Very interesting read.
What would you use as on-board adjustable timing control?
That's some thing I was thinking about as well, how could I adjust timing "online"...
I have an old Jacobs unit with a range of 15 degrees. If I set the dial to midway, and then set the timing to whatever, then the dial can add or subtract 7.5 degrees either way from where it is set...... while driving.
Jacob's is no longer in business but I think I saw a similar stand-alone unit offered from MSD. 8680
Looks like that can do the job.
You can also use it to help determine your
Power-Timing,
Idle-Timing and
Stall-Timing. All of which should be done BEFORE you get to
Cruise-Timing,
but is not mandatory on a vehicle intended for cruising only.
After you get it installed, do this; make yourself a $0.50 throttle-stop from an old coat hanger and adjust so it will get you about 60/65 mph. Exact number not important. Install a vacuum gauge readable from your seat. Then drive. Record your EXACT vacuum reading. Then dial-back 3 degrees and wait. When the roadspeed stabilizes, record your vacuum reading. Then add 6 degrees, and wait. When the roadspeed stabilizes, record your vacuum. Now do the math from the starting point, to whichever timing recorded the highest roadspeed. See what I mean? The vacuum did not change or was almost too small to register, yet the roadspeed may have changed 5 or more percent, at the exact same throttle opening.
So lets say you did NOT have the dialback, and you baselined the vacuum reading at 62 mph. Then you stopped the car, added 3 degrees of Idle-Timing, and again ran the car up to 62 mph. What would your vacuum gauge tell you? Answer; nothing. The graduations are too small to accurately read and compare. And are easily lost with tiniest changes in grade, wind, barometric pressure, etc and are not repeatable on another day or direction. It is, IMO, a complete waste of time, to try and use a vacuum gauge for trying to tune for fuel-economy, at ONE particular roadspeed.
To be fair, you can use it to tell you how hard the engine is working at 80mph, versus at 65, but again, now the rpm has also risen 23%, so now the RPM alone is triggering a change in fuel-consumption, and the timing has changed, and the throttle blades are further up the transfers, maybe on the mains, so really, what is the vacuum gauge telling you? Answer; the only thing it can possibly tell you is that the throttles are open further at 80 than at 65; and com'on, you already knew that. It's like the seat belt buzzer telling you that your seatbelt is not latched; I mean tell me something I don't know......., I've been putting it on for over 50 years, ... I doneedno steenking reminder.
Once you start using that dial-back, you will wonder how you ever managed without it.
Assuming this is pre-LeanBurn'
I can guarantee you that the first thing you will do after about the second run, is you will be pulling off the VA and sawing off the stops, to increase it's capacity. And you won't stop until the Cruise-Timing gets to be about 44 or more degrees at 2000rpm.
BTW; on a DD, this is why your other timings need to be worked out first, because if you do it afterwards, your ideal sub-2800 (or so) timing may put you into or too close to detonation with an over-modified V-can.
Here is something that looks like my Opto-timer; dial-back and dial rev-limiter. Comes with a built-in amp for the Chrysler magnetic pick-up. I use the rev limiter for an adjustable "cruise-control", by running the car up to 65mph, then setting the rev limiter to where it pukes the ignition, then slowing down to 62mph/100kph, the speed limit in most of Manitoba.
At other times it is set to 7300 or so, in case I miss a shift.
And YES, I did get my 335hp 11/1 367 4-speed/overdrive up to 32 mpgUS.
I know it was AT LEAST 335 hp cuz it went 106 in the Quarter at 3650 pounds, shifting the 223* cam at 7000 or more.
I know it was 11/1 cuz I built it to be that.
I know it was 32 mpg cuz I measured out a tankful of jerry cans in the trunk. then filled the tank, and ran til it puked, measuring the distance on the previously -calibrated odometer.
But I admit, my secret weapon was the overdrive gearing; namely 65=1600 rpm/ 85=2100
Butum, with 2.2s and lock-up, yur gonna be able to go about 65=1900...... not very far away, plus my engine is 4.04 x3.58 versus your 3.91 x3.315
My timing at 2100? Over 50 degrees....