I have a mildly built 440 six pack Challenger with a 4-speed and Dana. Pretty stock with a slightly hotter cam. I've been running a single point distributor for a few years and car ran good. I recently scored a correct prestolite dual point distributor and wanted to use it because that's what the car came with from the factory. When I bought it, I was told the distributor was stock. So I installed news points, checked the advance springs and greased the moving parts. The car now pings under hard acceleration. I checked the ignition timing and here is what I have:
8 degrees advance at idle with vacuum port plugged. 26 degrees total advance all in at 1900 RPMs. With vacuum advance hooked up, I have 8 degrees at idle, and 49 degrees advance all in at 1900 RPMs. I always though that you got about 20 degrees mechanical advance out of a point distributor, and another 15 or so more degrees with the the vacuum hooked up. Full advance coming in at 1900 RPMs leads me to believe it must have weaker weight springs. And the range from 8 degrees to 49 degrees with advance hooked up leads me to believe the slots on the weights were enlarges. Any distributor gurus out there who can give me some advice, other that putting in electronic ignition?
Thanks.

some of those 1968 and later smog 4spd prestolites had about 35 degrees in them. add that to your 8 and that's 43 and that won't work. you'll need some internal mods if this is the case.

try some stiffer springs. EDIT I'd shoot for 15-20 initial and 36 total (initial+mechanical) then play with the springs if it pings at WOT. The vac adv amount is non op at WOT & that is when it is pinging. As said above that particular dist might have way too much mechanical advance. Holler how it turns out.

What does it do if you run with the vacuum advance capped off?

Had that problem with a '69 340 in a buddy's car in the early 1990s. I had a fresh small block dual point on the shelf so we put that in. Car ran perfectly so I sent him home with my distributor. I went through his which included cleaning hard grease out of the advance plate bearing. Everything seemed perfect, but it still was pinging. Went out to a local yard that still had a bunch of factory dual points in search of a better breaker cam. After replacing that all was well with his car. I didn't have a dwell meter at the time, which may have shown the issue, but that is very likely the problem you are having.

What part number on your distributor tag? Starting in 68 cars where Emission cars with CAP. So besides leaning out carb, the distributor specs changed. Do you know what Letters are on the Cam stop plate?

For 70 normally looking at 13-15deg distributor advance. So that puts in 26-30 at balancer. Depending on Standard or Auto transmission. Timing was set between 0 degree to about 2.5 BTDC.
If distributor is worn, or sloppy, you will have even more advance. So what is your initial set at 8?

What is your carb jetting, is it stock CAP lean, or jetted richer?

What RPM are you checking for rmax timing?
Is this distributor stock or has someone modified it to get all the mechanical advance in early with light springs? Do you know either way?
If not find out first so we can give you good advice on this
BTW, I've never had a Mopar V8 engine, from 1955 up to 1976 year model, that the vacuum advance hooked up like stock, ported vacuum,would work on in neutral, no matter what RPM I revved them to

Will try tonight when I get back.

I have one of those fancy timing lights that measures timing using the TDC mark on the damper. It also reads out RPMs simultaniously. I can see that all of the mechanical advance is in at 1900 RPMs. I checked several times. I also check total mechanical timing several times. Starting with initial timing at 8 degrees, I measure 26 degrees from 1900 RPMs and up which gives me a total of 18 degrees mechanical, correct?

I don't have the distributor tag numbers handy but I'm pretty sure it was for a 1970 manual trans with a date of November 1969, but who knows if the tag was replaced or not. Jetting - I'm using 64s which is a little richer than the stock 62s. Maybe I should just plug the vacuum advance, set initial timing at 18 degrees so I end up with a total of 34 degrees? Will the car even start with 18 degrees initial?

Also what fuel are you running?

I miss read your first post. I guess going back to the beginning. First you need to make sure your dual point is grounded well. The rotating plate has a jumper wire that needs to be in good condition with solid ground to block. Second for a dual point you do need to check the gap and the dwell. Both need to be in spec. If a point set is not working well or grounding out your running on one point or with low dwell and not charging coil sufficiently. Since your on points now you need a good coil too. Once the distributor is in spec, knowing what the cam letters are and the slot condition would help know what mechanical is. If your measurements are correct (did you see what you had with old set up before swapping). Your distributor is only giving you 18 degrees as you stated and that means at the distributor it is a 9. That is low. So either someone welded up the slot, it is a racing cam/wrong cam, or both springs are too strong. Poor condition of weight and such can cause binding limiting advance too.

Your math is correct on 8 Init plus only 18 mech giving 26.

Your correct in tag can be moved, the distributor shaft has a Prestolite number, the cam stop has a 2 letter code that can be crossed from the manual to know it is correct and what it is. I have data on them so I can help.

If someone put a single point cam in, you will have low dwell, if they put a Right Hand SB one it, it will also not work right.

At this point your not really in an over advance condition when driving with only 26 total. IF that is correct.

What stamp # on the arm of the vacuum can?

I assume the pinging is when driving, not trying this at high rpm with vacuum in neutral?

