Can someone please explain this..

[Mark1972]

Regarding the ignition, I had originally bought one of the ready to run distributors from 440Source(yes, poor choice). Well it didn't work, so a few weeks ago installed a Proform 440-428 unit. Works great. No issues. Here's my question, and forgive my ignorance. The engine builder told me to never hook up the vacuum advance on the distributor. Plug it and leave it. When I asked him why, he said it would pull 55 degrees and the motor would detonate big time. Can someone please explain why this would happen? Everyone who has looked at the car or worked on the car has asked why I haven't hooked up the vacuum advance. The initial timing is set at 15-17, and the total is set at 36. Automotive electrical is a huge weak spot for me, and I literally need someone to explain. Thanks for any and all responses.

 

[turbine68rt]

The vac advance, when connected to a ported source comes into play off idle and during light load cruising when the fuel mixture is leaner. It needs additional advance to accomplish complete combustion under this type of condition. If your total all-in is 36°, the vac advance drops off under heavy load/full throttle and relies solely on the mechanical advance. If it's mainly street driven I would be running the vac advance. Just my opinion. I use it on mine and it performs great with no detonation @ 16° initial/34° all-in with the FBO limiter plate.

 

[440Coronet500]

Hook it up and take it for a ride. If you get detonation back out the timing a degree or two. 440'

 

[Don Frelier]

I would try it. Is your hearing good? Some people can't hear high frequencies. Maybe take a young person with you if you think you might not be able to tell. You can just stop and plug the vacuum line if it pings.

 

[jamie]

Sounds like your engine builder doesn't know how to build a proper ignition system.Hook up a mity vac to it and check the vacuum open and closed.Make sure that canister will work for your application.

 

[RJRENTON]

The vac advance, when connected to a ported source comes into play off idle and during light load cruising when the fuel mixture is leaner. It needs additional advance to accomplish complete combustion under this type of condition. If your total all-in is 36°, the vac advance drops off under heavy load/full throttle and relies solely on the mechanical advance. If it's mainly street driven I would be running the vac advance. Just my opinion. I use it on mine and it performs great with no detonation @ 16° initial/34° all-in with the FBO limiter plate.

I concur....the reason for the ported vacuum advance is because leaner fuel mixtures require more time to burn and therefore they must be ignited sooner. At wide open throttle, vacuum advance falls off to zero (no advance) the engine relies on the static timing plus the mechanical advance. Be prepared for a barrage of differing thoughts and opinions.
BOB RENTON

 

[Fran Blacker]

Ehrenberg in this months Mopar Action tech question said never run without a vacuum advance on the street. His opinion is gas washes your cylinder walls and wears rings prematurely.

 

[Mark1972]

I would take a good friend who is way better at this stuff than I am, and let him listen, but my hearing is good, lol. Much appreciate the advice. I will follow your advice, and report back what happens.

 

[440+6]

On mine i run 17 initial 38 total mechanical and around 52 total with ported vac advance.
Just perfect!

 

[myk r sanchez]

There is no standard when it comes to timing in general. What works for one car will detonate another. Same thing applies to the vacuum advance, and of course it can help to pull 55* of advance if it's set up improperly. Try it out on your car and see if it helps your fuel economy during light throttle and cruising scenarios...