RPM and timing

[diesel_lv]

Not sure if this is the correct area, 1967 Coronet, 383/496, 3.73 gears w GV overdrive and 26.5" tall tires. Timing is at 18° degrees initial w no vacuum, then 30° w vacuum from manifold at idle. Idles at 850 rpm w 15" vacuum very nicely. Distributor adjusted for 34° total mechanical, so 16° more than initial. I used the heaviest springs from 4 seconds flat that are available. My question, where I live, many steep 7% grade long mountain roads and 75 mph speed limits. At 80mph, I'm about 3k rpm and pulling 17" of vacuum. I don't have any help, so I don't know when my mechanical advance starts to come in and when I reach full mechanical. Before I go searching, I'd like some real world suggestions for what I'm looking for. I haven't driven above 1/4 throttle yet, and don't want detonation. With the RPM's at that level at 80 and the vacuum that high, that could lead to a ton of advance. Any suggestions on when I should have my mechanical advance starting and all in by? Thanks in advance.

 

[R413]

Rev it up in neutral and watch the timing mark with a light. Watch until it stops advancing. Have a helper in the car watching the tach and yell or signal them to note the RPM.

are you checking manifold vacuum? You shouldn’t have your vac advance on manifold vacuum. It should be on ported vacuum.

 

[diesel_lv]

Rev it up in neutral and watch the timing mark with a light. Watch until it stops advancing. Have a helper in the car watching the tach and yell or signal them to note the RPM.

are you checking manifold vacuum? You shouldn’t have your vac advance on manifold vacuum. It should be on ported vacuum.

This is not a discussion on ported or non-ported vacuum. I understand how to check the timing, I am looking for the 2 recommendations before I try to enlist help so my helper is not wasting his/her time. Thank you

 

[sam65]

This is not a discussion on ported or non-ported vacuum. I understand how to check the timing, I am looking for the 2 recommendations before I try to enlist help so my helper is not wasting his/her time. Thank you

Evidently you do not know how ! You wouldn't asking if you did!

 

[turbine68rt]

When you say you have 34° total timing, are you using a limiter plate or welded slots? As long as it doesn't go beyond 34-36 all-in you won't have to worry about a "ton of advance".

 

[forphorty]

I like to have my mech advance start above idle and be all in below my converter stall speed.

 

[PurpleBeeper]

This doesn't really answer your question, but you may find that adjusting the vacuum advance may help you too with those steep grades. I know it's not much help, but I've run mechanical only for a long time now

 

[diesel_lv]

When you say you have 34° total timing, are you using a limiter plate or welded slots? As long as it doesn't go beyond 34-36 all-in you won't have to worry about a "ton of advance".

Yes, I have a plate that I installed on the 16° slot. With 18° initial and the 16° mechanical, I get the 34°. When the engine is warmed up, n I press just enough to get a downshift, I've had a minor clatter, so I back off the throttle. I'm in AZ n the best gas we get is 91 octane. Fitech efi so I know I'm not leaning out.

 

[diesel_lv]

Evidently you do not know how ! You wouldn't asking if you did!

I won't get in a discussion of intellect, please re-read my original post. I was asking for real world suggestion on when to have mechanical advance start coming in and when to have it all in. "Not" how to set timing. I've got 23 yrs working on helicopters and certified turbine engine along w A&P license. I've built numerous motorcycle engines and diesel truck engines. But this is the 1st "car" gasoline engine and was asking for very specific advice.

 

[diesel_lv]

I like to have my mech advance start above idle and be all in below my converter stall speed.

If my converter stall is near my highway cruise rpm of 3k, you would suggest having timing all in by 3k. Then limit my vacuum advance to avoid too much timing?

 

[turbine68rt]

If my converter stall is near my highway cruise rpm of 3k, you would suggest having timing all in by 3k. Then limit my vacuum advance to avoid too much timing?

https://www.moparaction.com/2020/08/16/advance-to-go/

 

[moparedtn]

One of those el cheapo old handheld dwell/tach's might be just the ticket for you, sir.
That way you can play under the hood by yourself to your hearts' content.
Just a suggestion...

