Mapping my 340 ign curve

[KevinCar]

Hi
So i used an dial up timing light and "mapped" my distributor ignition curve, well, i wrote the timing curve down, not sure how to find a graph to "map" it?
1969 340, 10.5 zero deck, purple 276/284 .444/.453" , #2531894 heads, ld340 intake, mopar electronic dist with "oem black box" and dual ballast. 600 cfm eldelbrock, headers. 13-14" of vacuum @ 700 rpm idle. old school build from 2000, compression is 170-174, motor has low miles since build. I didnt build, bought in 67 dart. 727 tqflite, 3.55 suregrip rear.

initial is 12 degrees @ 650, 700-750
24 @ 1250
28 @ 1500
28 @ 1750
28 @ 2000
30 @ 2800
32 @ 3000
34 @ 3300

The car seems a little slow off idle untill 3000+ rpm, surges slightly at cruise, vacuum advance is disconnected and ports plugged.

i would like to reconnect the vacuum advance for more efficient burn and rid the nasty fuel smell at idle from exhaust.
It looks like i would need a lighter second spring or kit?
Would like more initial, car seems to like 16 degrees, idle speed stays same after 16 degrees, so i am assuming?
would need to limit the distributor above the 12 degrees , distributor has 22 degrees of mechanical, 18-19 may be best mechanical, not sure?
havnt tried hooking up vac advance, i should, but worried it will add too much, came disconnected with an initial of 10 degrees and pinged at 32 total but a tuneup with good plugs/cap, new wiring, and 94 octane cured that for present timing tune.
Vac unit appears adjustable type with good diaphram.
Tempted to just buy a new performance distributor with a performance curve or adjustability built in(would like to stay Mopar).

Or should i just try a new lighter advance spring setup for all in at a lower rpm, 2500?
Then add vac advance and adjust, just dont know if vac advance should come in early, near idle and continue up to the 20" vac i get at cruise.
too many unknowns for me and for here, but i guess the main question is this advance curve too slow? is 12 degrees "enough " initial, car does get hot during extended idle in hot weather but is fine when moving ( 7 blade solid, shroud, B body BB rad). I was thinking more initial might get me a cooler running motor(as would coated headers), but wouldnt vac advance at idle help that with even more advance at idle even with the 12 degree initial?
Need more test time with it , just looking for best approach.
thanks

 

[crackedback]

Depends on the advance unit in the distributor. What color is the rotor tower. Cast or bronzish looking.

OEM style or mallory on how you go about limiting mechanical advance so you can increase initial. You don't need much taken out. IMO, and as you've seen, the engine will probably like 16-18 initial better than 12.

Don't hook up the vac adv if it is surging. Surging can be a lean or detonation signal.

Heating up at idle can be not enough initial and fuel being burned in the exh port, heating things up. Set it to 18 and don't drive it, see if the temps at idle come down.

 

[KevinCar]

Yes , I am thinking that , although its not a big cam, it still has lope and at 14" of vac it would likely need more initial.
The "surge" is more like a stumble when cruising at moderate hyw speed or even at 30mph cruise, zero "surge" or hesitation when under throttle to accelerate, car does not bog at all off idle.
i dropped down a temp range to NGK BKR6E and they show a tan color, but i did not shut off after an rpm blast, just a regular check after driving and idling.

 

[KevinCar]

Rotor tower is cast color

 

[Plymouth 65]

I'd definitely increase the initial timing. If it starts to ping or is difficult to start retard it a degree or two. 65

 

[RustyRatRod]

What pistons are in it?

 

[KevinCar]

What pistons are in it?

Not sure

 

[RustyRatRod]

Not sure

So how are you sure about the zero deck height and "10.5"? I'm not bein smart. I'm just asking trying to help.

 

[KevinCar]

RPM drop from P or N to Drive results in a 150 rpm drop and what i feel is "too hard" of a clunk into gear

 

[RustyRatRod]

RPM drop from P or N to Drive results in a 150 rpm drop and what i feel is "too hard" of a clunk into gear

That's normally a sign that you don't have enough initial timing. The throttle blades get jacked too far open. But "just" a 150 RPM drop "ain't much". I'm seeing idle speed between 650-750, right? You might try pulling in about 18 degrees initial temporarily and see how it runs.

