Need experienced opinion - Can vacuum advance cause pinging?

[4406bbl]

Also remember the factory specs varied by 2-4 distributor degrees on centrifical advance, 12-14 dist degrees in a 383 2bbl autos case, initial advance was plus or minus 2.5, and vacuum advance was 9-12 degrees at 12", so 2 factory distributors at worst spec could be off 10 -12 degrees. That is the main reason one engine liked 2.5 degrees advance and the next wanted 10.

 

[Hemirunner]

Keep in mind that factory specs were established for the fuels available when these cars were new and were based on period technology. They mean nothing unless a combo is bone stock running high octane ethanol free fuel.

 

[Newkidonthebloc]

Well, this weekend I played around with carb tuning and timing. I set the timing at 7 degrees at idle and made sure that the timing with full mechanical advance does not exceed 34-36 degs. The car now runs much stronger at idle. I did notice that the car does run a bit hotter right now, not really sure what that means. Atleast the noise I was experiencing during cruising is almost completely gone. Next up, I will change the springs and bushings in the distributor to change the timing curve and make sure the mechanical timing is all in around 2500 rpm (as someone suggested to me).

Just to add to the info: I always run 98 premium which is readily available here. I do not know what kind of jungle juice was around when these cars were new but 98 can't be that bad right also given the fact that it was the 'low' compression 2bbl 383?

Thanks for all the feedback and replies guys! You all helped me out a ton! Thanks!

Best,

Thom

 

[4406bbl]

Your mechanical should not exceed 26-28, and your total timing...mechanical and initial, with vacuum can unhooked should never exceed 38 degrees.

 

[4406bbl]

On your fuel I think 98 ron in Europe is 92-93 mon in the USA, but yes it should be fine for your car.

 

[Newkidonthebloc]

Your mechanical should not exceed 26-28, and your total timing...mechanical and initial, with vacuum can unhooked should never exceed 38 degrees.

100% True! Wrote it down wrong, my bad!

 

[4406bbl]

Cool, just do not want to mislead you.

 

[AR67GTX]

There’s something called an FBO advance plate you can buy for the distributor that will allow you to dial in the mechanical advance degrees you want. I have my 67 GTX limited to 18 degrees mechanical advance and run 15 - 16 degrees initial advance (base timing) which helps give it a strong idle, strong response off idle and acceleration, and keeps pinging at bay as my car doesn’t like more than about 34 deg total timing or it pings on 93 ethanol. Also helps keep the engine a bit cooler in traffic. Only downside is that too much vacuum advance with it can sometimes create some pinging at highway cruise unless a stop is used on the vacuum can.

 

[68 Sport Satellite]

There’s something called an FBO advance plate you can buy for the distributor that will allow you to dial in the mechanical advance degrees you want. I have my 67 GTX limited to 18 degrees mechanical advance and run 15 - 16 degrees initial advance (base timing) which helps give it a strong idle, strong response off idle and acceleration, and keeps pinging at bay as my car doesn’t like more than about 34 deg total timing or it pings on 93 ethanol. Also helps keep the engine a bit cooler in traffic. Only downside is that too much vacuum advance with it can sometimes create some pinging at highway cruise unless a stop is used on the vacuum can.

Do you know if there's any correlation to the amount of vacuum causing the adjustable Vac Advance arm to start moving and the amount of added degrees advance so it can be roughly adjusted using a brake bleeder vacuum kit? Or is it just a lot of trial and error as in turn adjusting screw, hook up vac hose, drive it, repeat, repeat...?

I think I need to put a stop on the arm in my Vac Advance can. Bolt/nut is the way to go yeah?

 

[Geoff 2]

Using the spring adjustment in an adj VA unit to limit total amount of VA applied will lead to erratic engine performance.
First screw the Allen Key fully CW [ softest spring setting ]
The correct procedure is once you know how much VA you want to add, use a limiter plate to achieve this amount.
Then, if you get pinging, turn the AK two turns at time & recheck for pinging.

 

[68 Sport Satellite]

Using the spring adjustment in an adj VA unit to limit total amount of VA applied will lead to erratic engine performance.
First screw the Allen Key fully CW [ softest spring setting ]
The correct procedure is once you know how much VA you want to add, use a limiter plate to achieve this amount.
Then, if you get pinging, turn the AK two turns at time & recheck for pinging.

Do you mean to say that without a limiter plate, no matter the adjusted setting, performance will be erratic?

My distributor is the Firecore with set screws to limit the mechanical advance. It doesn't limit the Vac Adv can amount. If I install a limiter plate inside, would this also limit the Vac Advance applied from the can at off-idle?

