Choosing advance stop bushing MSD

[6667fan]

Changing distributors in my 482. Need to choose spring and bushing combo. I can change later but how about a starting point for my application? Whatever info is required I will provide. This is for max performance at strip. Engine is in a 67 Fairlane that probably weighs 3650 +\- with me in it. Old diz has two light silver springs with the 21 degree bushing. Engine has intermittently stumbled in 3&4 gear at top end of rpm range. Feel like it is not a fuel issue based on efforts made in that arena. Car gets off line fairly well.

Thanks

[blykins]

Drag race only?

[6667fan]

Brent, I’m hoping to hit my local track next month. The exhaust is currently off car so I have no concerns about making any changes that in theory will net the lowest ET. I can always change things later for more civil use on the street.

Are you gonna suggest locking out the distributor? I do have a 7AL-3 box in car so could utilize its retard feature.

[351crules]

lock it

[blykins]

Yes, in your situation, I would lock it out.

[My427stang]

Just to be clear, you are fixing the miss/stumble with the new ignition and just setting up the curve (or in this case no curve) for max power?

I have no issues with locked timing on a strip engine, especially with a start retard and if you know or figure out what the engine wants for total.  However, above 3000, if operating properly, the engine can't tell if it's locked or not.   

Good thing about an MSD is it's real easy to change either way but interested if the distributor swap fixes it

[6667fan]

Addressing both Ross, or hoping to. The distributor in engine has been in four different 427 iterations. The stumble has infrequently presented in all of them with that unit being the only constant. It currently has a phased rotor as an examination with a timing light showed the race part number rotor’s spark was not lining up well with the plug terminals inside the cap. Point being I just don’t have confidence in the existing distributor.

Edit:  I pulled the old distributor and measured its end play. It has .050 more than the replacement 8595. .083 vs .033.  Is there an accepted max end play on these units?

Edit:  Called MSD. On an 8595 they like to see .020-.030 or .025-.035 end play depending on who you speak to in the tech group, lol. I’ll be sending in the old distributor for repair and have it moved to lock out status.

Thanks

[Stangman]

will be in the dizzy tommorrow but if i remember correctly i have a silver spring and the next heaviest i forget what color. Timing at 16 with an 18 bushing. Now mine is more street.
Your car seems to take off pretty good. I have watched your car in the videos. Maybe try the new dizzy the same and go from there.

[6667fan]

Joe, there are two silvers. One is obviously heavier than the other and two heavy silvers are what those usually get shipped with. I decided to try the purple bushing, (19•), with the two light blue springs. Should be all in by 2800 but will confirm with my dial back. This is on the diz that is not all worn out. I wanted to move away from the 21• bushing that I had and put more initial in. My heads only need 32 total. MSD wants you to start with as much initial as the engine can manage without struggling to light off and finish up with the appropriate bushing for the remainder.

[fryedaddy]

on the street i use the purple 19 with 14 int,but i use 1 light blue spring and 1 of the next heavier springs because my timing was jumping around at fast idle with 2 light springs.when i added the heavier one on one side it stopped jumping around.

[mike7570]

Engine has intermittently stumbled in 3&4 gear at top end of rpm range. Feel like it is not a fuel issue based on efforts made in that arena. Car gets off line fairly well.
Thanks

The only time I had a stumble at the top end of the rpm range it was either fuel related or the spark plugs. Once your past the rpm of the advance in the distributor it should remain constant throughout the run. With it happening in 3rd & 4th gear it sounds like it’s running out of fuel. My smaller tunnel port developed a top end stumble when I tried a single 1050 carb. It was emptying a single dominator at the top end before it was worked out. What type of plugs do you run?

[6667fan]

Mike, I’m running Autolite 3924s gapped @.034. The two 715 cfm Quick Fuel carbs are fed a minimum of 6.5 psi via a RobbMc mechanical pump and his regulator. I have run as much as 8 psi trying to rule out fuel starvation. My A/F meter does not show a lean condition during the stumble. MSD tech says the amount of play in distributor could be the culprit. Maybe not from a timing perspective but from so much play something else suffers? I should know more when I get to the track with the other distributor.

Thanks

[gregaba]

I had a similar problem on my 351C about 15 year's ago. I chased it for about a year before I found the pin that hold's the dist gear was wallowed out and causing my timing to be off at low RPM. When I replaced the pin and gear in the dist the problem went away.
Greg

[mike7570]

Mike, I’m running Autolite 3924s gapped @.034. The two 715 cfm Quick Fuel carbs are fed a minimum of 6.5 psi via a RobbMc mechanical pump and his regulator. I have run as much as 8 psi trying to rule out fuel starvation. My A/F meter does not show a lean condition during the stumble. MSD tech says the amount of play in distributor could be the culprit. Maybe not from a timing perspective but from so much play something else suffers? I should know more when I get to the track with the other distributor.
Thanks

Your running similar to what I used most of the time. Autolites and two 660’s worked best for me. The four fuel bowls make it a harder to run them out of fuel. I never had any plug problems with the Autolites I gapped at .035. Your probably on the right track with the distributor. I wish I kept my old stuff, I hear the new msd stuff and others are not as good as they use to be.

[cjshaker]

I've had 3, or 4, can't remember now, MSD pickups go bad. Each time it started with a random miss, then got a little worse before just going bad. Once when the car was going down the road, twice (or 3 times  ) while parked, once for a very short time. Not saying that's your problem, but if you run out of ideas, it might be worth a shot. I've also seen coils cause a similar situation to what you've got. They can get funky sometimes. Just a couple things to consider if the distributor gear doesn't fix it.

Also, a few times while doing Drag Week in the Mach, I would get high speed misses at the track. Car ran great going down the road but missed a few beats in the higher gears on the track. New plugs fixed it every time. They just didn't like it after a few hundred miles of steady cruising. Not sure how much you street drive your car, but another consideration.