I have a 454 motor .030 over with KB flat top pistons (3cc valve relief). I currently run a set of Clay Smith Engineering ported oval port closed chamber (bath tub shape) heads, 98.4 CC with Manely 2.19/1.88 valves. No work done on the chambers, only runners. These heads are factory iron 1966 396 heads. The final CR is 9.43:1. It runs good now, but I'm looking for more.

I'm considering installing a set of World Merlin open chamber oval heads 269 CC runners and 2.3/1.88 valves that I have sitting in my garage.

I'm sure the Merlin heads are better, and would have less valve shrouding. But I've heard that the Merlins advertised 119cc chambers, are more like 124 cc. This would make my CR 8.12 or 7.86, and I already run a shim gasket to get .040 piston to head clearace.

Is it worth the time (I have young kids and time is hard to come by) and money to swap these heads? Not sure how much, if any, the Merlins will flow, and will it more than offset the compression loss. My version of desktop dyno does't take open vs closed chambers in condideration, it will take flow numbers, but I don't have that info.

Plan B is to build another motor (454 or 496) as time allows with the Merlin heads and an SRP piston with a dome to create around 10:1 CR.

I currently run a Crane HR288 (139731) cam, Performer RPM, 850 DP carb with annular boosters, 3.07 gears, and a Richmond 5 speed (3.27 1st gear). I also have the next step larger Crane HR296 (139741) cam available sitting in my garage.

This motor is in my 68 Chevelle. I know this is a Camaro forum, but since I've had good luck with posts regarding my 69 Camaro project, I wanted to post this question here.

Any thoughts?
Thanks, Jim

I bet a CC 270B solid lifter BOAT cam spec'ed at;

270/235/280/242, 110/106, .561"/.575" gross lift and lash at .028"In/.030"Ex.

would do your present 460", closed chambered head, motor fantastic!! I bet it would be EXPLOSIVE with your 3.07 gears and low first gear Richmond tranny!!!

As for your roller, I figure Crane would really like to see their HR288 cam ran in a 10.5 to 1 CR. motor AND preferrably an 11 to 1 motor!! BUT so much for advertising AND separating guys from their money...

I went with a good old CC 282S solid cam in my 496 motor for max. midrange grunt production!! And I also went with the 2.19"/1.88" Merlin ovals but pistoned and headgasketed it so it is up at 9.8 CR..

About 550hp at 5500 rpm and 580t at 4500 rpm so I just call it my great big "tow-truck" motor!!! Imho, a nice mild, low rpm motor!!!

pdq67

With the comp loss you'll see if you'd swap to the Merlin heads there would be a power loss in my opinion. I wouldnt do it...

Thanks, I think I'll wait to install the Merlin heads on another motor with the right pistons.
Does anyone have an opinion on the power difference between the open vs closed chamber heads? If all things were equal, except for the heads, what would be the power difference?
Thanks.

You really can't ask that question b/c it is in the motor combinations, and isn't an actual apples to apples sort of deal.

Open chambered heads will require high domed pistons whereas closed chambered heads low domes if not flat-tops depending on final chamber
and headgasket cc's for the CR. made.

Both heads can be made to run very well but differ in this respect, imho..

And as staTED, THE CLOSED CHAMBERED HEADS TEND TO WITHSTAND MORE cr. BEFORE DETONATION REARS IT'S UGLY HEAD THEREFORE THE TWO MOTORS cr'S WON'T BE IDENTICAL at THE max COMBINATIONS!

ah DARN CAPS AGAIN....

Sorry I can't be of more help here.......

Hunt up Ed's "BSE" engine combinations if you want to see BB closed chamber head power!!

pdq67

This is not based on anything other than the talk of 25 years ago, however the feeling then was that the better flow provide by open chamber heads on a closed chamber short block gave a net increase in HP even with the compression loss. In the case I've discribed, there was aloss of about 1 pt.(I was told) going from 10.5-11.0 to about 9.5-10.0 (101cc vs. 118cc). Your estimated loss is a bit sharper and more of a concern for me.

At least that was the talk. I'v had no big block since, so I am a bit of the loop.


LDR