smallblock ignition curve tuning

[jveik]

i will be eventually building a souped up 350 with about 9.5:1 compression, vortec heads, and a comp cams 274 extreme energy camshaft that is on the lopey side of the spectrum... and i was wondering about setting the ignition timing. I have heard that most likely i will need about 34 to 36 degrees of total timing at 2500 or 3000 rpm, but does that include any type of vacuum advance, or does the vacuum loss at higher rpm's pretty much rule out the vacuum advance as playing a role at all? basically the jist of the question is when i set the total timing at 34 or 36 degrees, should i have the vacuum advance disconnected and the port feeding it plugged or do i leave it in? i know that you disconnect it to set the timing at idle, but i want to be sure that it advances when i need it to, so i will be testing it at higher rpm's as well... sorry if this is confusing to any of you, im confused as well lol

[richtazz]

Actually, a vacuum advance runs reverse. Low vacuum = more advance. An engine creates less vacuum at WOT than at idle, so a low vacum big cam could cause the vacuum advance to start kicking in at low RPM, causing a stumble or miss at part throttle. Unless it's a light car, with a big gear and a 3500 or so stall, that cam is not streetable. If you're not going to run it over 6,000 RPM all the time, put a smaller cam that will match the way you're going to drive it. Those big SEXY cam specs sound good on paper, but your engine will be a low end PIG. As Carroll Shelby once said, Horsepower rules the track, but Torque rules the street.