is there any way to retard the timing mechanically. i see alot of people running the msd boxes but i dont have money for that. saw the suggestion of a vacuum can with a push pull diaphragm in it for boost reference, came out of a volvo. anyone have any kind of experience with something like that?

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1966 Plymouth Valiant, 225, 3 on the tree, 8 1/4 3.21 sure grip, hyperpac, holley 650dp, holset h1c

There were big blocks with an electric solenoid on the vacuum advance can to provide ignition retard for, I believe, NOX emmissions. Big block distributors rotate the wrong way though.

Did you see this discussion about HEI modules with built-in retard? http://www.slantsix.org/forum/viewtopic.php?p=393772

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Joshua

I have seen this, it would work, but I'm not sure I would do it.
A manual, mechanical, distributor retard mechanism. Made up from a manual choke cable and a few little extras. It basically pulled the dizzy back a set amount when you pulled the cable! The guy had it attached to the bottom slotted dizzy mount and it was all setup quite nice. He was using it to pull back the timing when he heard pinging. Just a funny thought!!

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Mattelderca
78 NYB (gone now), two S series, three old Snow Cruisers and a Doo.

Alternatively, to avoid turning the whole distributor, you could connect a cable to the arm in a dismantled vacuum advance pot, and set it to operate in 'reverse'.

Olaf

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Aspenized

What is wrong with the idea of using a stock-type, vacuum advance unit whose actuating signal would disappear (along with its spark-advance) when the vacuum goes away and boost come on board?

As long as it is spring-loaded to return to a solid, retarded position, it would seem to be the perfect answer, would it not? You would just have to test it for the proper amount of advance when vacuum is present, a not-too-difficult task, I would think.

Is there some reason why this would not work with a stock distributor, assuming the mechanical curve was what you needed?

What am I missing here???

Bill, in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

i did see that the other day. i was hoping for something a little more gradual.

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1966 Plymouth Valiant, 225, 3 on the tree, 8 1/4 3.21 sure grip, hyperpac, holley 650dp, holset h1c

lol im sure that would work but seems tedious.

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1966 Plymouth Valiant, 225, 3 on the tree, 8 1/4 3.21 sure grip, hyperpac, holley 650dp, holset h1c

i suppose you are right. im just afraid of detonation. seems to be the only thing that is gonna kill my motor and am wanting to be on the safe side. ill just have to get it going and see what happens.

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1966 Plymouth Valiant, 225, 3 on the tree, 8 1/4 3.21 sure grip, hyperpac, holley 650dp, holset h1c

Detonation used to scare me (still does, terribly!) so the ignition system we installed was the most fool-proof I could "design" though it might not work well on the street.

You think you're paranoid about detonation?

In the interest of NOT encouraging detonation. our system is this:

First, we determined where true TDC was on the crank/balancer, using a "positive-stop."

Once we had true TDC, we were after 18 degrees of advance on the damper.

We measured the damper's circumference.

1/20th of the circumference was 18 degrees. (.20 X 360 = 18.)

We made a mark at 1/20th (18 degrees.)

We installed a distributor that had NO advance mechanism of any kind... It was a Lean Burn distributor with 2 pickups.

We locked the distributor down with 18-degrees of advance.... no more, no less.

Our initial intention was to use one of the pickups for starting and one for running, but that proved unnecessary... it started perfectly well with 18 degrees of advance, much to our surprise!


To our continued surprise, it ran very well on the street with NO vacuum advance, and no mechanical advance... I'm talking about street-driving, here...

We now have access to a trailer to get it to and from the strip, so overheating shouldn't be a problem.

In a week or two, I should have some hard test-n-tune figures to look at.

Detonation/Paranoia is responsible for all this...

Bill in Conway, Arkansas

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1964 Valiant 4-door sedan, 225 turbo/904

Not to be difficult, but why re-invent the wheel? Engine parts are a lot more expensive.

CJ

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Part of Tyrde-Browne Racing

Can you be more specific? Everything we did here was to preclude too much spark advance, (one important factor in detonation.) That's all.

Maybe we went over-board on the "safe" side, but too much spark advance, accidentally, is not going to happen with this setup... that's all.

That was our thinking, anyway...

It seems to be working.

Bill

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1964 Valiant 4-door sedan, 225 turbo/904

By your equation, are you implying that 360 is the circumference?

On a 7" diameter balancer, 18° will be 1.098" from your TDC mark. It has to be measured and transferred to the balancer in an arc, not linearly, or you will introduce a lot of error into the reference mark and not get an accurate reading. You can easily have 4-5° too much if you do.

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There's no such thing as too much cam....only not enough engine!

He's saying that a computer is far more accurate and precise than you/we are.

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There's no such thing as too much cam....only not enough engine!

No argument there...


Bill

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1964 Valiant 4-door sedan, 225 turbo/904

I seem to have mixed up inches and degrees.... not an unusual circumstance for me.... particualary, early in the morning, when I usually write this stuff...

Thanks for the correction!

Bill. in Conway, Arkansas

P.S. In retrospect, I think we settled on one inch as representative of 18-degrees, and marked the damper accordingly.

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1964 Valiant 4-door sedan, 225 turbo/904