Quote Originally Posted by J[B
wrp, Simplification was a mantra. We ran Ford dual point distributors with mechanical advance only. We timed for no more than 36-37 degrees from 3500RPM-up, the rest took care of itself. I think we started the engine with about 10 degrees.
jim[/B]
Thanks, I guess this is where I was going, I will admit I spend a lot of time at 3500+ RPM, probably a good deal more than I need to on the street. If I drive like an average person is supposed to, I rarely get over 2000 RPM. That is especially true when I am cruising on a four lane highway. My SBC likes 12-14 degrees on starting. With the mechanical advance MSD setup I only had about 18 degrees of advance to play with. With the vacuum advance, I could back the timing down with a wider range of advance available but I still had issues because of the cam size and resulting weak vacuum. Without the computer controlled timing I had to set it around 18-20 degrees to get it to advance to 34 degrees at WOT. So when going through the gears from light to light I am likely to get over 3,000 rpm, cough cough, depending on the model 5.0 Mustang beside me. My Holley carburetor is trying to use the already weak vacuum to decide whether to be in the idle circuit, transition circuit, or the cruise circuit. With only the mechanical advance, the low speed performance resulted in a wide range of over fueling and under fueling (rich/lean). 2000 RPM seemed to keep me in the lean side of operations, read from my plugs. Some people are good enough to tune the carb and time the motor to meet specific driving conditions. I am not. Hence I noticed the operating temperature drop when going to the computer controlled timing EFI system. One thing I forgot to mention about is that I took the whole radiator down and had it pressure tested with the cap on and found I had a weak spring in the cap that came with the original kit. Changing that seemed to help too.