MS 360 12 Vacuum Advance pod

[Joe L.]

Re: MS 360 12 Vacuum Advance pod

Never mind, I see the answer elsewhere.

Ken------

AC Delco has available quite a few distributor vacuum controls. However, every single one is manufactured by Standard Auto Parts Corporation and carries a "B" number. Several of the ones once available have been discontinued, though, and I don't know if this means that Standard Auto Parts has discontinued them or if it just means that AC Delco has decided not to carry these particular ones anymore.

These old distributor vacuum controls have got to be a "dying market" inasmuch as the last vehicles using them were built in 1974. HEI distributors which were introduced in 1975 also use vacuum controls but they are different than the ones used on pre-75 points-type and TI distributors.

[Douglas C.]

Re: MS 360 12 Vacuum Advance pod

O/k guys, looking back to post #1, my thread.

So, today had car running and here is what I have so far, including vacuum readings so I can pick the correct vac. advance pod.

1. Timing at 12 degrees initial, all in at 34 at 2,500 rpm's. I probably should adj. springs to have all in closer to 3,000 rpm's.
2. Using an adjustable vac. adv. pod right now, but don't like it. Timing at idle shoots up to 30 + degrees with this hooked up, adj. is just erratic, but it is just to be able to drive the car for today.
3. For a L68 with a 280 Magnum Comp Cam I can tell you it runs at about 185 degrees, and it is hot out today. Even idling for about 20 minutes in the driveway it won't get past 190 on the gauge. Plus, you just sense it is not running hot.
4. Car feels a little lazy, so I suspect the vac. adv. is just not right for now.

Now, I hook my vac. gauge to the fitting on the back of the manifold off of the power brake fitting, have around 14 " HG at 900 rpm's, at 2,500 rpm's it jumps up to 20 " HG, if I nail the throttle it spikes down to zero.

Does the up to 20" HG as I raise the rpm's to about 2,500 seem odd?

I assume with all in of 34 and I probably can go to 36 degrees I need 16 more degrees with vac. adv. Now is that one marked with an 8, meaning that would be 16 degrees at the crank?

Suggestions on correct vac. pod and other thoughts appreciated.

Thanks,

Doug

[Duke W.]

Re: MS 360 12 Vacuum Advance pod

The "pod" doesn't work because it contains space alien embryos. Get rid of it before they hatch.

You want a vacuum advance control (VAC). Apply the Two-Inch Rule and select the best fit to your manifold vacuum listed in post #15.

Your data indicates that full centrifugal only adds 22 degrees to initial. Is this what the '69 distributor specs are in the service manual or AMA specs? I need this info before I provide further advice. I also need to know if there is any detonation with the current setup.

As you increase revs with no load manifold vacuum always increases. If you increase revs to beyond the point of full centrifugal the timing should be the sum of intial, full centrifugal, and full vacuum, which should be at least 50 degrees.

Before you proceed with any other changes, install the proper VAC.

Duke

[Douglas C.]

Re: MS 360 12 Vacuum Advance pod

The "pod" doesn't work because it contains space alien embryos. Get rid of it before they hatch.

You want a vacuum advance control (VAC). Apply the Two-Inch Rule and select the best fit to your manifold vacuum listed in post #15.

Your data indicates that full centrifugal only adds 22 degrees to initial. Is this what the '69 distributor specs are in the service manual or AMA specs? I need this info before I provide further advice. I also need to know if there is any detonation with the current setup.

As you increase revs with no load manifold vacuum always increases. If you increase revs to beyond the point of full centrifugal the timing should be the sum of intial, full centrifugal, and full vacuum, which should be at least 50 degrees.

Before you proceed with any other changes, install the proper VAC.

Duke

It is the stock distributor, but my car had a Comp Cam 280 put in by the previous owner. So, factory specs for a L68 I would think are out the window. The Comp Cam 280 has fairly similar specs to a L71 factory cam.

Right now with 12 initial and 22 centr. I am at 34 @ around 2,500 rpm's. Reving past that I get a reading of around 55 degrees. So yes, the adjustable vac. adv. can is advancing too far. That is why I stopped and now asked to confirm the proper vac. can. I get no detonation and runs fairly cool. No run on when shutting off.

With 14 " HG at idle I understand the rule to have full advance at least 2" below that.

So, I need first to have a clear knowledge of for example B28. I know the 8 indicates 8", I don't know what the 2 is for, and I don't see where I can see how much advance degrees that adds. Is B28 NAPA VC-1810, Delco D1312C? You guys have better experience and information than I do on which can to pick & specs.

I have searched the internet and can't clearly find what vac. can will give me full advance at 12" or less and will add 16 degrees in total. That would make my 34 all in + 16 = 50 degrees. If I bumped my timing to 36 all in, then I would hit the I guess ideal 52 degrees while cruising down the highway.

Thank you. Doug

[Joe L.]

Re: MS 360 12 Vacuum Advance pod

It is the stock distributor, but my car had a Comp Cam 280 put in by the previous owner. So, factory specs for a L68 I would think are out the window. The Comp Cam 280 has fairly similar specs to a L71 factory cam.

