I take the springs off, start the car to see what total timing I have. After that I put the springs back on and make rate changes form there.

 

Dear God you gotta be kiddin lol, first time Ive heard this too. I'll look into this, thanks.

 

You need to know initial timing, mechanical timing, total timing, and cruise timing.

Disconnect the VA and check the timing at an idle of about 600-700 RPM. Let's say it's 14*. That's your initial timing.

Rev the engine until the timing stops advancing, say 34*. That's your total timing.

Note at what RPM the total timing first occurs. I like mine to come all-in at 3,000 RPM, other cars need it earlier. A factory distributor will probably have stiff springs that bring it all-in much later, at 3500-4000 RPM. This can be tuned by changing the springs.

Subtract your initial timing of 14* from your total timing of 34*. 34*-14* = 20*. That's the mechanical timing provided by the distributor. Some distributors provide more, some less.

Knowing the mechanical timing in the distributor, if you want to experiment with your total timing, you don't have to rev it high each time. Just set it at idle and your total timing will be whatever the initial is plus the mechanical provided by the distributor. If the initial timing at idle is 10*, your total timing will be 30*. If the initial is 15*, the total will be 35*, etc.

Connect the vacuum advance and check the timing at idle, say 36*. Subtracting your initial timing of 14*, your vacuum can provides 22*. To calculate cruise timing (highway speeds), add that 22* to your total timing of 34* and you get 56* -- way too much. Cruise timing should be 44-52*. A vacuum can that brings it over 52* either needs a limiter plate (easily fabricated) or to be replaced with an adjustable vacuum can. Not all cans advertised as adjustable vary the amount of timing, some vary only the rate at which it comes in. Some adjust both the rate and amount. The adjustable vacuum cans I've used have had the diaphragm inside break fairly soon. That gets expensive. You can fab a limiter from sheet metal or aluminum for next to nothing and set it and forget it.

Once you're done, bring the curb idle to your driving comfort, say 700-800 RPM. Some engines need 1000. I like it so that when in drive and letting off the brakes, the car begins to creep forward.

 

say great ideas ,so write a small book on this! It will sell many need more than just basics and i have seen a few stab at this but never bring it home ! LOL

 

This is what I use to limit the VA to 10 degrees.

 

This is what I use to limit the VA to 10 degrees.

View attachment 831506

That looks slick.

Curios, why do you shorten the distance the arm travels by preloading it, instead of letting the arm rest and then limiting the amount it travels downward? The variation would look like this:

What is the advantage of preloading it?

 

That's not my design and it works just fine like it is. I use to get these from Lars.

 

I'm sure it works fine. It preloads the arm just like the Crane plate does:

However, many have repositioned the Crane plate to the center of the VA body by removing the VA, drilling a new hole, tapping it, reinstalling the VA, and installing the Crane plate. That eliminates the preload on the arm.

That's a relatively considerable mod for something that could be left as it is. There are many variations that eliminate the preload and there must be reasons for either approach.

I assumed you fabricated yours and was wondering about the logic behind it.

 

there's a sticky 'ignition 101' that you may find helpful.

Once the initial timing is set (distributor rotated to proper location) do not change that. Centrifugal/mechanical timing can not be 'adjusted'; it can be changed with different combo's of springs and weights.

Pete

 

And this rotation of the distributor is set at idle or rev the engine?

 

Set timing at 30* at 28-3000 rpm and what ever the idle is is good , that will be your idle timing.
If it starts and runs good you are good to go.
In hot weather you might have to turn it down 2* or so to keep it running where you want the temp at.

 

Copy.

 

My LAST timing adjustment is always with VA disconnected, and revving the engine until timing stops advancing. I lock it down at whatever I want - generally 34* with modern SBC heads that have vortec style chambers. If that leaves me with initial timing that's not optimal, I'll play with weights, springs, and advance limiting bushings, but the total timing is always where I go for the final adjustment and lock down. I also limit vacuum advance with the Crane limiter depicted above.

 

Also, I don't trust dial-back timing lights. I use fully degreed balancers on all my builds.

 

Well my dial label fell off, its a blind shoot! I calibrated it with my buds MacTools one and scribed a line.

65nWV -i went to setting total timing @ full mechanical advance ( +18 degrees @ 2900 for me) to where i want it ( 35 for this engine), and then just see where the idle timing lands at. This with a recurved and mechanically limited fully prepped distributor. ( as described above) Then i can always just check at idle, like most folks do. ( 17)

IF i ran vacuum advance ( and i don't anymore yet did limited to only 4 degrees), once i set my total @ full mechanical, i'd plug it back in, again to see now where initial + vacuum was. ( 17+4 = 21 in my case) That would now be my base idle timing for a quick check.

