Distributor advance spring choice

Metalmarty

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Hi all,

I've got a mopar performance distributor off of Richard Ehrenberg, which name is familiar with some people I guess.

I want to recurve it, the current advance springs in it are too strong. It seems to advance pretty late and I only seem to manage a total of 15 degrees of mechanical advance.

I want to dial in around 22-24 degrees of mechanical advance. And I want to have it advance a bit earlier. If I try to move the advance mechanism it's heavy to turn.

I've got a spring kit from summit with different color springs. I know that you can also mix and match springs to have a 2 stage advance curve.

What springs would be good to start with? And any tips? :)

The car is a 1968 Chrysler Newport 4dr HT. Weighs 4600lbs.
Current setup:
- mopar BB 400
- 452 heads
- edelbrock dp4b intake
- holley 750 double pumper
- mopar performance electronic ignition with blue box from Rick Ehrenberg
- Comp Xe268h cam
- hedman 78070 headers with 2x 2.5" full dual exhaust with magnaflow mufflers and no crossover
- 2300 stall converter
- 3.23 gears

IMG_20220628_205647.jpg


IMG_20220628_205741.jpg
 

volksworld

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ok i'm no authority on this...but many performance distributors are specifically modified to give less mechanical advance than stock, which now allows you to to run more initial timing to deal with agressive cam profiles and big carbs...so its highly doubtful that just throwing springs in it will change your 15 degree advance...it will just get it to max advance sooner which considering the amount of initial its designed to run with may be too much too soon and it may ping...idk if Rich is someone you can contact but i'd be talking to him before i tried to change anything
 

CBODY67

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FIRST thing to verify is that the degrees quoted are "engine degrees" or "distributor degrees". 15 distributor degrees advance would be 30 engine degrees advance, so this is important!

What is the ultimate actual compression ratio of your engine? The cam is slightly smaller (when all things are considered, like the assymetrical lobe configuration and the fact the valve stays at max lift for a full 10 degrees of crank rotation) than the factory HP cam. The torque converter stall speed should be approx the same as the 10.75" converter behind a 383 Magunm, too.

IF the "15 degrees" are distributor degrees, which would equate to 30 engine degrees, adding about 8 degrees initial BTDC timing would be appropriate, usually. Which would be about where the OEM stock 383 2bbl distributor specs would have been back then, I suspect. The reason I mention "383 2bbl" is that those motors usually had a pretty optimum advance curve, total 36-38 degrees total at 4500rpm or so. Lighter springs would make it happen sooner. The old Direct Connection Face Manual suggests to just remove the havey spring from the existing distributor, letting the light spring do all of the work. BEST to do any "playing/investigating" with the distributor on a distributor machine. @halifaxhops might could be a party to such action?

Enjoy!
CBODY67
 

Metalmarty

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ok i'm no authority on this...but many performance distributors are specifically modified to give less mechanical advance than stock, which now allows you to to run more initial timing to deal with agressive cam profiles and big carbs...so its highly doubtful that just throwing springs in it will change your 15 degree advance...it will just get it to max advance sooner which considering the amount of initial its designed to run with may be too much too soon and it may ping...idk if Rich is someone you can contact but i'd be talking to him before i tried to change anything

Thanks for the tip. It might also be that the springs are so strong that the advance is not all in yet at 3k rpm.
I've put a timing light on it and didn't rev it all to much over 3k rpm.
But I have to say, the springs are so strong that it is hard to turn the rotor by hand until max advance.

FIRST thing to verify is that the degrees quoted are "engine degrees" or "distributor degrees". 15 distributor degrees advance would be 30 engine degrees advance, so this is important!

What is the ultimate actual compression ratio of your engine? The cam is slightly smaller (when all things are considered, like the assymetrical lobe configuration and the fact the valve stays at max lift for a full 10 degrees of crank rotation) than the factory HP cam. The torque converter stall speed should be approx the same as the 10.75" converter behind a 383 Magunm, too.

IF the "15 degrees" are distributor degrees, which would equate to 30 engine degrees, adding about 8 degrees initial BTDC timing would be appropriate, usually. Which would be about where the OEM stock 383 2bbl distributor specs would have been back then, I suspect. The reason I mention "383 2bbl" is that those motors usually had a pretty optimum advance curve, total 36-38 degrees total at 4500rpm or so. Lighter springs would make it happen sooner. The old Direct Connection Face Manual suggests to just remove the havey spring from the existing distributor, letting the light spring do all of the work. BEST to do any "playing/investigating" with the distributor on a distributor machine. @halifaxhops might could be a party to such action?

Enjoy!
CBODY67

Hi CBODY67.
I got a dial back timing light on my car and revved to 3k rpm. All I got was 15 degrees of advance. (engine advance, not distributor advance). As I said above, this might be because of strong springs, that it's not all in at 3k rpm. I'd have to check.

