yes. it will help alot. it would help even more if you remove both cats (there are two inline) or atleast hollow them out. You will find some much needed horsepower. Even better if you install a 93 or 94 Ford Ranger exhaust manifold (its a tube header - will bolt in with no problems.)
After doing it, i would suggest two things, 1 is required, other is optional.
1. disconnect the battery for 10 mins to reset the computer - it needs to relearn the system - and usually takes a day for it to get the idle completely right - the 1st 10 minutes is usually the worst - feels like it will die, etc. but it will get better.
2. remove the air restriction in the air muffler (between the air filter and the throttle body). Ifyou undo that big bulge in the middle of the air tube - there is an inner piece that acts as a "muffler" and necks down the air flow to the throttle body. it can be pryed out with a screwdriver. Helps in the airflow.
A guy named Tom Renzo from the Ford Mustang - GT - Shelby - Cobra - Classic Mustangs forum is a mechanic constantly working on mustangs. He told me that punching out the cats will free up horsepower, but removing them completely will actually result in a loss of power. He has tried both on the 2.3L, and you do lose power. However, with the 2.3, the loss, he says, isn't really that noticeable. When I have time I'll find you his post, but I unfortunately have to go back to work lol.
A guy named Tom Renzo from the Ford Mustang - GT - Shelby - Cobra - Classic Mustangs forum is a mechanic constantly working on mustangs. He told me that punching out the cats will free up horsepower, but removing them completely will actually result in a loss of power. He has tried both on the 2.3L, and you do lose power. However, with the 2.3, the loss, he says, isn't really that noticeable. When I have time I'll find you his post, but I unfortunately have to go back to work lol.
While I'm sure that most of that is true - I suspect it's because the loss of heat and the expansion of the hollow areas of the cat. I'm fairly sure that the potential loss of just hollowing out completely is a little less, but once you punch a hole through the honey-comb - it's more prone to start breaking up and could potentially clog up things downstream - especially if its the 1st cat and gets collected in the 2nd one or the muffler. The ideal solution would be to have a nice pipe to replace the cats, but not always practical or elsewise (espcially if you have to pass a visual inspection). With that in mind, I'd rather know that I don't have the potential problem of the cat plugging up- if one was really energetic, they could install a pipe thru the middle of the cats to keep the exhaust from expanding and then having to collapse out the back end. I've read that the proper thing to do with flowmaster mufflers is to reduce the pipe size by one size on the exit of the muffler due to the cooling effect of the muffler and helps in scavenging the exhaust and helps in the preformance of the system.
Hey Delray, you know what would be genius? Punch a 2 1/4 hole through the cats, then run a pipe through the cats. That way you pass the visual inspection! Lol xD
I ran one open header for a few days after I did a t5 swap. aside from the noise and smell(convertible) it ran exactly the same. maybe a little more pull at the top end, but that could have been due to the new tranny.
ok i already took off that dumb air muffler and my car is in paint so when it gets out im putting a fresh motor in and a cut out and no cats. sweet.
thanks