Distributor curve help needed

[Ricks70Duster340]

I just checked the curve of my stock distributor (ported vacuum blocked) and need some help to optimize. Car is a 70 Duster with a stock 360, stock converter, 3.23 gears, 28" tires. Distributor currently has FBO black & gold springs with no limiter plate.

500-24*
1000-24*
1500-25*
2000-27*
2500-33*
3000-38*
3500-41*

 

[QuickDart360]

Have you spoke to Don at FBO? He can help with the curve set up as well.

 

[RustyRatRod]

Yeah, it needs a limiter. 41 is too much total. That's a pretty low RPM for it too. It would probably work better with 34-36 total in by 2500-3000. How does it start hot? Does it lug the starter any? What about spark knock (ping)? 24 is gettin pretty high for initial.....but some like it. Maybe back it off to 20 and put the limiter on the 14* slots and see how it does. It'll probably be really close spring wise with one light and one medium spring.

 

[67Dart273]

Not sure I agree.................if it is starting out at 500 with no advance or not? timing at 24BTC at 500? If so there's less than 20 crank degrees in the dist????

What kind of cam you running 24BTC initial and with a stock converter and 3.23??

 

[toolmanmike]

Yep, way too much initial. 15° is probably enough.

I just checked the curve of my stock distributor (ported vacuum blocked) and need some help to optimize. Car is a 70 Duster with a stock 360, stock converter, 3.23 gears, 28" tires. Distributor currently has FBO black & gold springs with no limiter plate.

500-24*
1000-24*
1500-25*
2000-27*
2500-33*
3000-38*
3500-41*

Set your initial at 16° and your total will then be at 33° which is about right.

 

[Mattax]

I just checked the curve of my stock distributor (ported vacuum blocked) and need some help to optimize. Car is a 70 Duster with a stock 360, stock converter, 3.23 gears, 28" tires. Distributor currently has FBO black & gold springs with no limiter plate.

500-24*
1000-24*
1500-25*
2000-27*
2500-33*
3000-38*
3500-41*

a. Mostly for drag race or general use?
b. Are you going to use vacuum advance?

 

[Ricks70Duster340]

Not sure I agree.................if it is starting out at 500 with no advance or not? timing at 24BTC at 500? If so there's less than 20 crank degrees in the dist????

What kind of cam you running 24BTC initial and with a stock converter and 3.23??

Not sure about the cam, but it feels dead stock.

 

[Ricks70Duster340]

a. Mostly for drag race or general use?
b. Are you going to use vacuum advance?

All street use, and using ported vacuum

 

[Ricks70Duster340]

Yeah, it needs a limiter. 41 is too much total. That's a pretty low RPM for it too. It would probably work better with 34-36 total in by 2500-3000. How does it start hot? Does it lug the starter any? What about spark knock (ping)? 24 is gettin pretty high for initial.....but some like it. Maybe back it off to 20 and put the limiter on the 14* slots and see how it does. It'll probably be really close spring wise with one light and one medium spring.

No hot start issues. Pings just a little under load in 3rd gear (auto) when it is really hot outside.

 

[toolmanmike]

a. Mostly for drag race or general use?
b. Are you going to use vacuum advance?

Zactly! A stock 360 doesn't need that much initial and non sure not that much total

No hot start issues. Pings just a little under load in 3rd gear (auto) when it is really hot outside.

Yep back it up like I suggested. 24° initial is unnecessary and 41° total can get you into trouble with detonation. Let the vacuum advance ad in what it needs. You can usually adjust that as well through the vacuum port.

 

[RustyRatRod]

No hot start issues. Pings just a little under load in 3rd gear (auto) when it is really hot outside.

Yeah, it definitely needs the total limited. You may need to back off initial.....but I wouldn't do it if it doesn't rattle once you get the total limited to about 34 or so.

 

[67Dart273]

Yep, wat too much initial. 15° is probably enough.

Set your initial at 16° and your total will then be at 33° which is about right.

Pretty much what I was thinking.............if I understood his post, 41 and 24 is 17* crank in the distributor which should be fine I'd think

 

[Mattax]

All street use, and using ported vacuum

OK. So my suggestion is to reshape the curve.
But you can start with simply reducing the initial.
I would not take it down to 15* just yet. If you do, it will probably be a dog from off idle to3000 rpmish when you stomp on it.

Here's what you measured.

Try something like 18* at 500 rpm.

 

[Ricks70Duster340]

OK. So my suggestion is to reshape the curve.
But you can start with simply reducing the initial.
I would not take it down to 15* just yet. If you do, it will probably be a dog from off idle to3000 rpmish when you stomp on it.

