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My dad had excellent luck with the splitfire's. They were in his 79 F-250 4x4 with a 351m with about 150,000 miles on it. He had them in for about 30,000 miles. They lasted a long time and he uses his truck for everything. He noticed a small increase in power right off the bat. The motor didn't blow until 330,000 :-X23 miles and only because the timing chain slipped and bent the pushrods and valves. :-( This is the engine I used for my truck.
Wanted: Winch for pulling out Chevys!
79 F150 4x4 410m "Built FORD Tough!"(9.1:1,KB pistons,custom Comp Cams X-Treme 210/218-.508/.524,roller rockers)/c6/3.5:1 gears,4.11:1 soon, Demon 4bbl, 285/75R16 BFG Mudders on alumn. mags with New Drk. Blue paint.
65 Ranchero 170-6, 3on the tree, solid mags, New Bright Yellow paint
I've never tried the plugs, so I can't say for sure. However, electrically speaking, only one electrode will produce a spark at a time. Kind of like if you have your body charged with static electricity, and touch bare metal with two fingertips, only one will get shocked.
So, to me, I think they're kind of a gimmick, if the intention is that both tips of the electrode are firing simultaneously.
That's just my opinion though, as I said, I've never tried them.
John Thomas
I've tried the splits and found that they are not really any better than OEM Motorcraft plugs. Never really got significant milage or performance. The thing that's advertised about them is the flame development thru the V. After taking the price in consideration I'd stick with Motorcraft. Don't use Bosch platinums - they foul too easy.
if your motor has fairly high compression or otherwise develops high cylinder pressures and you're running stock-type coil, then these new "irridium" (i think that's right!) plugs are supposed to be really good at firing where others might have a hard time making a spark. otherwise, platinum for reliability. regardless, i think the main thing is to get the heat range that works the best for your situation.
Plugs like the Split Fires tend to effectively increase spark timing because they expose the spark to the fuel mixture a little earlier. You can get the same effect from turning the distributor a little. I don't like the look of the insulator, no wrikles to increase insulating value.
Platnum plugs are best for fuel injection and not carbs from what I have heard and in my experience. I personally use the Accel "U" grove plugs and they seem to last well.