Aluminum Rectangle Heads vs Cast Oval
Thread Starter
Burning Brakes
Joined: Nov 2005
Posts: 840
Likes: 19
From: Oshawa
Aluminum Rectangle Heads vs Cast Oval
I have a 71 LS5 with oval port cast heads, my plan is to replace these heads with 1971 aluminum rectangle open chamber LS6 snowflake heads, what power difference or other performance advantages should I expect from this mod? Any thoughts or opinions are appreciated. The car is a M21 with 3.36 gear ratio.
Thanks
Thanks
Race Director
Joined: Sep 2000
Posts: 17,298
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From: The Top of Utah
You should see a reduction in throttle response and a general sluggishness in daily driving. You MAY see an increase in the above 5000 rpm performance. If the stock heads are closed chamber, you will be drastically cutting your compression ratio for an even greater reduction in power at all speeds. Other modifications could make those heads work, but there are better choices out there.
RACE ON!!!
RACE ON!!!
Burning Brakes
Joined: Feb 2005
Posts: 894
Likes: 91
I have a 71 LS5 with oval port cast heads, my plan is to replace these heads with 1971 aluminum rectangle open chamber LS6 snowflake heads, what power difference or other performance advantages should I expect from this mod? Any thoughts or opinions are appreciated. The car is a M21 with 3.36 gear ratio.
Thanks
Thanks
The early BB aluminum heads with the "Snowflake" DID NOT have the same size runners as their "cast-iron" counterparts.
The "aluminum's" have a 295 cc intake runner where the "irons" have some 325's.
Having said that, and having recently done a few OEM 100% stock-appearing LS-5 units, you can actually "get it
done" with EITHER head, but let me say this, IF you choose the aluminum you had better "up" the C.R. a point or so higher that if you go the OEM "iron" route.
Both "stock-appearing" LS-5's we just did, 9.5:1 C.R., Q-jet, and some "mild" porting on the "iron" heads with some SB chev intake valves, an "upstroke" however (496"), stock cast exhaust manifolds, and dynoed at 460+ HP @ 5700 and 540+ Ft.Lbs. torque @ 3700.
We recently delivered a 396 BB, solid-lifter, 10.5:1 pump-gasser (93), with the 14011077 "Winter's" castings. Came off the dyno past 500 HP and 467 Ft.Lbs. torque.
Thanks, Gary in N.Y.
P.S. I have a second unit in the works with the identical heads BUT on a 427". Goal is 575/600 on 93, also solid-lifter platform!
-
Thread Starter
Burning Brakes
Joined: Nov 2005
Posts: 840
Likes: 19
From: Oshawa
Just a "tip or two" for what it's worth!
The early BB aluminum heads with the "Snowflake" DID NOT have the same size runners as their "cast-iron" counterparts.
The "aluminum's" have a 295 cc intake runner where the "irons" have some 325's.
Having said that, and having recently done a few OEM 100% stock-appearing LS-5 units, you can actually "get it
done" with EITHER head, but let me say this, IF you choose the aluminum you had better "up" the C.R. a point or so higher that if you go the OEM "iron" route.
Both "stock-appearing" LS-5's we just did, 9.5:1 C.R., Q-jet, and some "mild" porting on the "iron" heads with some SB chev intake valves, an "upstroke" however (496"), stock cast exhaust manifolds, and dynoed at 460+ HP @ 5700 and 540+ Ft.Lbs. torque @ 3700.
We recently delivered a 396 BB, solid-lifter, 10.5:1 pump-gasser (93), with the 14011077 "Winter's" castings. Came off the dyno past 500 HP and 467 Ft.Lbs. torque.
Thanks, Gary in N.Y.
P.S. I have a second unit in the works with the identical heads BUT on a 427". Goal is 575/600 on 93, also solid-lifter platform!
-
The early BB aluminum heads with the "Snowflake" DID NOT have the same size runners as their "cast-iron" counterparts.
The "aluminum's" have a 295 cc intake runner where the "irons" have some 325's.
Having said that, and having recently done a few OEM 100% stock-appearing LS-5 units, you can actually "get it
done" with EITHER head, but let me say this, IF you choose the aluminum you had better "up" the C.R. a point or so higher that if you go the OEM "iron" route.
Both "stock-appearing" LS-5's we just did, 9.5:1 C.R., Q-jet, and some "mild" porting on the "iron" heads with some SB chev intake valves, an "upstroke" however (496"), stock cast exhaust manifolds, and dynoed at 460+ HP @ 5700 and 540+ Ft.Lbs. torque @ 3700.
We recently delivered a 396 BB, solid-lifter, 10.5:1 pump-gasser (93), with the 14011077 "Winter's" castings. Came off the dyno past 500 HP and 467 Ft.Lbs. torque.
Thanks, Gary in N.Y.
P.S. I have a second unit in the works with the identical heads BUT on a 427". Goal is 575/600 on 93, also solid-lifter platform!
-I have already put 10.5:1 pistons in and the cam is a 550 lift, does this change your thoughts?
