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Joined: Sep 2011
Posts: 2,676
L
Lugnutz Offline OP
'Bolter
**Update**

See the data I posted on the post just before this one.

After comparing the vacuum numbers I got earlier tonight, I felt pretty good that they were in line with what they should be.
I reconnected the Corvette dizzy vac advance line and drove the truck. RUNS TERRIFIC!

For now I think I can leave things alone for a few tanks of gas because it sure runs better than it did last week. What made the difference? I honestly think the remanufactured distributor had too much total advance. The Corvette 327 dizzy added only 22° of mechanical advance bringing the initial 12° to a total of 34°.

I’d like to thank everyone for their patience as I worked out this problem. grin
I have learned that a random rebuilt SBC distributor is not necessarily correct for my application. I’m glad the Corvette 327 dizzy fit the bill.

Last edited by Lugnutz; Wed Sep 21 2022 12:16 AM.
Joined: Oct 2021
Posts: 1,143
O
'Bolter
Panic,

What did Harley-Davidson drivers do during the Civil War? headscratch

Last edited by Otto Skorzeny; Wed Sep 21 2022 01:04 AM.

1939 Packard Standard Eight Coupe (The Phantom)
1950 Chevrolet 3100 (Ol' Roy)
1956 Cadillac Coupe de Ville (The Bismarck)
1966 Oldsmobile Toronado (The Purple Knif)
1966 Ford Mustang (Little Red)
1964 Ford Galaxie 500 coupe
1979 Ford F-100
1976 Ford F-150 (Big Red)
1995 Ford F-150 (Newt)
Joined: Feb 2004
Posts: 25,315
H
Kettle Custodian (pot stirrer)
You're almost exactly at the advance numbers I suggested- - - - -3 pages ago!
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!"
Abraham Lincoln

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!

There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self.
Ernest Hemingway

WAG MORE- - - - - -BARK LESS!
Joined: Feb 2000
Posts: 4,560
J
'Bolter
Thats good to hear, glad it's running the way you want. The Corvette distributor numbers are super close to the one I just modified. The older distributors have the center plated welded in so changing the advance rate is harder then the HEI's where all three pieces can be changed.

If you get time, look at the link from Crankshaft Coalition about vacuum advance, the number of different canisters alone with who knows how many different advance rates GM used, it's not really surprising the rebuilt distributors don't work.

Joined: Dec 2017
Posts: 1,183
D
'Bolter
Your vette distributor is sluggish to the tune of 1 degree at the distributor, 2 degrees at the motor. Using your numbers, you get a max advance (initial plus mechanical) of 34 with an initial of 12. That means your mechanical is 22 at the motor, 11 at the distributor. All chevy distributors that I have worked on, none were specificed at less then 12 degrees mechanical. So if the distrubutor was working correctly, at 12 degrees mechanical at the distributor, the vette distributor would be 24 at the motor, 36 total with the 12 initial (24 + 12). If you wanted to get to 38 total, you would bump your initial to 14 degrees (24 + 14). Fairly common timing for a gen 1 small block chevy.

On the rebuilt, that distributor is also likely within specification and not mal functioning. Chevy distributors generally come in 12 distributor degree advance versions and 14 distributor degree advance versions. Yours apparantly is the 14 degree variation. So instead of 24 degrees mechanical at the motor on a 12 degree distributor, yours is 28 degrees at the motor on a 14 degree mechanical. Add the 12 initial, you get 40 (28+12). So If you wanted to get 38 total on that distributor, you would time the motor for 10 degrees initial instead of 12 (28 + 10).

Now that you have installed the vette unit that is a little tiny bit lazy, you should also check your dwell specification and see if its within tolerance, and confirm its not jumping around. If it is, the lobes are worn unevenly.

Last edited by Dragsix; Wed Sep 21 2022 04:20 PM.

Mike
Joined: Jan 2022
Posts: 406
B
'Bolter
Originally Posted by Otto Skorzeny
Panic,

What did Harley-Davidson drivers do during the Civil War? headscratch

Maybe it was the Spanish Civil War (1936-9) ???

Joined: Dec 2008
Posts: 1,781
P
'Bolter
No, poetic license for "a long time ago"

Joined: Mar 2010
Posts: 10,289
5
'Bolter
Originally Posted by Dragsix
Now that you have installed the vette unit that is a little tiny bit lazy, you should also check your dwell specification and see if its within tolerance, and confirm its not jumping around. If it is, the lobes are worn unevenly.
I don't know that he can check the dwell. He is running a Pertronix unit in place of points.

Joined: Dec 2017
Posts: 1,183
D
'Bolter
Its a good question as I have never used, nor would I ever use, a Petronix conversion. So I will ask out of ignorance, exactly how does the Petronix trigger?


Mike
Joined: Feb 2004
Posts: 25,315
H
Kettle Custodian (pot stirrer)
It's some sort of variation on the Hall effect switch. Early versions used a trigger ring that slipped over the breaker cam and spun next to a sensor that turned the primary current on and off. Those were such a sloppy fit that they could be moved a degree or so by hand, resulting in a built-in random 2 degree timing variation at the crankshaft. Later models simply use the high spot on the cam to trigger the sensor. A slightly worn cam, or a little variation in the position of the high spot induces the same random timing errors. To the best of my knowledge, none of them have the idiot proof circuit the General Motors HEI has to prevent module burnout in case the ignition switch is left on accidentally. I think the engineering department at Pertronix includes M. Maus and R. Goldberg!

The General Motors HEI reluctor and pickup coil an be adapted to an OEM distributor housing, with the HEI module mounted remotely on a finned heat sink- - - -even under the dash or elsewhere out of sight if someone wants an electronic ignition system that actually works- - - -one with a 40 year history of reliability, and millions of units produced.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!"
Abraham Lincoln

Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!

There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self.
Ernest Hemingway

WAG MORE- - - - - -BARK LESS!
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