Timing Ignition (How-To), And why Duraspark Sucks.

[REDONE]

Hey chip! Both my Innova and Actron (Snap-On) timing lights will flash for every spark with MSD, but my cheapo HF one doesn't. It'll pick up an erratic spark every once in a while, but you can still see where the main spark is firing. If you just need a tach to set your idle it something, I think the grey wire from the MSD is the tach signal, and it works with my basic Sunpro tach without the adapter that the MSD instructions say you need.

[prospector]

Thanks guys, but one more question, while reading about the HEI MotorCraft ignition system "hidden HEI" mod. it says that it can be used with all Duraspark ignition modules. But I thought the point was to ditch the Duraspark, what am I missing here?

[REDONE]

Thanks guys, but one more question, while reading about the HEI MotorCraft ignition system "hidden HEI" mod. it says that it can be used with all Duraspark ignition modules. But I thought the point was to ditch the Duraspark, what am I missing here?

It's probably a typo meaning the hidden HEI works with all Duraspark "Distributors". You're right that the point is to get away from the module and it's resistor. The actual distributor is a solid unit.

[prospector]

Alright Redone, I'll read through it again in detail until I have a good idea of how it works, thanks very much, been a while since I tinkered with ignition systems.

[az chip]

Hey chip! Both my Innova and Actron (Snap-On) timing lights will flash for every spark with MSD, but my cheapo HF one doesn't. It'll pick up an erratic spark every once in a while, but you can still see where the main spark is firing. If you just need a tach to set your idle it something, I think the grey wire from the MSD is the tach signal, and it works with my basic Sunpro tach without the adapter that the MSD instructions say you need.

Thanks! I thought the innova actually worked with the MSD. Guess not. I will try a Sunpro tach on that gray wire. My instructions say that is for a tach as well.

[ghcoe]

I did a HEI module/Large cap motorcraft conversion on my Prestolite system a couple years back. It was a simple conversion. Oddly the wiring colors to the Prestolight module where the same color code used in the HEI system.

[REDONE]

I did a HEI module/Large cap motorcraft conversion on my Prestolite system a couple years back. It was a simple conversion. Oddly the wiring colors to the Prestolight module where the same color code used in the HEI system.

I think that's a carry-over from WWII. Cleveland Electric (Prest-O-Lite/Autolite) and GM were both military suppliers so they got standardized. Pure speculation, but makes sense.

[will e]

PORTED vacuum, which is "load sensing". The more air rushing through the venturis, the more vacuum it pulls, and the more it advances the timing.

Sir, I apologize but this is incorrect and unfortunatly it invalidates some of your other thoughts. You are describing 'ventri vacuum'. Ventri vacuum is what is used to draw in the fuel and to operate vacuum secondaries. The vacuum increases with the airflow.

To everyone, here is my understanding:

Ventri vacuum is not used in distributor timing control. With some exceptions there is typically not a 'ventri vacuum' port available.

Ported vacuum is created the same way that manifold vacuum is created but the location of the orifice is in the carb just above the throttle blades.

Manifold vacuum is the result of the air in the manifold rushing into the low pressure area of the cylinder when the intake valve is opened on the intake stroke. At idle, the carb throttle blades are basically closed and only a small amount of air is allowed to pass. This creates the low pressure or 'manifold vacuum'. Even when the throttle is partically open it will still limit the air flow and create a vacuum. As you approach wide open throttle the effect is reduced to practically zero since enough air can flow to fill the piston cylinder. Manifold vacuum ports can exist either in the intake manifold itself or on the carb somewhere below the throttle body or an orifice below the throttle bades. The PCV port is a great example of a manifold vacuum source that is on the carb base plate.

So what is the difference between manifold and ported vacuum? The location of the orifice. The opening for the ported vacuum is just above the throttle blades. At idle the Ported vacuum orifices experiences little if any vacuum from the intake valve and intake stoke since it is above the throttle blade. As you open the throttle the ported vacuum orifice ends up on the other side of the throttle blades (below) and experiences the exact same vacuum as the manifold does including partial and wide open throttle. As you 'put your foot into the gas' ported and manifold vacuum will decrease evenly, ported vacuum does not increase under engine load.

I won't go into which one is better. That's a question best left for the ages.

