Opinions on my advance curve

[66FBCharger]

I have a stock 440 with what I believe is a Mopar Performance electronic ignition. I borrowed a dial back timing light and checked my mechanical advance curve. Here are my numbers:
I unhooked and plugged the vacuum advance.
RPM   
685 (idle)    5* BTDC
1000           5* BTDC
1200           5* BTDC
1500           14* BTDC
1850           26* BTDC
2270           35* BTDC
2550           35* BTDC

What do you guys think?

[firefighter3931]

That's a typical MP replacement distributor timing curve. Too much mechanical advance which limits the initial timing hurting power and throttle response. 

Even a bone stock engine will respond to increased base timing and will be easier to tune. 

A quick test to see what your engine wants is to adjust the base timing using a vacuum guage. Keep advancing the timing until you reach max vacuum and stop right there. Snug the distributor down and get your timing light on it to see what you've got. Subtract that number from 36 and you will know how much mechanical advance the distributor needs to supply. The rate of advance is controlled with the springs.


Ron

[66FBCharger]

What are my options besides buying a new setup?
Am I correct saying, on this distributor I would need to weld the slots up to cut down the total mechanical advance and I should change springs?
I'm guessing that I am better off with more initial advance rather than the centrifugal advance?

Ron,
I will do the test with a vacuum gage in the next week to see what my engine likes for base timing.
I am still interested in the Firecore setup. Please PM your phone number and I will give you a call about it.

[firefighter3931]

What are my options besides buying a new setup?
Am I correct saying, on this distributor I would need to weld the slots up to cut down the total mechanical advance and I should change springs?
I'm guessing that I am better off with more initial advance rather than the centrifugal advance?

Ron,
I will do the test with a vacuum gage in the next week to see what my engine likes for base timing.
I am still interested in the Firecore setup. Please PM your phone number and I will give you a call about it.

Depending on what vintage distributor you have there are different ways to modify the mechanical advance mechanism. The older MP conversion distributors typically had ~ 30* of mechanical advance. Those had non adjustable advance plates so you would need to weld the slots after figuring out what your combo needed for initial timing. The newer MP versions had adjustable stops making mechanical advance changes a lot easier.

The problem with the MP distributors as a whole is the advance weights and the shaft bushing. Over time the bushing will wear and the advance weights were never properly calibrated. The combination of a worn shaft and the miscalibrated weights will create spark scatter (Unstable timing). An easy test to see if your distributor has spark scatter is to rev it up to 2500+ rpm and keep the engine at a constant speed with the timing light on it. If the timing mark is jumping around you have spark scatter.

The basic idea with tuning the advance curve is to achieve the maximum vacuum at idle as possible. This makes tuning the carb's idle circuit much easier to dial in. The more idle vacuum the better..... as the signal to the carb boosters will be stronger resulting in better manners and throttle response. Getting the timing curve right means the fuel is igniting at the right time during the cycle ; you want the spark to burn the fuel while it's in the chamber for maximum power and efficiency. Retarded timing sends unburnt fuel out the exhaust and has it igniting in the header tube/manifold creating excessive heat and reducing efficiency. This is why retarded timing causes "glowing headers" and lots of engine heat. 


PM sent 



Ron