Distributor recurve

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rich006

rich006

Learning as I go
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I'm rebuilding the distributor on my car to adjust the timing advance. My driving is mostly at lower RPM, almost never above 3000. What is a good starting point for total mechanical and vacuum advance on this build?

- 1974 Dart with 904 transmission and 2.71 differential
- 225, rebuilt with 8.9:1 static compression and Oregon 2106r camshaft (7.7:1 dynamic compression)
- Super Six intake manifold
- Carter BBD clone 2bbl carburetor

The original distributor is in good shape. It has a 15R governor and 8.5R vacuum pod. I also have the distributor from the Super Six donor car (a 79 Lebaron), which is a bit corroded due to being left outside with the cap off. It has a 9R governor and a 11R vacuum pod. I also have a set of different mechanical advance springs for adjusting the advance rate. I do not have a distributor test machine.

The engine seems to like a lot of advance at idle (it runs great up to 20 degrees BTDC), but pings at higher speeds under load. That's in large part due to the mixture being lean when the throttle is open (according to a wideband AFR gauge), but also partly due to timing.

My plan (unless I get advice to the contrary) is to use the original distributor, but with the Super Six governor and vacuum pod. Any thoughts?
 
Also, any tips on honing the governor? What tool to use? The 79 governor is a very tight fit on the 74 shaft, presumably due to some corrosion inside the governor shaft.
 
The 9R governor has shorter slots, so that it allows a lower maximum mechanical advance. Its heavy spring also has a shorter loop on the end, to go with those shorter slots. For that reason I used the 79 springs along with the 79 governor and vacuum pod. I left all the other parts from the 74 distributor in place, as it was working well.

I answered my question about honing the governor shaft. A rolled-up piece of 400 grit sandpaper did the trick. I was actually able to grip the paper roll with a drill and slide the governor up and down while spinning the paper. That red 3M sandpaper is pretty good stuff.
 
rich006 said:
The 9R governor has shorter slots, so that it allows a lower maximum mechanical advance. Its heavy spring also has a shorter loop on the end, to go with those shorter slots. For that reason I used the 79 springs along with the 79 governor and vacuum pod. I left all the other parts from the 74 distributor in place, as it was working well.

I answered my question about honing the governor shaft. A rolled-up piece of 400 grit sandpaper did the trick. I was actually able to grip the paper roll with a drill and slide the governor up and down while spinning the paper. That red 3M sandpaper is pretty good stuff.
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I would reach out to Halifaxhops he is the master of all things Dizzy. Sells repairs and guides folks all over the world with regard to distributors.
 
Doesn't surprise me that the engine likes more idle timing. Factory settings were conservative.
But you can have your cake & eat it too.....by connecting the VA to a manifold vacuum source [ MVA ].
You can add the extra timing that the engine likes with the VA. Say the static initial is 5*, you can add 15* with VA to give the engine the 20* it likes. The beauty of VA is that it is load compensated, & drops off under load to avoid pinging. You will probably have to fabricate a stop for the VA to limit the travel.

More on MVA, scroll down to post #6.

www.hotrodders.com/forum/vacuum-advance-hooked-up-directly-manifold-bad-47495.html
 
OP drop the cam plate from a 15 to around a 13 that wi give you totall mechanicall at 26 instead of thirty and where does your Vac advance go total in INHG? Might need a small adjustment on it.
 
I don't recommend manifold vacuum on a street car. If for no other reason, consider this. If the vacuum can goes out, the car's gonna run like **** until you can get to some tools and either replace it or bump the timing up until you can get it replaced. With it hooked to ported vacuum if the vacuum can goes out, you can at least still drive the car almost like nothing's wrong. There are a few more benefits to ported vacuum, but that alone should be enough.
 
What RRR says above the VA unit failing is correct.

But some common sense needs to be applied here. Right now I have two failed Mopar dist on my bench, both have VA. But the VA units haven't failed, the p/up wires have broken from flexing. No way you would get home with these with the best tools in the world. These dists came off production engines, & the VA units were connected to ported VA. Not that it really matters. Lots of things can fail on the road: dead battery, coil goes out, fuel pump fails. Etc.
 
halifaxhops said:
OP drop the cam plate from a 15 to around a 13 that wi give you totall mechanicall at 26 instead of thirty and where does your Vac advance go total in INHG? Might need a small adjustment on it.
Click to expand...

I don't have a 13, but I used a 9 (from the Super Six donor vehicle) which should give total mechanical of 18. The vacuum pod is stamped "11.0R". I plan to plot the new mechanical and vacuum curves today.

What is signified by the L and R stamps on the plate? On the bottom it's stamped "9R" and on top it's stamped "L". I understand 9 means 9 degrees of distributor advance, 18 degrees at crank. I'd upload a photo but I keep getting an error whenever I try.
 
Right is sb/slant L is B/RB Number indicated amount of distributor degrees. In your case a FBO plate can be your best friend also. On the vac advance if it is adjustable it WILL NOT adjust the total amount but adjusts the rate for when it gets there.
 
halifaxhops said:
Right is sb/slant L is B/RB Number indicated amount of distributor degrees. In your case a FBO plate can be your best friend also. On the vac advance if it is adjustable it WILL NOT adjust the total amount but adjusts the rate for when it gets there.
Click to expand...
Not too long ago, RRR said that there was no FBO plate for the slant 6's. Has that changed?
 
