Timing question

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Aug 4, 2024 | 09:01 PM

#16

440 sixpack

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Same thing, it shouldn't have vacuum at idle. all other ports are manifold vacuum and they should.

Aug 4, 2024 | 09:06 PM

#17

Dazman63

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That makes sense, but it’s funny it had a vacuum with the old spark plugs.

Aug 7, 2024 | 12:45 PM

#18

tbear853

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From: The Shenandoah Valley

The spark does not necessarily occur when the rotor is pointed direct at #1, it occurs when the current can make the leap. The points or reluctor serve to recharge the coil in concert with the rotor passing the plug wire terminal, so there'll be a charge ready to make that leap.

Aug 15, 2024 | 04:46 PM

#19

Dazman63

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So I dialed the timing back to 15 deg BTDC and it seems fine.

Two things I’m still wondering about, the erratic vacuum needle, fluctuating rapidly around 2” between 14 and 16 Hg and the RPM on the timing light varies about about 24 RPM. For example, 48, 55, 59, 66, 68, 47, 52, etc. it’s never steady, but the tach in the truck seams stable. Not exact RPM numbers, they’re just provided to give you an idea of how the RPMs are behaving.

Could these be related or is it normal for RPM to vary on the timing gun depending on the cam?

Aug 16, 2024 | 06:19 AM

#20

jflem

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From: Longview Texas

Vacuum fluctuation could be due to your cam for sure.
I have not seen a timing light that measures RPM. More information on that needed.

Aug 16, 2024 | 08:49 AM

#21

Dazman63

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The previous owner had the engine rebuilt and put in a Cams Xtreme Energy Camshafts 32-242-4.

Aug 16, 2024 | 10:15 AM

#22

440 sixpack

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most good lights give the RPM.

I wouldn't worry about the RPM. I would worry about the curve.

Aug 16, 2024 | 12:37 PM

#23

jflem

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From: Longview Texas

I have a Matco light but it does not show RPMs. I purchased it in 1982....that may be why. LOL

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Aug 16, 2024 | 05:40 PM

#24

Dazman63

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Quote:

Originally Posted by 440 sixpack

most good lights give the RPM.

I wouldn't worry about the RPM. I would worry about the curve.

You mentioned it before and that’s some good advice.

I have the MSD Pro-Billet 8477 and I’m contemplating getting the kit with the different springs and cams. The current set up from factory gives the slowest advance curve possible.

I researched a bunch of threads on how to determine the curve using various RPM’s. For example, 500, 1000, 1500, etc.

I think I may need my total timing all in around 2,500 to 3,000 RPM.

Thoughts?