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distributor recurve
https://slantsix.org/forum/viewtopic.php?t=42635		 Page 2 of 6
Author:  gato [ Mon Nov 22, 2010 6:56 am ]
Post subject: 
do u know what the numbers on the vacuum pod are mean? and what do i assume about the pod with now number on it?
Author:  Aggressive Ted [ Mon Nov 22, 2010 8:40 am ]
Post subject:  Distributor Recurve Instuctions
Gato,

You double the number on the pod for total vacuum advance.

You really need to read the link in FAQ and check out the 4 .jpg pages on how to tune and set up a distributor. See "Recurve Pages". Check out my graph "Ted's Curve" on how the advance progresses. I followed Doc's advice explicitly and have had excellent results. For having a heavy car, wide tires and a automatic, I get excellent mileage, especially in the traffic out here. My pinging problems went away and never came back.

72Polara,

Yes, the secondary spring has a long loop and is pretty stout. You can find them in high performance 383's and 440's. It limits the maximum throw so you never bounce at the end of the slots. It is very smooth at max mechanical advance. The VC-208 pod (11R) I am using adds another 22 degrees. I run 10 degrees initial, 22 degrees mechanical for a 32 degree total at 2500 rpm and another 22 degrees of vacuum advance for a 54-55 degree total at cruise.
FYI, I have found 60 degrees to be too much for my engine build. I haven't heard it ping, but it just goes flat a cruise and you loose the snap or spunk.

If you have a heavy work truck or a van, I would limit the vacuum advance with a 8.5R pod or less. Check the various pods under "Distributor vacuum can specs (list)"
Author:  gato [ Mon Nov 22, 2010 9:01 am ]
Post subject: 
Ted,

i have read over most of the recurve pages, tho, i have not committed them to memory.
i suppose i will need to check them again. i think i hear a difference in the way the vaccum pod works between ur opinion and that of 72Polara.
he says the vacuum only kicks in at low-midrange.
how do u get to 50+degrees? does it pull beyond the mechanical range?

do u know how to determine the range of a pod with no markings?

the 15R would require the static timing to be real close to 0*BTDC, rite?
Author:  Aggressive Ted [ Mon Nov 22, 2010 9:26 am ]
Post subject: 
Gato,
Quote:
he says the vacuum only kicks in at low-midrange.
how do u get to 50+degrees? does it pull beyond the mechanical range?
No it doesn't, it kicks in progressively as the engine vacuum rises. You can delay this effect by tuning the pod found on page four of the instructions. I run a vacuum gauge in my car and 60 mph cruise is around 18"-21" . The pod is fully engaged at that point. Look at the chart on the various pods as to when they fully engage or hook up a manually operated vacuum pump and gauge to test pods with no numbers.

The pod adds the frosting on the cake. Once the mechanical is in the pod takes over, or a soon as you get your foot out of the gas it kicks in. The vacuum has to go up above 10" or so before it engages. Drive with a vacuum gauge. It may help you get better mileage. Remember Doc's comment, "drive with a egg under your foot".

Look at the green line on "Ted's Curve". You can see how slow the pod kicks in by looking at the rpm on the bottom. For the pod to kick in early you really have to feather the gas to keep the vacuum high. I don't drive that way.....I drive rather aggressively, but keep the vacuum high as possible.
Quote:
do u know how to determine the range of a pod with no markings?
Manually check it with a hand vacuum pump and gauge.
Quote:
the 15R would require the static timing to be real close to 0*BTDC, rite?
True per the book and with stock springs, but you can change that with a heavier secondary spring. I run 10 degrees initial now with my spring set up. You could get there many ways, 10 degrees initial and 22 mechanical, 12 initial and 20 degrees mechanical (which I like too), 16 and 16, etc....32 degree total for the SL6 is the magic number for initial plus mechanical.

When rebuilding don't use heavy grease. It will slow down the response and may dry out over time and cause the weights and top plate to stick. I use 20-50 synthetic oil.
Author:  72polara [ Mon Nov 22, 2010 10:22 am ]
Post subject: 
Just to be clear, I did not say that the vacuum pod worked in low to mid range ( as in rpm ). I said:
Quote:
Only during low load cruise ( ie, light part throttle operation)
This lines up exactly with what Ted has said: High vacuum situations. I was speaking only of the throttle usage, nothing was said about rpm ranges.

Ted:

Got it - I made a bunch of changes at once with the stuff I had on hand, so I went ahead and limited the governor, went to a stiffer second spring & primary. Sounds like my governor change may have been unneeded, if the spring I picked was heavy enough. I've only measured initial timing (10 degrees) and total timing (33ish degrees). It seemed to get me in the ballpark, so I haven't put much more time into perfecting the curve. I was shooting for that 32 degree figure, since it is what keeps coming up in the recurve threads.

And with that, I think i'll shut up, I think I'm bordering on thread-jacking. :)
Author:  wjajr [ Mon Nov 22, 2010 10:27 am ]
Post subject: 
To clear up how the vacuum advance affects timing, keep in mind it works off of manifold vacuum, and adds timing to whatever initial degrees of advance, plus mechanical degrees of advance is at any given rpm & vacuum over approximately 6-10 inches Hg ( the point at which the pod starts to activate).

Manifold vacuum is highest under no throttle opening & high rpm such as coasting down a hill with foot off the gas. Conversely lowest manifold vacuum is during wide open throttle. Manifold vacuum varies between low & high while driving public roads (drag racing is another story not addressed here), and as Ted stated, during cruse condition, one wants timing to be advanced high enough to produce good fuel economy, and low enough under full throttle as to prevent pinging, or spark knock.

