Spark Plug Test...
Today I stopped by the parts store and requested the regular Bosch platinums for the LS4. The guy told me that the irridium was the recco'd plug for the car and that the Bosch would cause fouling and poor milage. 
I've been using Bosch Platinums since they hit the market in a variety of motors: Toyota 20R, 5M-GE, 1UZ-FE, Nissan inline 6 and V-6. All without fail or problems. The LS4 got these plugs at 60K and if the plug was that bad, I wouldn't have got 28 MPG. Now at 102K, the Bosch platinum still maintains a reasonable 25 MPG in mixed driving. The Bosch has done well for my cars and at $2 per, I haven't found any pressing desire to pay $6+ unless it will best 28 MPG.
Of course any incremental improvement, in the long term be worth it. It's been hard to judge in my driving unless there is an obvious problem. In those instances, it was traceable to some ignition issue like a high resistence wire, contact on the distributor/rotor...
YMMV as they say.
I've been using Bosch Platinums since they hit the market in a variety of motors: Toyota 20R, 5M-GE, 1UZ-FE, Nissan inline 6 and V-6. All without fail or problems. The LS4 got these plugs at 60K and if the plug was that bad, I wouldn't have got 28 MPG. Now at 102K, the Bosch platinum still maintains a reasonable 25 MPG in mixed driving. The Bosch has done well for my cars and at $2 per, I haven't found any pressing desire to pay $6+ unless it will best 28 MPG.
Of course any incremental improvement, in the long term be worth it. It's been hard to judge in my driving unless there is an obvious problem. In those instances, it was traceable to some ignition issue like a high resistence wire, contact on the distributor/rotor...
YMMV as they say.
Originally Posted by RA40
Today I stopped by the parts store and requested the regular Bosch platinums for the LS4. The guy told me that the irridium was the recco'd plug for the car and that the Bosch would cause fouling and poor milage.
I've been using Bosch Platinums since they hit the market in a variety of motors: Toyota 20R, 5M-GE, 1UZ-FE, Nissan inline 6 and V-6. All without fail or problems. The LS4 got these plugs at 60K and if the plug was that bad, I wouldn't have got 28 MPG. Now at 102K, the Bosch platinum still maintains a reasonable 25 MPG in mixed driving. The Bosch has done well for my cars and at $2 per, I haven't found any pressing desire to pay $6+ unless it will best 28 MPG.
Of course any incremental improvement, in the long term be worth it. It's been hard to judge in my driving unless there is an obvious problem. In those instances, it was traceable to some ignition issue like a high resistence wire, contact on the distributor/rotor...
YMMV as they say.
I've been using Bosch Platinums since they hit the market in a variety of motors: Toyota 20R, 5M-GE, 1UZ-FE, Nissan inline 6 and V-6. All without fail or problems. The LS4 got these plugs at 60K and if the plug was that bad, I wouldn't have got 28 MPG. Now at 102K, the Bosch platinum still maintains a reasonable 25 MPG in mixed driving. The Bosch has done well for my cars and at $2 per, I haven't found any pressing desire to pay $6+ unless it will best 28 MPG.
Of course any incremental improvement, in the long term be worth it. It's been hard to judge in my driving unless there is an obvious problem. In those instances, it was traceable to some ignition issue like a high resistence wire, contact on the distributor/rotor...
YMMV as they say.
I put the regular Bosch platinums in mine and it's driving fine. I'll probably pull a plug or two in the coming weeks just to check for deposits but I don't expect to find anything out of the normal.
Obviously if MPG drops like a stone, going with the factory recco'd plug is the right move and your GS may be more critical of the plug. My '97 LS isn't. Unless the +2 or +4 yeild even 10%, it will be undetectable in my drives with the lousy traffic encountered in LA/OC. With warmer weather and A/C, I average about 23.X on the highway, 17-18 city stop-go.
Obviously if MPG drops like a stone, going with the factory recco'd plug is the right move and your GS may be more critical of the plug. My '97 LS isn't. Unless the +2 or +4 yeild even 10%, it will be undetectable in my drives with the lousy traffic encountered in LA/OC. With warmer weather and A/C, I average about 23.X on the highway, 17-18 city stop-go.
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