Distributor curve

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Washington Twp. Mi
My Car
1972 Mach 1 Q Code
Hey guys, there has been some talk & I've read quite a few threads about timing & having the correct distributor curve for your application. I'm trying to figure out if my dist. is set up correct.

I have a 72 Q code with a/c. It has been rebuilt .030 over with a larger than stock hydraulic cam, stock 4v heads w/steel rockers, nothing wild, just a mild rebuild. I have a Performer intake on right now with a Holley 770 Street Avenger carb. It also has a c6 auto trans w/3.25 gears.

I will be switching the Performer intake for a Blue Thunder, but I really want to make sure my distributor is set up right. It's a stock unit w/the Petronix added to it. It's actually running pretty good, but I know there is more to this timing that I want to learn.

I the pic I have below, it's set up using the 10L slot, which is 20* of mechanical advance, & I set my initial at 15* BTDC. That gives me a total of 35* (w/distributor hose plugged off), am I in the right ballpark for my application?

I'm not sure about the springs, looks like one is different than the other. I don't know if the PO installed the lighter spring. Any help would sure be very informative. I've never really got this far into the timing.003.JPG

 
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The distributor will have a light spring and a heavy spring from the factory to bring in the curve in stages. You definitely have the right idea going with the 10L slot and the 16* base timing for a total of 36* as you mentioned. Now you could bring in the timing a bit faster by bending in on the tabs a LITTLE bit but don't get carried away or the springs could fall off or you could have an inconsistent idle from the base timing jumping around from to little tension on the springs. You might try playing around with the mr. gasket 925d springs to see what your engine likes. I would shoot for "all in" on the timing around 2500 rpms.

 
Mike is correct, its a two-stage centrifugal advance. The lighter spring controls when the advance starts and the heavier spring controls when the advance is fully in. Here's the instructions for the Crane advance springs, to give you an idea of how the adjustments work:

http://www.cranecams.com/uploads/instructions/272e_%281%29.pdf

 
The distributor will have a light spring and a heavy spring from the factory to bring in the curve in stages. You definitely have the right idea going with the 10L slot and the 16* base timing for a total of 36* as you mentioned. Now you could bring in the timing a bit faster by bending in on the tabs a LITTLE bit but don't get carried away or the springs could fall off or you could have an inconsistent idle from the base timing jumping around from to little tension on the springs. You might try playing around with the mr. gasket 925d springs to see what your engine likes. I would shoot for "all in" on the timing around 2500 rpms.
Thank's Mike, I think I will try the 925d spring change & see how it goes.



Mike is correct, its a two-stage centrifugal advance. The lighter spring controls when the advance starts and the heavier spring controls when the advance is fully in. Here's the instructions for the Crane advance springs, to give you an idea of how the adjustments work:

http://www.cranecams.com/uploads/instructions/272e_%281%29.pdf
Thank You Don, the more I read the more I understand.

 
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Disconnect and plug the vacuum hoses to the dist if you have any.

Start your timing at 10 degrees BTDC.

With the engine idling, advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

If the rpm increases and it still runs smoothly, reset the idle speed then increase the timing 2 more degrees and check for the same things.

Retard the timing 6 degrees to it's previous level.

Reset the idle speed.

Increase the rpm to around 2000 and advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

If the rpm increases and it still runs smoothly, reset the engine speed to 2000 rpm then increase the timing 2 more degrees and check for the same things.

POST RESULTS

DISTRIBUTOR SPRINGS

Removing the hevy stock spring and installing a 925d spring is usually very close.

 
Disconnect and plug the vacuum hoses to the dist if you have any.

Start your timing at 10 degrees BTDC.

With the engine idling, advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

If the rpm increases and it still runs smoothly, reset the idle speed then increase the timing 2 more degrees and check for the same things.

Retard the timing 6 degrees to it's previous level.

Reset the idle speed.

Increase the rpm to around 2000 and advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

If the rpm increases and it still runs smoothly, reset the engine speed to 2000 rpm then increase the timing 2 more degrees and check for the same things.