 

[Dragon Slayer]

The screw and spring pressure will control at what vacuum level the arm starts to move. The more preload you add, the higher vacuum required to move the arm. The rate of movement is already built into the spring based on spring length and rating (you can't control). The arm should have a number stamp to indicate max vacuum advance from the setup. High enough preload may preclude reach max advance, if your engine doesn't produce a high enough vacuum. You can measure with vacuum pump/gauge to see at what vacuum the arm starts to move and you can see what vacuum has the arm fully pulled in. If you need to limit max vacuum you could drill a hole and insert a spring pin. Touch of epoxy to ensure it stays.

 

[68 Sport Satellite]

I guess I'm confused by Geoff's comment. Does the limiter plate do anything different for mechanical advance limiting that my set screw firecore distributor doesn't do (or a welded setup)? Does the limiter plate do anything for the Adjustable Vac Advance max applied timing to limit it?

 

[Dragon Slayer]

Have to ask him I have no idea what he is talking about. I have not seen limiter plates for vacuum advance for mopar. I am explaining how vacuum can with adjustable spring pressure works. You're adjusting a preload on a spring inside the can. If you have an after market distributor what do the instructions say?

The FBO plate folks are talking about has different slot lengths and you install it over the rotating weights studs along with the cam. You can adjust the max mech advance based on which slot length you have. They have no effect on what the vacuum advance is doing. G

 

[68 Sport Satellite]

Have to ask him I have no idea what he is talking about. I have not seen limiter plates for vacuum advance for mopar. I am explaining how vacuum can with adjustable spring pressure works. You're adjusting a preload on a spring inside the can. If you have an after market distributor what do the instructions say?

The FBO plate folks are talking about has different slot lengths and you install it over the rotating weights studs along with the cam. You can adjust the max mech advance based on which slot length you have. They have no effect on what the vacuum advance is doing. G

That's what I thought. That means the advance limiter plate is achieving the same thing as the slotted/set-screw setup inside my firecore electronic distributor.

I would really like to make use of hooking up the Vac Advance, however, the stock adjustable cans add in too much advance, so I'll need to add a bolt/nut stop on the Vac Advance can arm.

Sorry to get a bit off-topic from the OP's post, but hopefully this info will also help him.

 

[Geoff 2]

68,
Sorry if I confused you. Post #50. The limiter plate I was referring to is a plate or other device to limit the travel of the VA actuator arm. The last Ch dist I did was a factory style & I brazed a small metal tab onto the arm to limit the total travel to the amount I wanted. Not sure about your dist. Most of the adjustable VA units I have seen & used allow have 30* of VA. That is, they can add 30* of ign timing. This can be more than reqd, so the above method limit the total amount.

 

[68 Sport Satellite]

Thanks Geoff, that clears it up
And to the OP - NewKid - I was at first thinking that none of my Vacuum Advance questions helped your situation since you have the MSD Ready to Run Distributor, however, when I look that up, it also looks like it has a Vacuum Advance can off the side. Can you post a photo of your distributor for us to see and make sure we're talking about the correct one?

 

[Newkidonthebloc]

Thanks Geoff, that clears it up
And to the OP - NewKid - I was at first thinking that none of my Vacuum Advance questions helped your situation since you have the MSD Ready to Run Distributor, however, when I look that up, it also looks like it has a Vacuum Advance can off the side. Can you post a photo of your distributor for us to see and make sure we're talking about the correct one?

I will be at the car tomorrow and I will shoot you a picture! The manual does not state any tunability of the vacuum advance. I am afraid it is not adjustable.

 

[68 Sport Satellite]

Has anyone used the adjustable vacuum advance cans that FBO sells?
FBO Ignition Systems

The description says 10-20 degrees advance and 5-12" Vacuum. Outside appearance is like the one that came stock on my Firecore distributor with the hex shape and allows Vacuum rate advance adjustment via the vacuum connection port using an allen wrench. Vacuum advance itself is fixed on mine and seems to apply too much fixed additional advance for my setup as evidenced by WOT full load pinging no matter what I set the vacuum rate at with the adjuster. So I've just been running without vacuum advance hooked up, but would love to run it if possible.

Is the FBO can really adjustable from 10-20 degrees advance as well as the rate? I wonder if it's adjustable without disassembly from the distributor once installed.

I emailed Don at FBO a few days ago on this, but no response yet. I've seen him post here as a member also, so maybe he'll chime in. I can always do the wire shim trick over the internal arm that I've read about to limit the max applied vacuum advance, but if this one is adjustable I'd rather have that.

 

[Geoff 2]

Some of the cheap dists that come with adj vac adv units are not much more than the VA unit itself. Could be an alternative & you get a spare dist out of the deal.