Total Timing Question

[Larry B.]

My car is a '61 283/315. I installed a set of gold (heaviest) advance springs from the Mr Gasket 928G kit. Stock spring were worn out. Initial timing is 18* stock. With the timing light set at 36, I am all in by 2150 RPMS. The normal range is 2500-3000. Would I need to add a heavier weight to get the timing all in at 2500-3000? Retard timing? Or should I live with being all in at 2150? Thanks

[Gene M.]

Re: Total Timing Question

Heavier weight will cut in even sooner, should run good with the set up you now have. If it does not pre ignite you should be ok. The 18 degree initial may be a bit rough on the starter when engine is hot.

[Larry B.]

Re: Total Timing Question

Thanks Gene. I thought a lighter weight spring would make it cut in even earlier. I have a lighter silver and an even lighter black spring. Should I try a lighter spring or leave it alone?

[Gene M.]

Re: Total Timing Question

Larry,
Do one change at a time and test it out. If necessary to speed up advance softer springs will do that. Again do only one spring at a time and test out. Two softer springs will most likely be too fast cut in.

[Larry B.]

Re: Total Timing Question

Ok Gene, I am totally confused! If I am getting all in too quickly now, wouldn't a lighter spring make it cut in quicker (make it worse)? If a lighter spring will make it cut in later than I can try swapping out one of heavier springs for the lighter.

[Gene M.]

Re: Total Timing Question

Larry.
A lighter spring will cut in sooner. OK that said try a heavy spring with a light spring to get something in between. Since two heavy springs cut in slower. Try one of each to get something like 2300 rpm. Do you see what I saying?

[Larry B.]

Re: Total Timing Question

Gotcha Gene

[Duke W.]

Re: Total Timing Question

The centrifugal advance starts at some RPM point and is all in at a higher RPM point. It doesn't just "cut in" like a light switch that's turned on.

The lighter the springs, the sooner (lower the RPM) centrifugal advance will start and achieve full value. Likewise the heavier the weights, the lower the RPM level that advance starts and full advance is achieved.

As a general rule, get full advance in as quickly as possible - down to about 2000 RPM - with detonation being the limiting condition. If yours is all in at 2150 without detonation, I wouldn't try to make it come in sooner.

Big port, small chamber 327 heads seem to work best with about 38 degrees total WOT timing - the sum of initial and full centrifugal. Small port, small chamber 283 heads might be best a little less advance due to the smaller chamber.

Since your '61 has 461 heads I would try at least 38 degrees and if it doesn't detonate take it up to over 40 in two degree increments. The more initial you run the less tendency it will have to overheat. The total idle timing should be in the range of 25-30, but you can't get there with a non-VAC distributor.

Getting the optimum spark advance map always involves some experimentation because no two engines or driving environments are identical. Also, a lot of "high compression" vintage engines have been rebuilt with low compression, so they will tolerate a very aggressive spark advance map on current day unleaded premium.

Most of the aftermarket weights are non-hardended steel, and, therefore, junk because the holes will wear. Use the OE weights.

Duke

[Timothy B.]

Re: Total Timing Question

Larry,

Are you saying with 18* inital and 18* centrifugal all in at 2150 rpm, you are concerned it's to fast. First, determine if you hear a ping at that rpm, if not leave it there. I like the idea of 18* inital on a non vacuum advance distributor, I bet your motor likes it also.

If there is ping leave the light spring and install one of the heavier springs to slow the curve then test again. You want the advance as fast as possible without ping for maximun torque and power at low rpms.

[Larry B.]

Re: Total Timing Question

The centrifugal advance starts at some RPM point and is all in at a higher RPM point. It doesn't just "cut in" like a light switch that's turned on.

The lighter the springs, the sooner (lower the RPM) centrifugal advance will start and achieve full value. Likewise the heavier the weights, the lower the RPM level that advance starts and full advance is achieved.

As a general rule, get full advance in as quickly as possible - down to about 2000 RPM - with detonation being the limiting condition. If yours is all in at 2150 without detonation, I wouldn't try to make it come in sooner.

Big port, small chamber 327 heads seem to work best with about 38 degrees total WOT timing - the sum of initial and full centrifugal. Small port, small chamber 283 heads might be best a little less advance due to the smaller chamber.

Since your '61 has 461 heads I would try at least 38 degrees and if it doesn't detonate take it up to over 40 in two degree increments. The more initial you run the less tendency it will have to overheat. The total idle timing should be in the range of 25-30, but you can't get there with a non-VAC distributor.

Getting the optimum spark advance map always involves some experimentation because no two engines or driving environments are identical. Also, a lot of "high compression" vintage engines have been rebuilt with low compression, so they will tolerate a very aggressive spark advance map on current day unleaded premium.

Most of the aftermarket weights are non-hardended steel, and, therefore, junk because the holes will wear. Use the OE weights.

Duke

How do I get to 38* total timing (a little confused on how to get this measurement)? Do I set the timing light for 38* and rev the engine until the timing mark aligns with "O"?

[Michael W.]

Re: Total Timing Question

If the strongest (heaviest) springs have the advance all in by 2150 RPM- what possible use would the weaker springs be? Possibly the gold springs are the weakest.

[Duke W.]

Re: Total Timing Question

How do I get to 38* total timing (a little confused on how to get this measurement)? Do I set the timing light for 38* and rev the engine until the timing mark aligns with "O"?

The first thing you should do is VERIFY the start point and end point of the centrifugal advance. If the end point is 2150, the start point will probably start below idle speed, which is okay.

You should rev the engine to at least 6000 to verify that the timing does not advance beyond the point where you THINK it is full advanced. A deteriorated limit bushing or other internal distributor problem can cause additional advance at very high revs.

Once you have verified and documented the centrifugal curve, set the dial on the light to 38, bring the engine to a few hundred revs above the point where centrifugal advance is all in, then ROTATE the distributor until the timing mark on the balancer is at zero on the tab.

Once this is done and double checked with the distributor tightened down, drop the revs below the point where the centrifugal starts to determine initial timing. As stated, initial in excess of 18-20 degrees could cause starting problems.

It would help if you tell us how much total centrifugal your distributor has - both the specs in the service manual and AMA specs and what you actually MEASURE.

It's easy to trade a little initial for centrifugal by filing the slot in the distributor cam assembly to add a few more degrees. About 24 degrees centrifugal on a SHP/FI small block is ideal, and 12-16 initial will yield total WOT advance in the range of 36-40 degrees.

Duke