Vacuum Advance

[JimKueneman]

Small Block. My 318 has a 9.5 degree vacuum advance stock. I am looking at replacements but none of them say if they are adjustable or what the total timing advance is. Where can I find one that is either adjustable or I can get one with more like 14-16 degrees?

Jim

 

[PurpleBeeper]

Small Block. My 318 has a 9.5 degree vacuum advance stock. I am looking at replacements but none of them say if they are adjustable or what the total timing advance is. Where can I find one that is either adjustable or I can get one with more like 14-16 degrees?

Jim

OK, stupid question #1 (it's early in the day, so I'm sure I will have more).....did you turn yours all the way with a small allen wrench?

Honestly, I have no idea what they "should" advance since mine has been disconnected for years....but
1. Maybe you could modify the little arm that attaches to the advance plate in the distributor to get more advance? Or the advance plate itself?
2. Maybe you figure out a way to use one of those circular "vacuum booster" things I've seen on early 70's small blocks to boost the vacuum signal?
3. I'm just shooting from the hip here.....not really sure about any of this.

Lastly, why do you need more vacuum advance? I've got so much initial timing on my motor I'd knock on race gas if I hooked up the vacuum advance.

Oh yeah, all the vacuum advance pods I've ever seen were adjustable.

 

[JimKueneman]

OK, stupid question #1 (it's early in the day, so I'm sure I will have more).....did you turn yours all the way with a small allen wrench?

Honestly, I have no idea what they "should" advance since mine has been disconnected for years....but
1. Maybe you could modify the little arm that attaches to the advance plate in the distributor to get more advance? Or the advance plate itself?
2. Maybe you figure out a way to use one of those circular "vacuum booster" things I've seen on early 70's small blocks to boost the vacuum signal?
3. I'm just shooting from the hip here.....not really sure about any of this.

Lastly, why do you need more vacuum advance? I've got so much initial timing on my motor I'd knock on race gas if I hooked up the vacuum advance.

Oh yeah, all the vacuum advance pods I've ever seen were adjustable.

The allen wrench adjustment is more like the preload spring adjustment to bring it in under less or more vacuum.
Because small blocks like about 32-34 total mechanical and about 50 for cruising so I am trying to hit that number. I only have about 42 with the vacuum now and 34 total mechanical. I will likely need to modify a cheap one from Summit.

Jim

 

[burntorng70]

I just got the aluminum one from Jegs . It is there own brand and comes with everything to adjust. Works very good and is a direct replacement for the stock distributor. It was around 150 bucks.

 

[burntorng70]

40500 is the part number.

 

[threewood]

9.5 stamped on the arm? I was under the impression that that number was crank degrees and that the true number was cam degrees, same as the mech adv plate (9.5 x 2 = 19 degrees vacuum) I may be waaay off here so I hope someone can confirm or deny.

Jim, how did you confirm the vacuum advance numbers? Curious because my advance is marked 9.5, non adjustable.

 

[JimKueneman]

9.5 stamped on the arm? I was under the impression that that number was crank degrees and that the true number was cam degrees, same as the mech adv plate (9.5 x 2 = 19 degrees vacuum) I may be waaay off here so I hope someone can confirm or deny.

Jim, how did you confirm the vacuum advance numbers? Curious because my advance is marked 9.5, non adjustable.

Yes mine is one without the "hex" end and is marked 9.5 on the arm. I have a high dollar Snap-On timing light with an advance dial. I have the advance on manifold vacuum and at 3000 RPM all I can get is about 42 degrees. Unplug the advance and I get about 32 degrees so I interpreted that as the can gives me about 9.5 degrees.

Now you mention it I know my weights were marked with 19.5 or something and I decided that with the 2 degrees ATDC on the emissions tag that would give me 34 degrees of timing when full in so the 2x theory makes sense......

Wonder if my diaphragm is getting hard and not pulling in all the way.... I need to buy a vacuum pump, my old Snap-on does not work any more.

Or I am thinking about this wrong and at 3000 RPM my vacuum is not high enough to pull it in all the way..... I need to look at it at idle.

 

[69Bee]

Get a MSD unit like I did for the Hemi. It can plug into your FITech, and makes the timing advance adjustable from the seat. Only cost a few dollars more than the MP electronic kit (which I already bought). If you want to borrow my vacuum pump, you can.

