Wow! You are way to smart fer me! I have all I can do just to plug the numbers into one of many online calculators!!!

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2 Mopars come with Spark plug tubes. One is a world class, racing machine. The other is a 426 CI. boat anchor!

12.70 @ 104.6

I teach physics for a living, so I had to figure it out for myself.

Of course I still don't know what the results mean.

You did a fine job of collecting and reporting data.
Concerning the test of the mechanical advance.
The data says that you have zero initial advance set in.
And you are getting 28 degrees of mechanical advance.
28 is close to being good for a slant. I believe that 32 degrees
of advance is considered to be a good target. But your total advance is already coming in late.
I have the distributor set up in the 83 D150 to have all the advance in by 2300 rpm.

Concerning the vacuum advance testing. You reported 12 inches of vacuum at cruse, and at that you will get 12 degrees of advance. That seem reasonable, see comments below on octane.

Did the engine get into pinging when you did the test with the vacuum gauge connected and the advance cab disconnected?

Are you running regular gas, 87 octane.
You may need to go up to mid grade 89 octane gas.

With your static of 8.9 and a dynamic of 8.5 you are likely pushing some high numbers on cylinder compression. The slant in my 83 D150 has 8.5 static and 7.8 dynamic and I get cranking compression in the 180’s. Running empty it never has a pinging issue on regular gas. I do run premium when towing.

A cold air intake can also help to reduce pinging. Reducing under hood engine temps by running a 180 degree thermostat can also help. I have both of those on the 83 D150.

So try it without vacuum advance, if that is successful hook up the VA and try a tank of higher octane gas. If that is successful, no pinging, figure out a cold air intake and then dial in a few more degrees of initial advance.

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Doo Ron Ron and the Duke of Earl are friends of mine.....
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The program I used spat out a DCR of 7.9, (everything assumed your numbers are spot on), Josh is right you have to be careful on the
DCR with short cams like this as they don't bleed down like the bigger sticks, the compression test would give us a good picture of what is
going on in there...

That being said a few other thoughts here:

1) After break in did you properly lash the valves?

2) I would rebuild the carb, if it's a holley 1945, I would set the linkage to the 1976 settings and make sure the main jet was a #61 (these are the same as Holley 2300/4160 jets)
The 1974 OEM carb is horribly lean and runs a #58 jet, once the jet is changed and the linkage set to handle it, it should drive better and not lean out under load.

3) What vacuum accessories did you hook up under the hood? OSAC???? Just the EGR? (The pics look like you installed the vacuum amplifier and all the factory spaghetti to the
emissions controls).

4) Something is not right with your mechanical springs, they are too light, the 1974 375504x distributor usually plateaus in the mid 20's crank degrees and doesn't give you the last
4-5 degrees of advance unless the engine was at 5200 rpm... sadly with a heavy A-body and the 2.71 heavy duty rear axle with an automatic and stock convertor
the mechanical curve needs to be a bit slower than what you have (or swap to 3.21's...LOL...to match that quick advance). I would suspect that one of the springs is not tensioning correctly,
or has broken,or some springs got swapped in it's past... Doing what Lou would help "I'd get a recurve kit from Charles Brooks and shorten the mech adv slots and use diff mech adv springs",
or ordering a 3874598 1976 (Federal) slant six distributor would be a plug and play (set to 8 BTDC), if not wanting to pull apart the old unit.

Good luck.

-D.Idiot

I'll do a cranking compression test when I get a chance.
1) Yes, .015" intake and exhaust for the 2106r.
2) I don't know what vintage 1945 I have or what jet is in there. I suspect it's newer than 1974, so it might already have the larger jet. I'll open it up and check.
3) OSAC is bypassed. EGR is connected. The vacuum amp has the manifold connection and the EGR connections. The other vacuum connections from the carburetor are to the heated air inlet and the charcoal canister.
4) I know I'm running a low-RPM, high load setup here. I'll consider a higher rear gear as well as modifying the distributor.



Yes, with distributor vacuum disconnected I still had pinging in the same situations. I noticed the vacuum gauge was reading 1-3 inches during those times. I am running 87 octane and it's a bit old, in the tank since February. I'm looking forward to burning it all off and refilling.

Funny you should mention cold air intake. I know the air cleaner has the heating system to provide 100 degree air to the carburetor, but my underhood temperature is actually much hotter than it was before I rebuilt the engine. That's because I filled the cooling system with waterless coolant. After a long drive yesterday and a few minutes of idling in the driveway, the block was 250 degrees (measured with infrared thermometer- radiator was 220 degrees). I wonder if I need to switch back to regular coolant. I'm running a 195 thermostat and I could swap in a 180, but I'm not sure how much difference that would make because either one will be open full time.

And before the rebuild, the block measured out at what temperature (in the same spot, after the same amount of runtime, measured with the same thermometer)?

Block temperature doesn't really determine intake air temperature. If you want to knock 30° off the intake air temperature, just duct the air cleaner snorkel to the front of the engine bay. There's often a nice round hole in the radiator support panel, near the battery, that you can use as a second preference if you can't adapt a later '70s duct that attaches to the top of the rad support panel. However you do it, make sure you don't create a rain scoop.




If you want more/worse pinging, yes, you should switch back.



Not much if any.

What spark plugs are you running? What do they look like? Read them carefully after a run where the engine pings. Follow DusterIdiot's suggestions (careful carb rebuild and appropriate jet, careful distributor advance mechanism map-out and dial-in). I think paying attention to these things (distributor, carb, plugs) is going to get you where you want to be.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Seems like this is an obvious place to start. If it's too lean, messing about with the timing and everything else isn't going to be very effective.

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Point taken.


Around 190-200. I never carefully noted the number. Because it was always close to the thermostat design temp, I just assumed the thermostat was working as designed.

They are brand-new NGK ZFR5N's, left at the factory gap 0.036". I'll see what they look like when I do the compression test, but I sure hope they look new because they have less than 100 miles on them!

That's not how this works. The thermostat sets the engine's minimum operating temperature, not its maximum or steady-state temp.

As for the spark plugs: you may wind up wanting a colder plug, like one or another NGK in their heat range № 6. But first get the distributor and carburetor squared away.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

I did a cranking compression test. To prepare, I started the engine and let it idle for maybe 10 minutes but I didn't let it reach full operating temperature. The plugs had more soot on the ends of their threads than I would expect after only burning a half-tank of gas since they were brand new (pic below). All the gaps required a bit of pull to get a 0.035" feeler through.

Compression results, after 5 engine rotations:
1 - 160
2 - 160
3 - 170
4 - 170
5 - 175
6 - 180

Plugs ordered 1-6 from top down in photo:

Those plugs are running hot. Check your fuel mixture (too lean?) and drop back to a № 6 heat range like these (Also, that looks like anti-seize compound on the plug threads. If it is, clean the head and plug threads and quit doing that.)

What kind of exhaust system is on this car?

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Could you elaborate on setting the linkage? It turns out the jet is a 61 already. Here are some pics.

(25) 22R-120-621 is jet number. jets for emissions came in close tolerance sizes. 621 jet flows slightly less than 622 jet, 623 flows slightly more than 622.

1974 was the first year for the Holley 1945, and they were very "buggy", notorious poor runners. It took a few years for most of the effups to be fixed. You will want to consider a different/better carburetor, whether that's a different 1-barrel or a 2-barrel (which, yes, can give better economy than a 1-barrel).

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一期一会
Too many people who were born on third base actually believe they've hit a triple.