I've got a smog era '77 400 engine in it with around 7.5 actual static compression. (although cranking compression is quiet good around 135-140PSI with the stock cam, haven't checked with the XE268H)
These low compression engines tend to like a lot of initial and total timing. I was aiming for 12-15 initial and ~36 total timing) around 2500-3000 rpm. But with 12 initial timing I only seem to reach 27-28 total timing at that RPM. Hence the reason of checking total timing and swapping springs.

@halifaxhops Do you have any tips and tricks for me? I'd love to visit you and learn a lot from you and your distributor machine (I saw on other posts). But it's a long way from home from the Netherlands :p
 

Boydsdodge

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Thanks for the tip. It might also be that the springs are so strong that the advance is not all in yet at 3k rpm.
I've put a timing light on it and didn't rev it all to much over 3k rpm.
But I have to say, the springs are so strong that it is hard to turn the rotor by hand until max advance.



Hi CBODY67.
I got a dial back timing light on my car and revved to 3k rpm. All I got was 15 degrees of advance. (engine advance, not distributor advance). As I said above, this might be because of strong springs, that it's not all in at 3k rpm. I'd have to check.

I've got a smog era '77 400 engine in it with around 7.5 actual static compression. (although cranking compression is quiet good around 135-140PSI with the stock cam, haven't checked with the XE268H)
These low compression engines tend to like a lot of initial and total timing. I was aiming for 12-15 initial and ~36 total timing) around 2500-3000 rpm. But with 12 initial timing I only seem to reach 27-28 total timing at that RPM. Hence the reason of checking total timing and swapping springs.

@halifaxhops Do you have any tips and tricks for me? I'd love to visit you and learn a lot from you and your distributor machine (I saw on other posts). But it's a long way from home from the Netherlands :p
On my 73 Imperial, I left the heavy springs in place, set the initial with vacuum gauge while adjusting carb for best vacuum and idle speed. 20 deg is what my initial is, then I recurved my mechanical advance for 16 for a total of 36 mechanical. Vacuum is on top of that.
 

HWYCRZR

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I went through recurving mine with my dial back timing light. Let me see if I can find the thread. It is trial and error and easier to change the springs on the workbench sometimes. Mine was advancing too fast so I went with progressively stronger springs until I was right on. The tricky part is getting the first spring light enough for the initial advance, then the second strong enough to hold off until you get further up the curve. This is where a distributor machine would be great, but not practical for one time use. Let me do some digging.
 

Metalmarty

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Thanks @HWYCRZR. That topic explains what I'm experiencing. I'm used to having most centrifugal advance all in around 2500-3000rpm. And not around 5k. With lighter springs it should come on a lot earlier with a lot more mechanical advance than the 15 degrees I've experienced.

I've disassembled my distributor. It has a light spring with preload for initial timing and a very heavy spring with no preload (and a little slack). I might try to leave the light spring and replace the strong spring.

What would a good all in rpm be for this type of engine, Trans, rear gear combination? It's a heavy car, I know. But getting the advance earlier can't hurt I think

IMG_20220629_195047.jpg
 
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HWYCRZR

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Our Mz Ruby has a driveabilty/tune issue. Any thoughts?

This thread has the specs for the 383 4bbl ‘68. These are the factory specs. These are in the service manual, I converted distributor rpm 2 engine rpm. It seems that I was told once that with today’s lower octane fuel a little slower advance doesn’t hurt anything (starting to advance at a little higher RPM). That being said my ‘68 383 2bbl is perfectly happy at the factory specs with 91 Octane, non ethanol. I rebuilt it bone stock, so don’t have to worry about Cam changes and such.
@halifaxhops knows a lot about distributors.
But setting the spring’s is a little bit trial and error.

Pulled from the linked thread above.

Below are the ‘68 383 4bbl conversions.
Between 750 -1050 engine rpm you should not get any extra mechanical advance from your base setting (5 degrees for 4bbl (68 spec for example)
At 1050 engine rpm it is within spec if you have 0 - 13 degrees advance above base (5 base +13 =18 total)
At 1520 engine rpm you should have between 20.2 & 24.2 degrees advance above base ( 5+ 20 to 24 = 25 to 29)
At 5,000 engine rpm you should be sitting at 29 - 33 degrees above base (5+29 to 33 degrees = 34 to 38 degrees total).
If your advance springs are a little weak. You will advance faster than you want. If you are running high enough octane and good quality fuel you may not get as much pinging but will run rough.
 

CBODY67

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Typically, the factory mechanical advance is spec'd for about 4200+ engine rpm. Some a bit later, usually. The 3000rpm level is usually for a bit more performance, but not as quick as the drag race engines at 2000rpm. As you can see, the weights in the Chrysler distributor are quite heavy when compared to weights in a GM/Delco distributor. Hence, the heavy springs in the Chrysler distributor when compared to those in the typical GM distributor.

From what I've seen over the years, there is no magical 30-50 extra horsepower in getting the advance curve in quicker than stock. The pay-off can be in a little bit more responsive engine and possibly better fuel economy on the road. So . . . you can spend a lot of time for little, if any, real gains.

