TII FC 3" exhaust

[NHDrifter]

i have an 87' N/A RX7 i was wondering how well a 3" turbo FC exhuast would fit on my N/A? would i have to do any mods to make it fit? or will it bolt up the flanges and fit nicely (cat back)...thanks----Rich

[apexdrift]

for a n/a a 3" is to big, becasue it wont produse enough back pressure!

2.5" is the largest you should go...

[GotNismo?]

are you sure about that..... many companies (which product test) make 3 inch plus exhuast for n/a's. I have a 3 1/8 in exhaust from corksport. its a test pipe that guts the cat, and and cat back from there. and my motor is doing fine.... i believe apex make a 3 inch n/a (n1 series) and thier huge....(if you dont belive the credability of corksport.

[SpeedMachine]

On the 86-88's, they 6 ports are actuated by backpressure from the front side of the exhaust, ie from the engine to the stock main cat. If you get a catback, then it can be as big as you want and your 6 ports will still work. It's when you get a header, and straight pipe and you don't hook up the split air pipe then you will actually loose HP. A 3" turbo catback is no different than a 3" N/A catback. If you get new front piping, make sure it is something like Racing Beat or the likes so it has the correct connections.

[new_to_drift]

i believe apex drift is right.3" is too big for NA,there is not enough back pressure so ur actually losing hp.2.5" is the biggest a NA car can go w/o losing hp.3" and up is mainly for boosted cars.

[SpeedMachine]

i believe apex drift is right.3" is too big for NA,there is not enough back pressure so ur actually losing hp.2.5" is the biggest a NA car can go w/o losing hp.3" and up is mainly for boosted cars.

Again, the only reason you need the backpressure at all is to open the 6-ports on the 86-88 N/A motor (89-91 6-ports are electronically actuated), and if you go 3" catback with stock front exhaust you will not loose HP. The only way you will loose hp is if you go just straight pipe and your engine can't open the 6-ports. Racing beat streetable headers, with a presilencer (comes with correct backpressure port included on it from RB) and a 3" catback is the ideal setup for a street driven N/A.

Think if it like this...stock exhaust on the catback is like 1 3/4 or 2". When you add both sides of the stock exhaust it is over 2.5" anyway, so how could that make sense to run the 2.5" catback? The RB catback is dual 2.5", so that is equal to 5" exhaust. Think about it...

[TeamSLIPdrifter]

Techniquly a 2.5 twin system isnt a 5 inch single cause the exhaust doesnt evenly split itself up into the two chambers evenly. especially if one side produces more backpressure then the other. if you do a downpipe and 3 on an NA then its not good. youll burn more fuel and can still lose power. and if its a rotory id be afraid of my apex seals blowing. i dont know how but i know that not enough backpressure on an NA rotory is really bad. and the difference between turbo catback and reg. catback is different. they test the two to produce better ranges through slight curves and such. like i know certain curves and patterns in the right places can actually produce more torque in NA motors. and i know a turbo catback is more smooth and eliminates those little torque spots. a regular catback is produce with NA in mind. its made to deliver an amount of backpressure back. while turbo catback is made to eliminate as much gas as fast as possible.

[SpeedMachine]

Techniquly a 2.5 twin system isnt a 5 inch single cause the exhaust doesnt evenly split itself up into the two chambers evenly. especially if one side produces more backpressure then the other. if you do a downpipe and 3 on an NA then its not good. youll burn more fuel and can still lose power. and if its a rotory id be afraid of my apex seals blowing. i dont know how but i know that not enough backpressure on an NA rotory is really bad. and the difference between turbo catback and reg. catback is different. they test the two to produce better ranges through slight curves and such. like i know certain curves and patterns in the right places can actually produce more torque in NA motors. and i know a turbo catback is more smooth and eliminates those little torque spots. a regular catback is produce with NA in mind. its made to deliver an amount of backpressure back. while turbo catback is made to eliminate as much gas as fast as possible.

