Anyone have experience with the Plus 4s? They are really cool looking, but how do they work? I've never known anyone with them. My car came with Split Fire plugs, and since they are the only ones I've known, I guess they are ok, but I have only put 5000 on the car since I bought it.

 

The difference in performance between various plugs can be measured in fractions of a horsepower. The real difference is in longevity. True full platinum designs are costly, but offer extended life...about 30-50K miles. This is something to consider when plug access is difficult. All electrodes on the plug must be platinum or the spark gap will widen in about 10K miles. The only plugs I'd stay away from is the OEM GM AC platinum. They usually drop their rock hard platinum electrodes into the combustion chamber within 10K-20K miles. This causes the spark gap to increase by about 0.030" which "tests" the marginal Optispark dielectric strength, not to mention the damage that can occur if the electrode gets lodged between the piston and cylinder wall. I personally like the costly new Autolite Titanium Pro plugs that are specifically designed to reduce damage to the threads in aluminum heads.

 

I'll go against the grain considering the stock platinum AC Delcos. After 90K all of mine still had the pucks and looked remarkably good. I replaced them with Bosch +4's ( the +2's weren't available at the time... I think they'd actually be the better choice).

The Bosch +4's did fine (no troubles... but didn't act any better than the stock plug) for another 15k up to the point I did my LT4/Hotcam conversion.
The plugs looked great and I stuck 'em back in to see how they'd do with a sloppier cam. They still work great. I don't expect any problems with them in the forseeable future.

I'll address one issue which some "spark plug expert" will be sure to bring up with the +4's. They'll state that the 4 ground electrodes prove to shroud the spark from the combustion charge. That is simply not true.
When inspecting the design of the Bosch + (2's or 4's) you'll see that the ground strap(s) leave a direct line of sight from the electrode to the ground for any spark to ignite the charge. In essence you can't incorrectly index the plug. This is one advantage of the design. Couple that with multiple points to ionize a gap and you have good reason to believe that this plug can indeed produce useable spark under most conditions.

But since nobody can produce results that favor one plug over another, I can't say that a Bosch plug actually performs better than any other brand. My point is that detractors of the stock AC plug or the Bosch plugs are also working with the same evidence and their claims will hold as much weight.

I've had no problems with AC Delco, Bosch, or NGK. They've all worked equally well in various applications.





[Modified by Dan Parker '96, 2:05 AM 2/22/2003]

 

Absolute DITTO here !!! The only reason for the Bosch 4s and platinum plugs is longevity. The old copper plugs are still the best for the money, or better for optimum performance use Beru Silverstone silver tipped plugs. SIlver has still better conductivity than copper. Splitfires are junk!!!!!!! I tried them in the HArley and the Vette....forget 'em. I personally would stay with the originals since it is not that easy to change them on our cars.....

 

The Splitfires are made by Autolite (now Honeywell). They are nothing more than a standard plug with the ground electrode smashed and split. If they are not perfectly gapped and level, you are only going to get a standard fire off one fork.
I ran Bosch plats once and took them out after the test ride. I never thought that a plug could so negatively impact the perfomance of a motor. I like just the good old copper electrode plugs, and they are what, 69 cents at K-Mart?

 

Copper plugs work great, but I prefer an extended service interval plug in my cramped LT1 engine bay. I'm lazy.

 

I used split fires on all my cars and seem to give a better throttle response IMHO

 

I run the Bosch +4's in both Vettes and the Jeep. The only spiff I can see is that you don't have to gap them. No noticible increase in performance, fuel mileage, or ease of starting. They do seem to last quite awhile. 84 CF 91 ZR-1