Here's what you measured.
View attachment 1715766055

Try something like 18* at 500 rpm.
View attachment 1715766058

I did put it back to 16* initial and it is most certainly a bow-wow. Very lazy at low speeds. Will put it up to 18 and try again.

 

[RustyRatRod]

Yup I figured. LOL The reason is because it has LOW cylinder pressure. That's why it likes a LOT of timing and if you back it off, it'll run like a dead dog. It's just something you're gonna have to play around with.

 

[CFD244]

Make sure that your balancer is true TDC. Maybe you are not at 24* at idle?

 

[Mattax]

Made a goof in the graphs above (at 3500 rpm) when I plotted out the timing you measured.
Fortunately doesn't change the main point.

In gray is the range where I think the timing ought to be.

So the next question is how to get there.
The first thing to do is reduce the tension of the primary spring. That's the spring with tension when the distributor isn't turning, or turning slow. On a Chrysler distributor you do that by turning the spring perch (circled).

You don't have to disassemble the distributor unless its really stubborn.
You can file a screwdriver into a tool to adjust from the top.

Or,
if both springs have tension on them, then turn both spring perches until they have the least amount of tension.

Or, better yet, if both springs have tension replace one spring with a long looped spring. In that case, don't reduce the tension on the primary spring. Not yet. Test first.
Example of a long looped spring.

The loop length and perch position determine how many degrees into the advance the second spring begines to assist.
But that's for later.

 

[Ricks70Duster340]

The pins in my distributor do not have those notches, so guess I will need to change the springs. Attached is a picture of my setup.

 

[Mattax]

I did put it back to 16* initial and it is most certainly a bow-wow. Very lazy at low speeds. Will put it up to 18 and try again.

You might be able to drop it to 16 or less at idle. My concern was how it was going to respond when you drove it.

If its an automatic, you can experiment by checking for most power (least drop in rpm and vacuum) with placed in drive at idle.
But within 50 to 100 rpms above idle rpm, the timing should advance.

Take a look at the factory timing specs to get an idea of how quickly timing is added above idle rpm.

That was true even with non-performance cams (with less overlap and better compression at low rpm)

 

[Mattax]

The pins in my distributor do not have those notches, so guess I will need to change the springs. Attached is a picture of my setup.

View attachment 1715766073

So with those you gently bend the perch.
Interesting though. I've only seen that on the Chrysler built magnetic pickup race distributors.
Wait. Is that a points distributor?

For street use. I'd still encourage using a long looped secondary spring.
With an ECU, for racing it will help insure no retard at top end.

8.5 on the governer (aka cam plate, aka slots) means there is around 17 degrees in the advance.
That matches well with what you measured.

Dont think you'll need to reduce the advance any.
I think you're pretty well set up if you pop in a heavy long looped spring and the softer of the primary springs. Then you'll be close enough to fine tune to whatever degree you're interested in persuing it.

 

[Ricks70Duster340]

So with those you gently bend the perch.
Interesting though. I've only seen that on the Chrysler built magnetic pickup race distributors.
Wait. Is that a points distributor?

For street use. I'd still encourage using a long looped secondary spring.
With an ECU, for racing it will help insure no retard at top end.

8.5 on the governer (aka cam plate, aka slots) means there is around 17 degrees in the advance.
That matches well with what you measured. View attachment 1715766092
Dont think you'll need to reduce the advance any.
I think you're pretty well set up if you pop in a heavy long looped spring and the softer of the primary springs. Then you'll be close enough to fine tune to whatever degree you're interested in persuing it.

I believe this was a points distributor that someone put a Pertronix unit into. I don't have a long looped spring, so should I replace the heavier black spring with a lighter one?

 

[Mattax]

I believe this was a points distributor that someone put a Pertronix unit into. I don't have a long looped spring, so should I replace the heavier black spring with a lighter one?

You could try that.
Or if your good with shaping little things, make the black spring's loop a little longer.
Just a heads up that being a spring, not going to be able to bend it too many times.
I'm sure we can find you a long looped spring if you want.

 

[Ricks70Duster340]

I found a heavy long looped spring in my stash, so replaced the black spring with that. Also replaced the gold spring with the lightest which is silver. That change produced:

500-18*
1000-18*
1500-20*
2000-25*
2500-25*
3000-27*
3500-27*

 

[toolmanmike]

I found a heavy long looped spring in my stash, so replaced the black spring with that. Also replaced the gold spring with the lightest which is silver. That change produced:

500-18*
1000-18*
1500-20*
2000-25*
2500-25*
3000-27*
3500-27*

I think still too much initial and the heavy long slot spring doesn't get you to 34° at rpm where you need to be.

 

[Mattax]

I think still too much initial and the heavy long slot spring doesn't get you to 34° at rpm where you need to be.

He's getting there.

He learn more going step by step and seeing the changes he makes.