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Old 07-17-2011, 11:49 PM
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Duraspark 2 mpg tip

I was doing some digging regarding the DS2 dizzy, and came across a good tip for better mpg. And it makes me wonder what was done to my dist. when I had it recurved. The point is that the DS2 was designed with emissions in mind, which means worse mpg. The author got 3 mpg better around town just by doing this.

Credit for this goes to Classic Inlines dot com.

If you have a DuraSpark II distributor, you also have smog-control spark advance curves inside. All of the DuraSpark units came this way, to reduce hydrocarbons. Unfortunately, it also reduces MPG. However... today's gasoline reduces the hydrocarbons for you, even more than the slow spark curve did. So, get a set of the Mr. Gasket #925D distributor springs and modify your distributor as follows: First, remove the lighter of the 2 springs in the DII and replace it with one of the #925D springs. DO NOT replace both springs with the #925D springs (more on that in a moment). Next, there is a support arm that holds the larger spring, on it's non-slotted end. Bend this arm in toward the center of the distributor, just 3/32 of an inch.

This combination replicates the "police interceptor" distributor spark curve for the 200 I-6, according to a local "guru" who helped build these for Ford in the early 1980s. It causes earlier spark advance up to 1200 RPM, which then remains steady until 1800 RPM, when the secondary spring starts its advance. This "plateau" of early advance, limited by the 3/32" inward adjustment of the heavier spring, provides more torque at around-town speeds. This improves your MPG because you don't have to open the throttle as far to get the same speeds you were running before. You'll also notice better off-the-line pep and cold-running performance. Mine also starts a little better when hot, and the plugs stay cleaner. My in-town MPG rose from 16.5 average to 18.1 average over 2 tanks of gas, winter driving to and from work. I haven't tested the highway MPG yet, but I don't think it will improve from the 23+ I've been getting. I'll re-post if it does.

If you make the mistake of replacing BOTH springs in your DII with the #925D springs, you will get a SLOWER spark curve unless you extensively modify one of them to provide a "slot", like the heavier spring already has. But I found, even after that exercise, that the engine "hit the wall" at about 2200 RPM and would not accelerate well up hills. Adding in the heavier spring, but delaying its effect until 2000 RPM, did the trick: now it loves to rev, even on regular gas (my compression is about 9.4:1). The maximum advance is reached at 2600 RPM on my engine with this mod: before, the max advance was at 3200 RPM.

I wonder if this can be done with the 300 DS2?
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Old 07-18-2011, 12:38 PM
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Absoletly! The only difference is the number of cylinders it's made for. Control module, coil, wiring are all the same.
There are a couple good articles, but this one is my favorite. Pretty pictures don't come up for me anymore, but good reading.
http://vb.foureyedpride.com/showthread.php?t=22229
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Old 07-18-2011, 04:44 PM
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I did this to mine back when I converted it to a 4bbl. It can be a real pain because of the design of the 300's duraspark distributor. There's pretty much nothing except the distributor itself to pry against when prying off the reluctor. I had to bend some things back into shape after the procedure.

I don't know about mpg, but it definitely gave it some oomph.
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Old 07-18-2011, 08:26 PM
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Quote:
Originally Posted by F-250 restorer View Post
I was doing some digging regarding the DS2 dizzy, and came across a good tip for better mpg. And it makes me wonder what was done to my dist. when I had it recurved.
When you had it recurved, I'm assuming the shop had a distributor machine? In the hands of a good distributor guy with a Sun machine you should be able to get whatever curve your engine needs.

I've never seen any hardcore data on timing specs for a 300, although it can't be all that different from any other engine. Dialing the mechanical advance all in at 3,500rpm is usual for street cars; light, quick revving vehicle maybe sooner.

Total advance is another question. One early Eighties V8 distributor I saw had weights marked 18 and 21 - i.e. 36 and 42 degrees of mechanical advance. So with 12 degrees base + 42 degrees a total of 54 degrees advance. Boggles my mind...

My '65 Mustang with a racy 331 is running ~40 total timing - ~16-18 degrees static and 21- degrees mechanical advance. I could probably get away with 25 degrees of advance, but better safe than sorry since I'm not running for money or time.

Anyway, I think a lot of issues people have with mileage and driveability after carb/intake/exhaust upgrades stem from timing/ignition.

A pro with a Sun distributor machine is tough to find these days, but with a good dial-back timing light and a harmonic balancer that doesn't apparently slip periodically and move the timing mark it's easy enough to dial in the curve yourself in the driveway. Easy enough other than removing and disassembling the dizzy a few times.
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Old 07-18-2011, 08:35 PM
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Quote:
Originally Posted by gfw1985 View Post
Absoletly! The only difference is the number of cylinders it's made for. Control module, coil, wiring are all the same.
There are a couple good articles, but this one is my favorite. Pretty pictures don't come up for me anymore, but good reading.
The Ultimate Duraspark Distributor Timing Guide. - Four Eyed Forums
Man, that white on black page layout is hard on the eyes. Good info, though.
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Old 07-18-2011, 09:22 PM
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One tip for adjusting the timing curve in your drive way is that, once the recurve spring is in, you can bend the spring tabs that adjust spring tension while the distributor is in the vehicle.

