340 dyno chart thoughts

frosty_the_punk said

On a stock stroke 340? that vacuum figure for that much duration seems unusually high to me. two possibilities come to mind. super wide lobe separation like you'd see on a blower or nitrous camshaft.

OR a solid lifter where about 10-12 degrees of the lobe duration is taken up by valve lash.

regardless, the point remains... everything else being equal. more duration and a tighter lobe separation will increase overlap and reduce idle vacuum. Your personal anecdotes are interesting, but there's just no disputing this fact as it's probably the most basic rule there is about camshaft theory.

Click to expand...

It's definitely possible. For example. Looking at hughes STL5054AS-8. It has 250/254 duration. 108LSA. Guess what the overlap is? 66. Very mild compared to the duration. My XE274H has an overlap of 60. And it's 230/236 duration with 110LSA. Comp says the XE274H has 11" at 800 rpm. 14" at 1000. So with only 6 more overlap, 10-11 inches is doable at 900.

Gotta remember that cam designs are much better now. Valve events and such aren't nearly as drastic compared to duration/lift as they once were. For example. Look at the mopar P4120655 cam. 252 @ 50 duration. 110 LSA. Yet the overlap is 76. Very similar duration to the hughes. Yet much higher overlap. And lift is down!

The whole "you can't run that cam, it's too big for the street" is LARGELY a thing of the past. Valve events in relation to duration/lift/lsa are better than they have ever been. Running that "HUGE CAM" isn't the same as it was 20-30 years ago. The sky really is the limit.