 

[KevinCar]

So how are you sure about the zero deck height and "10.5"? I'm not bein smart. I'm just asking trying to help.

I am not, just what the machine shop spec paper says, its old, "customer supplied" pistons. machine 001 C/R 10.5/ F1008 or could be E1008, smudged and 25yo paper. I just assumed a flat deck grind and was told it was "zero deck" compression so it required 91 or better, i use 94 from Chevron which is highest octane and no ethanol here in west coast of Canada.

 

[KevinCar]

That's normally a sign that you don't have enough initial timing. The throttle blades get jacked too far open. But "just" a 150 RPM drop "ain't much". I'm seeing idle speed between 650-750, right? You might try pulling in about 18 degrees initial temporarily and see how it runs.

That's normally a sign that you don't have enough initial timing. The throttle blades get jacked too far open. But "just" a 150 RPM drop "ain't much". I'm seeing idle speed between 650-750, right? You might try pulling in about 18 degrees initial temporarily and see how it runs.

Yes i try for a 650-700 rpm idle in D, 850 in P. when i lower the P idle to 700-750 the motor still idles around 650 in D but shakes and sputters, but never stalls. sounds nasty tho lol.

 

[RustyRatRod]

I am not, just what the machine shop spec paper says, its old, "customer supplied" pistons. machine 001 C/R 10.5/ F1008 or could be E1008, smudged and 25yo paper. I just assumed a flat deck grind and was told it was "zero deck" compression so it required 91 or better, i use 94 from Chevron which is highest octane and no ethanol here in west coast of Canada.

The 1008 is a FelPro head gasket number so that's not related to the pistons. From your cranking pressure, I'd bet you have the stock 2 eyebrow 340 pistons. You gave a lot of good info right off the bat. I commend you for that. Most don't and we have to assume.

 

[KevinCar]

I will try bumping up initial, will bring too much total. If it wants it, then i will have to figure out how to "limit" the total, still would need lighter springs in order to bring it all in by 2500? Dont have a welder for slots, not interested in FBO plate(cost to Canada and heard they can cause binding in plates), likely find a mechanic with dist experience and mopar slot /dist experience with welder (good luck in 2025)

 

[RustyRatRod]

I will try bumping up initial, will bring too much total. If it wants it, then i will have to figure out how to "limit" the total, still would need lighter springs in order to bring it all in by 2500? Dont have a welder for slots, not interested in FBO plate(cost to Canada and heard they can cause binding in plates), likely find a mechanic with dist experience and mopar slot /dist experience with welder (good luck in 2025)

Correct. You will have to limit total somehow. I know it's in depth, but I prefer disassembling the distributor, welding the governor slots and filing them back out to the appropriate lengths, once you determine where you want initial. The FBO limiter plate does not provide consistent or accurate limits. I don't know about 2500. That's pretty hot and you might get some spark knock. You'll just have to try it. My tried and true spring recipe is use one medium and one light spring from the kit. Almost without fail, unless it's an unusual combination, that nails it.

 

[KevinCar]

The 1008 is a FelPro head gasket number so that's not related to the pistons. From your cranking pressure, I'd bet you have the stock 2 eyebrow 340 pistons. You gave a lot of good info right off the bat. I commend you for that. Most don't and we have to assume.

Ya, its all speculation unless your the builder, as i bought it as is, much assumption on internals, shop paper doesnt specify parts except "customer supplied" as i believe it was assembled by owner and the info came second hand to me.

 

[RustyRatRod]

Ya, its all speculation unless your the builder, as i bought it as is, much assumption on internals, shop paper doesnt specify parts except "customer supplied" as i believe it was assembled by owner and the info came second hand to me.

Well, your compression numbers narrow the speculatin down pretty good. lol I'd say its a healthy stock early 340.....which is a good thAng.

 

[KevinCar]

Correct. You will have to limit total somehow. I know it's in depth, but I prefer disassembling the distributor, welding the governor slots and filing them back out to the appropriate lengths, once you determine where you want initial. The FBO limiter plate does not provide consistent or accurate limits. I don't know about 2500. That's pretty hot and you might get some spark knock. You'll just have to try it. My tried and true spring recipe is use one medium and one light spring from the kit. Almost without fail, unless it's an unusual combination, that nails it.

so your suggestion of springs with perhaps a 3000 rpm "all in" @ 34 degrees based on the initial i can find that the motor likes, which is likely higher than the 12 degrees its at. Is there a difference to which side the lighter spring goes on? because looking at my present curve it seems to rise fairly fast to 1500 rpm, then gain much slower through 3300 rpm, likely a light and heavy on it now?

