Receieved my Free Bosch Iradium Plugs for testing a couple of months ago. Figured my car was running pretty good so I didn't change the plugs as soon as they arrived. This week, I figured with 30K miles on the car it wouldn't hurt to change the plugs and I owed Bosch the review of their product.

All I can say is WOW. So much smoother than it ever has run. I'm loving these plugs over the stock AC12571164 plugs. Those plugs were gapped at .035. Or, at least that is what I measured when I pulled them out. I know some guys are running Iradiums as high as .050.

Mine came pre-gapped at .038. I was a little worried that the car wouldn't run as smooth with the larger gap. But, I was wrong to worry.
.038 seems to be just right. I do not see the need to run them at .050 because it runs so good at .038.

The Vette runs great. I did a idle test with car in 1st just creeping along. No surge at all. The exhaust sounds very smooth. I rev'd it up and it seem so much smoother. Did 6th gear load run at 40mph >>>> 100mph... Just pulled without any ping knock or any odd issues. It seems to rev all the way to 6200rpm without at dead spots in 3rd etc...

I will update this thread in six months and then again in one year. However, if these plugs are as good as the other Iradium out there I do not expect much change in performance. I've been using NGK Iradiums for years. I do not expect anything less from the Bosch plugs.

Now for the install - It was a little more difficult than I had hoped for but, I was prepared. The stock wires were stuck and I tore apart a couple of them just trying to get them off. I think I pulled a muscle in my left shoulder trying to get those darn spark plug boots off.

I bought a new set of Taylor Thundervolt 10.2mm wires and used diletric grease on the boots so that doesn't happen again. I also used anti-cease compound on the threads of the plugs to they don't get stuck like the AC plugs that were installed by the factory were. I'm glad I changed these at 30K and 8yrs. I could imagine what it would be like at 40K or 50K. They were so stuck that I was afraid the threads might have been damaged getting the plugs out of the aluminum heads. It's really easy to mess up the spark plug threads in aluminum heads. I can't believe Chevy says that you don't need to change the plugs for 100K. You should replace any spark plug at 30K in my opinion for best performance.

There was a little carbon and a little brownish coating on the old plugs. That is about what I expected for a car with 30K on it.

But with all things said, my Firebird ran about the same a my Vette from the factory. I have found that Iradium Plugs do smooth out the LS1's.

Would I do recommend these plug for a LS1? Yes, for sure... Very good improvement. With the few simple things I've done to my Vette I can't believe it is so nice. The Vette is a amazing car and with a couple of very simple mods it's that much better. Love this car.

I couldn"t believe that the car ran so strong in 1st gear to 60mph tonight. I do not think it was running that smoothly before so I'd shift at around 5800rpm. That seemed to be what the motor liked. Now it seems that the motor likes to rev over 6200rpm without any stress or vibrations. I thought I was starting to get valve float at 5800rpm. But, maybe it was just a weak ignition system.

I'm very pleased .....

Thank you Bosch !!!!!