They use the same electronic advance cam plates so I think they should, slots should be the same lengths. Kind of remember that also.
 
Ricks70Duster340 said:
Not too long ago, RRR said that there was no FBO plate for the slant 6's. Has that changed?
Click to expand...

The FBO plate fits the slant six distributor. I have one in mine. They are not accurate though. I have mine on the lowest slot and it's still more total than what it says. But it does work. My next distributor I will weld up the slots.....UNLESS I can find a 6 degree governor.....which they made.
 
halifaxhops said:
They use the same electronic advance cam plates so I think they should, slots should be the same lengths. Kind of remember that also.
Click to expand...

They fir the slant, but they aren't accurate. I asked Don if he would consider making a round with advance from say 0 to 10 but he flatly refused. You could simply file out the zero holes to "whatever" you need. I'm just going to weld the governor slots on the next one.
 
Haven't looked closely at it, but could the L & R marking on the Tee piece refer to [ Left and Right ] which way the Tee piece moves with respect to the shaft?
 
RustyRatRod said:
They fir the slant, but they aren't accurate. I asked Don if he would consider making a round with advance from say 0 to 10 but he flatly refused. You could simply file out the zero holes to "whatever" you need. I'm just going to weld the governor slots on the next one.
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Thanks for trying.
He asked here (on FABO) a couple times why shorten the inside, and I explained it and he disappeared. His plate is a clever device. It would be great if he made a couple different versions, that would cover the most common situations. Oh well.
 
rich006 said:
- 1974 Dart with 904 transmission and 2.71 differential
- 225, rebuilt with 8.9:1 static compression and Oregon 2106r camshaft (7.7:1 dynamic compression)
- Super Six intake manifold
- Carter BBD clone 2bbl carburetor
Click to expand...
What you didn't say is header or free-flowing exhaust.
Until you open up the exhaust, I highly recommend to not waste your time fudging with the Distributor. You will just get a lot of detonation and lousy fuel-economy.
 
Dunno who Joe White is no idea.
On a related note I have a couple of distributor questions to add in here after work.
 
AJ/FormS said:
What you didn't say is header or free-flowing exhaust.
Until you open up the exhaust, I highly recommend to not waste your time fudging with the Distributor. You will just get a lot of detonation and lousy fuel-economy.
Click to expand...

The reason I'm fudging with the distributor is I already have "a lot of detonation and lousy fuel economy" (15 mpg in town). My goal with the distributor is to reduce the mechanical advance to eliminate the ping.

I have stock 2" exhaust all the way back. I think the Super Six cars came with a 2.25" pipe. I asked the muffler shop to give me a 2.25" pipe with a 2" muffler, but the guy convinced me it wouldn't make a difference. I think he was wrong and I am considering telling him to do it anyway. This is what I am looking at:
and maybe this:
and maybe even this:
I don't want excess noise, but I do want the engine to run well.
 
rich006 said:
I don't have a 13, but I used a 9 (from the Super Six donor vehicle) which should give total mechanical of 18. The vacuum pod is stamped "11.0R". I plan to plot the new mechanical and vacuum curves today.
Click to expand...
The shape of the curve is as important the degrees in the slot.
The rpm for the advance to begin depends on the spring force of the 'light' spring on its weight.
The long looped 'heavy' spring slows the rate of the advance somewhere later in the curve.
So what advance will look like is not easily predicted.
Take a look through Rick's thread Distributor curve help needed
to see how important it is to remeasure after every internal change.
Everything shown there is applicable to your 6 except the timing curve.
 
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rich006 said:
The reason I'm fudging with the distributor is I already have "a lot of detonation and lousy fuel economy" (15 mpg in town). My goal with the distributor is to reduce the mechanical advance to eliminate the ping.

I have stock 2" exhaust all the way back. I think the Super Six cars came with a 2.25" pipe. I asked the muffler shop to give me a 2.25" pipe with a 2" muffler, but the guy convinced me it wouldn't make a difference. I think he was wrong and I am considering telling him to do it anyway. This is what I am looking at:
and maybe this:
and maybe even this:
I don't want excess noise, but I do want the engine to run well.
Click to expand...
Actually other way around in most cases.
The muffler is the most restrictive part of the system. Larger diameter muffler tubes in and out generally help minimize that restriction. Laerger over all size of mufller generally helps make a quiter muffler. VEOTOM (sp?) has some good posts about mufflers.
The rest of the exhaust tubing should be sized for least disruption of flow and maintaining enough velocity at low rpms exhaust gasses are always moving away from the exhaust valves.

Really dont see how this will make a major difference in the timing.
If its a hot cam, with lots of overlap, it will need more initial than factory.
Also you've ditched the factory emissions setup, depending on the year, it could run better with more timing.
I dont have timing specs for the super 6 or anything that late so I cant be more specific.

For ballpark idea of what the timing should look like, non-emmissions, this is range for a '67 225 set to the factory 5* BTDC at 600 or so.
upload_2021-7-20_8-32-12.png
 
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