superstreeter

I`m running a BBC 588 small 305 heads,and a 264/272 @ .050 w/.715 lift lobe separation of 108, flat top piston CR 10.1-1, I`m getting 170# crank compression, (I`d like to keep the compression),, and go to a 110 L/S cam with a 271/274, 750 lift cam and 357 heads, what do you guys think my compression will go down to with the new cam???also how much difference would it make if I kept the 715 lift as opposed to going to 750 lift???and take the 271/274 duration @.050

kwillymac

It will probably drop down a bit. You are running more duration @ .050. Hard to tell until you do it. Also I could be wrong but doesn't cranking compression change when you change the valve lash?

superstreeter

I know it will drop a little from the extra duration, but how much with the difference in the lobe separation

badrad

Use a dynamic compression calculator, it will show the difference using intake closing points between the two cams.

superstreeter

sure??? that sounds a little over my head!

badrad

There are dynamic calculators on the net, http://www.kb-silvolite.com/calc.php?action=comp2, this will let you see the difference. Shoot for 7.5 to 8:1 for dynamic, you can run higher on pump gas but tuning gets very important.

superstreeter

OK Badrad I think I got the dynamic figured out, But I installed the Cam at 2 degrees retarded,it didn`t change it much,all my figures show between 7.72 and 7.9, So I guess I`m ok,,I`ve never seen that method before,,Just out of curiousity,what does a longer connecting rod do for the ratio ? Whats the advantage of longer or shorter,other than it raises and lowers the Dynamic

badrad

The only other advantage I know of from running longer connecting rods is a better crank/rod ratio. As far as your question about the lift I would stick with the lower of the two. The 305 AFR only had one cfm difference between .600-.700 in stock form, therefore the lower lift should extend valve train life. It is only a guide line but I have plugged in the figures for a few build ups I read and the one with best power fell within the 7.5-8.5, usually ~8.