POST RESULTS

DISTRIBUTOR SPRINGS

Removing the hevy stock spring and installing a 925d spring is usually very close.
Thank's barnett468, I need to get the springs, then I will post results.

 
you should do the test before you buy the springs in case you dont need them.

 
Sorry its taken awhile for me to update, but I had to get a new timing light. Got a good one this time, it's got a digital readout & has all the features. I still need to learn how to use the advance setting, never had one of these b-4. I also had to make a new distributor wrench.

So anyway, I did the first 2 tests & got to 16* BTDC. Ran pretty rough after that. Then I was checking to see when the mechanical advance was coming on, & it started at about 1600 rpm. That's way to early, right? Should be around 2000 rpm? I didn't do anything after that.

I think I know why the advance starts so soon. One of the springs was pretty loose, no tension on it at all like the other spring. The other one just has enough to keep it in place, where as the other one is sloppy. I think I need to bend the tab on the loose spring to tighten it up a bit. Am I correct on this?

 
The advance should start coming in around 1300 rpms so if anything it is coming in a bit late. I would drop the initial timing down a couple degrees and try a lighter advance spring and see if you can it to start coming in a little sooner. You want full advance between 2500 - 3000 rpms depending on your gear ratio and engine combo.

 
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Oh, ok that's probably why one spring is so loose. I won't be able to try again for another 4-5 days. I live in Michigan & our early spring went south. It's 35 degrees snowing today, & they are calling for 1-3 tonight. This sucks!

Looks like I may as well install my new Blue Thunder intake & dial in timing after this weather warms up. Thanks again Mike.

 
You need to determine the best initial timing which it sounds like you did but we need EXACRT specific details of the results to make any sense out of it so we can make suggestions from there.

Do not sacrifice a best initial timing setting to achieve best maximum timing setting . You want the best initial AND max timing setting for optimum performance.

The factory light spring is supposed to have light tension on it . The other spring is a much stronger spring and it is supposed to be loose.

Please do not bend the spring tabs.

After you do the entire test, we will know if you will benefit from the 925d spring kit . As I mentioned, replacing the heavy spring only is what usually gets the curve very close in my experience, however, every engine is different.

After determining the best springs to use, we may have you bend one of the spring tabs just a tiny bit but I rarely do this.

If you advance the timing 4 degrees and the rpm goes up by maybe 75 or more, you need that additional advance.

If you advance the timing 4 degrees and the engine rpm only goes up by maybe 25 rpm, your previous setting was better.

As you increase the timing, the rpm will go up less for every degree the timing is increased until it finally reaches a point where there is very little to no increase . At this point, the engine will often start to run slightly rough . If you advance the timing far enough, it may run very rough . The more compression it has, the rougher it will run as the timing is increased.

.

h .

.

 
I would just be cautious about going with to much initial timing, to much may leave you stranded when your starter drags and won't allow the car to start in the middle of summer from engine heat soak. Some real world settings would be 10-14 degrees of initial timing with total mechanical timing in the 36-38 degree range all in at 2500-3000 rpms. I have tuned alot of my own Fords being 302's, 351w's and 351c's so I am giving advice from my own personal experience. Try not to overthink it and keep it simple.

 
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jpaz, I have been doing this for a very long time and I live in an area that gets to 100 or more degrees every summer . I will make sure that you do not have too much initial OR total timing when you are done and it will not come in too early.

When an engine turns over more slowly than normal, it can be a weak starter, weak battery, high gas level in the carb, hot fuel in the carb, high engine temp etc or a combination of any of these.

If you have a Holley or Quick Fuel carb and the gas level in it is below the inspection holes or near the bottom of the clear sight windows immediately after you turn the engine off, the gas level will not cause a hard starting problem.

If your gas level is correct and it turns over more slowly when it is hot, you can try retarding the timing 3 degrees, if it still turns over slowly, your timing is not causing the problem.

