Hi All,

Long time lurker, and even longer Oldsmobile lover, but this is my first post.

I recently bought a 1969 Cutlass from a gentleman who had been working with Rocket Racing to build a fairly stout 455. All of the parts (mostly new) came with the deal, but the engine is not yet assembled. Here are some specifics:

- 455 Block, currently .060 over
- Eagle 4.25 stroke crank
- Molnar 7" rods
- Custom ordered flat top Diamond Pistons with valve reliefs (3.98 cc total) and a 1.48 compression height
- Edelbrock heads (old casting)
- Harland Sharp Roller Rockers
- All MSD ignition
- Offy Port-o-sonic
- Holley Ultra XP 850
- Solid flat tappet single pattern cam .576 lift, 246 duration at .050, 108 LSA

Car has a quick performance 9" with 3.70 gears, and came with a new-in-crate TH400 and 3,500-3,800 stall converter. My goal is to have this be a fun street/strip car, so want to run on pump gas (mostly 91 in my area). Here are my questions:

- Using a standard .040 head gasket, compression comes in just over 11:1. I'm assuming this is too much for pump gas? I could lower it to about 10.25 with a .080 gasket. Is that enough to be safe on pump gas? Any downside to running the thicker gasket to lower compression?
- Is it worth selling the Offy to go to an Edelbrock RPM?
- I'm not crazy about the cam specs..I'd like to see a dual pattern with longer duration on the exhaust side. But maybe I'm crazy? And if I do swap cams, I'd probably go to a hydraulic roller.

Thanks for any feedback - would love to hear from the guys like Mark (cutlass EFI) and Joe!

 

If you haven't already done so I'd measure piston deck height and cc the heads.

 

Rear gear? Trans?
Yes you’re at 11.:1 or better.
I’m not a real fan of using a thicker gasket but you gotta do what you gotta do.
A dual pattern cam will bleed off a bit of your compression, a roller will do more because of more off the seat time.
You’re about 75% there but with a little change here and there you should be able to hit your goal.

 

Yeah, I plan to verify piston to deck clearance during assembly. For the heads, I haven't heard much about the Edelbrocks being too far off of the 77cc advertised, but agree that would be a good idea as well.

 

TH400 with 3.70s. Any reason why you're not a fan of the thicker gaskets? I was looking at a cometic mls. Are they more prone to blow?

 

Although I don’t put a whole lot of stock in squish, I do believe it has its benefits. When you increase the gasket thickness it negatively effects that.