3:1:3, 3:1:2, etc Exhaust Question


Dec 5, 2006
Durham, NC
Being that I'm not a serious gearhead, I have a stupid guy question...

Are there specific flow rate parameters that have to be met for an R3 exhaust?

The reason that I'm asking is that I've been reading a lot of the forum discussions about the various exhausts and how much they cost, and who's is better...

However, I've only seen where TravelGuy is attempting to build a one-off.

I'm trying to understand (Reader's Digest version) what decisions have to be made with regards to pipe diameters and the number of bends.

Can you block off one of the pipe outlets on the stock cat and convert to 3:1:2?
Can you transition from the stock pipe diameter to a larger, or to a smaller pipe without risking mass destruction of vital systems?

Can anyone shed some light on the subject for me?
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I built a custom exhaust for Rosie. All it is, is a 1 7/8 ID SS flex joint that is 6" long coupled to a Stainless Steel straight through muffler. The muffler is 2 1/2" ID inlet and 4" outlet. The body of the muffler is 5 1/2" in diameter and 12" long. All of this is coupled to the stock engine header and haniging from a custom support. I had my dealer install the 055 tune. Sounds good and she has a little more power. I have found no problems.
Being that I'm not a serious gearhead, I have a stupid guy question...Are there specific flow rate parameters that have to be met for an R3 exhaust?

Of course it matters. There's optimum back pressure for torque vs HP as a function of rpm. You have to know what you're looking for and then know mechanically what will produce it.
Correct me if I'm wrong... but I think travelguy is experimenting with backpressure by using a Staintune muffler that you can add or remove rings to change the flow. He might not have the calculations to prove the optimum flow but sometimes real world testing works just as well. I think he already had some tradeoffs in performance by tuning his exhaust.
guys, this has been a long, and shall we say expensive but very educational road. i still don't know s... compared to most of the guys(like my mentors at burns stainless) but i am in the next day or 2 starting a cumulation of what i have learned. as they say the proof will be in the pudding but you have to remember that T put power restrictions on these bike and will produce and design something that is quite and cheap to make and design, the last thing they needed was more power. if i am right the original design and even jars are sooooo off the mark it isn't funny. sorry, but i will not at this time "share" the design specs. this is not because i'm a *****but 2 fold.. 1st gotta build it and see if it works.. second i've got so much time and money in this i'm not willing to give it away just yet.
i'm sure nev will be marketing his design of a 3-1.. although we have exchanged some info with each other i will say that overal design specs are close. what physical appearance his will have i have not been nor want to at this time be privie to.
here is a taste for you though.
a comparison of his header flange design and mine.. mine is on the right in the pics.. putfile so click on pic to see other pic.
and p9, forgot about charging you, thanks for the reminder.. if i remember it was $1,150,23.00.. w/o shipping :bch:
and hey use it wisely.. they are hard to come by.
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Travelguy you can try it but my limit is just under that:D .

Keep us in the loop about how your system develops. I don't think there are very many, if any systems that are designed specifically for flow.

I work with air movement systems (centrifugal blowers) and air flow is a concern for us. Have you ever heard of a CFD 3D program that you can model a part in and set your conditions and set the flow in motion in real time and you can watch the characteristics on how the air (product) flows threw your design? It is similar to an Inventor Program.
Thanks Guys. You've gone WAYYYYY beyond where I would ever go.

I was pondering the lint in my navel the other day, and my mind wandered to what I remembered about the ZARD slipons posted on that other site. Wondering if I could:

1) Cut off one of the two right side pipe outlets
2) Weld a plate over the 'now-exposed' hole
3) Put bigger outlets on the remaining two outlets on the cat

and not blow up my engine.
p9, thought i start there and work my way down till i got something approved :eek:
paul, no i haven't but an interesting idea.. have gotten input from someone with lots of hydrodynamic flow back ground and also the complete engine specs on the r3 motor have been run through a computer program for exhaust design.
rb, unless you are emotionally attatched to your cat.. god i'm funny, i would loose it and at the least have a automotive exhaust place make you a simple 3:2 for the right side connectorpipe. notice i didn't say collector. using the stock header you will gain nothing from fab'g a collector. any competent exhaust shop can bend some tubes for you to run w/o the cat. if for some reason you want to keep your cat on your bike (the easiest (cheapest)way to do what you want) i'm sure you won't affect anything.