BBC : combustion chamber size recommendation
Thread Starter
Burning Brakes
Joined: Feb 2006
Posts: 1,223
Likes: 4
From: Regina Saskatchewan
BBC : combustion chamber size recommendation
I have a chance to pick up a 396 bbc that was built for a blower, but currently has none. The current heads have 109cc combustion chambers and I believe the motor to be 7.5:1 compression. What size combustion chamber head would I need to get this old girl up to 9.5:1 Any thoughts would be appreciated. (38 cc was the smallest I could find)
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
I'd have to agree, and say that you appear to be asking the wrong question. I'd stick with the more conventional sized chambers such as you already have and change the slugs to bring up your compression.
That said, depending on your piston/deck height and gasket thickness, 9.5:1 with 110 cc heads will require ~24 cc domes. Unfortunately, being that you're working with a 396, that may well require a custom order. Us 427 guys frequently run into a similar piston availability problem, despite its popularity.
Sorry, I know the above isn't exactly the info you are asking for, but figure you need to hear it.
That said, depending on your piston/deck height and gasket thickness, 9.5:1 with 110 cc heads will require ~24 cc domes. Unfortunately, being that you're working with a 396, that may well require a custom order. Us 427 guys frequently run into a similar piston availability problem, despite its popularity.
Sorry, I know the above isn't exactly the info you are asking for, but figure you need to hear it.
Thread Starter
Burning Brakes
Joined: Feb 2006
Posts: 1,223
Likes: 4
From: Regina Saskatchewan
I was thinking changing out the iron heads to some 38cc aluminum ones might do the trick. So the 38cc heads wouldn't work?
I 'd have to have someone else r & r pistons = $$$
I 'd have to have someone else r & r pistons = $$$
Le Mans Master
Joined: May 2006
Posts: 9,993
Likes: 1,136
From: League City Tx
There are NO BBC heads with 38cc chambers... Not even possible.
Smallest you are likely to find are around 100cc edelbrocks... Then maybe mill them to mid 90s CCs. I still doubt you'll see 9.5-1 comp with flat tops.
Gonna have to put pistons in it.
I have a 454 that has flat tops, we used 69' model closed chamber oval ports, I believe they CCd at 107, then we cut them some. That motor is still barely 9.0-1.. Very mild.
Rat motors need some domes for sure..
Smallest you are likely to find are around 100cc edelbrocks... Then maybe mill them to mid 90s CCs. I still doubt you'll see 9.5-1 comp with flat tops.
Gonna have to put pistons in it.
I have a 454 that has flat tops, we used 69' model closed chamber oval ports, I believe they CCd at 107, then we cut them some. That motor is still barely 9.0-1.. Very mild.
Rat motors need some domes for sure..
Thread Starter
Burning Brakes
Joined: Feb 2006
Posts: 1,223
Likes: 4
From: Regina Saskatchewan
http://www.jegs.com/p/Edelbrock/Edel...37229/10002/-1
Let me ask the question another way. Does anyone know the relationship on a bigblock head for compression ratio when going to a smaller combstion chamber. I found a site for a sbc head earlier. I think they said that 10cc lower was worth a point.
If I buy this 396 I can recover some of the cost by selling the iron 109cc heads. If I pull the slugs - I can't recover anything and its not such a good deal. The 109cc heads are off a 67' 360hp bbc
Let me ask the question another way. Does anyone know the relationship on a bigblock head for compression ratio when going to a smaller combstion chamber. I found a site for a sbc head earlier. I think they said that 10cc lower was worth a point.
If I buy this 396 I can recover some of the cost by selling the iron 109cc heads. If I pull the slugs - I can't recover anything and its not such a good deal. The 109cc heads are off a 67' 360hp bbc
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I think I'd be looking for an 8-71 blower to stick on it...or forget it and find a different motor. 396's are cool...and I've had some pretty fast ones..but a healthy smallblock will handle it...or find a 454 or something.
JIM
JIM
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From: Graceland in a Not Correctly Restored Stingray