cnc chamber vs compression and boost

[yevgenievich]

Trying to decide on better pathway. Can get 100cc head that would keep 9.9:1 compression on a bbc. Plan for 20psi of boost eventually. Or get a cnc chamber option that would have to be 110cc chamber resulting about 9:1 compression.

 

[Vbb199]

If you plan on the boost, I vote the 9:1 head would be better, seems like 20psi on 9:1 would put it at like, 20:1 dyn c/r , where as the 9.9 would be closer to 23:1

Obviously I'm sure you've already done the math

 

[Vbb199]

You said details concerning machined 110cc chambered heads... I'm curious... are you looking at the promaxx heads? I was investigating the same heads for when I decide to put a little boost to my big block.

 

[yevgenievich]

This is on a brodix race-rite heads. My thought even with 9.9:1 it should still be reasonable under boost while providing a bit better off boost. Bumping compression up a bit, will gain some power. Going with lower compression but cnc chamber would then be a wash and not worth extra cost to cnc.

 

[Vbb199]

Interested to know what you're running this in, I know it's off the topic.

 

[Grumpy]

This is on a brodix race-rite heads. My thought even with 9.9:1 it should still be reasonable under boost while providing a bit better off boost. Bumping compression up a bit, will gain some power. Going with lower compression but cnc chamber would then be a wash and not worth extra cost to cnc.

If possible, I would contact Brodix themselves for their input - it can never hurt.

Given the choice, I would always go for the CNC heads. Forced air only helps with the volume of air, the CNC chambers are what make everything equal from cylinder to cylinder, and this is important for smooth power production.

 

[Vbb199]

^ not to mention flow, the 3d machined contours will flow better than cast

 

[yevgenievich]

Interested to know what you're running this in, I know it's off the topic.

97 k2500 burban

 

[yevgenievich]

Brodix tech were essentially saying that it makes not much difference and might as well keep chamber smaller. I was somewhat thinking if larger chamber would help with air flow around the valve.

If possible, I would contact Brodix themselves for their input - it can never hurt.

Given the choice, I would always go for the CNC heads. Forced air only helps with the volume of air, the CNC chambers are what make everything equal from cylinder to cylinder, and this is important for smooth power production.

 

[Grumpy]

Larger chambers to increase flow around the valve has not been a concern since the 1980s, when the design of the chambers really came into its own. A larger chamber is simply a larger chamber these days. Your best option when picking out parts for your build are to keep the piston top as flat as possible to optimize quench. Yes, a smaller chamber will make it easier to increase compression, and most modern combustion chambers are superior to anything from the sixties (as it should.)

Dome pistons, large chambers and much of the fancy stuff is not normally the realm of us who don't live on the race track - those guys are creating purpose-built engines, and they spend hours and days just sorting out which valve to use on the intake or exhaust for their particular combination.

 

[yevgenievich]

Actually, I am starting to fall back to lower compression ratio just to keep things easier. Would allow to run 87 at first, and then run premium once boost is added.