Hi all,

I just found out my vacuum advance diaphragm is leaking, so I need to replace it. When I took the old one off, I found it had "6.5X" stamped on the arm. Just curious if anyone knows what this indicates? Is this related to the number of additional degrees advance? I couldn't find any other numbers on it, but the distributor had the number 2444648 stamped on it. Thanks for any info.

There is a thread in the FAQ that goes into the different vacuum advance cans, and what the numbers mean.

http://www.slantsix.org/forum/viewtopic.php?t=13198

On the page is discussion about the 6.5X being 6.5° of Distributor advance.

Dan listed a bunch of the part #'s in the first post, so take a look at it.



CJ

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Part of Tyrde-Browne Racing

Hey, thanks CJ!

Dan, That is a most useful thread in the link. I copied and pasted much of the data into a file I have called
"Timing ideas".

One of the V-8's turns the opposite way from the slant, so the bends in the advance arm would be backwards. It seems you might have to modify both the bend and the tab on the arm to use that V-8 can on a slant, but maybe the configuration of the internal plate allows it to work on both. According to Ed's research the small block and slant are listed for the same advance can.

I was especially interested in MPGFanatic's research. I wish I knew similar data for 1800-1900 RPM which is where my car lives on the highway. What is the ideal total timing advance for 2000 rpm at various vacuum readings? If you have it set up for 44 total at 3000 rpm, Then by 85KPA, which is about 5" of vacuum it would pull out the entire can advance of around 20, and drop it down to 24 degrees. So it seems this would be the range you would be driving in between min and max vacuum at cruise speeds.


With Ed's research and the way he has applied it to his car, at 2000 RPM the timing flows between 15 and 34 advanced. Does anybody know if this is the "ideal" for 2000 RPM? Erik seemed fairly convinced by now that the 44 degrees at 3000 rpm was kind of universal, although he did state he was hesitant to publish this lest folks run with this as a universal gospel.


Right now my map is set up for 39 degrees at 2000 for all below 85 kpa with no complaints from the engine. But I do not know if that is the most efficient. AT 85KPA, or 5" it is timed at 37 degrees, and at 0 vacuum or 100 KPA I have it set for 18 advance. This is kind of based on seat of the pants driving and avoiding preignition. But it would be nice to have some real research from guys like Erik who had applied math or physics to engines of similar bore and stroke to ours.

About six months ago I stated that both my Miata and Scion are timed with considerably less advance than the slants, and was scratching my head over this. I realized later that this is because of the small bore these engines have. The flame gets across the cylinder much quicker. I proved this to myself by advancing the cam position sensor on the Miata 2 degrees and it instantly went into preignition under light throttle. I guess the geniuses at Mazda know what they are doing.

So where does leave the discussion on vacuum cans? I think I would get the one that can get you in the 44 degree range at 3000 RPM while staying out of preignition under high load conditions. Ed's chart is still extremely useful there. Your own testing with your specific engine will yield the precise one that does the trick for you. Your cam and compression ratio will determine this. If it is stock, I would trust Ed's research.

http://slantsix.org/forum/viewtopic.php?t=46444

Scroll down to the chart Gunpilot pasted in of a basic outline for the timing range Ed's engine operates in.

Sam

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I think is because four cylinder engine has fewer power pulses per crank revolution, longer duration for flame travel, than 6 or 8 cylinder configurations. I think you will find that 8 cylinder engines like more static timing than a 6.

I suspect flame front travels at the same velocity in a four, six, or eight cylinder engine. Advancing ignition event provides more time for burn to take place.

I might be all wet on this, so a second opinion is welcome.

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67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Flame front travels at same speed but has further to go in big bore. That is why the v-8 with nearly 4" of bore in most cases can take more static timing. Greater distance to travel before flame fills the chamber. There are other considerations too.I am only vaguely aware of the impact of head chamber shape and resultant swirl on preignition and thus timing. I am pretty sure all new heads have lots of squish, and thus more turbulence inside the chamber. I am really out of my element and at the edge of my dummy window here. The car I know the most about is 42 years old now. Actually 43.It was built in December of '68.

Sam.

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Sam,

For reference: At 2000 rpm I am right at 50 degrees @ 20", 47 degrees @ 18" and 45 degrees @ 16". That is with 6 degrees initial and a VC-208 11R can turned
CCW 5 turns.

With the colder NGK UR6 plugs the engine is very happy. I run it pretty hot with a 205 degree electric fan switch and a 195 degree engine stat so the two 9" fans
rarely turn on.

Click on the red link below my name and look at the photos towards the end for the two 9" fans, radiator air scoop/dam, 2.5" exhaust, etc....

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

Ted, are these readings taken under the hood, while stopped, or do you have something rigged up to tell you this while you're driving?

And do you know if the VC-208 11R can will fit my 2444648 distributor? Thanks.

With the hood up, which is much safer! You can unplug the distributor line and use a hand pump to recreate/get the vacuum readings that you see while driving.

Yes, the VC-208 fits SL6 distributors. You may have to check your top plate to be sure it moves freely with no binding or old sticky grease. I have an old points type distributor I converted to the electric pick up and new style cans.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

The EI distributors have their pick up plate that has 2 holes one for each style of vacc. advance arm. I have found depending on the year of the points distributor they may or may not have the hold that is needed for the EI Vacc. advance arm. I know that the 1965- distributors i had did not, but the stocker late 60's-1972 distributors I have do... You can swap the plates around if needed, but you will need to look at your points plate to see if it will accept the later short arm with the bend going the other way.

-D.Idiot

Thanks, Ted. I have added a Pertronix Ignitor II kit to my original, points type distributor. The top plate moves but I'm going to lightly lubricate it to loosen it up a bit.

Good catch, Duster. I just checked my plate, and it does have only the one hole. Looking at pictures of the VC-208, I can see that the arm curves inward, instead of outward like my current vacuum advance does. Unfortunately, I don't have any extra parts to play mix & match. Anybody know of an adjustable vacuum advance that will fit my distributor?

Alternatively, I suppose it's possible to drill a second hole in this one, but that would be a one-shot deal! Can someone please post a picture of the later plate, so I can get an idea of the spacing?

Thanks Ted. This kind of information is extremely valuable. The timing of your ignition is one of the most vital tuning parameters. And yet without a dyno, it is very hard to get a handle on how to tune this. People who have played with it, and have hard data to report on add much to the discussion.

I copied and pasted your data into my timing ideas word file. It is easy to change your timing curve with EFI. My hat is off to you guys who have done this with mechanical timing.

Thanks again.
Sam

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I ordered a Standard VC93 replacement from Rockauto, only $17.28 including shipping. I'm still interested in an adjustable can if anyone knows which one would fit my early distributor (2444648). Thanks.

FAB64,

I have all my distributors and rebuild parts boxed up and can't get to them right now. Maybe over Christmas I can compare distributor plates and share a picture so you can drill the hole.

Is your distributor in a truck? I am curious about the low number on the arm and that it is a fixed/non adjustable can.

_________________
Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG