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1957 Roadmaster - Screw that disables vacuum advance


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Since getting the Roadmaster running, my heart told me it wasn't living up to its acceleration potential. Having no experience with how it should run and knowing that the dynaflow was built for smoothness, not acceleration, I was just happy it ran well. 

Then, Dad finally drove it and told me I should try premium gas because it had a lot more pep when he was 16.

I AM running premium gas! 

 

I had a feeling something was wrong with the timing advance. The timing light showed that the timing would advance when revved but it didn't seem like enough. 

 

Today I pulled the distributor and vacuum line to the carb. Since this was a complete replacement for the original damaged distributor, I thought the vacuum mechanism was maybe clogged or punctured. 

 

Actually, it was the screw that secures the condenser. I don't know the history of this screw, but it was just long enough that it locked the advance plate to the distributor body. 

 

I shortened the screw and will take it out for a test drive tonight once reassembled. 

 

20200906_162744.jpg

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Results are not impressive. The vacuum advance is now working but it only affects timing at partial throttle for fuel efficiency. Only the mechanical advance helps with wide open throttle conditions. 

Anyone know what the 0-60 times should be for this car at 6,000' elevation? Right now I think it runs about 14 seconds in Drive. 

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14 hours ago, High Desert said:

Right now I think it runs about 14 seconds in Drive.

 

10 hours ago, avgwarhawk said:

0-60 in 11.5 seconds. 1/4 mile 18.8 seconds.  Keep in mind these figures are on no corn gas and sea level or there about. 

 

Is the switch pitch working?

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If you don't already have one, get a timing light with a dial on the end of it.  So you can use that dial to adjust the flash of the timing light to measure the running advance in the distributor, vacuum and mechanical, at idle/1500/3000 rpm levels.  Only THEN will you know what's happening and how much.

 

There should be some specs somewhere online for what your vehicle had from the factory, which you can compare to what you have.  What was the orig application for the distributor you now have, determined by the 7-digit number on the side?

 

IF the vac advance unit is aftermarket, it is possibly internally-adjustable.  Find an Allen wrench that will just fit through the vac hose attachment hole and see if it will index with an internal screw adjustment.  One way would increase the spring tension and the other way would decrease it, IF it will do that at all.  Increasing spring tension requires more vacuum to move the plunger, opposite if turned the other way.

 

As for driving, remember that if it has a 4bbl carb, it would probably flow about 450cfm total.  Small numbers compared to today's world, but plenty for back then AND better-allows for idle-to-WOT throtoitle movements to happen with fewer "bogs" and such.

 

In general, rather than judge how it acts in the idle-to-WOT situations, try using idle-to-pert throttle initially.  This keeps some vacuum in the vacuum advance as the mechanical advance starts to work as rpm increases.  After the vehicle is moving, then WOT can do what it's supposed to do.  When going from idle-to-WOT/heavy throttle initially, puts manifold vacuum at its lowest levels, levels below which NO vacuum advance will happen, so you're waiting for the mechanical advance to happen.  Which can make ANY performance  seem to take longer to happen.  Having a two-speed automatic trans only makes things worse, compared to a normal 3-speed automatic, by comparison.

 

So, get the distributor advances determined and "dialed-in" with the basic initial timing.  Get things working as well as they can, even if you might advance the base initial timing a bit as long as spark rattle does not happen at any time.  The Research Octane number of modern Super Unleaded fuel is right about the same as the old Premium gasoline of 1957, so that much is good.

 

Once all of that is done and confirmed, the engine should feel "happier" in doing what it's doing.  Good part-throttle throttle response when crusing in town or on the highway.  LEARNING how to make "the equipment" work is, to me, a big part of enjoyment of using it.  You adjust to IT, rather than otherwise, is can result in much happiness for all involved.   Sometimes, little adjustments can make a BIG difference in how things work.

 

Of course, considering that an old saying was "IF it won't go, gear it", you could find some way to adapt a newer 6-speed automatic into the car.  With the approx 4.50 low gear ratio, plus any torque converter multiplication past that, those older DynaFlow-equipped cars would flat embarass others like it.  Not to mention putting some of the younger "whipper-snappers" vehicles "in the dust", I suspect.

 

Enjoy!

