timing my 440 TNT

[stain]

I recently did a distributor rebuild on my 68 Chrysler 440 TNT. New bushings, new/used shaft and a Pertronix ignitor and Pertronix coil. Ballast resistor bypassed.
The car seemed to run "ok" but seemed to be lacking to me. It felt like there was more on the table.
The timing was set to the factory 5 deg TDC initially.
After some research I set my timing using a vacuum gauge and setting it to highest vacuum then backing it off 2 degrees.
Highest vac was 22 degrees. I set it at 20. No starter kickback
WITHOUT the advance hooked up the timing was as follows.
RPM ADVANCE
650 20
1500 28
2000 34
It seems like it stops advancing at 2000 rpm
With vacuum advance
RPM ADVANCE
650 20
1500 43
2000 50

I figure I have 14 deg mechanical advance with an additional @15 degrees vacuum.
I thought this looked good? On the test drive huge spark knock. Big spark knock as soon as you accelerate from a 15mph roll on. I kept adjusting and it settled in at 12 initial to stop the spark knock.
I am new to this distributor recurve process and have been doing more than my share of reading. Am I missing something? Am I wrong in my calculations? Do my mechanical numbers seem low?
I do have an FBO plate on the way but at this point I am a bit confused as to what setting I need. I don't believe the balancer has slipped...
I think need to remove my distributor and see what the advance plate says.

 

[furious70]

Without adv numbers didn't look too bad.
What's the specs on the rest of the engine? Bone stock? Mileage?

 

[stain]

bone stock. Previous owner installed a new timing chain. @77k

 

[furious70]

What gas do you run

 

[stain]

I had been running 91 non-ethanol but the last fill went with 87.
Forgot to mention new vacuum advance can also.

 

[furious70]

Probably becomes a personal preference thing, try it with the most timing the 87 will take for a tank and then try 91 or 93 and give it all the timing it likes then and see what the seat of the pants difference is and if it's worth the extra fuel costs.
That's what I would do.

 

[stain]

Does 14 degrees mech. advance seem low?

 

[CBODY67]

If you're getting that 10.0CR motor to run on what used to be 91 Research Octane fuel, when the old Regular was 94 Research Octane and Premium was 100 Research Octane. You're not doing too bad. Especially when the old Premium the RB engines were designed for was 97 Research Octane and later 100 Research Octane would be 95 Pump Octane.

Figure out what your fuel budget is and go from there. Yes, at the lower octane levels, there WILL be something "left on the table" compared to what it could be with Super Unleaded or better.

In one respect, you can forget the ethanol issues and use some anti-ethanol fuel additive. Especially if you can get better octane that way.

As to your worries about advance curve, it's that quicker advance which can be adding to the "clatter" issue. In the FSM for 1968, or 1966, look at the advance curve for the 383 2bbl and you'll see a nice factory advance curve that hits all of the recommended numbers, other than it's a little slower to get to the top numbers. With an adjustable vac advance can, you can adjust it to start at 5" Hg rather than the normal 9-11" Hg.

As for "drag racing" advance curves, the old Direct Connection Race Manual has a short section on that. "All in by 2000rpm", as to max centrifugal advance. As you are trying to run a 10.0CR motor on what used to be "sub-regular", don't worry about total advance "by the numbers", just set things for the least clatter for the fuel you are running. Setting the base timing "back 2 degrees from clatter" is also knowing you are safely back from "noise".

Chrysler's recommendation was also to run a compression ratio low enough so that full 36-38 degrees BTDC total WOT timing could be used. Rather than trying to retard the spark timing to compensate for lower octane fuels. Reason? If the engine is not running optimally, more heat is put into the cooling system, which might result in hotter than normal coolant temperatures. You're in Vermont, so you have a few months to go until the hotter times of the year. A hotter engine needs more octane to keep things quiet, too. End result, "the good" you might be doing now can need to be revised when the hotter times of the year arrive in VT.

Enjoy!
CBODY67

 

[stain]

Fuel cost is not an issue, my wife owns a gas station!!!!
Is it possible that although I think it is stopping advancing at 2000 rpm it is actually coming against the heavy spring, and then going higher later in the rpm range?
I need to try it at 3000 rpm I guess.
My FBO plate arrives today. I am half tempted to set it at 16, run the light springs, and set base at 18 and give it a whirl.

 

[furious70]

If you haven't measured up to 3000 with your dial back I definitely would to see where you're at

 

[stain]

I did go to @2600 and did not see the advance move but did not go further, maybe a mistake on my part.

 

[Boydsdodge]

Fuel cost is not an issue, my wife owns a gas station!!!!
Is it possible that although I think it is stopping advancing at 2000 rpm it is actually coming against the heavy spring, and then going higher later in the rpm range?
I need to try it at 3000 rpm I guess.
My FBO plate arrives today. I am half tempted to set it at 16, run the light springs, and set base at 18 and give it a whirl.

I was just going to write about you hitting the heavy spring at 2000, the 73 service manual shows full advance at 4000 or rpm for example.

 

[stain]

I was just going to write about you hitting the heavy spring at 2000, the 73 service manual shows full advance at 4000 or rpm for example.

Do you think my decision to run the plate at 16, initial at 18 and light springs is a wise one?
That theoretically will give me full @34 mech at @1800 and full vacuum advance @49-50 degrees

 

[Boydsdodge]

Do you think my decision to run the plate at 16, initial at 18 and light springs is a wise one?
That theoretically will give me full @34 mech at @1800 and full vacuum advance @49-50 degrees

Sounds good, but if engine not happy you just have to keep tweeking. Sounds like you know the ins and outs of the distributor pretty good. Hardest part I have with setting the curve is the tiny retainer spring down inside the shaft. I only use premium fuel in my old cars.

 

[stain]

plate at 16, initial at 18 and light springs-----spark knock at accel in 40-50mph range.
I backed off the timing to 15 degrees and only have slight knock at heavy loads, high end acceleration. I filled it with 91 non-ethenol last night and will see if it changes. I will keep tweaking it.
The car does seem be smoother, crisper and idles better.

 

[carfreak6970]

Every motor is different, but the 70 polara I have is running a close to stock 440 is only running about 8 deg BTDC. anything more and it starts to ping under light to moderate acceleration. I believe the FBO plate on that one is set to 10 deg, but I think that means distributor degrees which is half from what you would be measuring with your timing light at the crank.

 

[stain]

I took the number on the FBO plate to mean total mechanical advance, 16 meaning limited to 16 degrees of advance. I measured the 16 degree slot and it was slightly over .390
I thought the number printed on the stock advance plate was half of what was measured with a timing light, i.e. my plate says 11.5 which I take to mean 23 degrees of mechanical advance.

 

[halifaxhops]

I took the number on the FBO plate to mean total mechanical advance, 16 meaning limited to 16 degrees of advance. I measured the 16 degree slot and it was slightly over .390
I thought the number printed on the stock advance plate was half of what was measured with a timing light, i.e. my plate says 11.5 which I take to mean 23 degrees of mechanical advance.

Yes in distributor degrees the advance cams are marked as.