hei gm ingntion
FTE Legend
Joined: Nov 2015
Posts: 30,912
Likes: 4,123
From: Angier, NC
It’s not just drop in the dist. set timing to factory spec, check sticker on firewall, and call it done. To get a little deeper into timing, below is a quick & dirty of what you do to check it.
There is what’s called timing advance curve. This is done both by vacuum & mechanical and specs should be in the factory book. I have also seen it in some tune up books too. You will need a dial back timing light to check this.
Because the HEI dist. was never in a Ford motor and being each motor uses different specs for both advances you need to check and maybe adjust them to work with your motor. It also could be the company has set the vac/mach. Advance close to factory spec but should be checked.
Check static timing as per factory. Most of the time you remove & plug vac hose, idle set to spec, check and settiming. Write down what it is set to.
Check mechanical timing: vac hose off and plugged bring RPM up to spec (2500rpm?) and check timing. It will be higher that static timing. Write down what you get.
Hook up vac hose and check vac timing: bring the RPM up to spec (2500rpm?) and check timing it will be higher than static & mechanical timing.
The book(s)should give you specs for each and see where yours is and hopefully it is close to factory. If not you will need to look into what is needed to fix it, there are kits made for this.
Dave ----
There is what’s called timing advance curve. This is done both by vacuum & mechanical and specs should be in the factory book. I have also seen it in some tune up books too. You will need a dial back timing light to check this.
Because the HEI dist. was never in a Ford motor and being each motor uses different specs for both advances you need to check and maybe adjust them to work with your motor. It also could be the company has set the vac/mach. Advance close to factory spec but should be checked.
Check static timing as per factory. Most of the time you remove & plug vac hose, idle set to spec, check and settiming. Write down what it is set to.
Check mechanical timing: vac hose off and plugged bring RPM up to spec (2500rpm?) and check timing. It will be higher that static timing. Write down what you get.
Hook up vac hose and check vac timing: bring the RPM up to spec (2500rpm?) and check timing it will be higher than static & mechanical timing.
The book(s)should give you specs for each and see where yours is and hopefully it is close to factory. If not you will need to look into what is needed to fix it, there are kits made for this.
Dave ----
Last edited by FuzzFace2; Dec 7, 2015 at 07:34 AM. Reason: word spacing
Lead Driver
Joined: Jul 2009
Posts: 6,477
Likes: 19
From: Sheffield, AL
Every engine is a case by itself, especially if any modifications have been made. The 4.9L engine in my 1986 was converted to Duraspark and is quite happy with the static timing @ 14 degrees BTDC. Original factory specs called for 10 degrees BTDC, for mine. The distributor was re-curved since my engine no longer has EGR and the carburetor came from a 1970 F350 with no emissions.
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