What's the performance worth of oval 112cc big block heads? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

coggonobrien · 08-21-2008, 10:35 AM

I've got a 69 396 big block. The cylinder head number come back as 3933148....69-84...oval...OPEN...'69 396/265hp, 366T, 427T, 112cc chamber. Performance wise are these worth using as I want to go with edelbroch's multipoing fuel injection set up and am gunning for 450 rear wheel horse.
Thanks, Dave

d10s69c10 · 08-21-2008, 10:39 AM

im not really sure but i know the options for ovalports are a little less than squareport heads just because there are less made.

FIVE 0 · 08-21-2008, 12:21 PM

Alot of factors here,

You can make 450 ponies prety easy with those heads if your engine is built around them and the FI.

If you are just bolting them on your 396 you need to make sure you have open chamber pistons or you will loose alot of compression.

If you are doing a complete build, you can get there prety easy. Make sure you buy pistons for open heads that make about 9.5 to 1 comp. If you are having the heads worked over I would suggest cutting the valves to 2.19 and 1.88, that should help your FI breath. Go with a cam that your FI calls for with the other components and your there.

If you have the cubic dollars I would go with Edelbrock aluminum heads, open or closed, for your piston choice. By the time you pay to have the cast ones done you may only be a couple hun off. JMO

Im making over 500 ponies with a 9.5 to 1 full roller 402 with iron heads and carb. Its in a boat though.

Good luck, should be no problem

coggonobrien · 08-21-2008, 12:53 PM

thanks for the advice. these heads are on original engine which I was told was around 9.0-1 cr based on factory specs.

If I decided to stick with iron heads and carb what did you do to make your power? obviously full roller (what brand of set up), intake style, carb size, cam specs, and ignition?

Basically what would it take to replicate yours.

Thanks!!!!!!!!!!!!!!!1

FIVE 0 · 08-21-2008, 01:34 PM

Due to the engine going in my boat, a v-drive drag boat, I wanted the peak curve high. I spin it 6500 on a regular basis. So a couple variables would change. However Ill give you what Ive done and it could be done with some changes to a street engine.

I have a .40 over 402. Started with closed chamber oval ports and cut them to 101 cc chambers. Did a full port, gasket and gasket match on the intake side. Did some porting on the exhaust side. Cut the valves to 2.19 and 1.88. Comp roller rockers and Comp dual springs. Decked to zero with .188 dome pistons, math says its a bit over 9.5 to 1 with a .39 head gasket. Comp solid roller .625 lift on both sides with Comp solid roller lifters. Running a single plane intake and a Holley 830 Nascar style carb. MSD with 6A box. I run the timing between 36 to 38 advanced and open headers. To help the survival the rods were polished and shot peened, some work on the oiling holes on the crank, Full balance including flex plate and PTO for my drive. Performance dampner etc etc etc.

What I have is a turn key, pump gas, smooth idoling reliable engine that I also race with. The reason I went with a 402 was due to wanting to stay in a specific race class. I am building a 427 with more compression and may up my class, not sure if I need to go that fast.

Again, its only money but I wouldnt go back to a flat tappet cam, I went through 2 of them before I went roller. I would have paid for it the first time with the gaskes and oil I went through breaking stuff.

67shortie · 08-21-2008, 01:40 PM

Those heads look like small oval truck heads, you will not make the power you want with them.

To keep it cheap, look for 336781, 353049 etc heads, these are large ovals and open chambers. Run a bowl cleanup, 2.19-1.88 valves and they will support the power level you are looking for.

bigsnookmaster · 08-21-2008, 08:37 PM

I second what 67 shortie said.

PanelDeland · 08-21-2008, 09:24 PM

If you are going to the trouble of changing heads then I wouldn't even look for GM heads unless they were required for a class reason.I would just go ahead and get some decent aftermarket heads that fit the overall combination.By the time you buy a set of heads and rebuild them you will probably have almost as much in them as aftermarket ones.JMHO.

FIVE 0 · 08-21-2008, 10:29 PM

Just to state my disclaimer, I agree with all for the most part.

However our friend asked if he could make 450 hp with those heads. Saying he could not, would be like saying you couldnt make that kind of power with any stock SBC 2.02 heads. Those heads have larger intake runners and valves than SB ones do. The peanut port heads make a ton of low end and mid range torque, and if cammed properly could be a nice combo.

I do agree that no matter what you do to them they would not perform like even the cheapest aftermarket heads. You can get the cheap aluminum heads now to your door for under a grand, and could be into stockers for up to 600. That couple hundred could be the differance between a hobby and full on obsession depending on your allowance.

Again JMHO and would never step on anyone on these boards, most are far more versed than I. This is where I learn alot and appreciate all opinions.

08-21-2008, 10:35 AM	#1
coggonobrien Registered User Join Date: Mar 2008 Location: Coggon, IA Posts: 580	What's the performance worth of oval 112cc big block heads? I've got a 69 396 big block. The cylinder head number come back as 3933148....69-84...oval...OPEN...'69 396/265hp, 366T, 427T, 112cc chamber. Performance wise are these worth using as I want to go with edelbroch's multipoing fuel injection set up and am gunning for 450 rear wheel horse. Thanks, Dave

08-21-2008, 10:39 AM	#2
d10s69c10 Built 4 Speed Join Date: May 2008 Location: Geneva FL Posts: 619	Re: What's the performance worth of oval 112cc big block heads? im not really sure but i know the options for ovalports are a little less than squareport heads just because there are less made. __________________ 1969 C/10 Short Box: 496/T-56 in worx. "To Be Old And Wise, First You Must Be Young And Stupid"

