Need Distributor Specifications

[AR67GTX]

Do you have any pictures of the distributor - springs, weights cam slots. The stock springs usually include one, very heavy one with a loop end on it with a lot of slack. That spring doesn’t come into play until the weights overcome the smaller spring first to rotate the cam and sling them out enough to take up the slack in the big spring and then from there, it’s stiffness slows the advance curve way down. I don’t know the rpm that big spring may top out at - it could be as high as 4500 to 5000 rpm’s. If that’s the case, you are only seeing a part of your total centrifugal advance by reving the motor up to 2500 rpm in the driveway. That could be another part of the mystery.

Got any pictures of the inside?

If dwell/gap gets way off, the motor will run poorer, but as Geoff said there is a broad range in the middle that you can’t really tell much difference from seat of pants. But if you don’t get the gap closed down and the dwell up, you are losing the advantage of a dual point and it’s increased voltage stability at higher rpm’s.

 

[AR67GTX]

Here is a picture someone else posted of what we concluded were likely stock springs. I’m not 100% positive of the thinner wire one but the heavier wire one definitely is - probably both are . But they would vary a little from a low powered motor to a hi-po motor.

I think there is sometimes a number stamped on the underside of the slotted cam that corresponds to its mech advance spec.

 

[AR67GTX]

Here is what Dragon Slayer wrote on identifying distributor cam specs:

”If you remove the cam, or clean off grease, either on top or underneath will be a number stamp. That would be distributor advance. 10 would add 20 degree mechanical at the crankshaft. What you could measure with timing light. Distributor turns half the speed of the crankshaft. By the 70s emission years most of those are stamped 15. Which means 30 total mechanical at high rpm. You service manual would tell you all the specs you need in chapter 8”

 

[4406bbl]

If you have the typical Mr gasket aftermarket light spring the wire is very fine, about half the thickness of the wire on the thin one in the pic. The pic is typical of stock springs.

 

[Dragon Slayer]

IBS-4006Y was used on the 67 440 4 speed but CAP car. It was the cars sold in CA and has a CA emission set up. Your distributor cam should be marked LV. It has a 15.5 degree advance at distributor. It puts in 31 deg mechanical at the crank and your initial timing was 0. The vac can would have a 10.5 stamped on arm and would add up to 20 deg vacuum at cruise at the crank.

So you need to validate the cam stop you have installed. You can NOT go with a high initial if you have the orig cam; you would have an excessive total. Total is just initial and mechanical. NO Vacuum. Unplug canister and plug carb port while tuning. You will not see full mechanical unless your arm is above 4000 rpm with orig springs.

Dwell matters. It is an indication of cam wear. It is a measure of how much time is available to charge the coil. Yes measured in degrees. If it is way low, you would probably start misfiring at high rpm because of insufficient charging of coil to fire spark plug.

The other thing you need to be aware of, is the single point Prestolite cams look just like the Dual point cams, except the diameter of the cam is smaller. This results in less dwell. They were the IBP distributors.

The Cam has the part number on the bottom, from that I can assist you with what it is. If stamped LV it is the correct 15.5 degree cam, you need to see if someone welded it up or left it stock.

 

[67 GTX]

IBS-4006Y was used on the 67 440 4 speed but CAP car. It was the cars sold in CA and has a CA emission set up. Your distributor cam should be marked LV. It has a 15.5 degree advance at distributor. It puts in 31 deg mechanical at the crank and your initial timing was 0. The vac can would have a 10.5 stamped on arm and would add up to 20 deg vacuum at cruise at the crank.

So you need to validate the cam stop you have installed. You can NOT go with a high initial if you have the orig cam; you would have an excessive total. Total is just initial and mechanical. NO Vacuum. Unplug canister and plug carb port while tuning. You will not see full mechanical unless your arm is above 4000 rpm with orig springs.

Dwell matters. It is an indication of cam wear. It is a measure of how much time is available to charge the coil. Yes measured in degrees. If it is way low, you would probably start misfiring at high rpm because of insufficient charging of coil to fire spark plug.

The other thing you need to be aware of, is the single point Prestolite cams look just like the Dual point cams, except the diameter of the cam is smaller. This results in less dwell. They were the IBP distributors.

