I have a stock 99 Sierra and have considered cutting out the cats. I've heard mixed reviews. You clearly gain more power but I don't want to lose low end. I've never been to the track and I usually race redlight to red light. I've heard gas mileage is improved some with no cats. I would think with a restrctive exhaust like our trucks have that no cats should be good for 5-8 HP or so. I've heard I don't need O2 Simms unless I don't want to see the SES but it's already on because I don't have EGR. So would I lose any low end, would I gain gas mileage? I just want some opinions. I don't have emissions. All I want is to gain some power without sacrificing gas mileage.

 

if it is stock and you are not going to some really good mods then leave them on there.

 

Leave Them On. Gas Mileage Goes To Sh@#. At Least Mine Did. I Did Loose Some Bottom End.

 

Gas milage wont go to **** if you retune for the gutted cats. If you don't then don't expect great results...

I have had really good results with gutting my cats on my T/A and on my C5 but I am still unsure about my truck. N/A before the cam didn't seem to do much but then again I didn't tune. I just turned of COT with LS1 Edit... After the cam install and tuning I don't think I could have ran the MPH I did with the cats on considering my T/A and C5 both gained at least 2mph form it consistantly.

I look at it this way... If people dyno with no cats, then dyno with the high flow cats in place and lose about 5rwhp then imagine if they put stock cats back on....

Like stated above though, if you don't plan on tearing into the engine and swapping cams or adding a power adder then I wouldn't worry about it.

 

What happens if you turn off the COT and you still have cats? Does it make any difference?

I got a tune from someone and I *think* that was turned off in the tune, but I've still got my kitty cats. LOL

 

I am not 100% sure but it is set up to help keep the cats from melting if I remember correctly.