268H cam tuning

Once the motor was installed I placed a Holley Sniper on it and timed it with a vacuum gage. I went to max vacuum and then moved it back one tick. It came out to *21 BTDC which I though was quite high, but the motor ran great at full throttle, even chirping the tires (1977 Jeep with Quadra Trac running bigger tires than stock) which was pretty impressive to me. However, the motor would ping pretty bad at cruise. I moved the timing back to what I was running before the rebuild which was *16 BTDC and it seemed to run fine, but not nearly the power it had at *21 BTDC. In fact it really seemed similar to what my old motor was except it does like 60-75 MPH much better. 

Shortly after the rebuild I removed the Sniper and went back to the stock 4350 Motorcraft 4BBL carburetor and I have driven it about 5000 miles with this set up. Fuel economy has not been much better than the old motor too, which may or may not be a issue. 

In my thinking I though I should have more power than I have and though back to when I had the Sniper and timing set at *21. I went ahead and moved the timing back up to *19 thinking that might keep it from pining. Yes, it runs much stronger and I have no ping at cruise now. Except now it is harder to start with a hot motor. 

In my reading on other threads (mostly GM) it seems the 268H likes a lot of initial timing. I did a search here, but am not finding anything useful. I know that this seems to be a liked cam for the AMC motor so I was wondering. Does anyone has some input on maybe a similar motor build with some timing direction such as initial timing, mechanical advance, vacuum advance, am I on the right track?

I am now assuming that the pinging at *21 at cruise was too much vacuum advance at this point from my reading. 

This is in a 1977 Jeep Cherokee 360cid, 4bbl, Turbo 400, 3.54 ratio, 33" tires. I have converted the old Motorolla ICM to 4 pin HEI (soon to be 5 pin to help with the hard starts). I converted the Motorolla distributer to a large cap Motorcraft. I have a stock Motorcraft high energy coil. 

Thanks for any help, George. 

Agree with Sonic Silver...
Ignition Timing at idle "doesn't matter" for sake of discussion...
Only thing that "matters" is Static Initial Advance & Total Max Mechanical Advance COMBINED!
Combined total somewhere between 34 and 42 degrees.
SO as you have experience 1st hand, more static initial advance at idle INCREASE POWER !
BUT the mistake "everybody" makes is they bump up the initial

BUT FAIL TO LIMIT THE IN-COMING MECHANICAL BY AN EQUAL AMOUNT !

In order to MAINTAIN the SAME Combined Total of Initial + Mechanical.
Resulting in over advanced timing at rpm, detonation, reduce power, & possible engine damage.
And as you experienced, the drawback to high initial static timing is it is difficult, or won't, start hot.

Vacuum advance alone usually does not cause the issue you had or have even with a

a re-curved distributor with say 20 Initial at Idle + 16 total max degrees mechanical for 36 total.
BUT cranked up initial WITHOUT reducing mechanical with Vacuum Advance thrown on top of that,

well yeah, definitely detonation and loss of power man... it could be 67+ degrees advanced with all 3 all -in.
Vacuum Advance it what "gives ya" your steady state cruise fuel economy and clean plugs,

and vacuum advance "evaporates", instantly goes away, when ya put your foot in it for power.

Peace

I am using a Motorcraft Duraspark Distributor with a 4 Pin HEI running the spark. 

I still not sure what the mechanical advance is. I hope to find that out this weekend. 

The vacuum advance, advanced the timing *21 when I give it full vacuum with a vacuum pump. I am not sure if the intake vacuum would advance it that much or not. 

I have been driving the Jeep the last two weeks and have not heard any pinging at all. I work 25 miles away and I drive the freeway most of that mileage. Since I moved the timing up, my fuel efficiency went up nearly 2.5 MPG. I drive the same route every day so know this is not a fluke after two fill ups came up with the same numbers. 

Hopefully I can get the mechanical numbers this weekend. 

Thanks for the help!

I already have the HEI conversion running a Motorcraft Duraspark distributor. I am also running the big cap and a stock mid 80's Ford high energy coil. 

Sounds good on the talk. I will PM you my number. Thanks!