NTX5467

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One other thing is that for "high altitude" vehicles, there used to be some guidance in the carb section of the service manual about adjusting the main jeet sizes downward at particular elevations to prevent a richer mixture.  Model A Fords sold in CO used to have higher mechanical compression reatios to help combat the thinner air "up there", from what I've read.

 

Some of that loss might be regained with a bit more initial timing, as one old-line service manager mentioned once.  A bit of trace rattle upon acceleration at 1000' elevations, but not as he got into the higher altitudes of NM, where it was quiet.

 

Just some thoughts,

NTX5467

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32 minutes ago, NTX5467 said:

If you don't already have one, get a timing light with a dial on the end of it.  So you can use that dial to adjust the flash of the timing light to measure the running advance in the distributor, vacuum and mechanical, at idle/1500/3000 rpm levels.  Only THEN will you know what's happening and how much.

 

There should be some specs somewhere online for what your vehicle had from the factory, which you can compare to what you have.  What was the orig application for the distributor you now have, determined by the 7-digit number on the side?

 

IF the vac advance unit is aftermarket, it is possibly internally-adjustable.  Find an Allen wrench that will just fit through the vac hose attachment hole and see if it will index with an internal screw adjustment.  One way would increase the spring tension and the other way would decrease it, IF it will do that at all.  Increasing spring tension requires more vacuum to move the plunger, opposite if turned the other way.

 

As for driving, remember that if it has a 4bbl carb, it would probably flow about 450cfm total.  Small numbers compared to today's world, but plenty for back then AND better-allows for idle-to-WOT throtoitle movements to happen with fewer "bogs" and such.

 

In general, rather than judge how it acts in the idle-to-WOT situations, try using idle-to-pert throttle initially.  This keeps some vacuum in the vacuum advance as the mechanical advance starts to work as rpm increases.  After the vehicle is moving, then WOT can do what it's supposed to do.  When going from idle-to-WOT/heavy throttle initially, puts manifold vacuum at its lowest levels, levels below which NO vacuum advance will happen, so you're waiting for the mechanical advance to happen.  Which can make ANY performance  seem to take longer to happen.  Having a two-speed automatic trans only makes things worse, compared to a normal 3-speed automatic, by comparison.

 

So, get the distributor advances determined and "dialed-in" with the basic initial timing.  Get things working as well as they can, even if you might advance the base initial timing a bit as long as spark rattle does not happen at any time.  The Research Octane number of modern Super Unleaded fuel is right about the same as the old Premium gasoline of 1957, so that much is good.

 

Once all of that is done and confirmed, the engine should feel "happier" in doing what it's doing.  Good part-throttle throttle response when crusing in town or on the highway.  LEARNING how to make "the equipment" work is, to me, a big part of enjoyment of using it.  You adjust to IT, rather than otherwise, is can result in much happiness for all involved.   Sometimes, little adjustments can make a BIG difference in how things work.

 

Of course, considering that an old saying was "IF it won't go, gear it", you could find some way to adapt a newer 6-speed automatic into the car.  With the approx 4.50 low gear ratio, plus any torque converter multiplication past that, those older DynaFlow-equipped cars would flat embarass others like it.  Not to mention putting some of the younger "whipper-snappers" vehicles "in the dust", I suspect.

 

Enjoy!

NTX5467

 

I can't help but think that Dad may have some rose-colored memories too. The only other car he drove back then was a 1952 Chevrolet. The Roadmaster may have been a relative hot rod. Today, even my anemic 2009 Civic has more respectable acceleration numbers. 

 

I've read that a vehicle loses 3-4% hp for every 1000 ft of elevation. So the 300hp sea level rating could be only 228hp. I don't know if that accounts for only the reduced air density or also the increasingly-rich fuel-air mix. 

 

Some local old timers told me it was common for mechanics to increase the initial timing on new cars in Albuquerque to help address the power loss. Since the air is thinner, it reduces the cylinder compression, which reduces predetonation. That allows for initial timing to be increased 1 degree per 1,000 ft elevation without causing pinging. 

 

I'll continue to work on tuning. Ordered electronic ignition yesterday and may look into some smaller main jets but the car runs extremely well and my inclination is too leave well enough alone. 

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Considering that our ethanol'd fuel needs a bit richer jetting for its optimal a/f ratio, I think I'd just play with the base timing, check the vac advance amount, and letr that be the extent of things.

 

Thanks for the info!

Enjoy!

NTX5467

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