I have a Clymer manual for '69-'85 truck with some curious info surrounding the '74 year...First, it states that the Solid State Ignition (SSI) was used on some '74 and all '75-'76, while an 'improved' SSI version, Dura Spark II, was used on all '77-'80 and some to '84...

I had been under an impression that it was all referenced as DSII, from the start of breakerless....in looking at the schematics they show side-by-side for breaker-point, SSI and DSII, it shows that SSI was adapted to the existing points harness, which makes sense since there was overlap in transition to breakerless...then for DSII the harness is laid out differently, but the working components look similar...there is description of a 'high-energy secondary' (coil?), larger rotor/cap and 'wide-gap spark plugs'... I note a pedestal-type dist. cap, and that the ballast override comes from the ign. switch rather than from the starter solenoid as previously...I am recognizing this dist., with its pointy cap and adapter section, from working on early-'80s cars...

However, in searching here I came across a member who stated that he was transplanting a '76 DSII engine into a '75 points-original... by this reading, neither variable can be the case, as (or, IF) 'all' '75-'76 were SSI...As for just 'some' '74's being SSI, I haven't seen any with points, at least with the 360...As to the new 'wide-gap spark plugs' for '77 (DSII), Clymer has them at .044 for all engines, the same as they show for all '75-'76 (SSI)...

For '73, with all engines still being breaker-point, all gaps are shown at .035, except the 460 at .054 (!)...then for '74, the 200 and 240 have points and are shown at .035, while both the 300 '49 state' with points AND 'Calif.' with SSI are shown at .044...the 302 is at .035 points/.044 SSI...the 360 shows 3 different gaps- an 'Over 6,000 lb. GVW' (which must mean the HD-truck version of 360) with points, at .034, a 'regular' points 360 at .044, and the SSI 360 at .054...the 390 and 460 show to refer to VECI label...

OK, is any of this wrong, or possibly misprinted? Does a '73 points 460 really take a .054 gap, while a '75 with SSI shows .044? Does a '74 points 300 take .044? Moreover, does my '74 SSI 360 really take a .054 gap, when at least the next 2 years show a .044? I do see .054 shown on what's left of the valve cover label, but after setting, power is down and it's stalling out after deceleration, though it starts well...should I just reset to .044?

Also, from '73 to '75, 3 different spark plugs are called out for the 360- BTF-42 for '73, BRF-42 for '74, and ARF-42 for '75...???

 

In terms of setting up what you have now, most important is to match up specs with a consistent year.

The "high energy" Duraspark does have a bigger cap vs earlier. As original, it uses a plastic adapter to mate up with the smaller diameter distributor housing.

The big cap, good silicone jacketed plug wires, later control box and matching later coil make it "high energy". With "high energy" you can run the .042" gap. If you don't all of the above, best to stick with .035".

 

To my knowledge, gaps were held down to that .035 area due to the nature of breaker points, in that they wouldn't hold up to the current flow necessary to spark wider gaps...such that with the elimination of breakers, higher currents and wider gaps could be used without shortening tune-up intervals...wider gaps give more-efficient combustion, a big driver of the move to electronic...

I just closed them back to .044, and it seems like it's going to run better....I was getting that nice tan color on the insulators...looked at the VECI label again, and it calls for '.052-.056 ' I know it's for the '74 year and that the engine is original...that kind of a gap would make much more sense as a next-step to the higher-output '77 system...but i'm perfectly comfortable with the .044, and that's what's called out for the same app in '75-'76...something's got to be off somewhere with that .054 spec....

btw, i'm really just getting going again after a top-end rebuild...i'd delayed it until finally coolant started seeping past a head gasket...the gaskets were actually just stamped sheet metal and had finally rusted through...anyway, the heads were atrocious, with one of the ex. seats totally gone, so I had them redone and added Edelbrock cam, lifters, timing set and intake....

I want to stay fairly original in appearance, but would consider upping to 'DSII' spec if doable...it also uses both mechanical and vacuum advance dist.- would simply adding the adapter and large cap along with changing the coil and controller (and adapting the harness) possibly work, and perform better?

 

In general, the bigger gap needs higher secondary voltage to make a good spark. Yes, the points are a weak spot. Also the cap/rotor. High voltage can arch between posts if they are too close. Also the wires... better wires are needed with higher voltage to prevent current "leaks". Finally the coil and control module needs to be able to generate the higher voltage... and hold up.

If I had the smaller cap, I would personally run .035". The (very) slight performance benefit of the bigger gap would not be worth the reliability risk to me.

 

I've gotten an opinion that this may have been a "tweak" by Ford at that time to achieve desired emissions testing results on both the points and SSI motors...Perhaps dealers/servicers simply knew to narrow them back up.....

 

Nothing wrong with .060" in a good healthy system with electronic ignition, but in these old girls with points I'd definitely be running .040" to preserve the contact faces.

- boingk