 
Dude, chill. I see some of the sketchy advice you pass around and someone is going to end up screwing up their car because of it. Thank you for the negative reputation point Barnett, take care

 
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You need to determine the best initial timing which it sounds like you did but we need EXACRT specific details of the results to make any sense out of it so we can make suggestions from there.

Do not sacrifice a best initial timing setting to achieve best maximum timing setting . You want the best initial AND max timing setting for optimum performance.

The factory light spring is supposed to have light tension on it . The other spring is a much stronger spring and it is supposed to be loose.

Please do not bend the spring tabs.

After you do the entire test, we will know if you will benefit from the 925d spring kit . As I mentioned, replacing the heavy spring only is what usually gets the curve very close in my experience, however, every engine is different.

After determining the best springs to use, we may have you bend one of the spring tabs just a tiny bit but I rarely do this.

If you advance the timing 4 degrees and the rpm goes up by maybe 75 or more, you need that additional advance.

If you advance the timing 4 degrees and the engine rpm only goes up by maybe 25 rpm, your previous setting was better.

As you increase the timing, the rpm will go up less for every degree the timing is increased until it finally reaches a point where there is very little to no increase . At this point, the engine will often start to run slightly rough . If you advance the timing far enough, it may run very rough . The more compression it has, the rougher it will run as the timing is increased.

.

h .

.
Ok Barnett, sorry I didn't do the entire test like you said. It got late & cold, & I was messing w/my new timing light. I will do the test again like you said, after this cold snap we are having, its 34 out.

I didn't bend any tabs or do anything to the springs.

Another thing that was mentioned was hard or slow starting. I have never really had that issue or a hot start problem.

It does run quite rough on initial start up, for maybe 30 seconds or so then smooth's out. I do have a new Holley carb.

It did seem like any higher than 14* and there wasn't much response after that, but I will try to give you more exact details.

Hey Barnett, thank you so much for the help! I'm learning slowly but surely.

 
Disconnect and plug the vacuum hoses to the dist if you have any.

Start your timing at 10 degrees BTDC.

With the engine idling, advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

If the rpm increases and it still runs smoothly, reset the idle speed then increase the timing 2 more degrees and check for the same things.

Retard the timing 6 degrees to it's previous level.

Reset the idle speed.

Increase the rpm to around 2000 and advance the timing 4 degrees . Listen for an increase in rpm and irregular/rough running.

If the rpm increases and it still runs smoothly, reset the engine speed to 2000 rpm then increase the timing 2 more degrees and check for the same things.

POST RESULTS

rpm increased in all tests and ran smooth.

DISTRIBUTOR SPRINGS

Removing the hevy stock spring and installing a 925d spring is usually very close.
 
ok, xlnt.

I would do the following next and leave the vacuum advance plugged for now . My "guess" is that increasing it by 6 degrees might be just a tiny bit too much but the drive and start tests will tel us.

TEST DRIVING

After setting the curve you can do the following test to see if you have too much advance.

Get the engine up to operating temp.

Drive at around 20 mph in second gear for a few seconds then floor the gas pedal as fast as you can until you reach around 30 mph and listen for even the faintest pinging sound coming from the engine . If it pings, you have too much timing for the octane gas you are using . You can either reduce the timing some or use a higher octane . The highest timing level you can run without it pinging and/or running erratic will SAFELY provide the most power.

It may ping in hot weather even if it does not in cold weather . If you find this to be the case, the easiest thing to do is reduce the timing until it stops or try higher octane gas . If it still pings with the highest octane gas, you can reduce the timing then.

If the engine turns over more slowly when it is hot, reduce the timing by 2 degrees and let us know.

JETTING

It may be rich or lean . If you installed new spark plugs, I would remove the front plug from each bank and post photos of them.

Black porcelain is rich.

Nearly white is lean.

Very light tan is typically very good and suggests the jetting is very close if not ideal.

 
Dude, chill. I see some of the sketchy advice you pass around and someone is going to end up screwing up their car because of it. Thank you for the negative reputation point Barnett, take care
Hey moderator, remove the negative rep please. Not deserved in my humble opinion.

Paul of Mo

 
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