Timing Question - 440

[Frank2304]

I am timing a car that I finished recently and find that it likes 18* BTDC or more at idle. The motor is a low compression 1975 440 and runs strong. Any less I get a bit of stumble. No ping. It has a mild cam, 800 Edelbrock, hi-rise performer, headers, pointless ignition. My problem is that the mechanical advance in my dizzy wants to add 28* at 2,000 rpm and I end up with 46* total when my target is 38*. No ping at 46* but I'm guessing I must be close. So I am assuming my fix is to mod the dizzy mechanical advance slots so it totals 38*.

Today I had a brainstorm to set the initial timing to 10* BTDC without vac advance connected and then connect the vac advance line to the lower port (full vac even with carb plate closed). This moved the timing at idle back up to 18* BTDC due to the vac advance being connected to manifold vac. The total timing with just the mechanical advance is now 38* at 2,000rpm and about 54* at 2,000 with vac advance connected. So I am hitting the target timing numbers but what is the down side of doing it this way as opposed to having the vac advance in the upper port and revising the dizzy mechanical advance slots ? Am I giving up performance somewhere in the power curve? It drove fine. It did surge a little on one run down a straight road at half throttle. Thanks in advance...

 

[dvw]

The only issue is that under load you lose that 18 degrees do to zero vacuum to the advance pod. Shorten up the slots and reduce the total advance. No way it needs 46 total. However being low compression it might like even more than 18 initial. Just because you can't hear it detonating doesn't mean it isn't happening. And my pet peave. It's a distributor.
Doug

 

[Mopars & Missiles]

...And my pet peave. It's a distributor.
Doug

Agree with you Doug, only BLONDES are "dizzy".

 

[Mopars & Missiles]

Mr Frank, here's a very handy little device you might want to try.

http://4secondsflat.com/Mopar Mechanical timing limiter plate.htm

 

[Frank2304]

The only issue is that under load you lose that 18 degrees do to zero vacuum to the advance pod. Shorten up the slots and reduce the total advance. No way it needs 46 total. However being low compression it might like even more than 18 initial. Just because you can't hear it detonating doesn't mean it isn't happening. And my pet peave. It's a distributor.
Doug

 

[Frank2304]

The only issue is that under load you lose that 18 degrees do to zero vacuum to the advance pod. Shorten up the slots and reduce the total advance. No way it needs 46 total. However being low compression it might like even more than 18 initial. Just because you can't hear it detonating doesn't mean it isn't happening. And my pet peave. It's a distributor.
Doug

Thank you for the clarity. Much appreciated. And I promise to call it a distributor going forward. I'm going to try a few initial settings tomorrow starting at 18* and increasing a degree or two at a time. What do you think of those FBO Systems Limiter Plates instead of welding?
http://www.4secondsflat.com/Mopar Mechanical timing limiter plate.htm

 

[Frank2304]

Mr Frank, here's a very handy little device you might want to try.

http://4secondsflat.com/Mopar Mechanical timing limiter plate.htm

View attachment 411036

That looks like a great alternative to sending it out for welding. Have you tried this device yourself or heard any feedback on it? I'm going to do a search and see what users have to say. Thank you!

 

[Mopars & Missiles]

That looks like a great alternative to sending it out for welding. Have you tried this device yourself or heard any feedback on it? I'm going to do a search and see what users have to say. Thank you!

Yes, I'm using one now in one of my cars. MUCH better solution than trying to get the slots welded and ground to the proper size. Very easy to install also. I plan to install one in all my cars when/if needed in the future.

 

[IQ52]

The only issue is that under load you lose that 18 degrees do to zero vacuum to the advance pod. Shorten up the slots and reduce the total advance. No way it needs 46 total. However being low compression it might like even more than 18 initial. Just because you can't hear it detonating doesn't mean it isn't happening. And my pet peave. It's a distributor.
Doug

IT'S A DISTRIBUTOR............yeah baby!

While we're at it, it's probably not prolly.

 

[69L48Z27]

That looks like a great alternative to sending it out for welding. Have you tried this device yourself or heard any feedback on it? I'm going to do a search and see what users have to say. Thank you!

I have one in our 68 points distributor. Pretty slick product. I was basically having the same issue, lots of base timing them total timing was way out there. I definetly had a ping.

 

[oldbee]

Are you sure ur harmonic balancer hasn't slipped? Just throwing something out. 18deg. sounds awful high for trying to crank it over(?).

 

[67 coronet]

Are you sure ur harmonic balancer hasn't slipped? Just throwing something out. 18deg. sounds awful high for trying to crank it over(?).

i run my motor at a bit over 20,but i have a giant flat tappet cam.i need it to idle ok.

 

[Slap Stick]

And while we are at it, they are lifters. They dont tap anything. The tapping is done at the rocker arm and valve.
If we want to get technical they are followers.
Sorry. Couldnt resist.