Spark Plug opinions

MikeD0106 · **Posted:** Mon Dec 19, 2005 1:41 am

SavageSS27 wrote:

Does anyone know what the gap on the stock plugs is and what gap i should run on either the platinum or iridium plugs?

The stock gap is .044. As far as what you should change it to... :?:

kickit_in4wheel · **Posted:** Mon Dec 19, 2005 3:07 am

Ok, I'm all for saving some cash, but if one wanted to increase the performance of their KJ, is there a spark plus that will make a difference? I put the Bosch Platinum +4s in mine as soon as I bought it (used) trying to accomplish this, so I don't have a baseline with the the stock stuff to compare to. but I think it's a little strange how so many defend the stock plugs and say it's best to stick with what the KJ comes with, but yet we perform countless other swaps in the name of better than "stock" performance. So I'm not doubting you guys, I'm just wondering if it is possible to do better?

Rick

Calvin56 · **Joined:** Fri Jul 08, 2005 1:59 am **Posts:** 345

Splitfire plugs are good in theory because they should increase from one spark to 3 or 4 sparks going off at once which should increase the amount of fuel that detonates.

In actual studies these plugs do make more power... up to 10-15 more HP than their single spark bretheren for about oh..... 15 minutes of run time.

After 15 or so minutes, carbon and other pollutents from the engine change the potential energy (volts) required to jump each gap and all/most of the charge sticks to the easiest path of resistance, and you go back down to one spark, thus negating the cool 4-prong effect. Also, if the gaps aren't perfectly set, you have the same problem.

ManicMechanicJoe · **Posted:** Mon Dec 19, 2005 3:36 am

Calvin56 wrote:

Splitfire plugs are good in theory because they should increase from one spark to 3 or 4 sparks going off at once which should increase the amount of fuel that detonates.

In actual studies these plugs do make more power... up to 10-15 more HP than their single spark bretheren for about oh..... 15 minutes of run time.

After 15 or so minutes, carbon and other pollutents from the engine change the potential energy (volts) required to jump each gap and all/most of the charge sticks to the easiest path of resistance, and you go back down to one spark, thus negating the cool 4-prong effect. Also, if the gaps aren't perfectly set, you have the same problem.

In one of my classes in tech school we spent a week on this subject. I actually turned it into a goodsized project. Using a test rig (no engine, just distributor, coil pack, 6 oem quality plug wires, and 6 spark plugs (we tested Bosch Platinum +2,+4, and AC Delco plugs). It's simple physics, energy always takes the path of least resistance (kinda like an open diff). So no matter how well you set the gap on these "multi-prong" plugs you will only get one spark. I spent three days trying to get multiple sparks. Good Luck. My instructors (both mechanics of 20 plus years at a GM/Jeep dealership) said that the big advantage to a "multi-prong" plug is that if one prong gets fouled (carbon buildup or oil), an arc can still go to a different prong giving you a more reliable spark. If your engine is in good condition and you change your plugs regularly (every 30,000 miles) you won't have this problem. The big advantage to a platinum plug is in its longevity. If you change your plug every 30,000 miles, you wont need this longevity and can get away with a cheaper copper plug. Unless you are supercharged or run nitrous and need a "colder" plug, stick with the OEM NGK's or a quality copper. Make sure your plug has a resistor or you will get distortion in the radio.

kjrenegade · **Posted:** Mon Dec 19, 2005 4:14 pm

I think there is a lot of good information to be gained from this thread. Many here are very well informed. Joe's setup above is the exact reason I went with the Bosch +4s on my last change (at 60k)- I didn't expect a performace, or initial MPG gain, but I don't plan on changing them until at least 100k, so I'm hoping they will hold up better for the extra 10k I plan to put on them.

I'll post back in 40k miles and let you know how my "experiment" worked out. That should be about two years from now, but I should remember

SavageSS27 · **Posted:** Mon Dec 19, 2005 7:45 pm

So basically you're saying that i should go with just standard copper plugs as it will keep or improve stock performance, increase HP and MPG's but i'll have to change them every 20K miles?

-EDIT-

Let me re-phrase, i'd like to get the best performance boost and i don't mind changing the plugs every 20K and i don't mind spending upwards of $5.00 per plug, basically i want the best performing plugs there are, and i want to know what they need to be gapped at. Thanks

-Savage-

lilmatty · **Posted:** Mon Dec 19, 2005 8:13 pm

I put the +4s in for about 5000 miles. At first the engine ran noticeably smoother but the same mpg. The it started to give me terrible performance on the highway and an mpg drop. I put in NGK's the factory recommends and immediately got goof performace and have maintained that now for another 15,000 so far.

SavageSS27 · **Posted:** Mon Dec 19, 2005 8:23 pm

ok, so the v-power copper core NKG's, and change them every 20K?

lilmatty · **Posted:** Mon Dec 19, 2005 8:36 pm

Sure. What elseo are you going to do with your spare time? :mrgreen:

SavageSS27 · **Posted:** Mon Dec 19, 2005 8:40 pm

cool, thanks for your help....

jdumont · **Posted:** Tue Dec 20, 2005 1:36 pm

I put a set of the Bosch platinums in mine and noticed the mpg actually went down very slightly. This is very odd considering the plugs that came out of the KJ seemed to be stock (at 60K miles) and were beat to hell. Im going to switch back to the NGK and see what happens...

lilmatty · **Posted:** Tue Dec 20, 2005 1:45 pm

Exactly my experience with the +4s except the mileage went down after about 200 miles. Felt like it ran better though.

winkelhawk · **Posted:** Tue Dec 20, 2005 7:52 pm

I just installed a set of Denso Iridium plugs. So far I have been pleased with them. Slight increase on mileage and it runs smoother. Only downfall is the price, $12.95 per plug :shock:

!

Spark Plug opinions

Who is online