Nope, that's wrong, CEL is caused from the increase in pipe diameter (There are LT set ups that don't change O2 sensor configuration by much). I have even seen cars throw codes from a cat back when you increase pipe diameter too much from stock (those CELs have absolutely nothing to do with O2 sensors at all because you are not touching those sensors). Same issue when you do headers, you are increasing flow of exhaust which messes up A/F ratio which all boils down to timing (engine timing that is). Tuning will fix all of that by optimizing the engine valve timing to get the proper A/F ratio & valve timing necessary for the entire power band.
I never said you can't get power gains from LT without a tune, I am just saying it is not optimized without a tune. The engine needs to be calibrated so you don't run too rich and so that you have the proper back pressure. Increasing flow in the exhaust changes all of that. When the GM engineers designed the car they had the engine calibrated to function with the stock pipe diameters, changing any of that messes with that. It's not drastic, but I it's not optimal. You'll still see power gains, but you'll get even more if you get a proper tune and you engine will run with the proper A/F ratio.
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Originally Posted by Fraxum
Recalibrate the timing?
I disagree about power, with LTs you will see most of the gain without a tune and while you will get CELs its because you moved the rear O2s too far downstream. So one of the main benefits of the tune is suppressing those CELs.
I am not necessarily recommending doing LTs with out a tune. But I have done it and picked up 3-4 tenths in the 1/4, drag raced often, read and turned the CELs off often, and drove the SS as a DD for about 2 years. Never lost my warranty, then put it back to stock, and got top trade in $$ for my SS. Although I did get dinged for needing rear tires.  |