled heads, piston swaps..... other ways to get it done if you know what needs to be done.
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Safety Car
Joined: May 2001
Posts: 4,747
Likes: 1,642
From: Fairfax Virginia
I still have a set of the cast iron Double Hump heads that came on a small block I bought three decades ago. They were used on a 1970 LT1 Block and the engine was running great with them. I remember the compression was around 11.1-1 or in that neighborhood. They were perfect for a good running small block back in the day. I guess the newer aluminum relegate them to the parts pile. Does anybody even use them any more?
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
Dart has iron 49cc chamber heads 180,200,215,230 cc take your pick. Valve angle ends up 21 degree. That can be changed with pistons from both mahle or probe. Or you can simply fly cut the valve notches in any 23 degree piston. Isky makes a fly cut valve to do the job or you can use old valves with either some emory or sandpaper glued to the valves.
Le Mans Master
Joined: Apr 2006
Posts: 5,403
Likes: 95
I still have a set of the cast iron Double Hump heads that came on a small block I bought three decades ago. They were used on a 1970 LT1 Block and the engine was running great with them. I remember the compression was around 11.1-1 or in that neighborhood. They were perfect for a good running small block back in the day. I guess the newer aluminum relegate them to the parts pile. Does anybody even use them any more?
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,063
From: altered state
St. Jude Donor '05
Ooh..forgot about those dart 49cc ones...nice
OP those trick flows I mentioned are aluminum. They have a 1.94 valve but still flow ok for what they are certainly better than GM double humps. If you take a head with a reasonably thick deck you can always mill them down from 64
Heck why not grab some trick flow alum double humps and have them milled for you? So you might have to have your intake cut some no big deal. Goal accomplished! The china double humps dont flow worth a chit barely as good as stock fwiw.
I had 64cc dart heads..by the time they chambers got reshaped they were almost 72!! Then milled to 62
Been milled a few times, finally at the point they cant be done again as it would cut into the valve job or making sealing the intake tough. Thats hot rodding!
As said tfhe modern shaped combustion chamber is where its at!! So many overlook that as a source of additional power.
OP those trick flows I mentioned are aluminum. They have a 1.94 valve but still flow ok for what they are certainly better than GM double humps. If you take a head with a reasonably thick deck you can always mill them down from 64
Heck why not grab some trick flow alum double humps and have them milled for you? So you might have to have your intake cut some no big deal. Goal accomplished! The china double humps dont flow worth a chit barely as good as stock fwiw.
I had 64cc dart heads..by the time they chambers got reshaped they were almost 72!! Then milled to 62
Been milled a few times, finally at the point they cant be done again as it would cut into the valve job or making sealing the intake tough. Thats hot rodding!
As said tfhe modern shaped combustion chamber is where its at!! So many overlook that as a source of additional power.
Race Director
Joined: Jul 2015
Posts: 13,082
Likes: 3,399
From: SW Florida.
i did a little playing last night. 4cc dish, .029 head gasket, .016 in the hole 11.06 with 58cc. 10.27 with 64cc. .8 diff in CR. above 10 to 1 the rule of thumb is 2% for each point of compression. so you are talking 7 hp on a 350 hp engine. now, this is with everything else identical. and any aftermarket head is worth a lot more than 7 hp over the best iron GM head. and you are not gonna feel 7 hp unless you are looking at your et and your launch will get more variation in time than 7 hp.
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
Dart has iron 49cc chamber heads 180,200,215,230 cc take your pick. Valve angle ends up 21 degree. That can be changed with pistons from both mahle or probe. Or you can simply fly cut the valve notches in any 23 degree piston. Isky makes a fly cut valve to do the job or you can use old valves with either some emory or sandpaper glued to the valves.
Burning Brakes
Joined: Oct 2020
Posts: 1,149
Likes: 265
From: The frozen wastes...
i did a little playing last night. 4cc dish, .029 head gasket, .016 in the hole 11.06 with 58cc. 10.27 with 64cc. .8 diff in CR. above 10 to 1 the rule of thumb is 2% for each point of compression. so you are talking 7 hp on a 350 hp engine. now, this is with everything else identical. and any aftermarket head is worth a lot more than 7 hp over the best iron GM head. and you are not gonna feel 7 hp unless you are looking at your et and your launch will get more variation in time than 7 hp.
A small, tight, modern design chamber is sooooo important, as the engine is basically designed around the combustion chamber. Using a (basically) almost SEVEN DECADE old design is just absolutely unforgivable... unless you are outright restoring the car to stock. Remember, those 'awesome' camel-bump LT1 heads are pretty much the same damn head as the 265 head... designed in what, 1953...??? Just with bigger holes. 1953. Man... thats when people were still flying across the country in PROP-engined planes... Half the country didn't even have a television at this point in time.
A nice bonus to swapping heads is maximizing the quench as much as possible.