It takes some finesse and patience, but you can reach the tabs with a screw driver by rotating the engine until the tab is underneath the wire clip hole. If you remove the wire clip, the hole is big enough to give you room to work. Not easy, but way better than popping the reluctor every time.



As for a Sun machine, no one around here has one. I wish they did. I'd pay them.
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Old 07-18-2011, 09:34 PM
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I put 2 lighter springs in, and it is a little less at the top end than I'd like, but up to 3k is great. I mainly drive it in town anyway with no hills to worry about. I did a whole lot of adjusting in the past 3 years, and have the spring tabs bent out almost to where they hit the dizzy case(max spring stretch), just to slow the advance. Plus, have the limiting tab for the weights bent over a little to limit total timing. It really helped after the cam install, and there's no low rpm power loss. I get 15* initial, and 38-40 total(cant remember exactly). The timing light with a dial-back is THE way to tune!
I even swapped out to 2.75 gears, and it's hard to get over 13mpg....Oh well, at least it's fun to drive.
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Old 07-19-2011, 08:17 PM
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Originally Posted by AbandonedBronco View Post
As for a Sun machine, no one around here has one. I wish they did. I'd pay them.
I've never used them before, but I'm going to send my dizzy to Advanced Distributors for a rebuild/recurve. They sound like they know what they're doing.
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Old 07-19-2011, 09:23 PM
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This outfit posted instructions for a recurve and sells recurved units too:Duraspark_distributor_recurve_instructions_index
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Old 07-19-2011, 09:41 PM
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Quote:
Originally Posted by nevrenufhp View Post
I put 2 lighter springs in, and it is a little less at the top end than I'd like, but up to 3k is great. I mainly drive it in town anyway with no hills to worry about. I did a whole lot of adjusting in the past 3 years, and have the spring tabs bent out almost to where they hit the dizzy case(max spring stretch), just to slow the advance. Plus, have the limiting tab for the weights bent over a little to limit total timing. It really helped after the cam install, and there's no low rpm power loss. I get 15* initial, and 38-40 total(cant remember exactly). The timing light with a dial-back is THE way to tune!
I even swapped out to 2.75 gears, and it's hard to get over 13mpg....Oh well, at least it's fun to drive.
I don't mean for this to sound like a put down. That is not my intention; I'm just trying to understand. You've done a lot of testing, but your current setting is not what you would like at top end, and it lost some of the bottom end, you stated, so why do you keep it there? What is the benefit?
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Old 07-19-2011, 11:42 PM
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I've done a lot of setting & resetting, but I dont think it's optimal. I need a little stiffer spring to get it where I think it makes all of its potential. I was saying that normally, you lose bottom end with a bigger cam, but it hasnt lost any bottom end, or at least it feels that way. I keep it set there mainly because all the power I use in daily driving is under 3k. That, and I keep forgetting to go out and buy the springs. It still has great power above 3k, just not to its full potential. It's still feels more powerful than the 302 I had in my old 48 F1.
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Old 07-20-2011, 11:46 AM
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Great tip Restorer, but there is something else I feel could be added to our bag of tricks for the DS-II. Most of them left the factory with an adjustable vacuum advance unit. So the timing can be tweaked even further, to really get everything dialed in. Simply remove the vacuum line going to the distributor and insert a 3/32 (IIRC) allen wrench into the vacuum nipple and turn it clockwise for quicker advance, and counter-clockwise for less.

It helps when you can only get the mechanical springs and weights adjusted so much.
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Old 07-26-2011, 12:37 PM
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Any idea of how much to turn this critter? I can't do the arms/springs - but I do have the right wrench? Fuel use advantages?
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Old 07-26-2011, 03:15 PM
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Only thing adjusting the vacuum canister does is control how soon( how much vaccum) it takes to start vacuum advancing. Vacuum advance only comes into play under load conditions. It's just one part of doing a custom advance curve for your engine. If your engine is spark knocking under load, it can be used to eliminate that, but only as a fine tuning tool in conjunction with everything else.
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Old 08-10-2011, 04:37 PM
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I'm going to do this on my truck (302), I would have done it the other day but I discovered it was on the "21L" slot so I have to limit it first. (10 initial + 42 centrifugal = 52 degrees)

Does anyone have any info on the weights? I have one dizzy with G1 and G3 weights and the one I'm using has G4 and G5 weights.

Is G1 the heaviest or the lightest?
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