A vacuum advance cleverly takes advantage of manifold vacuum to advance timing during light throttle (increasing vacuum), and retard timing during throttle openings (reducing vacuum). This action can be almost off & on or gradual, depending on how fast the throttle is opened & closed and or how much the throttle is opened or closed. This takes place regardless of where the mechanical advance is in its curve.

No wires, no sensors, no black box stuffed with logarithms’, real simple.
Author:  gato [ Mon Nov 22, 2010 3:05 pm ]
Post subject: 
sorry &2Polara.

it sounded different to me on the first time thru.
Author:  gato [ Mon Nov 22, 2010 3:23 pm ]
Post subject: 
the main shaft with the shorter Fly-weight plate has a groove spiraling up it. i assume it is for increased oiling. the other 2 shafts do not have this groove.

is it any real advantage to try to stay with that shaft?
Author:  olafla [ Mon Nov 22, 2010 3:32 pm ]
Post subject: 
Hi gato, I sent you a pm.

Olaf.
Author:  DusterIdiot [ Mon Nov 22, 2010 6:18 pm ]
Post subject:  Pass...
Quote:
the main shaft with the shorter Fly-weight plate has a groove spiraling up it. i assume it is for increased oiling. the other 2 shafts do not have this groove.

is it any real advantage to try to stay with that shaft?

For points only to use with the body that has the sideoiling port. A true EI shaft will not have this and has adjustable posts (hex heads at the bottom of the shaft plate). This way you can adjust how soon the loop in the spring starts to put tension on the advance...

-D.Idiot
Author:  72polara [ Mon Nov 22, 2010 6:24 pm ]
Post subject: 
Gato, no need to apologize. I'm sorry if I came across as a bit testy. Fortunately, wjajr followed up with an excellent explanation!

At the risk of information overload, the only thing I would add to what he had to say is that the vacuum pod should be connected to the ported (timed) vacuum port, not a straight manifold vacuum port. Manifold vacuum will be high at idle, and behave as described everywhere else. The timed port will be at or near zero at idle, and behave like manifold vacuum once the throttle plates open up.

The reason for the distintion is that if the pod is on a manifold vacuum port, you will have full vac advance at idle, and as soon as you crack the throttle, you'll lose all of it, most likely resulting in a stumble. It may also cause an erratic idle.
Author:  gato [ Mon Nov 22, 2010 6:33 pm ]
Post subject: 
@ Olaf. .. .

got it. . . .and back atcha.


@DI.

none of the shaft plates i have have any provisions for adjustability. i guess that means the dizzy that had the EI pick up was converted?



i'll look closer for the side oiling port. i didn't notice any such thing. but i didn't know what i was looking for either.


the inside of the housing that had the points in it was heavily greased in a spraying sorta pattern. . . .HHMMM. . .
Author:  Aggressive Ted [ Tue Nov 23, 2010 9:07 am ]
Post subject:  Recurve info
Gato,

Look on the bottom of the plate at the spring posts. There should be a hex nut to adjust that rotates the post like and eccentric that will fine tune spring tension. They are stock on the 15R governors and few others. I run a medium light red spring as my primary spring for a quick advance. I rotated the post all the way out to further tighten the spring so there is no slop. This helps to keep the weights in at idle...

The secondary spring which is heavy black long looped spring, I rotated the post all the way in to limit the max throw to 22 degrees even though the slot will provide 30 degrees.

With this spring combination it provides a full 32 degrees advance @ 2500 rpm when you set the initial advance @10 degrees. It provides good spunk off the line and a nice progressive advance for good performance and mileage. In other words it is allot of fun to drive and no longer a slug in terms of response and no more pinging.......
Hope this helps.
Author:  The Kenosha Kid [ Wed Nov 24, 2010 9:13 am ]
Post subject: 
"the 15R governor is best for mileage". I've read this before, could you elaborate? Is this because the longer slots allow control over more of the advance curve?
Author:  wjajr [ Wed Nov 24, 2010 11:00 am ]
Post subject: 
The Kenosha Kid:
Quote:
"the 15R governor is best for mileage". I've read this before, could you elaborate? Is this because the longer slots allow control over more of the advance curve?
TK,
Remember what Ted stated, 2x the number stamped on the governor or vacuum can for amount of advance in degrees. 11R=22degrees, 15R=30degrees, or whatever as there are several ratings. As timing advances closer to that magical 50-54 degrees (stock build generally speaking) good gas mileage number, your highway fuel mileage will increase. Go over 54 degrees, mileage drops, engine becomes less responsive, flat, doggie...

Remember all these timing adjustments, or inputs are additive. So if you start with 10 degrees initial advance, 22 degrees from governor (100% rpm dependent & spring weight controlled), and 30 degrees from a 15R vacuum advance, this adds to 52 degrees when engine is running at speed with small throttle opening or high vacuum condition.

With these three variables, initial, mechanical & vacuum; along with the additional ability to fine tune mechanical dip-in via spring selection, and vacuum advance dip-in by adjusting vacuum pod stop with hex wrench, one can with a bit of fiddling around, custom tune an advance curve to fit any engine build.

I have to admit it took me a while to wrap my head around this re-curve process, but Ted kept holding my hand until it soaked in.

Practice fiddling around with spring selection, and vacuum pod flub-dubbing around eventually yielded an advance curve that takes full advantage of my less than stock engine’s build.
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