Curious...how many people do you personally know that blew up their N/A rotary because of putting on a 3" exhaust? Just wondering. My guess is none. I have been working on FC's the better part of 10 years and I haven't heard of it. And the statement about "not enough backpressure is bad, even though I don't know why" is still false. It's just more "internet misinformation" The best exhaust for making power in an N/A rotary is the true dual Racing beat system. No one else produces an N/A exhaust that makes as much power, and it has 2" runners from the engine all the way back to the exhaust tip. I would poke a guess that 2 2" pipes are larger than one 2.5" wouldn't you agree?

Once again for those just walking in... On the 1986-88 13B 6-Port engines, the auxiliary intake actuators are operated by backpressure from the exhaust system. Other than that, there is no "risk of blowing up your apex seals" by an exhaust. Turbo engines there is, because the turbo can make alot more boost when the intake and exhaust are opened up, which will cause a lean condition and cause detonation...which will blow your apex seals.

You guys should read Racing Beat's catalog. It has alot of info in it that alot of you could use. 32 or so years making power in rotaries is pretty much more experience than this thread combined.

[TeamSLIPdrifter]

I know 3 people that have. two FCs and one FD. and its not internet misinformation. i dont get my information from the internet, i get it from my cousins shop. ive been working there for the better part of 5 1/2 years and you start to pick up some things. i cant explain to you how it happened but the FD put was an NA. he put on an intake and a turbo back 3 inch exhaust. he came back a few weeks later and his apex seals blew. the two FCs had 3 inch exhaust and for the most part they were pretty much straight through. one complained about gas mileage being really bad for some reason, 2 days later the apex seals blew. and they were drag cars, drift cars take ALOT more stress from your motor.

[f8ldzz]

3" exhaust on an NA is overkill and kills low end torque.
Well, not like the car makes that much torque anyways.
2.5" piping is the compromise size for most NA applications (unless radical porting or mods) which makes good low end and top end power.

The Corksport 3" cat back was *designed* for turbos - not NA's.

[NHDrifter]

geez people,i didnt mean to start a damn war.i just wanted to know if it was possible. SpeedMachine seems to know a lot about the FC's,im gonna go off from his information and get a apex N1 (3") CAT-back that should be good enough for me,im not afriad of blowing my apex seals so much becuase this winter im doing a engine rebuild,or im just gonna do a TII conversion. thank you for all the help/info.

p.s. isnt their like 3 cats on a N/A FC? i think if i kept the stock header,stock first cat w/that thin pipe(auxiliery pipe),then Apex 3" from there back,it should even out properly.if not i dont really care its not the end of the world,ive just seen some N/A FC's with sweet exhuast systems,i may do a custom exhuast,not sure yet though ...thanks agian

[theflatlander]

^Get a header and do a full exhaust you'll thank yourself. And as forTeamSLIPdrifter,The FD blew his motor due to detonation.Adding intake and exhaust gives better boost response and prob. a little boost creep both which the FD ecu hates and cannot adjust to thus pinging and blowing the motor. And the FC going out was prob. due to the fact that the motor was tired and thats why it blew. getting a freeflowing exhaust will not harm a N/A motor.

[NHDrifter]

cool..thanks for your help man ...read my FB post i have...its really exciting...lol

[TeamSLIPdrifter]

The FC was a rebuilt motor, new rotors. i doubt it was tired. and ive seen TONS of cars blow from not enough backpressure. ask any racing crew that builds all motor cars. theyll tell you that backpressure can be your friend. and how can an NA FD get boost creep?

[theflatlander]

The FC was a rebuilt motor, new rotors. i doubt it was tired. and ive seen TONS of cars blow from not enough backpressure. ask any racing crew that builds all motor cars. theyll tell you that backpressure can be your friend. and how can an NA FD get boost creep?

Well was the motor broken properly? And when it was torn down what failed? Yes piston motors need a little backpressure to some extent but we're talking about rotary, i really wanna hear your reasoning on why a rotary needs backpressure and how the lack there of can cause a motor to blow? and one other thing for rotary it's not about back pressure its about flow velocity which will vary accordingly to applicaition and setup.