Jma_1

Recently I came upon an hollowed cat, pipe and headers for my 87 944 ( the price was right, next to nothing). Did you, or do any of you run such a setup in any of your cars ? If so do you notice any performance gains worth the time it takes to install it ? Also, I don't know if the car will pass emissions even though it's in good state of tune. I also plan to install Skip's MSD ignition and coil, that should help I think. My plan is to install the gutted cat and run with it if it passes inspection, provided I notice any extra power. I welcome your input if you have any experience with this. Exhaust systems are not my favorite area to work on, the thought of rusted bolts or broken hardware easily come to mind.... But if I gain a little power and keep it legal I'll crawl under it.
Thanks,
Jma

Skip

*cough* I've heard of folks center boring the cat and installing an inner pipe for even flow-thru. This retains the natural appearance for visual inspection, while eliminating the "inert HP block" from the cat. The na cars need backpressure to create the favorable low-end torque... so, you could say that the same person would install a moderately restrictive muffler or a tuneable muffler at the end to control the back-pressure. This is all here-say though *cough*

This will give you more power at the top end mostly... and quicker revs (ever so slightly). The exhaust note changes considerably depending on the final exhaust type. Hollowing out the chamber will reduce back-pressure, but (IMHO) may disrupt the natural exhaust pulse due to the mis-shaped chamber... especially important to a Supertrapp user like myself.

The MSD will aid in lowering emissions (cleaner burn), but unless the rest of the fuel/air mixture is in good order, you do stand a chance of failing. Be certain the O2 sensor is working correctly.



Skip

Manning

You have to jam a pipe through as Skip suggested or you wind up with a wildly out of tune expansion chamber (like on a 2 stroke motorcycle) that may negatively impact performance.

Longtime76

I have straight pipe from where the cat used to be to the muffler, which is simply a resonance muffler (no sound dampening). I then put K&N cone filter on my air intake, completely removing the stock box. It has not been dyno'd ever, but I can feel the diffence after doing the mods, mainly in the higher RPM's. I think if I added a fuel pressure gauge and bumped up the pressure that would help out more. It is extremely loud though, which is one disadvantage m(although I like it like that). The more clogged your original cat is the more performance you will pick up. My car "passed" emissions supposedly, but the guy who took it off (that is not supposed to happen) did the inspection.

Steven

What would be the difference in gutting the cat and installing a test pipe? Or is there any difference?

Dave

With a gutted cat you can pass a visual inspection, if your state does that sort of thing. At least that's what I've heard. You can also string tennis rackets with the remaining cat gut