Is the dwell the same for a Petronix set up? - Team Camaro Tech
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post #1 of 18 (permalink) Old Apr 23rd, 16, 01:50 PM Thread Starter
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Is the dwell the same for a Petronix set up?

Is the dwell the same for the Petronix II set up verses the points? With points the dwell should be 28-32. When I set the timing I noticed that when I switched the meter to dwell it was way off from the recommended dwell. The 300 hp 350 automatic seems to run okay but then it might run better if the dwell is correct?

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post #2 of 18 (permalink) Old Apr 23rd, 16, 03:33 PM
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Re: Is the dwell the same for a Petronix set up?

Depends on which Pertronix. The standard one will run at 30 dwell. The II and III will vary the dwell automatically for performance across the RPM range. It is not adjustable.

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post #3 of 18 (permalink) Old Apr 23rd, 16, 08:18 PM
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Re: Is the dwell the same for a Petronix set up?

You only need to set the timing. There is no dwell settings to worry about when using Pertronix or Crane.

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post #4 of 18 (permalink) Old Apr 23rd, 16, 09:14 PM Thread Starter
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Re: Is the dwell the same for a Petronix set up?

Thanks. I won't worry about what it shows then. I did have the timing set higher than the 4 degrees BTDC and since I've timed it to 4 it wants to diesel a little when I turn it off. Should I advance the timing a little? Usually I would get a little ping on acceleration if it were timed a little advanced. This engine won't ping anywhere on the timing range. These engines used to diesel when we used regular instead of premium gas back when we could still buy real premium gas with a higher octane than 91.

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post #5 of 18 (permalink) Old Apr 24th, 16, 08:48 AM
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Re: Is the dwell the same for a Petronix set up?

SB like to see 36* total advance. If you don't have a back dial light then set it between 14*-16* initial. 4*-8* were factory settings to pass emissions and ran slow as a turtle.
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post #6 of 18 (permalink) Old Apr 24th, 16, 09:25 AM Thread Starter
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Re: Is the dwell the same for a Petronix set up?

Okay. Before I got my timing light and dwell meter out I had set it by ear. The timing light showed the mark was before the marker tab so I probably had it just a little too advanced or maybe close to where it should actually be. I had run it even advanced higher but the engine was running hot so I had retarded it. After I had set it to 4* it seemed to run smoother but it didn't have the power it had earlier. I remember now that my 69 SSRS 350 automatic I had in 1978 did the same thing. If I set it at the factory 4* it was a dog. If I advanced the timing to where it just pinged on acceleration and then backed it off about a degree it seemed to be just right.

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post #7 of 18 (permalink) Old Apr 24th, 16, 07:41 PM
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Re: Is the dwell the same for a Petronix set up?

Is your vacuum advance connected to manifold vacuum or ported vacuum?

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post #8 of 18 (permalink) Old Apr 24th, 16, 09:29 PM Thread Starter
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Re: Is the dwell the same for a Petronix set up?

It gets the vacuum from the port on the right(if you're facing it from the front)lower place on the 4 barrel Quadrajet.
When I get a little time I'm going to advance the timing. The timing also acted like it affected the air mixture when I set it lower.

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post #9 of 18 (permalink) Old Apr 25th, 16, 06:28 AM
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Re: Is the dwell the same for a Petronix set up?

Quote:
Originally Posted by 69ndpce View Post
It gets the vacuum from the port on the right(if you're facing it from the front)lower place on the 4 barrel Quadrajet.
When I get a little time I'm going to advance the timing. The timing also acted like it affected the air mixture when I set it lower.
That's the timed ported vacuum source on a Q-jet.

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post #10 of 18 (permalink) Old Apr 25th, 16, 07:28 AM Thread Starter
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Re: Is the dwell the same for a Petronix set up?

And? Is that good or bad reelknots?

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post #11 of 18 (permalink) Old Apr 25th, 16, 07:47 AM
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Re: Is the dwell the same for a Petronix set up?

Quote:
Originally Posted by 69ndpce View Post
And? Is that good or bad reelknots?
You'd be better off running manifold rather than ported (timed) vacuum to your vacuum advance canister. It will allow you to lower your idle speed screw which will help prevent after-run or dieseling which you mentioned you had an issue with. It will also allow more advance at idle and under low load conditions but when you step on the throttle the vacuum advance will drop out retarding the timing a bit to prevent the pinging you have. Read the "Timing 101" article for a detailed explanation (www.camaros.org/pdf/timing101.pdf). Ported or timed vacuum was an emissions thing, you don't want it, you don't need it and you'll most likely be much better off without it as will your Camaro.

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post #12 of 18 (permalink) Old Apr 25th, 16, 08:03 AM
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Re: Is the dwell the same for a Petronix set up?

You want manifold vacuum unless you have a newer smog motor.

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post #13 of 18 (permalink) Old Apr 25th, 16, 02:48 PM Thread Starter
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Re: Is the dwell the same for a Petronix set up?

Okay. I ran the vacuum like it was originally. Again, this is a 350 automatic. The power brakes, transmission modulator and RS vacuum run off of the multi vacuum port on the manifold. There is also a nipple that sticks our from the left side of the carb that goes to the air cleaner heat valve, which I'm not using. I think that has constant vacuum. Will that work?

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post #14 of 18 (permalink) Old Apr 25th, 16, 07:51 PM
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Re: Is the dwell the same for a Petronix set up?

Quote:
Originally Posted by 69ndpce View Post
Okay. I ran the vacuum like it was originally. Again, this is a 350 automatic. The power brakes, transmission modulator and RS vacuum run off of the multi vacuum port on the manifold. There is also a nipple that sticks our from the left side of the carb that goes to the air cleaner heat valve, which I'm not using. I think that has constant vacuum. Will that work?
Yes it should as long as it has full manifold vacuum at idle.

69 Camaro Z/28 RS, original Azure Turquoise, M21 & 3.73 12-bolt posi. NOM 406ci, AFR 210 heads, Straub hyd. roller cam & Dynatech 1-3/4" > 1-7/8" headers, QuickFuel 750 Annular. Photos at:
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post #15 of 18 (permalink) Old Apr 25th, 16, 07:58 PM
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Re: Is the dwell the same for a Petronix set up?

Quote:
Originally Posted by 69ndpce View Post
Okay. I ran the vacuum like it was originally. Again, this is a 350 automatic. The power brakes, transmission modulator and RS vacuum run off of the multi vacuum port on the manifold. There is also a nipple that sticks our from the left side of the carb that goes to the air cleaner heat valve, which I'm not using. I think that has constant vacuum. Will that work?
Yes it should as long as it has full manifold vacuum at idle.

69 Camaro Z/28 RS, original Azure Turquoise, M21 & 3.73 12-bolt posi. NOM 406ci, AFR 210 heads, Straub hyd. roller cam & Dynatech 1-3/4" > 1-7/8" headers, QuickFuel 750 Annular. Photos at:
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