Engine timing, high milage 327/300?

[Dwight P.]

Had a discussion with an experienced mechanic regarding the timing on my 1965 327/300. He said the the original factory setting applied to new engines that were using high octane/high lead fuel. My car is a high milage (over 100K miles). He also said that there were three different timing settings....fixed timing, centrifigal timing, and vacuume advanced timing and that all three had to be considered to accomodate the high milage and low octane/low lead.

Is this guy blowing smoke? What is the correct timing for my car?

Thanks,

DP

[Mike M.]

Re: Engine timing, high milage 327/300?

he is correct in that three factors (fixed, vac and centrif) will impact the TOTAL Timing #. set it at factory timing specs and you'll do fine. mike

[Mike McKown]

He's not really blowing smoke he just talked

and didn't really say anything definitive. If he wants to alter something that's stated in the GM manual and says it's a necessity and wants to charge MONEY, then I'd say he's blowing smoke.

Many people have known for years that you can alter the stock timing curve and values and pick up some efficiencies and power. That was true and was frequently done when your car was new but it's not necessary for it to run well even today.

[Joe C.]

Re: Engine timing, high milage 327/300?

Dwight

Correctamundo! Do you have an issue with your engine? Specifically, does it detonate. Medium performance vintage smallblocks are more sensitive to spark advance than SHP smallblocks (oddly enough, it would seem), because, in addition to the factors the good mechanic pointed out, the low-med perf engines develop higher dynamic compression than the hi horse SHP engines. This is due to high valve overlap in the SHP motors' killing the dynamic compression.
So, unless your engine has significant carbon buildup in the chambers/piston tops, then it will probably run fine with modern 92 octane gasoline, @ factory timing recommended settings. With a 100,000 mile engine, if you have detonation issues, then there is a potential "hot spot" problem. There might also be issues with the heat riser, lean mixtures, or possibly, even blocked coolant passages.

Joe

[Duke W.]

Re: Engine timing, high milage 327/300?

Altering the spark advance map by either changing initial timing or modifying the centrifugal or vacuum advance curves is only necessary if the engine detonates and the detonation cannot be eliminated by adjusting the initial timing to the lower end of the recommended range. All the timing map information is in the CSM and AMA specs.

The nominal OEM recommended timing for your engine is 8 deg. with a range of 6-12. If there is no significant detonation, no alteration is required, but it may have to be set at the low end, and you can go as low as 4 deg. if necessary to ward of detonation.

So the question is: Does it detonate at the current initial timing setting, and at what value is it set? Are the centrifugal and vacuum advance curves still in compliance with OE specs?

If it works it doesn't need to be "fixed".

Most SBs of all HP ratings will operate on today's unleaded premium with no more than adjusting the initial timing to the low end of the range, and some will operate detonation free at the mid to high end of the initial timing range.

Duke