Spark Timing

[bobc455]

Originally Posted by retrorocket

Get a vacuum gauge and see if you can monitor the pulse width of your injectors. Someone on this site should be able to help you there.

If you had an msd ignition box then you could buy an adjustable timing control and adjust it from inside the car and monitor what is happening to the injector pulse width while cruising down the road.
other wise just keep adjusting the distributor, vacuum canister, weight travel, and springs

Get a dial back timing light and plot your timing curve.

Keep playing with it till your mileage seems its best.

Actually, I can get every single bit of data through a laptop, including manifold pressure, injector PW, and virtually everything else.

The trick is right now I am trying to fine-tune the timing tables (did I mention that the computer also controls timing so I don't need the other MSD thing). I cruise around 2400 RPM and about 9-10" of vacuum at 75 MPH.

I had the "cruising" timing at around 50-53 degrees, but I noticed some stumbling (not detonation). I backed it down to 40 and it is smoother. However I think 40 degrees is too low, so I'm trying to find out what other people run for timing on the highway.

I've thought about disabling injectors, but I don't believe that will give any significant savings. I have port injection (not throttle-body) so I could do some nifty wiring and shut down some injectors, but I think that would cause too many other problems.

-Bob C.

[omgwtfbyobbq]

Originally Posted by theclencher

Why do the manufacturers disable the valves?

Probably to minimize vibrations, although I'm sure there's some energy lost from pumping air in and out of the exhaust too, just not as much as friction in a deactivated cylinder. By trapping all the exhaust gases in a given cylinder, maybe increase the size and dampening ability of that air spring?

[DRW]

All engines are different. The timing that works for one engine may not work for another. From what I recall, a large bore needs more timing than a small bore. Compression ratio has an obvious effect, too. My car has a 2 liter 4 banger with a 7.9:1 comp ratio and likes about 33 to 35 degrees at steady cruise on the freeway. I don't think this timing will work for a 455ci V8.