I wanted to get a new exhaust for my 87' gxl. I was just going to buy 2 mufflers on the internet and have the muffler shop by my house build me the piping.

On other threads that i have read, people were talking about 3.5" inch piping or somewhere around 3". I know this is for a turbo, so my question is, what would be a good size piping for a n/a. The muffler shop guy said
2 1/4" but i thought this sounded too small cause the stock piping is already 2".

Also, i was wondering if anyone knew of some good mufflers that i could buy of the internet.

 

Also, the muffler shop guy quoted about $180 to $200 just for the piping. Is this reasonable?

 

2" - 2 1/2" is fine for a N/A

Remember, N/A's need backpressure. Its different on a turbo cause you don't want backpressure, so you open it up as much as you can.

 

I would probably go with 2-2.5 inches.
I had an aluminized catback made and installed for $60 when I got mine done.

 

2.5" is fine. Depending on how your car is configured, you may need backpressure to open your 5th and 6th ports. If you go too wide, they won't open and you will loose power.

 

Damn, I was gonna make a smart-*** comment about backpressure being bad, and exhaust scavenging being a good thing, but then I saw Aaron's post and clued in...

...but in general, backpressure is a bad thing, the reason why it "adds torque" (on a non s4) is because of the scavenging effect of a small exhaust diameter....



there... I made my smart *** comment anyway...
...and it was right...
...so hopefully I don't appear to be a complete dumbass now...


Oh, and the discussion about the 3.5" pipe was for a 20B 3-rotor twin turbocharged engine.... (look in the 20B forum, in the rotary performance section, for info... )

 

Thanks for the replies.

But does anyone know of some good mufflers to use, or is universal ok.

 

www.corksport.com or www.dynomax.com

Get the SS Corksport or a Dynomax packed with Steel Wool. Fiberglass just won't do, and will burn up in no time.

 

www.magnaflow.com
www.borla.com

backpressure = bad
high exhaust gas velocity = good

 

Hey Liquid Anarchy, at www.corkspot.com i cant find the SS Corkspot. Can you help me out.

 

I have twin 2" Headers into a single 2 and 1/2" system...

with twin 12" resonators then out through a fatt stainless

 

It's under the Exhaust section in general parts. $89

it cost me $98 to my door.

 

Click this

http://www.corksport.com/main.php3?p...3Fcat%3D237823

That should work for you. For future reference it's "corksport" ...

 

2.5 all the way to a single out apexi dunk bam....heheh

 

Talking to another fellow rotory nut he told me of some expeimenting he and another did a few years ago. The engine was a stock 6-port series 4 with a Weber sidedraft carb and a Racing Beat header collected at about 40". From there a single 2 1/4" pipe lead to a 5" supertrapp with no caps on it. This combination produced the most torque in the midrange with little loss on topend. They tried 2.5 - 3" pipe and found the 2 1/4 worked best for autocross where it made the most usable power. They were running in CSP so there gear choice was limited. I'm going to run the same basic setup on my FP car but will use a 2.5" pipe after the presilencer to a Borla muffler in the rear. Eventually I'll have the porper rear gear to take advantage of the slightly higher torque peaks of the 2.5" pipe on a stock port engine. Remember that a smaller(but not to small) pipe will keep the exhaust gas velocity at a higher speed which is obviously more efficient than an oversized pipe will be.

I'm sure someone will disagree with me and thats fine. Just explain/convince me why I'm wrong and I'll be glad to listen.

 

This is good general info for properly choosing the right size exhaust pipe. Scroll down to the bottom of the page for the chart.

http://www.dynomax.com/techsupport.stm

 

According to that .. we should be using less than 2IN.? thats a good chart for a pist'on but not a rotary.

 

Rpeck - The standard for measuring engine capacity doesn't lend itself well to the rotary engine. Measuring wise what works good for a piston engine doesn't work for a rotary engine. Roughly you can double the displacement(others say to triple it) of the rotary and get a good idea of the needed exhaust pipe size to use.

If you have problems with that let me help 1.3L + 1.3L = 2.6L

With that in mind look at the chart again and see if you can figure it out this time before you say its no good.