Originally posted by warmonger:
I would only gut the pre-cats when they are beginning to fail.
I'm only speaking from experience since I've done both of the mods we're talking about.
warmonger
I agree. I started with a gutted main cat after talking with Ray McNairy (RIP). It had definite noticeable gains in power and TQ - immediately felt more low end TQ steer. I dyno'd like this with a KKN, UDP, SVT TB and a dynomax on the stock 2" SE piping I got 154hp and 156 tq. Then shoot ahead a few years, and I suspect my pre cats to be failing - so I gut them. Notice ZERO gain in power and huge bog around secondary tranistion, plus car sounds just a bit like a deisel truck. Given I now have 3 expansion chambers which has got to be bad, but I go ahead and put a new main cat back on. The mid range bog goes away, but I still feel like I lost top end power vs just the gutted main.
Anyway, gutted precats may give you some power, but in my expeience it's even less than what you get with a gutted main cat (which everybody claims will make you lose power.)
Oh and on the envvironmeent thing - I passed CA sniffer tests with the main cat gone, and with the precats gone.
My .02
97 Contour SE MTX
K&N 3530, UR UDP, 19# Injectors, mystery mod, FMS wires, Fordchip.com chip, SVT: TB, Flywheel, clutch, exhaust
04 Grand Caravan SXT
| 
