[Indyguy]

........says the "Tech" at Pertronix

I just want to say right up front that I use FULL MANIFOLD vacuum. My new MJ 467 has been running beautifully with 12* initial, all in at 36* and with 10* vacuum advance limited with a hard stop.

The other night I was almost home, came up to a stoplight and my idle dropped about 300 RPM from where I have had it set. So the next morning I went out and took a look, decided to check timing and it was 12* WITH my vac can hooked up. OK, bad vac can on my new Pertronix Billet distributor.

Yesterday I called Pertronix (I bought it direct from them in March 2022) and sat on hold for about 30 minutes waiting for a tech. He picks up, I explain what happened, I have my receipt in front of me and give him the info, and asked if he could send a replacement vac can under warranty. “I guess” he says. I asked if I pay special shipping can we make sure I get it by Thursday this week, car season is short here in the Midwest and I’d like to have it back on the road for the weekend. He said he can’t do that and maybe I would have it in about a week.

Then he asked where I have it plugged into, ported or full manifold. I told him full manifold and he went off on me telling me how wrong that is and why would I ever want to do that. I let him talk and, as calmly as I could, told him “thanks, I look forward to getting the replacement” . And we hung up.

So I looked in the directions and it says to use a ported source, just for fun I looked at MSD’s directions for the Ready To Run distributors and it also says to use ported.

Why would two large distributor manufactures say to use ported when there is so much that supports using full manifold?

 

[Pete 67]

Dave Ray would like to have a word with them.

 

[swampy 6x6]

My genuine GM workshop manuals say for manual transmission use ported and for auto transmission use manifold vacuum .
IMO
the M/T is loaded as soon as it accelerates . Ported allows advance to slightly later and prevent pinging .
the A/T is not loaded heavily till convertor stall is reached so the manifold connection might help the transmission pull thru the convertor .. This only occurs on initial acceleration.

The manuals I have apply to pre emission vehicles .

 

[Bob Tiley]

Ported vacuum adds advance at part throttle and full throttle but not at idle. This actually works as a timing retard. It retards the timing at idle resulting in higher engine temperatures and higher exhaust temperatures to burn off excess emissions. Under cruise and full throttle it does nothing and allows the regular 36 or so degrees of timing with the vacuum advance. So you get higher idle and low speed engine temps so you overheat in traffic and no idle / part throttle timing advance for better driveabilty.

 

[Indyguy]

Not arguing ported v/s full manifold.

I am wondering why the two big distributor manufacturers want ported vac to the can?
The Pertronix "Tech" told me that's why my vacuum can failed, and that the new can he is sending will fail too if I connect it to full manifold vacuum.

 

[Leadhead]

I always had mine hooked up to ported vacuum. No specific reason. That's just the way my cars were when I got them. I never actually heard of hooking them up to full manifold vacuum until I joined this site.

 

[mr 4 speed]

Once the throttle plates open, manifold/ported are the same.
Ported just doesn't add anything at idle.

 

[2/75NastyNewbs]

Because the early 70s cars went ported advance with very retarded timing for emissions purposes, I wonder if there is some sort or legality as to why these distributor companies insist on ported vacuum.

 

[vortec710]

Interesting how mfg's instructions change'd once emission controls were put into effect, I'm gonna stick with manifold vacuum, and as to Pertronix techs' remarks....is his vacuum can smart enough to know the difference between ported and manifold vacuum ? Suggest try calling Pertronix again and see if different tech gives same answer

 

[oldcutlass]

Not arguing ported v/s full manifold.

I am wondering why the two big distributor manufacturers want ported vac to the can?
The Pertronix "Tech" told me that's why my vacuum can failed, and that the new can he is sending will fail too if I connect it to full manifold vacuum.

The tech does not know what he is talking about. Cans fail, but that is not the reason. The distributor manufacturers go by what GM spec'd the vacuum hookup was because of government emission regs. As others stated, there is no performance gain between ported and manifold vacuum, the difference is what it does at idle.

 

[Indyguy]

Because the early 70s cars went ported advance with very retarded timing for emissions purposes, I wonder if there is some sort or legality as to why these distributor companies insist on ported vacuum.

That's what I was wondering, guess it makes since that they "tow the line" of what the mfg's recommend.
But the guy was arrogant and rude, I realized right away that nothing I was going to say was going to change his recommendation. It's not my job to educate him, just send me my frickin' can.

Thing that made me think was that he was stating that the failure of the vac can was directly related to me having it hooked to full manifold, it wouldn't have happened if I "hooked it up correctly" . I only have 1500 miles on that vacuum can, that's a pretty quick failure.

 

[2/75NastyNewbs]

That's what I was wondering, guess it makes since that they "tow the line" of what the mfg's recommend.
But the guy was arrogant and rude, I realized right away that nothing I was going to say was going to change his recommendation. It's not my job to educate him, just send me my frickin' can.

Thing that made me think was that he was stating that the failure of the vac can was directly related to me having it hooked to full manifold, it wouldn't have happened if I "hooked it up correctly" . I only have 1500 miles on that vacuum can, that's a pretty quick failure.