I think a '70 manual trans Prestolite is going to have around 35 crankshaft degrees in it. if so that's your problem with 8 degrees initial.

I haven't paid as much attention to the 6 pack duals as the hemi, but some interesting stuff in the presolite book and mopar service manual. Some errors/omissions too.

The Early 6 pack Manual was 4014C. That would have 30 mech at crankshaft with about 22 max vacuum. Initial is 5BTC

The 70 Service manual seems to have an error and the manual shows wrong distributor and data is same as Auto (Auto matches Prestolite). I think your 70 Manual should have 30 mech and 5 or less Initial.

You should only have about 25 total at 1900 which you see. But you get the rest or 32 to 35 total at 4800 rpm. Vacuum plugged. Have you reved that high for total?

The 71 service manual which has the tune up data and matches the Prestolite shows a IBS-4019B with 11 mech max. With Initial at 5BTDC. Really interesting.

The 4019 and 4019 A do have 18 max mechanical which seems to match what you are seeing. The 4019 have vacuum max at 19deg.

The 71 had a flat curve too. All in at 1900rpm from the service manual at about 27 deg total.

I can't explain why the 71 six pac total advance is so low.

Getting confusing huh

All the OEM stock Mopar distributors I've work on have the amount of mechanical degrees stamp on the bottom of the rotor advance stub, you have to disassemble the distributors to read it. They are stamp with 11,12,13, and so on which is the amount of distributor advance, not crankshaft advance Which means 11 distributor degrees is 22 crankshaft degrees due to the distributor rotating at half of the crankshaft speed Ma Mopar liked a lot of mechanical advance, which make the motor have less initial or idle timing which is not good for what we hot rodders normally like
It is all fixable though
Shorten up the mechanical advance and use more initial, idle, advance
All the BB and most 426 hemi motors I know of seem to like between 34 and 36 degrees total, depending on which fuel and altitude

pretty sure all manual trans initial timing was 0 degrees and auto's were 5 degrees BTDC. I have a '69 service manual that shows 17-19 distributor degrees in a 4014b prestolitie and 9-12 distributor degrees in the vacuum advance. I bet a '70 distributor's about the same. a lot of degrees. if so any initial would be a killer on todays gas. a 4014a hemi distributor has about 3 degrees less in it, but the service manual still shows initial timing at TDC. basically degrees have to be taken out of the distributor to run much initial.

Tag number is 4017DS, date 340, part number 3438316.

Some of you guys are confusing Prestolite versus Chrysler distributors. Chrysler have the adv stamp # with L or R. Prestolite do not. They have 2 letter code L- or R- then you go to the Prestolite service manual to see what the advance is.

Only one Prestolite distributor of this vintage had 36 mechanical built in the distributor and that was the 69 440 HP manual tran. Auto got a Chrysler distributor.

6 pack and Hemi are different beast. Typical max since these where emission cars was 15 deg stop, or 30 at crank.

Did some research last night and matched service manual to Prestolite. Basically the 4014C and D which first used on the 69 1/2 A-12 and probably on the early 70 cars became 4017X types. The only difference in internal parts was the shift from the Prestolite type vacuum advance can to the Chrysler looking vacuum can.

4017D is correct for 70 6 pack manual late. DS means it was the service distributor provided over the counter. (Your shaft should be marked as an IAZ-3139LN May only be stamped 3139 LN.

If original here is what it should do:

Initial Timing set at 5deg BTDC

It has a 13 deg cam stop so max of about 26 deg mechanical at crank.

0 adv at 1150 eng rpm
2 deg at 1220
20 deg at 1800
24 deg at 3800
26 deg at 4800

add your 5 intial to the above. So ultimately you get about 31 at 4800.

Vacuum is 23.5 deg maximum at crank
0 adv thru 9"
2 deg 10"
10 deg 12.25"
20 deg at 15"
22 deg at 15.5"

I will repeat, that you need the gap and dwell to come in spec. Can't have one point set grounding out due to contact with frame or ground wire. Got to have a good coil and battery voltage.

Your initial can come down some.

I'll back off initial a few degrees and see what happens. I dont have a dwell meter, but I was very, VERY careful setting point gaps. Even if I had a dwell meter, how to you check with dual points?
OBTW THESE F-ING POP UPS ARE KILLING ME. IM USING MY DROID TO POST AND IM TYPING IN THE BLIND BECAUSE THE ADS ARE COMPLETELY COVERING MY SCREEN!!!

You set the dwell individually by blocking one set of points open with a piece of cardboard and setting the opposite set. Reverse the procedure for the other set. If I remember correctly there is a different dwell setting on dual points. For what its worth when I went to a Sun tool class we set distributors up using a feeler gauge as well as the dwell. Man that was a long time ago. As I recall you made changes on the settings to lessen the arc scatter. As cams wear along with bushings there is a lot more wiggle room on adjustment. Do as you said recheck the points and pull a little initial base timing out. Two degrees at a time. Have you tried different fuels? What octane are you running? No need to over think whats going on.