cat removal replace w/ midpipe questions...
 

I have a 94 rx7 that is almost stock only mod is a downpipe that removes the 1st cat. I am going to be putting a racing beat cat back system and thought i would go ahead and put a midpipe, they have to different styles one has a resonated section and the other is a straight pipe. i just wanted to know which i should use? i dont have any problems with noise or emission tests. I want to know if you think its going to be loud without the resonator or just any constructive comments. thanks...

Your poll should offer "don't do it" as a choice.

It'll be real quiet after you blow the motor... do a search for "boost creep" to learn about the risk.

thanks for the input i almost did have it as an opition... i just thought it was better to remove for heat build up.

Ya, you will need to modify some other components prior to putting in the midpipe, but after thats done go with the straight through, cheaper and should add a little more efficient.

what other mods should be done?

If you go with a straight through midpipe it will be much louder and it will smell a lot more. Going with a straight through exhaust should definitely go along with a better flowing intake, a ported wastegate and some sort of aftermarket ECU (PowerFC). At this point all you need is a better intercooler and you will be in for a serious power increase.

Exactly.

Keep in the main cat on, unless you plan to open up a can of worms. You're better off going with all of the other bolts ons first, then delete the cat last. With stock twins/internal wastegate anyway....

Neither option is cheaper since you'll have to spend money on various items to control boost - boost controller, some kind of exhaust restriction etc...

After you port your wastegate ;) you should look into a resonated midpipe.

I had that combo before: dp, resonated mp and racing beat duals. It was a perfect balance between quiet cruise, deep tone at mild acceleration, and watch the fuck out roar at WOT.

I have a 93 fd, had a doodie catback, and a pfc, all of that b4 I took the cats out, I'm sure the pfc is the main thing to do b4 pulling out the main, im sure everyone else will comment on this, but dam it made a huge difference with how hot the car ran, the power curve, and I am in cali where we have the worst tuner car friendly gas on the face of the planet.....but they are right you dont want to over boost with out more fuel, the shit would def. hit the fan!!!

No boost creep?

before i tore down my car i was runnin a stock motor w/ straight all the way back to stock mufler. it sounded and ran nice w/ no damage or boost creep. i was also running a hks BOV

you should get a restricter plate to help with the boost creep/spike. someone in the forums is selling them. or you can go to a muffler shop and have them make a restricter cone to put inside your exhaust.

Jyro makes the restrictor plates.

The stock muffler kept the boost creep away: it's probably as restrictive as the cat...

Wouldn't a restrictor cone defeat the purpose of removing the main cat anyway? gotta be almost as restrictive as a HF cat..please no flaming lol

-Nick

No, it still leaves you further ahead than with a cat.

And you still get the ear-splitting noise and toxic stench :)

That is why the metal substrate cat works so well. It adds just enough restriction to help control boost at a price similar to Jyro's restrictors.

I considered buying his restrictors but wound up with a metal cat instead. Got the added benefit of getting rid of the nasty smelling exhaust fumes.

I'm selling it if anyone is interested. Built another one

I see. So my guess is that straight pipes with a restrictor cone is that happy median between a cat and just straight pipes huh

-Nick

I had them make the cone a 2 inch one. then point the cone towards the front. still high flowing with no creep and best of all.......fireballs!!!1!!

I've got a straight through to my stock muffler (also intakes n' walbro fuel pump) and haven't blown my engine due to boost creep. Are there any other ways to safely boost w/out a PFC (don't have the funds right now) or restrictor plate when I kill the muffler?

-Ali

Port your wastegate and install a manual boost controller.