Originally Posted By: Dumc87
Originally Posted By: splinter
Easy enough to experiment and doing so costs next to nothing. Try it and report back with your findings.
My 10:1 SBC is happy w/ ~36° beyond 2600 consuming 91. Shortened its curve to allow 18° initial.
Good tip-in and solid mid-range.
That jargon is above my pay grade lol
Not really sure what you mean by shortening the curve. Did you rotate the distributor? I'm just looking to install the timing chain and crank gear either +4 or -4, or simply keeping it 0 and install it stock.
The above jargon isn't applicable to a crank-triggered ignition engine. He's talking JUST about spark timing. "Shortening the curve" means limiting the amount of mechanical advance that the distributor will apply with increasing RPM. It is usually performed when you want *more* spark advance right off idle, but you want to keep the *same* advance you already have at high RPM. For example, the older Mopar LA smallblock (273/318/340/360) engines prior to the Magnum liked about 38 degrees total advance (not counting vacuum advance) at 2500-3000 RPM (with a mild performance cam, more like 36 with a stock cam), but from the factory for emission reasons the idle advance was set to between TDC and +12 TDC depending on year. This meant that the mechanical advance curve was "long," because it had to take the engine all the way from 0 to 38 degrees as RPM increased. For more performance-oriented applications, its often good to shorten the curve so that you can keep ~38 degrees at 2500-3000 RPM, but start out with as much as 18-20 degrees at idle. That gives a car a lot more punchright off the line, and with a looser torque convertor, the right cam overlap, etc. it won't have a detonation problem. It will have high NOx emissions, though.