Since an engine creates more vacuum at a steady state cruise than idle, I can’t for the life of me understand how that could possibly be. The problem with distributors and many other systems on these cars is that people do not grasp the concepts, and just regurgitate what they’ve been told and hang onto it like gospel. Much like your pertronix tech.

 

[David Ray]

" Why would two large distributor manufactures say to use ported when there is so much that supports using full manifold? "

So very simple, they cannot sell those distributors to persons that do not adhere to EMISSIONS settings.

Anybody actually know the real identification for a " vacuum advance ", and where it came from?

Ford Flathead I6 and V8. Those engines only had the vacuum adjusted ignition curves, NO mechanical until 1935 or so, and some right up until 1957 or so.

Ford called as it was / is, a " LOAD COMPENSATOR ". More load, less timing, less load, idle, cruise, more timing.

That calls for full manifold vacuum

EMISSIONS settings require hotter combustion chamber and exhaust manifold temperatures to help burn off more unburned hydrocarbons, which use PORTED vacuum for the Load Compensator..

This is why I don't get along with most supposedly top techs, most are totally ignorant of how it really works, and include in that group, dyno heroes, ones that have NO idea as to carburetor jetting, and ignition timing for a street driven engine, ONLY A TOP FUELER / FUNNY CAR for the street. Most of which, make power in the stratosphere of rpms, and not enough power / torque to back the car off the rollers.

The OP had it right, and proved it to himself. Then, the Top Tuner PerTronix and MSD "Techs" proved not to know much about things timing.

I see, hear, and fix their insanity EVERY DAY.

 

[Indyguy]

" Why would two large distributor manufactures say to use ported when there is so much that supports using full manifold? "

So very simple, they cannot sell those distributors to persons that do not adhere to EMISSIONS settings.

Anybody actually know the real identification for a " vacuum advance ", and where it came from?

Ford Flathead I6 and V8. Those engines only had the vacuum adjusted ignition curves, NO mechanical until 1935 or so, and some right up until 1957 or so.

Ford called as it was / is, a " LOAD COMPENSATOR ". More load, less timing, less load, idle, cruise, more timing.

That calls for full manifold vacuum

EMISSIONS settings require hotter combustion chamber and exhaust manifold temperatures to help burn off more unburned hydrocarbons, which use PORTED vacuum for the Load Compensator..

This is why I don't get along with most supposedly top techs, most are totally ignorant of how it really works, and include in that group, dyno heroes, ones that have NO idea as to carburetor jetting, and ignition timing for a street driven engine, ONLY A TOP FUELER / FUNNY CAR for the street. Most of which, make power in the stratosphere of rpms, and not enough power / torque to back the car off the rollers.

The OP had it right, and proved it to himself. Then, the Top Tuner PerTronix and MSD "Techs" proved not to know much about things timing.

I see, hear, and fix their insanity EVERY DAY.

I was waiting to hear what you had to say David, I knew this one would get your attention

He had an attitude right away and told me the new one will fail too if I hook it to manifold vac.
Guy pissed me off and still hasn't responded to my email confirming receiving the receipt and info I emailed yesterday. It will be interesting to see how long it takes to get my vac can.
And it's a bummer the distributor has to come out and apart to replace the vac advance can.

 

[chaze]

This thread amplifies why I never rely on vendor's tech guys. I never even call them anymore. Better info right here on this forum and elsewhere on the interweb.

 

[pannetron]

Using ported vacuum is an old school emissions helper. There is so much folk lore out there on how things used to be that disregards progress over the decades! Heck, if your cam is big enough it might not make any difference anyway

 

[65cayne]

. ...Anybody actually know the real identification for a " vacuum advance ", and where it came from?

Ford Flathead I6 and V8. Those engines only had the vacuum adjusted ignition curves, NO mechanical until 1935 or so, and some right up until 1957 or so.

Ford called as it was / is, a " LOAD COMPENSATOR ". More load, less timing, less load, idle, cruise, more timing. ...

Yep. My '59 Ford 223 "mileage maker" inline six has a vacuum compensated distributor. No mechanical advance at all. They called the distributor the "load-o-matic"

 

[drivejunk]

Rule #1: The customer is always right.

My take is that it depends on the combo and the operator. Meaning whichever camp you were raised in. But that part of the discussion was irrelevant, a leak is a leak and a vacuum advance unit that doesn't hold is bad. They don't make em like they used to. Blah blah, prompt replacement is what matters.

Seems to me like plain stock ones work for like ever, while new adjustable ones are too often bad in the box or after a few miles. Who wants adjustment?

I am from the ported camp, I only have ever advanced as far as mild stock iron head junk. But I got a badly overcammed 400 once and it liked full vac. It depends, but you just can't have a leak. As Gomer said about tires vs gas n oil... thats another matter entire.

 

[Jerry70]

They want the approval of the California Resources Board so they can include that silver sticker that says the part is legal to use in California and other states that use California smog regulations.

 

[2/75NastyNewbs]

^^^^ Boom there it is