 

Copy. Thats what i wondered, dont worry about idle timing, just check it for fun maybe.

 

I would also add that after revving the engine hard to make sure you "see" or get all the advance that the distrib has, rev it HARDER to make sure. You aren't going to hurt anything. Unfortunately "rev hard" to alot of folks is 3000. You gotta hit that thing!

 

Absolutely. Especially since many HEI distributors have hidden timing in them at higher RPM, as noted by Schurkey and Rocky Rotella. In the video below, the tech tests a new Accel HEI. The timing stops advancing at 22* at about 2700 RPM but at 5500 RPM it goes up to 28* and at 7000 PRM it maxes at 30*. With an initial timing of 16*, that distributor would provide a total timing of up to 46* -- without vacuum advance and at full load. Way too much.

That's probably why MSD distributors have those variable stop bushings and why many will weld up the slot to limit the advance as the tech did in the video or tap threads into one of the existing holes and insert a stop screw. I did a quick-and-easy fix as suggested by Schurkey of flipping the centerplate upside down. That causes the weights to rest on the dog-leg portion of the centerplate and eliminates any high-RPM timing advance. It reduced the mechanical timing in my HEI from 24* to about 19*. The cons to that are there is only one adjustment of about -5*, which for me was perfect, and that the weights won't nestle as tightly at idle rpm and if you're using light springs the weights could "chatter" and causing timing wander.

 

For sure. You only "stretch" rods when u rev it up quickly w/o load, so when you just bring it up slowly to check total, you creep up on it.

PS Some oem curves stop at like 4000.

 

I did not know this 👍

 

You need to rev the engine until the timing stops advancing when checking total timing. What rpm that is depends on the advance springs. Many as delivered curves take 4500 rpm to reach full advance.

Once you see the value you want, lock the dist down. Then check what rpm it reaches full advance, and change springs as needed to bring that value to what you want. For any performance build, 2800-3000 rpm is going to work. Having it come in sooner, as long as you don't have detonation, will increase power at the lower rpm. You don't have full power at wot until you reach full advance (deto free).

Then hook up the vacuum advance, I start on ported vacuum, and rev the engine to the rpm you know the centrifugal is all in. Hold it steady, and see what the advance reads. Subtract what you know the full advance was before you hooked up the vacuum advance, from what you now see. That's the total which is being added. Then decide of you need to limit that amount. I use msd plate 84281. It fits in all hei (sometimes I need to add additional spacers to have the limiter contact the advance rod properly), and it fits in small billet MSD style if you cut off 3 of the 4 arms, and use spacers to set the limiter height. Yes then the total amount is no longer adjustable, but using position D, that is going to give you 10 degrees.
At the same time, use a vacuum pump to measure when the advance cannister starts to move, and when the rod hits the stop. Then based on that, you will know if you can use it on full manifold vacuum or ported, by comparing it to the engine vacuum at idle and in gear. If the cannister doesn't stay pulled in all the way at idle in gear, you will have excessive rpm drop park to in gear. And in a manual trans vehicle, if the vacuum is borderline, you will need more rpm and throttle when letting the clutch out and starting off. So you would have to decide if you are ok with that.
I also decide if manifold or ported connection based on what the idle timing is, and what the engine combo may want. Or if you want to maximize engine cooling at idle. More timing at idle always lowers engine temps, and exhaust temps. A vehicle that burns plug wires, often stops when using more idle timing as the header primary tubes temps drop.

 

Excellent, I second pockets, that’s what I do as well.

 

I have someone power brake it while I advance the distributor until the engine pings n back it off a hair n lock it down. Hasent failed me yet!!!

 

This is probably most accurate.

 

An old-school way is to advance the timing until it pings on acceleration, then back it off until it stops pinging. That method works for any altitude.

 

I'd still check the spark plugs. I had detonation but couldn't hear it over the big exhaust.

 

well, some great tips and tricks on this thread. on most stock to mild builds where most of us are, I use a HEI dizzy and just power tune it to whatever gas you want to run. if you want to run over 89 then it can have a pinch more timing. carb needs to be tuned as well. my truck is 350 tired, edelbrock 1406 with a progression ignition HEI dizzy, flies through DEQ even.

 

If I may throw a monkey wrench into the mix...

A lot of people throw around arbitrary numbers for initial and total timing, but it's imperative that the engine combination be taken into consideration when determining those numbers--i.e. not all engines want (or need) 14°-16° initial and 34°-36° total--some will require more or less.