 

[KevinCar]

Well, your compression numbers narrow the speculatin down pretty good. lol I'd say its a healthy stock early 340.....which is a good thAng.

It seems like more cam and compression than a buddies 1969 340 4 spd car with stock cam, motor seems very healthy its just more of a desire to get into the RPM quicker, being an auto, and getting rid of the surge when cruising. i had begun to believe it was from lack of vac advance, the fuel smelling exhaust could be settled down also, just unsure if thats the cam or partly the timing. Dont notice fuel smell when driving, beyond being an older design motor.

 

[KevinCar]

Correct. You will have to limit total somehow. I know it's in depth, but I prefer disassembling the distributor, welding the governor slots and filing them back out to the appropriate lengths, once you determine where you want initial. The FBO limiter plate does not provide consistent or accurate limits. I don't know about 2500. That's pretty hot and you might get some spark knock. You'll just have to try it. My tried and true spring recipe is use one medium and one light spring from the kit. Almost without fail, unless it's an unusual combination, that nails it.

There is an older mechanic here in my town with a Distributor machine, but he told me by phone that he can only spin point type distributors, he thinks, has never spun an electronic distributor but was gonna investigate if it can be done the same. Was considering just buying a new performance distributor from a shop that can spec the curve based on the MP map and my motors initial it likes. But i also see that as $$ and i should learn sometime lol. Or "the hard way"

 

[CFD244]

Following

 

[MOPAROFFICIAL]

How about removing one of the advance springs?
idle speed RPMs are enough to give around 18 degree initial from where its at now, with just one spring out. cant remember which. Whichever is slotted

 

[RustyRatRod]

There is an older mechanic here in my town with a Distributor machine, but he told me by phone that he can only spin point type distributors, he thinks, has never spun an electronic distributor but was gonna investigate if it can be done the same. Was considering just buying a new performance distributor from a shop that can spec the curve based on the MP map and my motors initial it likes. But i also see that as $$ and i should learn sometime lol. Or "the hard way"

@halifaxhops can help you with that and he's a member here.

 

[Mattax]

mopar electronic dist with "oem black box" and dual ballast.

That was added at some point 'back in the day'

13-14" of vacuum @ 700 rpm idle. old school build from 2000, compression is 170-174, motor has low miles since build. I didnt build, bought in 67 dart. 727 tqflite, 3.55 suregrip rear.

Decent compression and vacuum for that cam IMO

The car seems a little slow off idle untill 3000+ rpm, surges slightly at cruise, vacuum advance is disconnected and ports plugged.

Lets look at the timing. A little surge at interstate cruise could be a little lean in the main jets/rod combination. Go one step richer in the combo.

not sure how to find a graph to "map" it?

A piece of graph paper or computer spreadsheet. Lets do it.

initial is 12 degrees @ 650, 700-750
24 @ 1250
28 @ 1500
28 @ 1750
28 @ 2000
30 @ 2800
32 @ 3000
34 @ 3300

Timing on the vertical axis and rpm on the horizontal. Comparing your measurement with a Chrysler built Mopar Performance Distributor.

I don't know what's going on with no advancing from 1500 to 2000 rpm but I don't think the advance is why car feels sluggish to 3000 rpm. Might be a little too quick in for vacuum advance.

Yes with that cam, the engine probably would like more initial. But to do so you need to adjust the curve.

 

[RustyRatRod]

so your suggestion of springs with perhaps a 3000 rpm "all in" @ 34 degrees based on the initial i can find that the motor likes, which is likely higher than the 12 degrees its at. Is there a difference to which side the lighter spring goes on? because looking at my present curve it seems to rise fairly fast to 1500 rpm, then gain much slower through 3300 rpm, likely a light and heavy on it now?

No. No difference in what side the springs install on. It rises fast to 1500 because of the STOUT factory spring. It has a slotted loop on one end that allows quick advance before spring catches it.