I didn't get any kind of increase like that with timing. On the PI intake, when we went from 33 indicated on the timing tape (28 actual) to 38 indicated on the timing tape (33 actual), we picked up about 4 HP. And on the Streetmaster, when we went from 33 actual to 38 actual, we lost 10 HP. I'm guessing we hit the limits of the 92 octane fuel, and were starting to get into the zone of detonation at 38 total.
IMO timing requirements are primarily cam, compression, and chamber dependent, but not as much intake dependent. So, I think on this engine the timing probably wanted to be in the 34-36 range regardless of intake, but that's a guess. Based on the loss of 10HP at 38 total, no way is this engine going to pick up large amounts of HP with a few degrees of timing advance.
I have to admit I'm a little skeptical about your numbers. Are you sure there wasn't something else going on that could have increased your HP besides the timing change? I've never seen an improvement like that with just a few degrees more advance before. That's a stunning improvement with 2 more degrees of advance...
Jay Brown
1968 Shelby GT 500 Convertible, all aluminum 489" 1030 HP Supercharged FE
1969 XL Convertible, 460
1969 R code Mach 1, 706 HP 511" all aluminum FE, 10.457 @ 127.47, 2005 Drag Week Winner, Naturally Aspirated Big Block