[dodgerammit]

Thank you for this write up. Just my unofficial "dialing in" has gotten me from 9 to an impressive 13mpg, haha. I will be going MSD on mine and will revisit this thread. Even with it now running, ahem, correctly, it still exibits the high throttle first start, then gets lopey at load idle when warm. Goal is to get 15mpg outta this pig.

[tgreese]

It is my understanding that the only difference between ported vacuum and manifold vacuum is the location of the port where the vacuum originates. The ported vacuum originates from the throttle venturi and is physically blocked by the throttle plate. I'm not sure if that's above the plate or at the plate, but the result is that ported vacuum goes to zero at idle. Off idle, the vacuum from either port is the same.

Pretty easy to see this if you look at a carburetor closely.

I am running a Duraspark distributor and a HEI module on my CJ-6 (which came from the factory with the dreaded Prestolite ignition). Works fine - no complaints so far. This works because the trigger signal made by the HEI distributor and the Duraspark distributor is electrically identical - it's a VR (variable reluctance) trigger, and is one of the three industry standard signals currently used for ignition triggering (the others being optical and Hall effect). Any ignition that uses a VR signal can be triggered by the Duraspark or the HEI ignition ... you could run a HEI distributor with a Duraspark module if you wanted. Lots of mixing and matching is possible. The aftermarket modules like MSD accept a few different signals, including a VR signal.

Combining the Duraspark distributor with HEI module is usually called "Stealth HEI." There is coverage of this on the net. Personally, I don't see any reason to switch to HEI if you already have a Duraspark distributor. Electrically it's the same (or can be made the same) and you don't really gain anything other than the huge distributor head of the HEI that smooshes all the HV (high voltage) parts into a small space (not good IMO). Personally I'd rather have the mix and match potential of the Duraspark, which can easily be upgraded to a big cap that uses the superior HEI-style wires. With a little reading and study you can understand this and decide for yourself.

One problem with the Duraspark is there is no aftermarket source for the vacuum advance canister on a Duraspark distributor (AFAIK). However, you can buy a reman Duraspark distributor and take the advance can from that for your distributor, and turn in the bones of the reman. You can probably take the sense coil too, for a spare, and they will accept your core. If you really must have a Delco distributor, the Delco points distributor for AMC can be upgraded to a big cap using the MSD CapAdapt, and it can be fitted with a VR module (there's another article online how to do this). Then you can run whatever module you want. Or you can fit a Pertronix Ignitor module, which will switch your coil or trigger the MSD module. Or you can trigger the MSD module with the points. There are many, many possible combinations of parts using a VR-trigger distributor. Once you pick a distributor to fit the block, you can mix and match as you please.

Note that the only exception to this is the Breakerless Inductive Discharge (BID, made by Prestolite) used by Jeep 1975-77. It's not compatible with any of these other parts. Don't spend any money on it - instead replace it with aftermarket HEI, 1978-up Duraspark, or 1974-down Delco, your choice.

[dodgerammit]

Tell me if this looks correct to clean up the spaghetti? (no emmisions)

[tedlovesjeeps71]

That's weird. On yours the green line goes from the manifold to the base of the carb. On mine, the manifold has two ports. The bigger one goes to the brake booster and I have the other one blocked off.


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[dodgerammit]

Yeah, the brake booster and other accessories are omitted from the sketch I modified.
Mine is the same. Just went out to check what I have and realized my Waggy is missing the vapor canister/egr stuff.

Wonder how important that is to economy?

[dodgerammit]

Well, not all is lost for me. I discovered the egr system was all there, just hacked badly. It is now hooked up. Still missing the vapor stuff.

This is what my system currently is:

[Charles Kline]

Search my posts for the vacuum diagram I did with layers you can hide. You can just hide the systems you don't want.

[falconte43]

I just ordered a DUI distributor, new wires, spark plugs, and a vacuum gauge to do an ignition system overhaul. Hopefully it will arrive Saturday!

[csuengr]

Glad my engine doesn't have a distributor.

[dodgerammit]

Glad my engine doesn't have a distributor.

Rattle, rattle?

[csuengr]

Glad my engine doesn't have a distributor.

Rattle, rattle?

Coil packs.

[dodgerammit]

Glad my engine doesn't have a distributor.

Rattle, rattle?

Coil packs.

Ah! LS?