 

[67belvedere/225]

vacuum advance is for dancing the timing when your off the throttle to give the engine better fuel economy
so if like me your on it , you really don't need it or much advance

 

[JimKueneman]

vacuum advance is for dancing the timing when your off the throttle to give the engine better fuel economy
so if like me your on it , you really don't need it or much advance

I need it a lot! I have a 100 mile round trip just to get to a town! I need fuel milage when I can get it.

 

[JimKueneman]

Get a MSD unit like I did for the Hemi. It can plug into your FITech, and makes the timing advance adjustable from the seat. Only cost a few dollars more than the MP electronic kit (which I already bought). If you want to borrow my vacuum pump, you can.

Yeah if my FiTech supported timing I think I would cave in and do that. I am really thinking about getting the 2-barrel Sniper and putting the stock intake back on..... Only Holley supports timing control in the 2 barrel units right now....

 

[threewood]

Yes mine is one without the "hex" end and is marked 9.5 on the arm. I have a high dollar Snap-On timing light with an advance dial. I have the advance on manifold vacuum and at 3000 RPM all I can get is about 42 degrees. Unplug the advance and I get about 32 degrees so I interpreted that as the can gives me about 9.5 degrees.

Now you mention it I know my weights were marked with 19.5 or something and I decided that with the 2 degrees ATDC on the emissions tag that would give me 34 degrees of timing when full in so the 2x theory makes sense......

Wonder if my diaphragm is getting hard and not pulling in all the way.... I need to buy a vacuum pump, my old Snap-on does not work any more.

Or I am thinking about this wrong and at 3000 RPM my vacuum is not high enough to pull it in all the way..... I need to look at it at idle.

I wanted to test mine but my cheapo vac pump is wasted after ingesting brake fluid. I have another on order....but a way to test the vacuum advance is to pop the cap off. Rig a degree wheel over the shaft. Rig a pointer to the rotor and pull vacuum on the canister which lets you see the amount of advance and at what in/hg.

You added shims to your vac advance, correct?

 

[JimKueneman]

I wanted to test mine but my cheapo vac pump is wasted after ingesting brake fluid. I have another on order....but a way to test the vacuum advance is to pop the cap off. Rig a degree wheel over the shaft. Rig a pointer to the rotor and pull vacuum on the canister which lets you see the amount of advance and at what in/hg.

You added shims to your vac advance, correct?

I was, that is why I am now confused, I thought I was getting 50+ degrees back when I had points. This is the first real look at this with the Pertronix. I am sure it is not binding.... Need a gauge.

 

[69Bee]

Yeah if my FiTech supported timing I think I would cave in and do that. I am really thinking about getting the 2-barrel Sniper and putting the stock intake back on..... Only Holley supports timing control in the 2 barrel units right now....

I am going to use the FITec dual quad setup. It allows timing adjustment, so I changed to the MSD distributor. My "low buck" hemi project has shifted into the "holy ****" arena...

 

[JimKueneman]

Ok I spent more time trying figuring this out. It is clearly only getting about 10 degrees of advance with the Pertronix III, and it was clear (based on me rereading my build thread) that with the points I was getting more like 20. I have this nasty feeling that the magnetic fields that the Pertronix III use to fire the coil against the points cam are not sharp enough and get smeared out. The real electronic ignition reluctor is sharp gear teeth not the soft bumps for the points.

 

[Nacho-RT74]

All vacuum pods arm I have seen personally states the lbs, but not the X whathever the X means

 

[91r/t]

All vacuum pods arm I have seen personally states the lbs, but not the X whathever the X means

Is that what those numbers are? I have had people tell me that it is the amount of timing that is added to the distributor, so multiply it by 2 for the crank timing. I never got a definite answer.

 

[69Bee]

The number on the arm is for the amount of distributor (cam) "DEGREES", not pounds. The number is multiplied by 2 to get the amount of crank degrees.

 

[91r/t]

The number on the arm is for the amount of distributor (cam) "DEGREES", not pounds. The number is multiplied by 2 to get the amount of crank degrees.


View attachment 570865

Awesome! Thats what I thought. There is also an L or R on some of them to tell which way they mount in the distributor depending on its rotation I believe .

 

[JimKueneman]

And if you do the math with a 2 degree ATDC initial + (19*2) = 36 BTDC total mechanical + (9.5*2) = 55 BTDC total. Just about right, maybe a bit more than ideal

Jim