I'm lost on the whole 'total movement of timing'. I set my truck to 10degrees btdc advanced ever since I built my motor. How do I know what the total should be? How do I check? Does finding the total have anything to do with the little dial on my timing light? Thanks!

 

I can't help you use the dial on your timing light...

Your total timing is your initial plus your advance. Now your advance can be part mechanical and part vacuum or both (typical FE dizzy). The total will be about 35ish BTDC. That means your plug fires at 35 degrees (crank rotation I assume) before the piston reaches top dead center. higher RPMS generally like more advance, but you don't want the same advance at lower revs...


So, to check your advanced timing: have a buddy rev the motor while you watch the timing. A tach is a big help here.

A typical FE, has full advance by 2500-3000rpm. So, you may start at 10 BTDC and be at 35ish BTDC at 2500+rpm....

not sure if I made any sense. I'm running on beer and brake cleaner fumes...

 

Hey if that's a dial-back timing light, rev the engine (with the vacuum disconnected) until you don't see the timing advancing anymore, that's the rpm of your total timing. While holding that rpm (or a little higher), turn the dial back until the damper reads 10 BTDC again. Now read the number on the dial, assuming it's marked in degrees. That's the number of degrees your centrifical advance is putting out. Add that number to 10 and that's your total advance (vacuum advance is not figured into the total).

 

centrifugal

 

i wanted to know what the timing was set at on my 352(i had timed it by ear after rebuilding it), so i took it down to the engine shop in town. he said i was at 17 deg before base timing, 33 deg before base+mechanical advance and 50 deg before base+mech+vacuum advance. seemed high to me but he told me that this should be about right for a street driven motor and not to worry about. just throwing this out as an idea of what you should see i guess. total mechanical advance hit at around 2500 rpm's and vacuum maxxed out close to that.

 

Gtex, BB, I'm close to understanding but not quite. WillyB, sent me an article which made me understand a lot but I'm still lost on how to do it.

My timing light has a dial (advance degrees) on the back of it that reads in degrees and goes up to 60.

I do have a tach in my truck.

Ok, so I know my truck is already set at 10btdc. Now what, as far as trying to figure my 'total'?

What do I want my total to be with my mild built motor? Also, what about my 6000ft altitude and 85octane pump gas?

1. hook up timing light
2. disconnect vaccum hose from dizzy (do I plug the pod or just leave it open?)
3. then rev motor until I can't see the 10btdc anymore
4. turn the dial on the light up until I see 10btdc again (while motor is revved).
5. then add, the say 20deg + 10initial= 30 total?

 

Thinking about it, you might have to really rev the sheet out of a stock dizzy to get it to max out, like around 4K.

Anyway, do you understand how the timing light works? The dial is a variable delay for the strobe and is calibrated in degrees. Try it out while the engine is idling, look at your initial timing of 10 degrees BTDC with the strobe on the damper and then slowly turn the **** until the strobe now shows 0 degrees or TDC. The dial should be pointing to 10 degrees or real close.

Now do the same thing at 4K (if you dare) but turn the **** until you see 10 degrees BTDC with the strobe, not 0. The reason is 10 degrees BTDC is your starting point of the advance curve, the initial advance is always there. The reading on the dial is all centrifugal only.

As an example, lets say the dial reads 26 degrees. That is the amount of centrifugal advance it's getting. Add 10 degrees to that number (remember your 10 degrees of initial advance is always there) and you get 36 degrees total advance (not counting any vacuum advance).

When you disconnect the vacuum advance, just plug the hose and leave the canister alone. Vacuum advance is different, it's load dependant and all over the map. Best way to check it is with a distributor machine.

Hope this helps.

PS. Anybody know where I can get bearings for a Sun distributor machine? One of mine is howling.

 

BB, you know anything about these questions?:
WOW, 4000 free revving is really far, and LOUD with my pipes, lol. Is that really nessessary?

"Anyway, do you understand how the timing light works? The dial is a variable delay for the strobe and is calibrated in degrees. Try it out while the engine is idling, look at your initial timing of 10 degrees BTDC with the strobe on the damper and then slowly turn the **** until the strobe now shows 0 degrees or TDC. The dial should be pointing to 10 degrees or real close."

I do understand that. So I'm gaining. Now what?

 

Well, higher altitudes allow the use of lower octane fuels so I think it's a wash on that. Only thing is you pay the same for it, what a rip-off.

On the curve, I don't remember what your engine/tranny/rearend setup is but a good ballpark setting would be 10-12 degrees initial with 36 degrees total all in by 3K.

There's another way to tell what the dizzy advance is but you have to remove the breaker plate in order to see inside what advance slot is being used, it is labeled in distributor degrees. That number (converted to engine degrees) plus your initial with give you the total but you still won't know at what rpm it's all in.

 

I think we have to rethink this whole advance thing. The centrifical advance works
according to engine speed and vacuum advance accoring to engine load. In effect we have two advance systems and the total advance is not added they over lap. In other words if the vacuum advance at max vacuum is 28 degs. and the mechanical 28 degs
with base timing at 10 degs max engine advance would be 38 degs.

 

[QUOTE=BB]Well, higher altitudes allow the use of lower octane fuels so I think it's a wash on that. Only thing is you pay the same for it, what a rip-off. On the curve, I don't remember what your engine/tranny/rearend setup is but a good ballpark setting would be 10-12 degrees initial with 36 degrees total all in by 3K.QUOTE]

BB, 390, mild cam, 4bbl, 670cfm Holley, headers, duels, 3.54LS d60, 4-speed. At this altitude should I go with more initial advance? Maybe 12? What should my total be? Then we can go from there.

 

Yeah go with 12 and see how it runs, maybe even 14. With a stick I've noticed that you don't need as much initial and the curve does not have to be as fast as with an automatic but these FE's like a lot of timing though. It's all trial and error but be sure to listen for ping or detonation. I'd still keep the total at 38 or less degrees.

Hey you know I just thought of something. You (and I) were worried about free reving that over 4K. Here's the deal, if you see that the centrifugal advance is still advancing above 3K, stop there, you've proven that your curve is already too slow and there's no need to go any higher.

 

Ok, so lets go through this again:

1. hook up timing light
2. check to see if my initial timing is at 10 or change it to 12 (but listen for pinging,
if so go back.
3.rev the motor to 3g's then turn the dial on the timing light until it reads 10 or 12 (depending on what I set it) and read the number of degrees the dial takes to get to initial. Then ad that to my initial and thats my number. And it should be close to 38? Correct?
4. Then, when I screw up I'll be back here emailing you again, telling you what I did wrong, right? LOL

 

Sounds like a plan but you won't hear pinging while it's idling, only when you test drive it.

I can bet money that after adding what you found at 3K and the initial together you won't have 38 total.

Good luck!

 

BB, ok. Here's what I did:

I warmed up the motor by driving around. Disconnected vac advance and plugged the hose. Checked my initial timing, I'm about 9-10 initial. I revved the motor to about 3,000rpm and moved the dial until I went to to back TDC. That number was 30 on the dial. So, 30+10=40. Good or no good?