To give you all the background info,

The car is a 1968 Valiant with automatic transmission. I'm helping another forum member super six it. He will be using a Carter BBD. He plans on putting bigger exhaust pipes, but not headers.

I'm sure he want's to keep his gas mileage as high as possible and his intent for the whole project is to upgrade to super six and electronic ignition for increased street enjoyment.

I am building him an electronic distributor to replace his points. I want it to be idiot proof to some degree so that a future mechanic doesn't adjust it wrong. The factory service manual says 5 *BTDC.
He won't be using an EGR valve.

Does anyone have advice about what Vacuum Advance pod would be best to use, how to identify it (at the parts store, they want a year and model) and why it works.

If it where for my car, I would be fine with trial and error, but I'd rather build something that's ready to go when it's for someone else. I'm open to comments and suggestions.

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1980 Aspen 225 super six

if you want to boost mileage I'll try using a 9r govnor and at least 8.5 vac can. That way you can go like 12 BTDC and be safe abot moromechanics

later cars had biger vac cans on near zero initial timing dists, so you may wanna grab some 74 or up dist for donor.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

Thanks for the suggestion. Let me try asking it a again is a slightly different way.

I currently have an 11r vacuum advance pod. Will that work? It is adjustable, so I would imagine that if it was overkill, some advance could be adjusted out of it.

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1980 Aspen 225 super six

Yeah, it will work. You can't adjust the amount of vacuum advance, you can adjust when it comes out. The harder you adjust the spring, the sooner it will stop acting. In the other hand, if you regulate the can fully clockwise, the vac can will remain active for wider vac range. If you wanna go for mileage on part throttle and performance when WOT, then a good starting point will be turning the regulator all the way clockwise, then back 5 or 6 CCW turns, and test if it pings on part throttle.

On one of my recurved dist, while I was 30º total w/o the vac line plugged, it pinged at 2300 rpm cuz I used light springs and the can was light so at that spot I had the can overadvancing my "fast" curve.

My present curve is 15º BTDC initial, 14º mech (29º total) and a 8.5 vac can. The spring on the can is hard nuff to fade when the last 5º kicks in (above 2500 rpm)

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.

I understand your reasons for lots of initial and a short mechanical advance, but I am confident that my design will be predicatable and stable for a daily driven car. I also feel that the level of difficulty is a little easier when tuning. Which do you think is better for fine tuning in the design I have described?

A vac can such as a 9r adjusted soft

or

A 11r adjusted to pull out sooner?

I feel like I've answered my own question. It seems like the 9r is a closer match than an 11r. Or is 4* a negligable difference when it comes to tuning? Is the potential for extra advance likely to be an advantage when tuning, or is it more predictable that it will need adjusted so firm (to prevent ping) that it will never make any noticable improvement to mileage?

I'm thankful of your replys, and I've lurked on many of your topics to get some of your experience. I'm surprised I haven't gotten any second opinions. This must be a pretty "advanced" topic? Pun intended.

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1980 Aspen 225 super six

If you're going with 2 light springs (remember that one has to have a loop on the end wether is light or heavy) I'd use the 9R can. If you keep your stock type light-heavy springs, then you can go with the 11R can. In my experience with recurving, fast curves likes less radical vacum pods. I'll consider a "fast" curve anything going full mech advance below 2300~2500 rpm.

I think that your setup will be easy to tune, much more easy than a short mech coupled with high initial advance. When you go over the edge, you can have troubles dialin in radical recurves, since even values as low as 1° makes diffrence and you know that the way of measuring timing isn't that accurate... I don't mind getting my hands dirty, I even have a 7/16" T wrench next to my bucket, so if i feel that's something wrong, I just park the car aside the traffic, pop the hood open and jam my claws on it...

Couple more tips from my personal experience doin this:
a) don't try to dial everything in on a 4 blocks drive test. Take it easy and go one step at a time.
b) for giving the last mastertouch, wait ill the car is HOT, and I don't mean just warmed up, but HOT. Take it to the highway and beat it up, this way you can check for spark knockin, pinging, etc at diff'rent rpm ranges and throttle opening.
c) when optimum overall adjustments are achieved (initial, mech, vac) your car has to be snappier than ever off the line, keeping pep over the whole rpm range at any throttle opening. If it turns into a dog over a specific rpm range, mixture may be lean on that point, indicating that you're having too much advance at that rpm rather than you have poor mixture (since increasing advance causes leaner burn conditions and higher manifold vacuum)
d) if it's kinda "bovine" off the line (engine loaded, transmission engaged, car actually moving, feeling like carrying a cow upstairs till you have reached, say, 20~25 mph), you may have too much vac advance (or a horrible fast curve, or spring/s broken) this is assuming that you have a proper initial timing value.
e) if you have pinging above 2000 rpm that disappears if you WOT, your vac pod's spring needs to be stiffer (like 4 turns CCW or even more, 4 turns is a good starting point)
f) if you have light throttle pinging, you can go 1 turn CCW at a time (I'm ruling out too much initial timing since you're gonna use 5°BTDC)
g) once you've dialed it in, plug your brake booster hose to a vacuum gauge, start the motor and slowly close the idle needles till it starts to sputter and kinda wanna stall, then slowly and evenly open idle needles till you have max vac reading (if you're working with 2 barrels, close/open 1/4 turn each needle then the other, don't go over 1/4 turn on a single needle at a time)

well, I guess that you're going to have success on your buildup. Slants aren't too picky with advance curves, they're just very sensitive to initial+mech not going over 32° they say, I prefer to keep it under 30°.

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Juan Ignacio Caino

Please use e-mail button istead of PM'ing. I do log in sometimes but I'll be answering quicker thru e-mail.