Has anyone ever used them? I installed them about four weeks ago, no improvement noticed, but my gas mileage has gone down. I haven't been driving any harder then usual, if anything quite the opposite because when I noticed my gas mileage went down I made a point to take it easy and I'm still getting about 20 miles per gallon. I do mostly highway driving, so I think it should be better. Ditch the plugs or do you think it's something else. Also, I always run 93 octane, should I change? I was always getting around 21-22 before, so its not a HUGE difference, but it is a difference, and a bad one.

 

they are junk.

you are better off with a good ngk or some other good name brand.

 

There is no reason to run 93 unless you need to because of detonation. Otherwise, it's a waste of money. As far as the plugs are concerned, I don't know much about that brand but I do know that most folks have had alot of success with NGK or Denso spark plugs. V grooved copper plugs work best for me but I've heard good things about iridium plugs.

 

Why are you running 93 octane? There is no benefit for a stock car to run anything other than 87.

Edit: beat me to it.

 

I'm curious as to what your mods are. I get 19mpg in the city and 26-27 highway. If you're stock, you should be getting better numbers. Much better.

 

the splitfire plugs and 93 octane is your problem. go with a single diode plug (i got ngk tr6's) and use 87 octane unless you have a tuner,blower,or turbo then you'd need it

 

Not quite stock, but I thought my mods would only increase HP, I just have the K&N intake, Steeda Pullies, and Flowmaster exhaust. All three boast gas mileage increases. I'm going to order new plugs for this weekend. As far as the octane, I was under the impression that running the higher octane would help keep the injectors clean because it is better gas, now that I think about that is that BS? I mean, is it the same gas, just higher octane? Never really thought it would hurt anything, and I figure it only costs me about 10-12 dollars a month so it's not exactly putting me in the poor house.

 

I had put splitfire plugs in 2 previous vehicles (neither mustangs though) and have had horrible results, up to and including ruining my plug wires. I wouldn't recommend splitfires to my worst enemy.
As far as 93 octane goes, I have to use 93 in my '04 GT. I was having a lot of tapping of the valves with 87 so I changed to 93 and have had no problems since.

 

Splitfire plugs are a waste of money as is running higher octane fuel.I run 87 with a Steeda timing adjuster set at +3 with no knocks and I picked up two MPG.If your engine is making noise while running 87 then there is something wrong with it.There is excessive carbon in the combustion chambers or the engine is running extremely lean.Carbon can be cleaned out by spraying a fine mist of water into the engine and steam cleaning the carbon out.A lean mix can be helped by cleaning the MAF element with carb cleaner.https://mustangforums.com/m_617228/tm.htm Check out this sticky.

 

Ditto...splitfire = junk.