I am helping a neighbor put together a '73 455 with stock 4 eyebrow flattops. He has a set of '68 casting #16 heads with the 2.11/1.77 valves. What type of compression will he be ending up with?    He is planning on running a CompCam XE274H cam. 230/236 @.050". Would this help bleed off some of the low rpm cyl. pressure? Any help would be appreciated. Thanks,Steve  

Check the Pontiac Street Performance website or the Wallace Racing website they have info about chamber cc, and Comp Ratio calculators that are easy to use. Cam should be ok but shoot for 9:1 comp or it will be a pain on low octane gas.  

It depends on the chamber size. I am not too familiar with the older stuff though.  

Steve,
The #16 heads (72cc chamber) on a 455 has a static CR around 11.5- 11.75:1, but with that cam the dynamic CR will drop to around 9.6 to 10:1, still requiring better fuel than pump gas. I'd run that cam straight up for starters, and keep the advance conservative (under 30 degrees). You can always add a few more degrees later and see if the motor will run with the gas you're using.

I have the same heads on a 400 bored .030 over which gave my motor a 10.75:1 CR, and I ran a Crane cams Energizer 284 cam with 228@ .050. It ran fine on pump gas, had a nice lope at idle, and still had enough vaccum to run the 4 wheel disc brakes I have on my Firebird.

Geno