I've read, as a lot of every youses several ways of getting to the same end.

Setting timing by a book value or suggestion

setting total timing at the mechanicals rpm value. This one has me quite confused since there isn't any reason to do this.
Please explain the need to do this and not the next.

setting total timing but at idle, you can do math.

Setting timing not by a value but by what the engine can take.

I do the last. I do have a dial back light but its just gravy. The reason I set timing this way is I can adjust static until detonation and back off just a bit. My best test instrument is my ***. My ears are the fine tuning instrument. Timing light is just for repeatable changes. Information gathering.

I have BB and don't think the spoken number applies to me anyway.
I've only done a book listed value and dropped that method to road testing. Never knew of setting timing based on mechanical timing and just don't understand its value as a method of ignition timing.

So please What method do you use? Why do you use it? Have you tried any of the others?

If theres one not mentioned add that.

 

leave the distributer a little loose and keep cranking it clockwise until you get some pinging under acceleration then back off a tad.

i don't need no stinking timing light.

 

I think you know my way, 36 in at 2800 rpm with a 20 degree range.

 

You need to read Lars tuning paper on timing at www.corvettefaq.com .

Most small blocks like 36 degrees of advance under load and can tolerate up to 52 degrees under cruise. So, we set a centrifugal curve that comes in faster (say all in by 2800 rpm) and set it for a total centrifugal advance of 36 degrees. Then we add a vacuum can that adds an additional 16 degrees for a total of 52.

Now, most stock smog dist have a lazy curve that tops out at about 24 degrees with an additional 20 from the vacuum can. Good for emissions, not performance. Now, we can adjust the centrifugal easily but the 20 degrees of vacuum advance would give us detonation since we would know be up at 56 degrees (36+20).

Now every engine is a little different. Some like 38, some like 32 or 34. But 36 is a good basic number from which to deviate.

And, I don't car what my advance is at idle, since I don't drive at idle.

My $0.02.

 

Hey, where were you earlier week?

There was a five page thread on this same subject a couple of days ago. Lots of good information was shared. Check it out.

 

Same method I use now but to advance I turn my distributor counterclockwise. I seem to recall something in a Haynes manual with both directions shown. I think the pre HEI was shown with the rotor turning the other direction. Not sure though.

 

It's entirely possible for power to fall off long before audible pinging/detonation is heard.

Every cylinder head,piston,cam combo (as well as many other engine combo differences) have a place they 'like".

My 427 liked 40* total with ported Merlin iron oval ports. With GM closed chamber heads 38* was it. Open chamber regular heads liked 39*. All this was worked out at track looking at time slips and MPH numbers.

My 540 was pretty sensitive when Brodix heads were stock. It picked up 17 hp going from 36* to 38*. It picked up another 5 at 40*. At 42* it dropped 10 hp, yet no audible noise was heard.

After chambers were modified, it was a lot less sensitive and now stays flat between 38*-41* on the dyno.

My buddies 351 Ford with TFS heads picked up over 20 hp moving from 34* to 36*!! Then stayed there until we got past 39*.

I can go on and on, but there is significant power to be had by optimizing cylinder pressure with piston in proper position on down stroke. Even though it's not detonating, it's very possible that peak cylinder presssure is not occurring where it needs to be. With all the variables of how a given cylinder reacts you can only tell with measured testing. It's really hard to feel 5-10 hp..it has to be up near 20+ before most butts can really feel a difference, especially on higher hp stuff. For sure it's more noticeable on lower HP combo's.

All that said, I work on what the engine/combo likes for peak power and then recurve dist for street manners. I like LOTS of initial..really helps driveabilty, especially with big cams etc. I'm talking about 22-30* at idle without vacuum advance.



JIM

 

I spent a few years researching various buildups before building my 406 and most dyno tuned combinations I saw ran in the 34-36 degree range. This would be mechanical advance with the vacuum can disconnected. When I recurved my own distributer I re invented the wheel,keeping an open mind that not all combinations would work the best set this way. I experimented for a month with different springs,inital settings and even vacuum lockout.

Guess what. The best overall setup was 36 total mechanical and for me a 10 degree vacuum,for a total of 46 degrees with the can connected.

During the process I learned the mechanical curve and now I set the timing at idle to keep the peace with the neighbors.

 

Sunnen Distribuscope, and someone who knows how to use it!!!!!! and of course, your time.....