The Cam has the part number on the bottom, from that I can assist you with what it is. If stamped LV it is the correct 15.5 degree cam, you need to see if someone welded it up or left it stock.

Thank you very much. It being a CAP distributor meant for very little (or no initial advance) does make some sense based on what I was seeing.

So from the factory then, no initial, so 0. 31 degrees mechanical, and then another 20 from the VA would give a full total of over 50 degrees. Isn't that way too much?

I'd have to check the cam to see if I can see any markings on it.
I believe the VA arm says 10 on it.

If total does not include VA, is 34ish degrees a good overall number to still shoot for?
I have the original carb on the car and I believe it only has a ported vacuum port, no manifold port. So then the VA always comes into play with my setup.

From what I found, it appears my mechanical advance is only around 12 degrees.
This is what I got last week:

RPM Adv (wo/w VA)
Idle 13/13
1500 25/44
2000 26/42
2500 24/47
Total Dwell: 27 degrees

For my VA being the style with the removable spring, can you please elaborate on how adjustable it is?
Will a different spring limit the amount of advance, or just change when it comes into play?

 

[Dragon Slayer]

Vacuum is during cruise. Low load, medium rpm. That would not be excessive and yes it is on ported which is off at idle and turns on as the rpm rises and the ported hole is exposed to venturi/manifold vacuum.

You need to rev it to 3500 to 4000 to see what total timing is (no vacuum).

 

[67 GTX]

Vacuum is during cruise. Low load, medium rpm. That would not be excessive and yes it is on ported which is off at idle and turns on as the rpm rises and the ported hole is exposed to venturi/manifold vacuum.

You need to rev it to 3500 to 4000 to see what total timing is (no vacuum).

Thank you. So just for my understanding, then having timing in the 40s due to the vacuum advance is ok?

And even with my ported VA, when I go wide open, that should drop off or still remain?

 

[AR67GTX]

Vacuum advance drops to essentially 0” and 0 degrees timing advance with wide open throttle. Yes, with vacuum advance connected you could see total timing + vacuum advance timing totally in the 40 + range While cruising at speed with light throttle (vacuum high) - not unusual. But, with those springs in the distributor slowing down goal centrifugal advance you might have to be cruising at 80 mph + to reach 40 degrees. It’s when your high speed cruise gets into the high 40 range (depends on a lot of variables) that problems may crop up.

 

[AR67GTX]

I have a IBS 4006 WS CAP Hemi distributor in my 66 Hemi Satellite with the lousy mechanical advance curve. I used The FBO timing plate to reduce centrifugal advance to 18 degrees at the crank and then I run 15 degrees initial timing - idles and responds very well. It has a reproduction Hemi vacuum advance can hooked up to ported advance…

 

[Dragon Slayer]

That IBS-4006W is the same cam (15deg at distributor) that the 68-69 Hemi used since 68 and 69 were all state emission.

 

[67 GTX]

Before I decide to tear into the distributor again, I did some more testing yesterday that I would like your guys opinion on.

I lower the gap on the primary points to .016, and with the secondary set blocked, my dwell was at 18, which is below spec. So I lower it to .014, and dwell went up to 20, makes sense.

Then I unblocked the secondary, which was previously set to .016 as well, and total dwell was only 24.
Then I lowered the gap on the secondary set all the way down to .009, and total dwell went to 25. It was at 25 the whole time when I incrementally lowered the secondary gap.

I then lowered the primary set to .010, and total dwell stayed at 25.

Now it is possible my meter is acting wonky, but something seems weird here. Dwell is charging time, so as the gap decreases, points stay closed longer, so the dwell should increase.

Any idea why the dwell seems to have plateaued, and I can't get it to increase anymore even with smaller gaps?

 

[Dragon Slayer]

Measure the diameter of the cam lobe flat to flat and point to point. Dual points should be in the .980" Flat and 1.03" pt to pt. A single point cam is .950" flat to flat and .995" pt to pt.
If the cam is wrong, dwell will be less.

 

[67 GTX]

Measure the diameter of the cam lobe flat to flat and point to point. Dual points should be in the .980" Flat and 1.03" pt to pt. A single point cam is .950" flat to flat and .995" pt to pt.
If the cam is wrong, dwell will be less.

