Timing & Vacuum Advance Questions

[Martin N.]

On a 1974 (convertible) L-48, TH400 trans, 3:08 gear & A/C I have eliminated the TCS system and the vacuum supply to the EGR valve. The factory timing spec for this motor is 8 degrees @ 600 RPM in drive. I'd like to know if I should have ported or full vacuum to the vac. advance can now at idle / in gear? The vacuum advance can does not appear to be original, but is working. I can get 93 octane fuel here and would like to see how much advance I can plug into this car, but need a good starting point, let's say 12 degress BTC? Will carb enrichment come into play here, maybe with the secondary jets? Any thoughts or guidance would be appreciated....THANKS.

Marty

[Edward J.]

Re: Timing & Vacuum Advance Questions

Martin, I would set the base timing to spec.s within 2 degrees of the factory spec., once you accelarate the car the mechanical advance kicks in after about 2000 RPM, and use full time vaccum advance.it will give you that little extra power your looking for driving around town.

Don't forget 74 is a lower horsepower year and a smog engine,and the carb.which is really leaned out. if you have the L82 it will give you extra HP.

You can also look at Dukes posts in the archives he's had much to say about exactly how the vaccum advance system and mechanical advance system works.

[Paul B.]

Re: Timing & Vacuum Advance Questions

as per Lars Grismund's timing papers, I'm going to put my '74 L-48 auto no A/C coupe to 10* to 12* initial timing, going to install the NAPA Echlin's VC #1765 vacuum canister which pulls in all the way @ 12" of vacuum. I'm also going with manifold vacuum, NOT ported.

...I did this exact set-up to the '68 327/350hp coupe that I just sold which used run hot. Before I sold it I couldn't get it over 165*. I couldn't let the car idle for 15mins and it would want to start getting over 210*.