63 L84 timing question

[Jerry G.]

Re: 63 L84 timing question

I didn't "forget" anything. I've seen recent dyno test data where a 10.5:1 327 made best power with 45 degrees, but that was with high octane leaded race gas. There's nothing magic about 38, and most vintage high compression engine total WOT timing is limited by detonation on pump gas.

You forgot about the timing tab error that I mentioned; 18 on the tab is 15-16 at the crank, which is 39-40 total with a 24 degee distributor.

Typical engine power drop is about one percent if the timing is 3 degrees from optimum. That's within the range of dyno test accuracy/repeatability, so you can't nail down a specific number - just a range.

Duke

I second what Duke says. i just ran a series of tests on an engine dyno( real not simulation0 with my 327 motor. It's for vintage racinge but it clearly liked 42 degrees total advance.

[Michael H.]

Re: 63 L84 timing question

I can't say anything specific about Elgin cams. In those cases where it was suspected that the drive gear on the camshaft was not indexed per OE spec, which through out the distributor clocking, the actual source of the camshaft could not be positively identified.

Duke

About three years ago, right here on this board, we discussed this exact problem with 63 FI distributors. I mentioned that I've seen several FI distributors over the years that required the gear index to be 180* from the commonly accepted clocking. I don't think anyone was "buyin my story" though.

[Duke W.]

Re: 63 L84 timing question

I second what Duke says. i just ran a series of tests on an engine dyno( real not simulation0 with my 327 motor. It's for vintage racinge but it clearly liked 42 degrees total advance.

There's a rule of thumb for SBs (I think it's attributable to Smokey Yunick.) that once optimum spark advance is determined for best peak torque, best power above peak torque speed is achieived by increasing advance one degree for every thousand additional revs. The reason is that beyond the torque peak VE falls off so mixture density is slightly less and likes a little more advance. Also, combustion chamber shape and volume have an influence, so piston crown design (flat, dome, dish) and variations in head chamber geometry over the years also have a slight influence.

Since it's tough to get a mechanical advance distributor to achieve the extra degree per thousand revs as above, you end up having to compromise, which is another reason why "best power advance" can only be described as a range rather than an absolute single number, but careful testing can usually get it to within a couple of degrees.

If you don't have the knowledge, facilities, or patience to do thorough testing, then 36-38 degrees will usually get you in the ballpark.

So, Jerry, what did that "stock" vintage racing engine do on the dyno?

Duke

[Michael G.]

Re: 63 L84 timing question

I finally got around to reworking the distributor. I turned the gear 180 degrees from the usual position and put it back in the engine. The car started right away and I had no trouble adjusting the timing to 18 degrees advanced. The vacuum can is actually about half way between the coil and plenum now. Car runs very well at that timing, (I'm using 100 low-lead av fuel, so detonation is not a problem).

Thanks for all your help guys. Mike

[Michael H.]

Re: 63 L84 timing question

I finally got around to reworking the distributor. I turned the gear 180 degrees from the usual position and put it back in the engine. The car started right away and I had no trouble adjusting the timing to 18 degrees advanced. The vacuum can is actually about half way between the coil and plenum now. Car runs very well at that timing, (I'm using 100 low-lead av fuel, so detonation is not a problem).

Thanks for all your help guys. Mike

I kinda knew you were going to find that installing the gear 180* from a conventional index would fix your problem. Glad it solved the problem.

As I mentioned earlier, I posted this here on this board three or four years ago about some 63-65 FI distributors but it didn't conform to what the rest of the world thought so it was ignored.