Don't understand guys running 12 to 17 degrees initial. Would like to see the rest of the curve.
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Crackedback
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Camshaft is a factor. Larger cam, more initial.
Factory timing numbers were not the best as they had emission levels to meet. No way should a 71-73 340 be timed where they were. Even 68-70 340's like 15-18 initial. Makes the idle so much easier and cleaner. No smell like a fuel truck losing its load behind the car.
You limit mechanical and put the correct spring in to get the curve correct. Pretty simple in most cases.
Factory timing numbers were not the best as they had emission levels to meet. No way should a 71-73 340 be timed where they were. Even 68-70 340's like 15-18 initial. Makes the idle so much easier and cleaner. No smell like a fuel truck losing its load behind the car.
You limit mechanical and put the correct spring in to get the curve correct. Pretty simple in most cases.
More initial lead gives you more torque down low and a more complete burn, as long as the engine doesn't detonate... A longer than stock cam bleeds cylinder pressure so you need the torque & usually don't have detonation issues....
When adding initial (Base) timing you need to limit the mechanical advance to keep total timing around 34-36 maybe 38 degrees....
In some applications it's advantageous to completely lock out timing.. (Long duration cams) That may or may not make you starter happy.. If not it's common to separate the crank function from the ignition switch so you can start cranking the turn the ignition on once the rotating parts have momentum....
When adding initial (Base) timing you need to limit the mechanical advance to keep total timing around 34-36 maybe 38 degrees....
In some applications it's advantageous to completely lock out timing.. (Long duration cams) That may or may not make you starter happy.. If not it's common to separate the crank function from the ignition switch so you can start cranking the turn the ignition on once the rotating parts have momentum....
Triple Black 73
Well-Known Member
The progress of initial timing on my 383 is interesting one. I started off with the book 8 degrees. But that wasn't working so I went with 10-12 degrees and the car was happy. I then switched to a single plane intake and I had to run 12 to 15 degrees for the engine to be happy. Then, I switched to colder spark plug. I had to run 15 to 17 degrees of timing for the car to be happy. Then I switch to Holley Sniper EFI HyperSpark system which is an ECU controlled MSD CD ignition. Now I'm running 20.5 degree and the car is really happy.
Why so much? Well, I found out it's a lot to do with the way the air flow through the intake, cylinder pressure, and the spark plug.
There are timing calculators (science!) that will guess the best timing based on stroke, bore, cam timing, intake, spark plugs, ignition, and RPM. Mine came out to 22 advance from idle to 1800. I backed that off a bit to 20.5. Cruise is 37.5 and the WOT advance is 41.5. Runs super smooth with more power through the range. There is a slight stumble from idle to 1000 rpm when cursing through the neighborhood, but meh. What you going to do?
Why so much? Well, I found out it's a lot to do with the way the air flow through the intake, cylinder pressure, and the spark plug.
- The cam opens earlier than stock which builds more cylinder pressure, which required more timing.
- The single plane intake slowed the incoming air, thus more advance was needed.
- The colder spark plug held less heat so it was given more advance.
- And the CD put out one hell of a spark so it need to fire more advance.
There are timing calculators (science!) that will guess the best timing based on stroke, bore, cam timing, intake, spark plugs, ignition, and RPM. Mine came out to 22 advance from idle to 1800. I backed that off a bit to 20.5. Cruise is 37.5 and the WOT advance is 41.5. Runs super smooth with more power through the range. There is a slight stumble from idle to 1000 rpm when cursing through the neighborhood, but meh. What you going to do?
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Triple Black 73
Well-Known Member
The stock distributor can be adjusted for whatever curve you need via the vacuum adjuster, so it's hard to "see" the curve. There's a mechanical advance and the vacuum advance gets added together. But if you don't have enough vacuum, you're limited to how much the vacuum can advance timing.
I got tired of that guessing game, so I use a computer now to "see" the advance curve.
I got tired of that guessing game, so I use a computer now to "see" the advance curve.
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I run 17 degrees initial with the mechanical advance adding another 16 degrees for a total timing of 33 degrees. I have a 10 to 1 440 based 493 with the MP 528 solid cam.
Ranger16
Well-Known Member
Maybe a dumb question, but here goes.
Using a dial back timing light, why can't you set the timing to 34 or 35 degrees, run the RPM up to 3000 RPM and adjust the distributor til your timing shows zero on the timing mark and lock it in there? I did it that way and my initial timing was at 14 degrees. That's where I left it. Seems to be running fine.
Using a dial back timing light, why can't you set the timing to 34 or 35 degrees, run the RPM up to 3000 RPM and adjust the distributor til your timing shows zero on the timing mark and lock it in there? I did it that way and my initial timing was at 14 degrees. That's where I left it. Seems to be running fine.
