Cam comparing question

[hogmandon]

Reading the specs on cams I know intake opening and closing determines if power will start early or late. Do the exhaust numbers tell you how far out the power will last. Don't really hear about exhaust.
I have Andrews 37s at 9.8cr now 96ci BB, TB, Heads, pipes and ac in an 06 RG
int 18/36 ex 46/14 with 510 lift power starts at 2200 to 5500  nice low end

would like to try crane 290-2
int 18/42  ex 46/22 with 570 lift crane says 1800 to 5800
with the latter int closing I would think the crane would start to come on a little latter or is it all in the extra lift. I am going to try the crane any way but would like to learn more
Thanks for any info

[dynaglide]

probably get more hits over in the Twin Cam section... 

The 290-2 will be soft at 9.8; advancing them 4 degrees to close at 38 deg will help, although the cylinder pressure they build will still be less compared to the TW 37 due to the greater overlap and exhaust duration (earlier exhaust opening).  However, they will be stronger up top for the same reasons.

By "up top" I mean about 4K and up (basically from the torque peak up to the HP peak). They will also continue pulling longer than the 37s, again due to the longer durations and greater overlap.

http://harleytechtalk.com/htt/index.php/topic,62567.msg669195.html#msg669195

[panic]

I knew this was a mistake.

[dynaglide]

I agree, sort of...

You're correct in that the earlier exhaust closing does not bleed off pressure.  However, the greater overlap does.  Even though pressure does not begin to build until the intake closes, with the greater overlap, some of the intake goes out the exhaust at low speeds (just like you say), so there's less in there to be compressed once the intake closes.

I agree with you that the order of magnitude is small, but it is enough to make a difference at cranking speeds (hence maybe a bit easier on the starter).

I think we're both saying the same thing in different ways.