Rowdy /6 Timing Curve Recommendations

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mario03srt

mario03srt

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All,

I'm looking for a recommendation to set up a timing/vac adv on a Mopar dizzy for a perf slant six. I want to give the builder some good info. Street use on a light car (60 Valiant). No HVAC. But a open 8 3/4 in the back. 4 Speed w/ a 3.55 and 15x8's out back.

Motor is a 232 cube /6 with 9.2-1 compression, a 268 Clifford Cam, full head work, long tubes, Offy Intake, Edel 600 Performer 4 bbl, MSD 6AL & Coil, DUI Live Wires.

Been tuning it up with a stock /6 points distributor and have it running pretty good. Now its time for a electronic setup with a good curve to take advantage of the setup and going to have a member fab me one up.

So if your have some experience and would like to share vac can and timing curve recommendations please let me know or if more info is needed please let me know.

Thanks,

Marion
 
My Slant 6 was a Doug Dutra built Super Six with an automatic. It liked 22 initial and 32 total. I also ran the vacuum advance on manifold vacuum, so that added to the dynamic timing at idle.
 
jbc426 said:
My Slant 6 was a Doug Dutra built Super Six with an automatic. It liked 22 initial and 32 total. I also ran the vacuum advance on manifold vacuum, so that added to the dynamic timing at idle.
Click to expand...

Ok thanks. That musta been nice. How did that engine run out? What octane? Big Cam?
 
If you are going to an electronic ignition you need to find out how much it retards and where it retards. Then you have to compensate for that.
 
Only because it advances, what goes up must come down
 
87 octane All in by 3200? Sooner with better gas? Something like MSD's timing curve table and use a setup similar E or F if a Mopar dizzy can be reconfigured to that exactness?
 
Timing at full load (such as wide open throttle 3 or 4th gear on a high compression, cammed engine does relate to octane. People will call the situation octane limited. In other words the combination could take advantage of a higher octane fuel if it was available. But if its not available, then the timing under the high load conditions has to be reduced.

Low rpm 'All in' was something that made sense when drag racing and using points. The same concept applies with electronic ignitions with the caveat that high rpm retard will occur if its not compensated for in the distributor's advance. (There apparently are now ways to compensate in the control electronics but that's not what you will find in the ECUs available for your project). The higher the engine rpm, the worse the problem. At 5000 rpm it might be 1 or 2 or 3 degrees. At 8000 it could 4 to 8*.

However you wrote this is a street car, so this changes the story even though it will see some strip use (my understanding).
1. The engine will get heat soaked when used for trips longer than 1/4 mile each way. ;) An hour or two driving is what the timing needs to be set up for.
2. Vacuum advance will eventually be used. So while a fast 'all in' is usually fine with no vacuum advance, once the vacuum advance is taken advantage of, the 'all in' early curve will result in way too much advance for cruising and moderate throttle around town and even on highways.

I would start with the slant distributor you have.
1. Measure the timing vs. rpm from as low of an rpm as you can, to as high an rpm as you feel comfortable. You'll need timing tape or a dialback light. Timing tape is better. And tach of course.

^This is now your baseline^
You know how it performs, and if you haven't yet, measure how much vacuum changes the advance. That's also a part of the baseline.

Then make one change! The simplest will be to increase the initial timing and reset the idle speed to the same as before. See if it is as strong when you slip it into gear. if you need to rev the engine more so it doesn't stall, note that. That's a step backward. But keep going with the test. Drive it and see how it tolerates or likes more timing cruising at different speeds. Also test WOT in 3rd or 4th and if there is any detonation (ping) back off. Again, take note. If you have to put that off until the drag strip opens, so be it.

You can also change when the advance begins. That's a little more involved. I don't think you'll have to do that with a mopar distributor and a manual transmission.

IMO the Mopar distributor advance is superior to the MSD. It can handle a fast advance off idle and then slow it down when combustion efficiency picks up.
 
Timing is advanced only to get maximum pressure when the maximum leverage is on the crank.

More timing is not always good. Its simply neccessary because fuel takes time to burn. A faster burning combustion doesn't need to be ignited as early as a slow burning mix.
Timing is increased with rpm because the time (in fractions of a second) to burn doesn't increase as fast as the time available befoer the piston has moved down.
That's it in nutshell.

When you are experimenting, especially with a manual transmission, you can experiment with 'crutching it' higher intial using manifold vacuum like Charlie did.

When switching to electronic, try to find a distributor that is close to what you want. Check out this '78 /6 curve.
cool-gif.gif
 
Last edited:
Mattax said:
When switching to electronic, try to find a distributor that is close to what you want. Check out this '78 /6 curve.

View attachment 1716209006
Click to expand...
I have 2 of those same ones.
One of them I bought NOS a few years ago, it's in my truck now. Just as removed from the box.
So far all I have done is to break in a fresh overhaul with it, no miles on it just a couple of hours running in the garage.
The 2nd one, same tag number, I've taken apart to clean it up and I changed the heavy spring to a lighter one (I think it was referred to as the "medium" level)
There was a guy on here a couple of years ago that had a **** ton of Mopar distributor springs listed for sale, I got a couple of sets of them at the time. I also replaced the VA can because it was shot. At one point I knew what governor was in them, I don't remember.
Also there's different advance cans they have numbers on the arms that attach to the advance plate within, at one point I read (either on here or on the /6 forum, can't remember) a recipe of sorts for exactly which VA can and which governor was ideal for different application, can't remember where I saw it. I do know that the VA can that I put in the used dist had a different number in it than original, and was the one suggested for my type of build/usage. I have another can the same as that one, that I was gonna swap into the nos one, but wanted to see how it does with the nos distributor "as is/untouched" then experiment with the other one I have here, keeping the original one as a reference of sorts.
That dist is spec'd for factory super 6 apps.
My app is 85 d150, 2wd long bed. 3.21 rear, at this point still have the original 727 in place. (yes it's a 727, I know the differences)
Engine is a fresh 74 short block 0.020 over, rebuilder grade pistons, 0.185 in the hole (even after a 0.030 block shave) 77 peanut head, shaved 70 thou, Aussie head gasket, think it was something like 0.039 installed thickness, calculated and measured CR came out right at 8.4:1 (expected higher since that's exactly what the manuals claim these engines were from factory without the deck/ block shave but measurements prove it is what it is) ported, oversized SI brand valves, super 6, nos BBD 318 "heavy duty spec" from about 1977, ported stock exhaust manifold, outlet opened up to true 2-1/4 to match the head pipe and outlet gasket matched. Oregon #819 cam.

Final configuration undetermined, have parts on hand to put either an 833OD or else an A500 behind that engine, I don't know how either of those would effect how I would have to set up the distributor curve.
I have put in a factory 4 pin ignition box, also considering swapping out in favor of an HEI module. Also unsure how that change might also change how the engine Will want the distributor to be calibrated vs the stock Mopar box.
The specific Mopar box I have is a niehoff brand replacement from late 70s/early 80s....it too is brand new old stock. (And American made) for Nothing special, don't know specifics between it and an Orange box or blue box as was common in 80s trucks, or any other Mopar style 4 pin ignition box.if there truly is a difference between them that is
 
I found a slant friendly guy with a distributor machine.
He set up my unit for what I asked for.
Send me a message if you want his contact info.
 
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