vacuum advance question
If you read the MP engine book, it clearly says that up to and a little over 60* part throttle is normal with a hot street engine. It's all in what combo you have.
Thx Rusty, I did not know this, and I have the book,somewhere......lol
I tried up to 64* or so, but with my 10.7 SCR, and tight squish aluminum heads, I found no advantage.
The dial-back allows me to add timing from the cab. My usual method of determining the optimum cruise advance, is to travel a known route 13 miles long that is dead-flat. I run it with the timing set at a baseline, and a throttle stop that allows a repeatable butterfly angle. Then I add 3 degrees and watch the speedo and tach. If speed goes up,I repeat. And so on until speed plateaus.
With my overdrive, 60 MPH is 2064rpm, and 44 was the magic number. In direct the tach jumps to 2650, and the timing jumps to 49*.
The maximum mechanical advance I run is 34* at 3400, to which the Vcan adds 22* for a total of 56*; and to that I could add 8*;so a grand total of 64*. But on my combo I find no advantage in the additional up to 8 degrees.
The Jacob's unit, as I have now set it, allows up to 8 more degrees in every situation. It has a range of 15*. I haven't dicked with it in a few years now.
But the thing to think about is that every combo is unique, and that there is a lot of potentials that some guys leave on the table by not exploring the timings of their combo
On another note,using this same device is how I discovered the cure for my low-speed jumpiness. She likes retard at 500/600 rpm, pulling herself around the parking lot at idle in the 10.97 starter gear. Yup 14* was too much. Sometimes I take it down to the minimum 7 degrees......
Rumpidy-rumpidy-rumpidy......ruumpidy.......ruumpidey...........rhuuumpideeey......
