Uleepera

iTrader: (9)

Greets and thanks for reading!

I would just like to say before asking the questions that I have a very elementary knowledge about mechanics and autos which may be the reason for these two questions. Aside from swapping a battery and a clutch line that blew this is the most advanced task I've ever undertaken.

Info: Recently purchased a '93 RX7, had a talented rotary mechanic review the car and it appeared to be in excellent shape for its age. Its running around 120k miles still on the original engine but has rebuild turbos about 25k ago. Exhaust was redone with a mid-pipe and racing beat muffler. I registered the car as a classic and unfortunately in PA you still have inspections also classic tags avoid emissions testing they still look for a cat. So today I swapped the mid-pipe out for the original cat so they could see it on the car.

Question 1: I was surprised that the car seemed more peppy with the cat on than without, I know free flowing exhaust can rob power and that some resistance improves performance but I thought the original cat would likely provide too much resistance... any thoughts?

Question 2: Now that I have swapped out the mid-pipe I took it out for a test drive to see how everything performed and for the most part it seemed everything improved a little. When I pulled back to my house though there seemed to be a small amount of smoke coming up from the engine. I used WD40 to help remove the old bolts and I'm guessing that was the smoke but I wanted alternative opinions. I didn't hook up any of the air pump apparatus as it was all removed by the previous owner and I won't need it anyway since they won't emissions test it.

Comment/Question 3: After adding the cat back on I find that the car is significantly quieter and I am now torn because I think I might actually like it quieter... Anyone else have any thoughts on this? I figure if I decide to keep it quieter I might go with a hi-flow cat...

juicyjosh

iTrader: (29)

1) The only way a cat would have less flow resistance than a straight pipe would be the case if the cat had a larger internal diameter than the straight pipe.

The stock cat piping is highly restrictive. Simply replacing my stock cat - which has a new "OEM" Magnaflow welded in - with a wide-pipe high flow significantly reduced backpressure. With the Power FC and AVC-R and everything else left alone, I went from consistently boosting 13 to consistently boosting 14.5, and getting there quicker. Plus the stock cat designed in 1992 was a heat-soaker and ridiculously heavy, so I saved about 35 lbs and the interior doesn't get heat-soaked anymore either.

2) The smoke should be burned off by the time you read this.

3) My recommendation is to go with a (high-flow) cat on, for several reasons, in this order:

1-You're helping to keep the air less polluted at the cost of 5 hp.
2-The car's interior will no longer be your daily sauna.
3-You won't attract the attention of the few cops who know what a catless exhaust smells like.
4-It'll keep uncatylized hydrocarbons from turning your bumper black.
5-The car's quieter.