View Full Version : A few cat question. Still good and what size should I do?

08-10-2002, 09:35 PM
I have two questions.

One is that I have about 400 miles on my 2.25" high flow cats when I began to show mild symptoms of headgaskets. I never billowed white smoke, I caught it quite early. How can I tell if I contaminated my cats or should I operate under the assumption that I did.

Second, I have the following modifications and would like to know whether 2.25" or 2.5" cats are right for me:

- Magnum Powers 3.5" Fresh Air Inlet System
- C&L 73 MM MAF
- BBK 70 MM Throttle Body
- 1" Raised Supercharger Top
- 36# Injectors
- 190 lph Fuel Pump
- Ported and Polished Heads and Intake Manifold
- Light Valve Job with stock Valves
- Ported Stock exhaust manifolds
- 2.5" - 3" - 2.5" Exhaust

I think that's it for the horsepower stuff.

Future modifications could include underdrive pulleys, 5%, blower porting, or minor things, probably nothing big for a while until it gets a cam which is whenever it blows up.

Adam Mullen
The SC Kid

08-10-2002, 10:04 PM

I would pull the O2 sensors. If they had lots of white deposits on them, you could say that the cats would have similar deposits. If the O2 sensors look and work fine, you could probably assume that the cats were in good shape to. If someone has contradictory information to this then please post it.

You could always remove your cats and dump catylytic converter cleaner in them......

Concerning your question on 2.25" cats and 2.5" cats. I would recomend the 2.5" cats based on the fact that you have a 2.5"-3"-2.5" exhaust system.

Plus, with overdriving the blower and adding alot of intake stuff, it wouldn't hurt to have the 2.5" cats. Have you done anything to the exahust manifolds? I would think that with the 5% on there (plus the other intake goodies) that the stock manifolds would be representing a greater restriction than the 2.25" cats.

08-11-2002, 10:53 AM
I changed my O2's and they were very clean, a little carbon no white residue. As for my manifolds, yes I did open up the collectors but they are less than 2.25" in diameter you know. I have always stood by the theory that for good torque and horsepower you want the system to flow gradually better as it comes away from the engine so I think with the 2.25's assuming they are good, exhaust manifolds to the less restrictive 2.25 too the still less restrictive 2.5 then to 3" is achieving that goal rather well and the fact that my car will spin a 1/3 throttle take off every time on good take tires is a good sign.

Adam Mullen
The SC Kid