I took some measurements on both of my distributors. Here is what I got (avg of all readings, which were all close):

Single point
Flat to flat: .948
Point to point: 1.004

Dual point
Flat to flat: .987
Point to point: 1.029

I also took vacuum readings, by putting a vacuum gauge onto the same line that went to my vacuum advance.
In inHg, at idle I have 11, then 1500-2500 I have 19, then at 3000 it’s 18.
With a quick Rev at idle, it jumps up to 25.

Based on those numbers, especially with the dual point, any idea why when I made the gaps on the points themselves smaller, the dwell wouldn’t go up?

 

[67 GTX]

Here is a picture someone else posted of what we concluded were likely stock springs. I’m not 100% positive of the thinner wire one but the heavier wire one definitely is - probably both are . But they would vary a little from a low powered motor to a hi-po motor.

View attachment 1314120

I think there is sometimes a number stamped on the underside of the slotted cam that corresponds to its mech advance spec.

I believe I have similar springs. One has a large loop and has less loops, the other is orange and has more loops on it.

 

[Dragon Slayer]

No unless the points are wrong, or the cam on point arm worn. You should not have vacuum at idle. If you do you are on the transition slot and blades open more than stock exposing the timed vacuum port. So you would have to factor that into your initial timing.

 

[67 GTX]

No unless the points are wrong, or the cam on point arm worn. You should not have vacuum at idle. If you do you are on the transition slot and blades open more than stock exposing the timed vacuum port. So you would have to factor that into your initial timing.

Hmm, points are new.
And that vacuum doesn’t seem to pull the VA enough on either the single pt or dual pt distributor to affect the timing.

I’ll have vacuum at idle as that’s the only available vacuum port that I have. I believe I don’t have a manifold vacuum port, only a carb vacuum port.

 

[67 GTX]

IBS-4006Y was used on the 67 440 4 speed but CAP car. It was the cars sold in CA and has a CA emission set up. Your distributor cam should be marked LV. It has a 15.5 degree advance at distributor. It puts in 31 deg mechanical at the crank and your initial timing was 0. The vac can would have a 10.5 stamped on arm and would add up to 20 deg vacuum at cruise at the crank.

So you need to validate the cam stop you have installed. You can NOT go with a high initial if you have the orig cam; you would have an excessive total. Total is just initial and mechanical. NO Vacuum. Unplug canister and plug carb port while tuning. You will not see full mechanical unless your arm is above 4000 rpm with orig springs.

Dwell matters. It is an indication of cam wear. It is a measure of how much time is available to charge the coil. Yes measured in degrees. If it is way low, you would probably start misfiring at high rpm because of insufficient charging of coil to fire spark plug.

The other thing you need to be aware of, is the single point Prestolite cams look just like the Dual point cams, except the diameter of the cam is smaller. This results in less dwell. They were the IBP distributors.

The Cam has the part number on the bottom, from that I can assist you with what it is. If stamped LV it is the correct 15.5 degree cam, you need to see if someone welded it up or left it stock.

Please see below pics:
The cam is stamped B on top, and LU underneath. Do you know what that cam belongs too/it’s specs?

 

[Dragon Slayer]

Yep, That is the Hemi in the cap years also 68 440 4 speed. 15deg at the distributor. So 30 at crank, and initial was 0 deg for hemi. For a 440 probably about 2 to 4 deg BTDC initial. You can look at the service manual for detail spec, but I would assume vacuum would start adding at 11. It should be 0 at idle with that carb. Try lowering idle and see if vacuum goes off.

Make sure the screws holding the points down, are not grounding out the arm when it opens. One screw head looks large.

 

[67 GTX]

Yep, That is the Hemi in the cap years also 68 440 4 speed. 15deg at the distributor. So 30 at crank, and initial was 0 deg for hemi. For a 440 probably about 2 to 4 deg BTDC initial. You can look at the service manual for detail spec, but I would assume vacuum would start adding at 11. It should be 0 at idle with that carb. Try lowering idle and see if vacuum goes off.

Make sure the screws holding the points down, are not grounding out the arm when it opens. One screw head looks large.

Thank you, I’ll look into this. I’ll also check on the vacuum. I believe it was also around 11 at 600 rpm.
Based on that, the total timing in my case would be initial + mechanical + vacuum? And that total should be around 34ish?