[plain 69]

I was just wondering if anyone had any thoughts on this. We have a late 69 truck 402
big block chevy that was a crate motor from 69. It has 9.1 to 1 compression with open chamber heads, with the regular 10.25 closed chamber piston. Would the engine make more power if we put the closed chambered heads on
the engine. I know the compression will come
up to 10.25 to 1 but will the heads flow less
because of the closed chamber design.

 

[shannon]

For street driving and mild street/strip action, you will definitely notice more power w/ the closed chamber heads.....especially in the lower and mid RPMs.
Run a cam around the 278-280 degree Adv. Duation range and 524 or so lift w/ 3.73 gears and you will have a Torque'n street motor.

Shannon

 

[Guest]

I agree with 69...I've read that open chamber heads allow better breathing. But on the other hand, compression is important too. I'd go for for the closed chamber strictly because they'll raise your compression to a reasonably high but not unstreetable level.

 

[plain 69]

I was just reading a book on how to build high performance big blocks and it says to use the open chamber heads. They pointed out that with a L-88 427 in 68 had closed chamber
then they went to open chamber and power was
increased about 70 horsepower with the same
compression. They even state that even with lower compression the engine made more power.
My 402 has 049 castings which have 120cc chambers and also installing 2.19 & 1.88,s

[This message has been edited by plain 69 (edited 05-31-99).]

 

[shannon]

You're not talking "apples to apples".
A bascially stock 402 is a far cry from a "stock" L88. The L88 is built to operate constantly in upper-mid to upper RPMs....where the open chamber and bigger valves work and make more power.
The 402 was built to make good lower and mid-ranger power.
You will notice more power and torque from your 402 w/ the closed chamber heads IF your intentions are to build a mild street motor.
If, on the other hand, your intentions are to keep the motor wound above 4500 RPMs constantly, then yes, you will be better w/ the open chamber heads.

Shannon

 

[Gene Chas]

Shannon, some of us goofballs only drive our 'Elles once ina while and we like to have maximum grunt between 4000 and 7000. That's exactly what my 427 does.( open chamber L88 heads with 10.6:1) So the distinction shouldn't be between a street motor and a "strip" motor, but between a daily driver and a sometimes driver. Otherwise, your comments to plain 69 are right on the money.

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[plain 69]

It will be a double duty car. Occasionally
maybe a 6300 shift or so. Thanks guys.

 

[snow427]

In my opinion go with the closed chamber heads from the flow data I've read I don't think they flow enough extra to warrant the loss in compression. And to get the compression back you have to run big domes and then you end up blocking the flame travel.