i just picked up a RB turbo catback for a good deal seeing as my stock exhaust has holes and is rusted dead.

I have an NA FC and i was wondering does the fact its 3 inch piping going to affect anything at all? Im going to fab a pice to adapt the 2 inch to 3.

 

Mazdatrix (no linky handy) has an article on NOT going above 2.5 inch exhaust on an NA. Hell, I stumbled on that article by accident. So based on their advice, I do not recommend larger than 2.5 inch exhaust.

 

Yes and if searched with the terms exhaust size you would find a lot of threads

 

On an N/A piping should not be any bigger than 2.5 inches or you will not have enough pressure to open your aux ports!

 

What if you have all cats still in place (POSSIBLE) exhaust leak near the headers and like a 3in catback? Will that be enough to open the aux ports? I have no idea if mine are even working......

 

ive read that echaust article before but i figured it was about having a full exhaust system.

Its just from after the cat to the end of the car that will be 3 inches.


(my 5th and 6th ports arent hooked up right now any way. ill hook up when i get a chance
)

 

3" is too much. The car will not be easy to get rolling from a dead stop. You will lose torque at low rpms. The car will not be fun to drive.

 

The restriction of straight pipe (or even curved pipe, to some degree) is miniscule, even at stock size. Increasing the size changes that from ~nothing to ~nothing. I wouldn't expect it to affect anything, positive or negative, except weight.

The necessity for restriction for low end torque is a myth. If large pipe affects anything on the auxillary ports, it would have to be from velocity near the pickup tube only (everwhere else could still change), and even then I dunno how/if that's supposed to work. Again, it wouldn't be from the restriction changing from near zero to near zero. Normally the cat and maybe the mufflers have the biggest impact. Aaroncake.net has a guide to see whether or not your aux ports are working, though when I did it it was hard for me to tell.

For extreme horsepower applications, I could see increasing size because of the added flow, but even then we're talking single digit horsepower numbers.

 

Well from the header to the end of the cat is stock. The y pipe and mufflers are going to be 3 in.

Does it matter at all that the motor is streetported?

 

We aren't talking restriction, we are talking about gas velocity. They are two different beasts entirely.

 

It should work just fine, although there will be an increase in noise and a very slight decrease in performance vs. a properly-designed NA exhaust. Try to limit your transition piece to a gentle taper (15deg or less is optimal). Burns Stainless sells pre-made 14deg transition pieces which may work for your application.
http://www.burnsstainless.com/mildst...sitions-2.aspx

No, street porting doesn't increase the flow enough to change the optimal pipe diameter. The primary pipe is about 1.75" ID for stock and street ported engines, and this only increases up to about 2" ID on a peripheral ported race engine. Note that this is for the primaries. The diameter can be gradually increased as it leads to the rear of the car.

 

i have a 3" cat back on my n/a and it didnt really effect the power or performance noticeably. yes it is probably louder but not as loud as not having any exhaust at all