Not a dumb question at all... Thats pretty typical when you don't know how much advance is built into a distributor.... Only thing is while 3000 RPM should be save some Mopar distributors have really heavy springs & the advance continues to climb past 4000 rpms... So watch the timing marks & once you've set it to zero push the rpms a little higher to make sure you've seen the full advance...
Ranger16
Well-Known Member
Would that still be true with a MP orange box ECU and distributor?
Yes
Ranger16
Well-Known Member
OK, thanks. I'll check it again at higher RPM next time I have it out and up to operating temp.
Crackedback
Well-Known Member
Total timing method is not a good way to set timing on a car that is street driven. It might be fine for a race car that spend it's time on the drag strip. Sometimes you get lucky and the car runs well, it still isn't likely the best it can run.
I can hand you two distributors, set them to 36* total timing method. One will run great all around, the other will run like garbage at idle. The issue, one might have 18* of mechanical timing, the other 32*. Resulting in one providing 18* initial, the other 4* (horrible).
Ignition timing in the most basic form is a two piece puzzle. Initial + mechanical = total. And before the what about vacuum crowd starts screaming, this is POWER related only. Vacuum is fine for trying to squeeze out fuel mileage AFTER you get the base timing sorted out.
Simple test. Start the car, warm it up to operating temp. At idle, twist distributor a smidge to give more advance. If the engine picked up RPM, it wants the timing.
Throw the book numbers in the garbage if you want the engine to run its best, especially if you have no emission testing requirements. A cam change will alter what the engine want. IMO, let the engine tell you what it wants, not what some book that had numbers to satisfy things other than operating efficiency.
I can hand you two distributors, set them to 36* total timing method. One will run great all around, the other will run like garbage at idle. The issue, one might have 18* of mechanical timing, the other 32*. Resulting in one providing 18* initial, the other 4* (horrible).
Ignition timing in the most basic form is a two piece puzzle. Initial + mechanical = total. And before the what about vacuum crowd starts screaming, this is POWER related only. Vacuum is fine for trying to squeeze out fuel mileage AFTER you get the base timing sorted out.
Simple test. Start the car, warm it up to operating temp. At idle, twist distributor a smidge to give more advance. If the engine picked up RPM, it wants the timing.
Throw the book numbers in the garbage if you want the engine to run its best, especially if you have no emission testing requirements. A cam change will alter what the engine want. IMO, let the engine tell you what it wants, not what some book that had numbers to satisfy things other than operating efficiency.
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I set my initial strictly from a vacuum / rpm gauge. Kept advancing until the vacuum stopped going up and rpms slowed then I dialed it back a touch. Verified no kickback on start-up. I ended up at 22° initial and then fixed mechanical to 15° for 37° all in at 2400rpms.
Cam is a Highes solid lifter STL3842, runs great where it is. It's a street car and is running a vac advance off the ported carb barb.
Cam is a Highes solid lifter STL3842, runs great where it is. It's a street car and is running a vac advance off the ported carb barb.
Thanks for the help guys. I'll let you know how mine wrings out. Didn't take the long cams into consideration. Mine is short with lots of extra lift. This project is trrying sqeeze what mileage I can from a 440. I like a challenge or just old man syndrome!
383man
Well-Known Member
Thats close to my setup on my street/strip 440/493. I run a race dist with no vacuum advance since it has no vacuum advance on it as its a Mallory race dist. It has all mech advance in by about 1800 rpm the way I set it and I set the total at 36 which my eng loves. I let the initial fall where it did and it is right around 22 to 24 at idle. My eng had good quench and is 10.6 comp with aluminum heads. The car loves the full 36 in by 1800 to 2000 rpm and really likes the 22 to 24 initial. The car runs great like that and has great driveability on the street and strip.
And has no detonation at all. But as many have said not all combo's are the same and on hot rodded engines most of the time we may a good baseline but you have to work with the combo and see what it likes best as you cant go to a book and find a timing spec for a 500 stroker with a 266 @ .050 cam and Trick Flow heads if you know what I mean. Many times depending on your dist you will have to limit the total mech advance if the car likes a lot of initial timing but that's all part of tuning our hotrods.
Right now I still run the MP orange ECU and an old Accel super coil with no ballast. You can just see part of my orange ECU behind my air cleaner beside the voltage regulator. This has worked great on my car as we took it off my sons Dart and added MSD to it. Then his car still idled the same and ran the same et with MSD as it did with the orange ECU. So I took the orange ECU and Accel coil and use them on my 63. It runs in the 10's with them and never misses a beat. Ron
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Thanks, lots of variabls to account for. I'm thinking of having it tuned on a chassis dyno.
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