Originally Posted By BradH
Originally Posted By krautrock
I remember there was a thread here about LSA (i think) and Monte Smith seemed to like a wider LSA if the heads were good.

Monte, along with some others on here, built/build serious sh!t with mega-flow heads, high CR and/or power adders, and comparatively narrow usable power ranges at high(er) RPM. When you're flying at that altitude, the "right" LSAs are in a different range than what Joe Average needs... IMO.

Junk like mine w/ moderate cubes, semi-pump gas CR, a lower RPM limit and comparatively small-port & limited-flow heads doesn't necessarily see improvements from wide(r) LSAs. This is one of those topics that I've seen David Vizard and other established engine builders having to agree to disagree on, 'cuz DV seems to lean towards as tight an LSA as possible on builds that the others just shake their heads at. "They" will say 110 or 112, and he'll say 105 or 106. He's got his methodologies, but as Andy pointed out, they're far from universally accepted.

My own tests years ago on a much milder combination than I have now didn't pan out like I'd expected. Three SFT cams dynoed on a pump-gas 440 making in the low-to-mid 500s HP:
- 251/255 on 108
- 254/254 on 108
- 255/263 on 110

For THAT COMBINATION, the 255/263 on 110 was the worst across the board. The 251/255 x 108 and 254/254 x 108 were very close with the best peak #s coming from the 254/254. However, the 251/255 revved out much farther before valve float kicked in w/ the 254/254. I went with the 254/254, but on the track when I ran shorter tires (275/60R15 drag radials vs my 29" slicks), I was getting into valve float on the big end and killing my MPH. In retrospect the smaller cam might have worked better overall in the car and not have beaten up the valve job as quickly.

None of this stuff is a "for sure" thing. And even the best educated(?) guesses of the results sometimes miss the mark by a pretty large margin vs what the real world shows.

OK, I've probably broken my soap box from standing on it so long. We now resume your regularly scheduled programming...

Brad, if you look at the opening closing points of the 255 vs the 254 cam, and were to install them both at say 108, the only event that changes is the exhaust opening discounting the ondegree difference in intake timing. Maybe your motor had great exhaust ports , which makes me wonder how your motor would have responded to something like a 252/248/107 or 106 lsa cam

Last edited by gregsdart; 02/24/18 02:02 PM.
8..603 156 mph best, 2905 lbs 549, indy 572-13, alky