Best possible mileage?
i will try aj's timing trick,and get back
When you do this,
and after you have discovered the perfect timing
Then you can simultaneously twiddle the mixture screws to find the highest rpm for that cruise timing.
Be advised, that not every combo can be made to cruise at those settings..... because
it is sometimes physically impossible to either;
A) achieve that number with the parts you have, or
B) the engine might not have enough power to get to the cruise rpm and still be on the low-speed circuit, or
C) if it does, it might want to detonate the whole way, or
D) the rpm is just too low.
The method I detailed just tells you what the engine wants. Sometimes you cannot give it to her, because of the limits of the parts.
Furthermore;
You really need to work out your timings in the following order
1) establish the Power-Timing first. How much and how soon, without detonation.then
2) the Idle-Timing, then.
3) the rate of advance, then finally,
4) The Vcan tuning is last on the list because; if you change any of the first three, that will automatically change your Max V-can timing.
You can do things in any order you want to, but if you want optimum, you will be doing things multiple times.
If your cruise rpm is less than 2200 rpm, it becomes extremely difficult to get the cruise timing she wants. If you are serious, you will have to get an adjustable spark-delay box. Mine is in the cabin where I can reach it. This will reduce your learning curve very substantially.
I'll give you an example;
1) Say your power-timing (that's at WOT) works just fine without detonation at 36* at 4000 rpm.
But at 3600, it will only tolerate 32*. So you can figure out that the timing curve cannot be faster than 4* per 400 rpm which is 1* per 100.
But suppose that at 2800rpm she detonates with anything more than 22*. So then from 2800 to 3600 your rate of advance cannot be more than .75* per 100.
And at idle, she likes 12*, so from say 800 to 2800, you can dial in at the rate of .50* per 100.
Such a curve is impossible to build. At the very most, factory parts will only support ONE change in the rate of advance. So which one will you sacrifice? Put that on hold
2) Now lets say, your .73 overdrive and 3.23s cruise at 65=1900, your mechanical timing with the above curve will be 1900 less say 800) x.5*=5.5, plus the Idle-timing of 12=17.5. But Suppose the engine wants 40m degrees to get the peak pressure to occur in the window of 25 to 28 degrees ATDC. So then the Vcan has to bring in 40 less 17.5=22.5. This is just barely doable if you mod your Vcan But if the slanty wants more than 42* she's sol.
Now. the slanty still has to get to 1900! And if that Vcan modification cannot be slowed down enough to keep her out of detonation.... Yur gonna have to sacrifice something; what will it be this time?
Sometimes, the lowest cruise rpm is not the right answer. By 2200, optimum timing targets may be a lil easier to attain; and will get you better fuel economy than crappy timing at 1900.
By 2400, optimum cruise timing should be doable with the factory parts.
From 1900 to 2400 is plus 26%, which is the difference from 3.23s to almost 4.10s
But 4.10s with a 3.09 low and small tires like 26.7s(84"rollout), is brutally low. You will be reaching for to shift into second before having crossed the intersection. I highly advise against 4.10s with 26.7" tires,lol. But with 235/75-15 (92" rollout), 4.10s would be fine.
