I just finished recurving another distributor and made an 'educated guess' on springs since the light ones in the MR gasket kit wind up too easy.

Currently my curve is:
8 BTDC initial
32 mech adv. & topping out at 34 @ 3000+
at 3000 rpm total advance is 54 degrees...

This thing runs realllllllllllyyyyyy good now, I'd like to recurve another with 10 degrees initial. It likes the high-end really well, unfortunately that means I need some gears...currently power shifting at 4K isn't productive
(shift out of second gear at 55mph at 4K, made it to 100 mph on a straight away today but never made it past 3500 in 3rd gear...FYI, OD with 3.55's at 100 mph and P205/70 tires is 2700 rpm.... )


Acceleration is awesome, pick up is great, will have to see what my mileage turned into (gotta keep my foot out of it...), off idle/off the line acceleration needs a bit of carb work (got that covered....darn skinny transfer slots...)....


BTW, had to shave about 5/32" out of the advance plate to make the slots longer, I used two medium springs (the stock slant light spring, and a similar big block light spring). Works pretty good for a modified 1975 EI distributor...


Thanks for the help again! Get the carb buttoned up and see about a 1/4 mile time for 'reference'...


-D.Idiot

"You D' Man!"

My guess is that about 15 degrees initial and 30 total will be better for ya, as you say. 32-34 is getting to be too high, at least for the Slants I've tuned. Over 50 deg total will give great mileage.

Lou

_________________
Home of Slant6-powered fun machines since 1988

Cool!

Thanks Lou, I'll give that a shot, but may need some timing tape to find 15 BDTC (my tab only goes up to 12....LOL).


I always wondered if more initial would've been better(light the fire earlier and be able to use the results), I have no pinging anywhere when I advance this thing (not even a hint of it...).

I'll try that...Thanks Lou!

-D.Idiot

No problem, DI. I would suggest getting a Sears advance timing light - makes these adjustments much easier and it's only $60. On my Darts, I have not found 15 deg to be too much initial at all, even with my current 2200 RPM stall converter ('68 Dart).

More initial is good for idle and throttle response, but tends to give a little higher HC readings on a sniffer and can ping if stall is too low or cyl pressure too high, which I believe is why the timing was set up that way. Personally, I'm all for limiting emissions, but I don't believe idle emissions are that much of a contributor to overall emissions from a car.

Lou

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Home of Slant6-powered fun machines since 1988

That depends on whether you ever get stuck in traffic in Chicago or DC or LA...

There are ways to determine your exact optimized timing curve, by the way. Jacobs Electronics used to sell a wonderful textbook describing how to simulate a dyno by driving on the street with a tach and a stopwatch... I just sent their 'tech support' people a question about whether the book is still available; will let you all know. In a nutshell, the best (centrifugal) timing for a particular RPM is the one that allows the engine to accelerate through that spot the quickest. For example, measure your elapsed time from 1500 to 2000, to find the spot for 1750. Pull over, change a couple degrees, tighten the distributor and try again. And so on. You'll need a handful of data points from about 1000 to 3000. I can't remember if I went higher, but it hardly matters because the springs controlling a curve usually run out of room by then. It takes all afternoon to map the coordinates, but when you're done you can graph a truly "optimum" timing curve for your engine (in your car with your gasoline at your atmospheric conditions)... and then choose the springs which approximate that curve the closest.

"Seat of the pants" just doesn't measure up, by comparison. Besides, the dyno method eliminates the potential of minor detonation that is too small to hear but can still slow the car down.

A "dial-back-to-zero" light is handy, but not essential. Timing tape is sufficient. Even masking tape and a marker will do.

- Erik

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Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

Hi Erik, good to see you contributing over here.
BTW, Erik is the webmaster of the Early Valiant Barracuda site.
http://www.earlycuda.org/

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Just curious if any more info was forth coming on the book?

I also found another brand new dist. in another pile of 'to do' stuff...so I'll play with that one a bit too.

The weird things I noticed were:

Small block and big block advance governors are the same as the slant six ones (pulled a handful and matched them up and the slots are the same size, length and in the same location....).

I also would like to know if there is a mopar table of stock 'spring' rate information. Several distributors I've pulled apart still have paint on the springs an I'd like to know the difference between an orange and a blue one..(both have the same amount of coils, same loop type on both ends...)

-D.Idiot

so I recurved another one with stock parts from 3 distributors to replace the ailing one in my '74 duster.... 10 initial, 30 mech+init, and 48 with vacuum advance all in by 2300...for a 1 barrel road oiler manual 3 spd with 2.76's it likes to 'get up' on the highway...hope my mileage doesn't suffer badly from leadfoot...


You've created a monster!

-D.Idiot

Unfortunately, my inquiry to Jacobs received no response. Zip, zero, zilch, nada, big fat goose egg. Either they don't want my business, or things changed pretty drastically now that they sell only through their dealers, instead of directly from the factory. I guess I'll have to make some phone calls.
It makes sense that springs and stuff would be the same, between engine families. The distributors are all about the same size, and I'll bet the advance curves aren't a whole lot different. At least, not the wimpy way they program those curves at the factory. And the total recommended centrifigual timing figures I've seen are all between 30-35 degrees, no matter which engine.

I ended up just putting a spring in the distributor and charting the result. When I got the one that was the closest to my "ideal", I stopped. I suppose I ought to scan graph paper from my experiments and post it, but I'm afraid someone might think it's a definitive answer to what their engine needs. Really, it's not that hard to chart your own needs, and you'll be much more accurate.

I don't recall seeing different colors of springs, or I'm sure my curiosity would have driven me to catalog the results exactly as you described.

- Erik

_________________
Lots of early Valiants and Barracudas have crossed my path.
Also a handful of other toys for variety now and then.

I think before I get too wild about things I'll get an accelerometer so I can actually see what the results are in 'certain' ranges and be able to look at 'spring/weight/jet/etc...' changes with some numbers with rpms...

thanks again,

-D.idiot

DI - time to bring you car up to Portland for a run on a chassis dyno. With a wide-band O2 sensor in the tailpipe you'll know in minutes if it is tuned correctly or not. I'll try to post a picture of my car on the dyno. Made 460 hp at the rear wheels. Of course, this one isn't slant powered but you get the idea.

http://www.arengineering.com/photogall/ ... no_600.jpg

Guess I don't know how to post images so I'll just provide the link.