A few examples: The 489 I built for my Suburban (but is currently in service in my dually) has a flat top piston and a 119 c.c. chamber 049 cylinder head. Compression is right at 8.5-1. When the engine was on the dyno, I experimented with total timing, and as it turns out, this engine only wanted 32° of total timing--and it actually made the same power with the total at 30°. Anything more than this cost power everywhere. Of course it did idle better with the higher initial, but more on that in a moment. Note that this engine made peak HP at only 4700 RPM (by design).

My 13-1 306" dyno mule has a large dome piston and angle milled 462 heads with a 58 c.c. chamber. When I had it on the dyno, we started at 32° and went up in 2° increments to see what it wanted for total. We stopped at 42°--not because that was where it made best power, but because that's where the plugs were telling us to stop. It was still picking up significant power each time we added timing. Initial isn't a factor on this engine as the distributor is locked out. This engine made peak HP at 7500 RPM but the valve springs weren't quite up to the task above that. It too will be re-dyno'ed soon and should make peak power at 8000 or slightly above.

My 572" engine that's destined for my dually has a reverse dome piston and (at the time) a 119 c.c. chamber, compression was about 8.6-1. I built it that way intentionally as I wanted it to be able to run on even the worse pump fuel, and it will see a lot of low rpm heavy load which as we all know is where detonation is most likely to occur. My dyno guy set initial timing to 34°, and after a number of pulls he wanted to bump it to 36°. I agreed, but told him "don't be surprised if it loses power"--which is exactly what it did. I had him roll it back to 32° total and it picked up power everywhere--much to his surprise. 😁

Lastly, my 10.5-1 505" dyno mule has a small dome piston with 119 c.c. chamber 990 heads (radically reworked). We started at 32° and wound up stopping at 40°--it may want even more, I'll find out (hopefully) soon when I re-dyno it. We found a ring issue and had to abort the first round of testing.

As far as initial timing, more often makes a dramatic improvement in idle quality and vacuum, but this also makes the engine more sensitive to lower rpm detonation. There are a number of ways to address that problem, but the point is "more is better" doesn't always apply here. (I learned this lesson the hard way on a 406 small block that broke a ring land due to detonation--that could NOT be heard audibly)

Lastly--re: locked out distributors--I've seen instances where a locked out distributor slowed a car down a full .4 in the 60'--yes, you read that right. This was many years ago on a "pure stock" race car with an L72 427, a "stock" (<3000 rpm stall) converter, 400 Turbo and a 4.56 gear. It didn't slow down due to wheel spin, it slowed down because all that low rpm timing absolutely slaughtered low end power at WOT. Unlocking the distributor brought the car's 60' times right back where they were previously.

I have other examples I could share, but lest I ramble....

The take-aways here are: more isn't always better, the old "advance it `till it pings and back it off 2° is bunk, and the dyno is your friend--if you know what to look for.

 

If I may throw a monkey wrench into the mix...

A few examples: The 489 I built for my Suburban (but is currently in service in my dually) has a flat top piston and a 119 c.c. chamber 049 cylinder head. Compression is right at 8.5-1. When the engine was on the dyno, I experimented with total timing, and as it turns out, this engine only wanted 32° of total timing--and it actually made the same power with the total at 30°. Anything more than this cost power everywhere. Of course it did idle better with the higher initial, but more on that in a moment. Note that this engine made peak HP at only 4700 RPM (by design).

Absolutely. I spent a great deal of time playing with the timing of my 1984 GMC 454 with peanut port heads. It's been rebuilt to stock except with an Isky 270 cam, high-rise intake, and headers, keeping the compression to about 8:1. It is a low RPM, high-torque build. I've read several reports that these low-compression engines like a lot of timing. I tried that out, starting with 30* total. I don't have the objective data that a dyno provides, but the Seat-O-Meter determined that going above 32* noticeably decreased acceleration. The engine sounded a little meaner with each 2* bump, but it seemed to get in its own way, as though driving uphill into a headwind. Bringing the timing back allowed the engine to flow better, and required less pedal pressure throughout the RPM range. Even though this interpretation is entirely subjective, I feel it's accurate as my expectations were biased by the reports of others and the results were the exact opposite.

I do have the objective data of the spark plugs -- the burn mark on the ground strap is just before the bend on some spark plugs, and just after on others. Pretty much optimum. My present curve is 13* initial, 31* total, and 46* cruise.

Even though I came to this conclusion several years ago, and just spent a good deal of time of re-trial-and-error, I still have the stupid urge to squeeze more out of this engine (even though it runs great) and chase "the numbers" of higher total timings as reported by others with different engines. "If I can just get a few degrees more, I'll get even more performance..." Nope. The subjective says otherwise, and I have to use the objective results of the spark plugs to convince my foolish, gung-ho self that the engine is happiest where it is.