08-21-2008, 12:21 PM	#3
FIVE 0 Registered User Join Date: Mar 2006 Location: Idaho Posts: 84	Re: What's the performance worth of oval 112cc big block heads? Alot of factors here, You can make 450 ponies prety easy with those heads if your engine is built around them and the FI. If you are just bolting them on your 396 you need to make sure you have open chamber pistons or you will loose alot of compression. If you are doing a complete build, you can get there prety easy. Make sure you buy pistons for open heads that make about 9.5 to 1 comp. If you are having the heads worked over I would suggest cutting the valves to 2.19 and 1.88, that should help your FI breath. Go with a cam that your FI calls for with the other components and your there. If you have the cubic dollars I would go with Edelbrock aluminum heads, open or closed, for your piston choice. By the time you pay to have the cast ones done you may only be a couple hun off. JMO Im making over 500 ponies with a 9.5 to 1 full roller 402 with iron heads and carb. Its in a boat though. Good luck, should be no problem

08-21-2008, 12:53 PM	#4
coggonobrien Registered User Join Date: Mar 2008 Location: Coggon, IA Posts: 580	Re: What's the performance worth of oval 112cc big block heads? thanks for the advice. these heads are on original engine which I was told was around 9.0-1 cr based on factory specs. If I decided to stick with iron heads and carb what did you do to make your power? obviously full roller (what brand of set up), intake style, carb size, cam specs, and ignition? Basically what would it take to replicate yours. Thanks!!!!!!!!!!!!!!!1

08-21-2008, 01:34 PM	#5
FIVE 0 Registered User Join Date: Mar 2006 Location: Idaho Posts: 84	Re: What's the performance worth of oval 112cc big block heads? Due to the engine going in my boat, a v-drive drag boat, I wanted the peak curve high. I spin it 6500 on a regular basis. So a couple variables would change. However Ill give you what Ive done and it could be done with some changes to a street engine. I have a .40 over 402. Started with closed chamber oval ports and cut them to 101 cc chambers. Did a full port, gasket and gasket match on the intake side. Did some porting on the exhaust side. Cut the valves to 2.19 and 1.88. Comp roller rockers and Comp dual springs. Decked to zero with .188 dome pistons, math says its a bit over 9.5 to 1 with a .39 head gasket. Comp solid roller .625 lift on both sides with Comp solid roller lifters. Running a single plane intake and a Holley 830 Nascar style carb. MSD with 6A box. I run the timing between 36 to 38 advanced and open headers. To help the survival the rods were polished and shot peened, some work on the oiling holes on the crank, Full balance including flex plate and PTO for my drive. Performance dampner etc etc etc. What I have is a turn key, pump gas, smooth idoling reliable engine that I also race with. The reason I went with a 402 was due to wanting to stay in a specific race class. I am building a 427 with more compression and may up my class, not sure if I need to go that fast. Again, its only money but I wouldnt go back to a flat tappet cam, I went through 2 of them before I went roller. I would have paid for it the first time with the gaskes and oil I went through breaking stuff.

08-21-2008, 01:40 PM	#6
67shortie Green club Join Date: May 2002 Location: Central CA Posts: 1,059	Re: What's the performance worth of oval 112cc big block heads? Those heads look like small oval truck heads, you will not make the power you want with them. To keep it cheap, look for 336781, 353049 etc heads, these are large ovals and open chambers. Run a bowl cleanup, 2.19-1.88 valves and they will support the power level you are looking for. __________________ 71 short/fleet ECE 4/6 drop, LQ4/700r4/3.42 gears 70 SS396 Chevelle 427/200-4R/3.73posi 61 Lincoln Continental, black on black Son you are going to drive me to drinkin if you don't stop drivin that hot rod lincoln

08-21-2008, 08:37 PM	#7
bigsnookmaster Registered User Join Date: Jan 2008 Location: St.Petersburg,Fl Posts: 1,267	Re: What's the performance worth of oval 112cc big block heads? I second what 67 shortie said. __________________ greg http://community.webshots.com/user/68406Stepside

08-21-2008, 09:24 PM	#8
PanelDeland I am a Referee of life. Join Date: Jun 2000 Location: Greensboro N.C. Posts: 13,993	Re: What's the performance worth of oval 112cc big block heads? If you are going to the trouble of changing heads then I wouldn't even look for GM heads unless they were required for a class reason.I would just go ahead and get some decent aftermarket heads that fit the overall combination.By the time you buy a set of heads and rebuild them you will probably have almost as much in them as aftermarket ones.JMHO. __________________ The 47-present Chevrolet and GMC Truck Message Board Network,it's owners,moderators,members,and associates of any type should not be held responsible for my opinion. You can't fix stupid,not even with duct tape. "My appearance is due to the fact that "GOD" does punish you for having too much fun!" Barrett-Jackson has perfected alchemy,they make rust into gold! "You can lead a horse to water but you can't saddle a duck" "Cleverly disguised as a 'Responsible Adult' "Sometimes your Knight in shining armor is just a retard in tinfoil"

08-21-2008, 10:29 PM	#9
FIVE 0 Registered User Join Date: Mar 2006 Location: Idaho Posts: 84	Re: What's the performance worth of oval 112cc big block heads? Just to state my disclaimer, I agree with all for the most part. However our friend asked if he could make 450 hp with those heads. Saying he could not, would be like saying you couldnt make that kind of power with any stock SBC 2.02 heads. Those heads have larger intake runners and valves than SB ones do. The peanut port heads make a ton of low end and mid range torque, and if cammed properly could be a nice combo. I do agree that no matter what you do to them they would not perform like even the cheapest aftermarket heads. You can get the cheap aluminum heads now to your door for under a grand, and could be into stockers for up to 600. That couple hundred could be the differance between a hobby and full on obsession depending on your allowance. Again JMHO and would never step on anyone on these boards, most are far more versed than I. This is where I learn alot and appreciate all opinions.



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