Right now with 12 initial and 22 centr. I am at 34 @ around 2,500 rpm's. Reving past that I get a reading of around 55 degrees. So yes, the adjustable vac. adv. can is advancing too far. That is why I stopped and now asked to confirm the proper vac. can. I get no detonation and runs fairly cool. No run on when shutting off.

With 14 " HG at idle I understand the rule to have full advance at least 2" below that.

So, I need first to have a clear knowledge of for example B28. I know the 8 indicates 8", I don't know what the 2 is for, and I don't see where I can see how much advance degrees that adds. Is B28 NAPA VC-1810, Delco D1312C? You guys have better experience and information than I do on which can to pick & specs.

I have searched the internet and can't clearly find what vac. can will give me full advance at 12" or less and will add 16 degrees in total. That would make my 34 all in + 16 = 50 degrees. If I bumped my timing to 36 all in, then I would hit the I guess ideal 52 degrees while cruising down the highway.

Thank you. Doug

Doug------


The numbers in "B28" (or, any other "B" number) have absolutely no relationship to degrees advance or any other parameter. They are simply identification numbers used by Standard Motor Products.

A vacuum control marked B20 or B26 will come the closest to the specs you want. It's available under NAPA #VC1765 or GM #88924983. A B28 will also work and it is known as NAPA VC-1810 or Delco 1312C.

[Douglas C.]

Re: MS 360 12 Vacuum Advance pod

Doug------


The numbers in "B28" (or, any other "B" number) have absolutely no relationship to degrees advance or any other parameter. They are simply identification numbers used by Standard Motor Products.

A vacuum control marked B20 or B26 will come the closest to the specs you want. It's available under NAPA #VC1765 or GM #88924983. A B28 will also work and it is known as NAPA VC-1810 or Delco 1312C.

Thanks Joe. I finally did find internet info and it looks like the B20 (VC 1765) or B26 (VC 1808) is a good choice. The info list indicated both have 8 distributor degrees ( so, 16 at the crank) @ 11 to 13 " HG. And my L68 shows 14" to 15" vacuum at idle and at my current 34 degrees @ 2,500 rpm's all in mechanical the additional 16 degrees would give me a cruising total advance of 50 degrees. Since I have no detonation and runs fairly cool I can probably easily bump up the 36 mechanical giving me a cruising total of 52 degrees.

Does the above details sound like it would be on the money?

[Timothy B.]

Re: MS 360 12 Vacuum Advance pod

Douglas,

Sounds like your thinking is right on regarding timing and vacuum advance with your camshaft. With that idle vacuum reading of 14" and full manifold vacuum advance (total idle timing approx 30*), you may find the idle can be reduced some and still be stable. Hopefully a 12" control will still work as it may be best suited if that vacuum stays around 14".

[Douglas C.]

Re: MS 360 12 Vacuum Advance pod

Douglas,

Sounds like your thinking is right on regarding timing and vacuum advance with your camshaft. With that idle vacuum reading of 14" and full manifold vacuum advance (total idle timing approx 30*), you may find the idle can be reduced some and still be stable. Hopefully a 12" control will still work as it may be best suited if that vacuum stays around 14".

Thanks, I'm going to give a try to a B20 or B26, whichever I can locate, as my vac. at idle never records anything below 14 " HG.

Doug

[Duke W.]

Re: MS 360 12 Vacuum Advance pod

You didn't provide the centrifugal data for your distributor as I requested, so I took the time to look it up. According to the AMA specs for the 1111926 distributor, the centrifugal is 0 @900, 26 @ 3800. You claim you have a "stock" distributor. Either it has been modified or it is not functioning properly.

My recommendation is to correct your modified or malfunctioning distributor so it achieves the specified 26 degrees or up to 28. Then reduce initial timing to the range that provides 36-40 initial plus full centrifugal, and use the high end of this range if it doesn't detonate that that level.

If you are satisified that your reported idle vacuum is 14" @ 900 then the 12" NAPA VC1765 is correct for your setup. If you want to idle it lower it will generate less vacuum and may need the 8" VAC.

Duke

[Douglas C.]

Re: MS 360 12 Vacuum Advance pod

You didn't provide the centrifugal data for your distributor as I requested, so I took the time to look it up. According to the AMA specs for the 1111926 distributor, the centrifugal is 0 @900, 26 @ 3800. You claim you have a "stock" distributor. Either it has been modified or it is not functioning properly.

My recommendation is to correct your modified or malfunctioning distributor so it achieves the specified 26 degrees or up to 28. Then reduce initial timing to the range that provides 36-40 initial plus full centrifugal, and use the high end of this range if it doesn't detonate that that level.

If you are satisified that your reported idle vacuum is 14" @ 900 then the 12" NAPA VC1765 is correct for your setup. If you want to idle it lower it will generate less vacuum and may need the 8" VAC.

Duke

Yes Duke, I should have been more specific. It is the stock distributor unit, previous owner put a Pertronix in it and changed the advance weight springs. So, I started by putting springs to get all in at 2,500 and 34 degrees all in. As the car also has an after market cam I figured the stock L68 dist. specs would no be right. The cam is actually spec wise fairly close to a stock L71 cam.

So, that is my starting point and hoping now if I put in a B20 vac. can I'll be close to then dialing in good overall running.

I'll update as I go along and I appreciate your thoughts / information.

Doug