I'm gathering parts to build a 489 BBC and I have 2 sets of heads to choose from. The motor will not see over 6k rpm and is going into a 72 Monte. The heads I have are 063's and 292's. I will build the motor to have somewhere in the 9.5 to 9.8:1 compression range. Need to run power brakes, so the cam won't be too radical. I can't find any real good info on the 292 casting. I will likely machine the head I choose for larger valves (2.19 + 1.88) and do some minor port cleanup, etc. I know the 063's flow pretty good, but would the open chamber of the 292's help flow? Which would you use?

Tom

With the 063's, if you are close to zero deck height, you can run a flat top/minimal dome piston to get 9.5:1 CR. Since you are not planning on spinning it past 6K and are going to put a mild cam in it, I don't think you need to worry about getting max flow out of a set of heads.

just my opinion though.

Jim, Thanks for the reply. Do you know if the 292's flow as well as the 063's? I would think with a 489, the motor would be able to use the extra flow of whichever stock head is better, even at 6k rpm. I would think the larger valves and minor porting would benefit either head also. Looking at the heads, it looks like it would be easier to install larger valves in the 292's because of the open chambers.
I will be zero decking the block, and I do know a flat top piston will perform better than one with a dome, all other things being equal, but does the gains with a flat top piston outweigh the gains of unshrouded valves in the open chamber head. Or am I over-thinking this?

Thank You,
Tom

a friend of mine in florida built a 498 just like mine, he's running 049's just like me, pocket ported,bowl blended, intake matched with 2.19/1.88 valves. he's got a rpm air gap and a 750 holley. comp hyd roller 232/570 on 110 and he pulled 585hp @5200 & 624!!ft/lbs @4000 pump gas 10:1. v @ 2500 he had 560 ft/lbs talk about a torque pig!

Again, just my opinion from seeing what other folks run,.....I don't think an Chevy iron open chamber 9.8:1 motor is going to outperform a Chevy iron closed chamber 9.8:1 motor whether it is in a 498 or a 454. If both heads have 2.19/1.88's and a decent port job, you would be fine with either. Go with whichever you feel most comfortable with and can get pistons for to meet your desired CR.

Thats what I was going to suggest, select your pistons now in light of your head choice and then make your final selction.

Thanks for the replies.

Jim, I appreciate your opinion! I was thinking that they were probably going to be nearly equal, but I had not heard anything on the 292's, so that was an unknown. I'm going to cc both heads to see exactly where I'm at and look at the piston options.

70Flamed, Your friend's and your combo sound great. I may do a HR cam if I can get the parts used/or cheap. Retail price on these is too high for this build up.

Thanks Again,
Tom

The late JL said that reworked large oval heads would support up to a mild 540 motor! Therefore, choose your piston to give you the CR. you want and use either one.

It has been proven that the closed chambered heads are slightly better detonation resistance-wise with either flat-top or low dome pistons, but they don't quite flow as good as the open chambered heads due to slightly more shrouding at the expense of them needed taller domed pistons which create a less than ideal flame front deal!

It seems to be a trade-off between detonation resistance and the ability to run a slightly higher CR. over a comparably reworked open chambered head and the open chambered heads slightly better flow.

This tells me that since guy's successfully run both with the closed being ever so slightly better due to the detonation resistance thing that both heads will out flow a motor up to the mild 540 size that Mr. L. talked about so have at it!!

pdq67

Thanks PDQ67.

Tom