HEI module dwell time.

Many times I've told people on here that to the best of my knowledge only GM and NAPA premium ignition modules vary dwell. Some of you realize it's important,some are like WTF is he talking about. I just stumbled across an article explaining dwell and ignition modules and how to check. Something this article doesn't cover,or I skimmed it too quick and missed it it,. Dwell is the amount of on vs. off time on the coil and module,too much on time is going to cause modules and coils to fail early due to excessive heat. Which is what concerns me about dwell.

Interesting read Rick. As you might remember GM called out 28-32 degrees of dwell on the 8 cylinder, point distributor. I was taught to try for closer to 28 degrees because as the rubbing block wears, the dwell increases. The change in dwell also effects the timing. So always set dwell first, then check timing.

@Rusty Nail Hey Rusty, Rick said "dwell"

Hey, who knows what point float is?

Turbo4whl said:

Interesting read Rick. As you might remember GM called out 28-32 degrees of dwell on the 8 cylinder, point distributor. I was taught to try for closer to 28 degrees because as the rubbing block wears, the dwell increases. The change in dwell also effects the timing. So always set dwell first, then check timing.

@Rusty Nail Hey Rusty, Rick said "dwell"

Hey, who knows what point float is?

Click to expand...

Another neat trick was run a dual point distributor wired to a toggle switch,set dwell different between the 2, flip the switch to run on one or the other to gain or lose a couple degrees of timing. Before they had Knock sensors.

Wow.^

Lemme dwell on that a minute.
Wait.




As we see here (example given) dwell can have more that one meaning.



Anyone know the term used for a word that can be both a Noun AND a Verb?

I think it's a

collocation​

Hope this helps!


Thanks @turbo4wheel?
Did I miss the joke?

Ive got a new gig. Cant play online all night anymore.
I'm now @ City Hall!

Moar Joe Walsh?! Sheesh!

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Moar Joe Walsh!
What are the chances?


Hold on.
I am creating my own reality.
You're watching.
She's gonna be a real knockout.

Used to roll around with an extra HEI module in my '78 K25. Got me out of a jam once or twice. Nowadays, HEI distributors are so cheap, I have a whole spare in the race tool box.

This made for higher potential energy to be stored in the coil. GM took advantage of the electrical power by increasing the spark plug gap from the previously customary0.035 inch to 0.060 to 0.080 inch.

Click to expand...

Really? What years models are they talking about. My 81 k20 plug gap is specs is .035 .
That article is pretty vague

Turbo4whl said:

Hey, who knows what point float is?

Click to expand...

Basically same as valve float. Inability to control opening and closing. Solving point float sounds easy, increase closing spring tension. Problem with that is increased rubbing block wear and wear to advance pin, especially on Fords.

A friend had a Sun distributor machine. Was educational testing various points and seeing the actual RPM they lose control. Some failed at rather low speeds.

When HEI's came out many local racers changed to that distributor. HEI's have dependable spark until the 6500 RPM area. Good enough for low dollar hobby class racing.

Rusty Nail said:

Thanks @turbo4wheel?
Did I miss the joke?

Click to expand...

No. You called me out some time ago when I said "dwell". I didn't want you to miss.

fast 99 said:

Solving point float sounds easy, increase closing spring tension.

Click to expand...

This is the answer! Worn out or weak point spring. So with a dual point distributor you could dial out point float on a high revving engine. One point set starts the dwell charge, the other point completes it. Back in the day we had a distributor machine and we also had a Sun oscilloscope. Amazing what you could see, each cylinder's spark path and faults.

Turbo4whl said:

No. You called me out some time ago when I said "dwell". I didn't want you to miss.



This is the answer! Worn out or weak point spring. So with a dual point distributor you could dial out point float on a high revving engine. One point set starts the dwell charge, the other point completes it. Back in the day we had a distributor machine and we also had a Sun oscilloscope. Amazing what you could see, each cylinder's spark path and faults.

Click to expand...

Those Sun machines were state of the art and expensive. Cost 8k in the late 70's. An 1115 came up for sale close to me cheap, bought it. Needed an infrared board and a lead. They take up a lot of real estate in the garage but worth it if working on points vehicles and carburetors.

Tonimus said:

Used to roll around with an extra HEI module in my '78 K25. Got me out of a jam once or twice. Nowadays, HEI distributors are so cheap, I have a whole spare in the race tool box.

Click to expand...

I've heard a lot about module failures over the years and guys carrying spares. But I've installed several HEIs in 50s-70s project vehicles starting in mid-1990s, and none of those ever had a module, pickup, or coil failure. Some had stock internals, others were upgraded to MSD module, coil, rotor, and cap back when those kits were made in the USA and reasonably priced. Also put a Proform HEI in my 82 C10 in 2015.

I also had stock GM HEIs in four 74-81 Chevy and Buick daily drivers that I can think of. None of them ever failed. However, your comments and others make me want to carry a spare module. Just need to find one that isn't Chinese junk. What do you all recommend?

I run an OLD Well's white module, never any problems.
I look for a module that has GM stamped on it and hoard those..
Both are very good,
without SHORTING out Your coil and have a melt down in the windings..
cheap chyna crap modules will.
J my 2 cents.

Found this. Around $50, but hopefully you get what you pay for.


Ignition Control Module
Part# D1906 - ACDelco
Part# 19180771 - GM

Per Veh: 1
Years: 1975-1976

MikeB said:

I've heard a lot about module failures over the years and guys carrying spares. But I've installed several HEIs in 50s-70s project vehicles starting in mid-1990s, and none of those ever had a module, pickup, or coil failure. Some had stock internals, others were upgraded to MSD module, coil, rotor, and cap back when those kits were made in the USA and reasonably priced. Also put a Proform HEI in my 82 C10 in 2015.

I also had stock GM HEIs in four 74-81 Chevy and Buick daily drivers that I can think of. None of them ever failed. However, your comments and others make me want to carry a spare module. Just need to find one that isn't Chinese junk. What do you all recommend?

Click to expand...

I bought my '78 in 2004 or 2005. Had some unknown HEI dizzy in it. Probably the cheapest one the P.O. could get. I was a teen and abused that truck. Something went bad with the ignition. Could've been a loose connection or something like that. I would check nowadays, but I didn't know what I was doing at the time. Just winged a new module at it and it worked.

I have found modules to be hit or miss. I've run a pair of chinese HEI dizzys. Both have been flawless. One was in my '84 which was totaled and the other has been on several different motors on our run stand. Works, even when the battery is super low. It's honestly been very impressive. I would just get a chinese spare, throw it in right away and keep the good module you pulled as the spare.

I have a cheap china HEI distributor in mine, but when the module went out I replaced it with an AC Delco module and it has been working well since then. The replacement Big Block has been converted to the LS CNP setup... so no concerns on dwell or module failure there. I have well over 300k miles on several LS engines and have never seen a factory coil pack fail.

If you are not using a GM module in your HEI distributor then there is a good possibility your dwell time is not correct thru the entire RPM range, which also affects timing. I also use TPI on some engines which uses a small cap HEI, it has no advance built into the distributor it is all controlled by the computer. In this case there is a setting in the chips program that can compensate for the different dwell characteristics of different GM modules that can be installed, its called "Latency compensation". for each different p/n, all GM modules have this offset. Any off-brand module has no information on what to set the "Latency" to, so the dwell/timing advance is corrected. Lots of testing has been done to prove how the dwell/timing advance is affected by just swapping modules without changing the latency.
Use original GM pickup/modules that are for your engine. If you can find one.