Now, contrary to somewhat popular belief, you CAN make a low compression motor clatter with too much distributor advance. Just put more than the optimum timing in and it'll happen at part-throttle and WOT. So, 38-40 degrees BTDC max on a B/RB engine (initial + distributor).

Just some observations and experiences,
CBODY67
 

halifaxhops

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That smaller spring in the picture is a bit to heavy for what you are trying to do. I might have the one to get you close pm me exactly what you want to do. PS that kit you got from summet is for the "mallory" style MP distributors the chart there is not applicable to what you have and they are a bit shorter than the stock springs. Just FYI
 

Metalmarty

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Our Mz Ruby has a driveabilty/tune issue. Any thoughts?

This thread has the specs for the 383 4bbl ‘68. These are the factory specs. These are in the service manual, I converted distributor rpm 2 engine rpm. It seems that I was told once that with today’s lower octane fuel a little slower advance doesn’t hurt anything (starting to advance at a little higher RPM). That being said my ‘68 383 2bbl is perfectly happy at the factory specs with 91 Octane, non ethanol. I rebuilt it bone stock, so don’t have to worry about Cam changes and such.
@halifaxhops knows a lot about distributors.
But setting the spring’s is a little bit trial and error.

Pulled from the linked thread above.

Below are the ‘68 383 4bbl conversions.
Between 750 -1050 engine rpm you should not get any extra mechanical advance from your base setting (5 degrees for 4bbl (68 spec for example)
At 1050 engine rpm it is within spec if you have 0 - 13 degrees advance above base (5 base +13 =18 total)
At 1520 engine rpm you should have between 20.2 & 24.2 degrees advance above base ( 5+ 20 to 24 = 25 to 29)
At 5,000 engine rpm you should be sitting at 29 - 33 degrees above base (5+29 to 33 degrees = 34 to 38 degrees total).
If your advance springs are a little weak. You will advance faster than you want. If you are running high enough octane and good quality fuel you may not get as much pinging but will run rough.

Again thanks for the info :)
Currently I had set initial timing to 12 degrees (electronic ignition etc) and got ~27 degrees at 2500rpm.
I'd love to see it come in a lot quicker.

Typically, the factory mechanical advance is spec'd for about 4200+ engine rpm. Some a bit later, usually. The 3000rpm level is usually for a bit more performance, but not as quick as the drag race engines at 2000rpm. As you can see, the weights in the Chrysler distributor are quite heavy when compared to weights in a GM/Delco distributor. Hence, the heavy springs in the Chrysler distributor when compared to those in the typical GM distributor.

From what I've seen over the years, there is no magical 30-50 extra horsepower in getting the advance curve in quicker than stock. The pay-off can be in a little bit more responsive engine and possibly better fuel economy on the road. So . . . you can spend a lot of time for little, if any, real gains.

Now, contrary to somewhat popular belief, you CAN make a low compression motor clatter with too much distributor advance. Just put more than the optimum timing in and it'll happen at part-throttle and WOT. So, 38-40 degrees BTDC max on a B/RB engine (initial + distributor).

Just some observations and experiences,
CBODY67

I'd love to be more around the performance side with the distributor. I know that timing can sometimes result in little to no improvement, especially with the last tiny changes around the ideal ignition curve. However, sometimes it can make a big difference. For example in attached picture is a Chevy 383 smallblock (Yes I know... didn't remember a mopar engine comparison, but this works) that typically makes 480 torque and 470 hp with 36 degrees of timing. In picture below they (Engine Masters Motortrend) were testing the effect of ignition timing on HP and torque.

The ghosted blue and red line was with 21 degrees of timing
The normal blue and red line was with 31 degrees of timing.

They also did the test again comparing 31 and 36 degrees of timing, that resulted in smaller numbers (480 torque and 470 hp).
So again, if you are close to ideal, it probably won't matter as much.
But big changes can make big differences even at lower RPM.
I know I'm not going to pickup 50HP by a long shot in my case, but it is fun to fiddle with this stuff and it's nice to make it better, even with small changes :).
And in my case, stepping the timing up from 27 deg @ 3k rpm to 36-38 deg @ 3k rpm might make a nice difference.

Screenshot_20220630-081227__01.jpg


That smaller spring in the picture is a bit to heavy for what you are trying to do. I might have the one to get you close pm me exactly what you want to do. PS that kit you got from summet is for the "mallory" style MP distributors the chart there is not applicable to what you have and they are a bit shorter than the stock springs. Just FYI

I also came to the conclusion that I got the wrong kit when I dissassembled the distributor yesterday :). But thanks for noting that.
The springs are on the short side, bit still a lot lighter, might be fun to fiddle with it.

I will PM you to see if you have the spring setting I'm looking for. Thanks
 

halifaxhops

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I can send you a set f these if needed still have a few stashed. Prob do exactly what you want.
1656586597964.png
 

halifaxhops

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Hey Jerry yes O-189 as usuall. Man I have crap.
 

halifaxhops

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Those sets I have some how many I will put them on the side for you. I doubt they will be around long.
 
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