disti vs engine rpm

[danno 128]

I am adjusting the disti centrifugal advance on a factory 302 C9AF-N distributor. The book lists the specs as " distributor rpm".  Is this half engine rpm? The distributor rpm is either half or twice the engine rpm.  Or is it the same as engine rpm? 

[barnett468 418]

dist is 1/2 of the engine rpm.

[danno 128]

Yes! thank you.  Now I can continue with the adjustments!

[barnett468 418]

xlnt!

[aslanefe 333]

13 hours ago, danno said:

I am adjusting the disti centrifugal advance on a factory 302 C9AF-N distributor. The book lists the specs as " distributor rpm".  Is this half engine rpm? The distributor rpm is either half or twice the engine rpm.  Or is it the same as engine rpm? 

Danno, it is my understanding that when spec says "distributor RPM=1000, advance ( dist or camshaft degrees) is 2 1/2- 4 3/4";it means when crank rpm is 2000, crank advance is 5 -9 1/2 degrees. So you have to double both the dizzy rpm and degrees to get crank rpm and degrees.

On a side note, do you have the table for advance for a 69 302 advance curve handy? If so, can you post it as I am trying to tune my dizzy also?

[barnett468 418]

1 hour ago, aslanefe said:

 

On a side note, do you have the table for advance for a 69 302 advance curve handy? If so, can you post it as I am trying to tune my dizzy also?

I typically do not use the factory settings. I tune each distributor reasonably close to each engine. It is fairly easy to do.

[danno 128]

Yes, I have the table in the Ford manual, and I will start with that.  So with the example above, at  1000 distributor advance and 10 degrees initial timing, the total ( engine idle + centrifugal) is  15 to 19.5 degrees. 

For my motor,  the book has 6  to 8.25 at 1000.  So that is 22 to 26 crankshaft degrees at  at 2000 rpm engine speed.  I will get it close. 

From what Barnett suggested,  next I will check to see if the engine speeds speeds up when the carb is set for 2800 rpm and timing is advanced. 

[danno 128]

Ok, I now have it at:    10 degrees at 700 (engine rpm), 13 at 1000, 20 at 1500, and 22 at 2000.  23 is max at 2200.   So it is very, very close. So at 1000 and 1500  it is just a hair low.  I find that bending the things that the springs attach to makes a delicate difference. 

It makes no noticeable  difference in engine speed by  advancing the timing 4 degrees at any engine speed, including 2800.  

Shall I call this good enough for an every day driver, or ( as long as I am working on it) get it perfect. 

[barnett468 418]

1 hour ago, danno said:

Ok, I now have it at:    10 degrees at 700 (engine rpm), 13 at 1000, 20 at 1500, and 22 at 2000.  23 is max at 2200.   So it is very, very close. So at 1000 and 1500  it is just a hair low.  I find that bending the things that the springs attach to makes a delicate difference. 

It makes no noticeable  difference in engine speed by  advancing the timing 4 degrees at any engine speed, including 2800.  

Shall I call this good enough for an every day driver, or ( as long as I am working on it) get it perfect. 

yup, it sounds good enough, now you should set up your vacuum advance.

good job, it's not hard, it just takes time....and patience, lol.

[danno 128]

No kidding, patience! I must have had the lower plate off and on 20 times. 

I am not aware of any adjustments on the vacuum advance.  Don't you just hook it up?  Will adjusting make that much difference? 

[barnett468 418]

1 hour ago, danno said:

I am not aware of any adjustments on the vacuum advance. 

Don't you just hook it up? 

Will adjusting make that much difference? 

Some are adjustable and some are not. The adjustable ones are adjusted thru the hose fitting on the front with an allen wrench.

Nope, you need to determine the max amount of advance it gives your engine hen determine how much more advance your engine needs at steady throttle then set it to provide that amount of vacuum which is typically around 6hg if the distributor curve has been set to the optimum level like it soulds like yours now has been.

It can prevent problems if it is currently giving it too much advance.

[aslanefe 333]

On 8/4/2019 at 4:26 PM, danno said:

No kidding, patience! I must have had the lower plate off and on 20 times. 

My D1 dizzy has a hole on the base plate (at about middle of the ground strap). I just remote crank the engine while watching through the hole till the spring tab comes under the hole (if it passes or stops a little short, I loosen the dizzy clamp and turn the dizzy to align the tab). Then bend the tab with a screw driver through the hole. I know it is too late for you, but this will eliminate you from removing the plate 20 times just to bend the tab next time if your dizzy also has the hole on the plate.

[RPM 1,190]

 The allen wrench size for adjustable vacuum cans is 3/32.

[barnett468 418]

adjustable cans are smp vc31 and bw v311

[aslanefe 333]

1 hour ago, barnett468 said:

adjustable cans are smp vc31 and bw v311

Barnett, when you adjust those cans to increase the hg needed to pull, does the max amount of advance it provides drop? Do you know the part number of a can which you can adjust the hg needed to pull and the max advance it pulls separately? Don't know the part number of my can but when I increase the hg needed, with allen wrench, max advance it pulls goes down. I remember bending the stop tab on a can to adjust the max amount of advance it provides but can't remember what can it was, on what car.

[barnett468 418]

45 minutes ago, aslanefe said:

Barnett, when you adjust those cans to increase the hg needed to pull, does the max amount of advance it provides drop? Do you know the part number of a can which you can adjust the hg needed to pull and the max advance it pulls separately? Don't know the part number of my can but when I increase the hg needed, with allen wrench, max advance it pulls goes down. I remember bending the stop tab on a can to adjust the max amount of advance it provides but can't remember what can it was, on what car.

Adjusting the can from max advance, (which is the screw turned all the way in until it stops), will increase the amount of vacuum required to make it advance and will also reduce the total amount it can advance.

I have never seen a can that has dual adjustments to separate the two.

Also, in case someone doesn't know, the vacuum advance does not add any advance when accelerating moderately or hard. It is designed to add advance at steady throttle and low engine loads like when driving on fat ground or going downhill.

When both the distributor advance curve and the vacuum can have been set up properly, the can will only increase mileage by around 2 mpg at the most.

[danno 128]

On 8/6/2019 at 10:22 PM, barnett468 said:

Also, in case someone doesn't know, the vacuum advance does not add any advance when accelerating moderately or hard. It is designed to add advance at steady throttle and low engine loads like when driving on fat ground or going downhill.

 

I had to laugh at your typo, because I do feel like driving on fat ground after some of those evening dinners on the road :-) 

I do not have a way to measure vacuum, but will see what the mileage is like in the next weeks when I am driving on the fat ground. 

Thank you!

[barnett468 418]

1 hour ago, danno said:

I had to laugh at your typo, because I do feel like driving on fat ground after some of those evening dinners on the road :-) 

I do not have a way to measure vacuum, but will see what the mileage is like in the next weeks when I am driving on the fat ground. 

Thank you!

That was not a typo. That's my story and I'm stickin to it, lol.