 

[dvw]

If I understand your question correctly you have spark knock at tip in at cruise? If so is this with the vacuum advance connected? What heads, compression ratio, cam, intake?
Doug

 

[diesel_lv]

One of those el cheapo old handheld dwell/tach's might be just the ticket for you, sir.
That way you can play under the hood by yourself to your hearts' content.
Just a suggestion...

Yes, that would help. The hardest part is operating the throttle from the engine and watching the timing. Ma Mopar for some reason put timing pointer on other side of engine. So unless you have some crazy long arms, it's not possible to increase rpm and watch timing at the same time by yourself. And I'm a bit of an asshole n opinionated so I don't have any "friend/associates" that I can enlist to help w operating the throttle for me. Hence wanting an idea of what I'm looking for before I recruit a friend from 150 miles away to lend a hand.

 

[diesel_lv]

If I understand your question correctly you have spark knock at tip in at cruise? If so is this with the vacuum advance connected? What heads, compression ratio, cam, intake?
Doug

Not quite tip in, but close n usually when ambient temps are hotter or engine temps are up. 440 source heads ported n valves done by Muscle Motors in Michigan, 10.5:1 compression, Comp hydraulic roller Extreme Energy .230 intake .236 exhaust at .050 lift, .544 intake and .537 exhaust lift 110° separation with 106° centerline, Edelbrock Performer RPM intake. This is truly a daily driver, will "Never" be raced.

 

[dvw]

Step 1; Assuming the vacuum advance is connected. Disconnect it and test. Fixed? Then either reduce the amount of vacuum advance or possibly speed up the rate it retards. Step 2: Assuming the vacuum advance is disconnected and you still have the issue. I'd note the rpm at cruise that this issue occurs. I'm betting somewhere around 2500? Then set the idle speed to that rpm and read the amount of advance. then 2 schools of thought. reduce total advance a few degrees. Or slow the curve beyond the problem rpm. Another possibility is the injection is going lean on tip in. Does the knock go away under acell or persist?
Doug

 

[HEMI-ITIS]

Since your by yourself,take out a few degrees of timing and drive, continue until there is no knock. Also verify no knock under accel with load.

 

[diesel_lv]

Step 1; Assuming the vacuum advance is connected. Disconnect it and test. Fixed? Then either reduce the amount of vacuum advance or possibly speed up the rate it retards. Step 2: Assuming the vacuum advance is disconnected and you still have the issue. I'd note the rpm at cruise that this issue occurs. I'm betting somewhere around 2500? Then set the idle speed to that rpm and read the amount of advance. then 2 schools of thought. reduce total advance a few degrees. Or slow the curve beyond the problem rpm. Another possibility is the injection is going lean on tip in. Does the knock go away under acell or persist?
Doug

I'll give the suggestions a try next week, working on my Ram Cummins. Replacing all the a/c vent doors. All 5 were broken. Cheap plastic. 2nd time I'm replacing them, 1st time I had it done n it was 1,300 and they replaced w stock plastic. This time I'm doing it n using metal doors that cannot break.
Not sure if it persists, as soon as I hear it, I let off the throttle. I've broken ring landings on high performance Harley engines before, so I'm a bit gun shy.

 

[Don Frelier]

My 77 360 used to ping on a grade. I always found it better to give it more throttle.
Have you tried it with the vacuum advance unplugged?
You can also adjust the spring tension inside the canister.

 

[1967coronet]

get or barrow one of these pumps, grab some distributor springs and a 3/32 Allen wrench for the can nipple. With the distributor cap and rotor off you can watch the weights and the vacuum.
I think your going to need a little more spring than you have now. If I recall the can adjuster will let you you pull in or out vacuum point a couple degrees each rotation of the adjuster.
I do not remember what direction to turn to go up/ down , just have to mess with it.
Like posted, try pulling a grade with the can unhooked and the hose plugged.