View Full Version : 8 to 10 more discs difusers??

Nadim Dao
10-16-2009, 12:12 AM

I have a new pair Supertrapps 2:2 on my Sportster 883 with 12 discs difusers on each one..

I was reading that increasing 8 to 10 more discs difusers on each exhaust you gain more horsepower but less torque..

Did anyone have experienced with this?..Any advise ?


10-16-2009, 07:34 AM
All combinations are different; however on some applications just adding or removing a couple discs can have a dramatic effect. When tuning we suggest adding or removing 2 discs at a time and then tweak with one.

Nadim Dao
10-16-2009, 08:20 AM

I was in contact with Daniel Dunn from NHRS Performance..

They did a Supertrapp Dyno Test on 2:1... see :


As you can see they use 28 discs on..He suggested for 2:2 XR use 20 to 22 disc..

What do you think?

10-16-2009, 09:48 AM

That article is clear on the SuperTrapp's ability to increase power output, as you mentioned, but it's vague as to what else was done to their "typical mildly modified ['04 Sportster] street bike." You might want to find that out.

It would be my guess that they raised the jet needle (http://www.nrhsperformance.com/tech_cvneedles.shtml) to enrich the mid-range circuit as at least one of those mods, main jets one size up too. I've performed these modifications on my 900cc sportbike in conjunction with adding discs to my SuperTrapp and I can tell you that there is a lot of torque & horsepower that can be added.

However, on a stock motor, Bshultz's recommendation would be the correct route to fine tuning your power.

6 bhp more though. That's awesome!

10-16-2009, 10:10 AM
Keep in mind the flow characteristics for a 2:1 are different than the 2:2 and has greater flow potential.
Another factor to consider is the altitude at which the Dyno results were taken. If the Dyno pulls would have been taken at sea level the results would most likely be different and the number of discs vs HP/Torque numbers different.
What's your goal? Usable (Steetable) power or sustained high RPM riding?

Nadim Dao
10-16-2009, 06:39 PM
Tks kz550 & bschultz for the tips..!

I live 2,900 fts over the sea level..

My goal is Usable power

I have also in my 883 a NRHS Hurricaneflow Air 2", Screamin'Eagle Coil, SparkPlugs & Cables

10-16-2009, 06:57 PM
~3,000. You won't need to rejet then if you don't want. If you're after torque, a freer flowing air filter will compensate somewhat for the elevation change. And if you want to experiment raise the jet needle (assuming you have carbs), 0.8mm - 1.3mm. It doesn't take much. My base elevation is 4,500,' so I think you're very very close to perfect on the a/f.

On the Supertrapp 2-2 end, 12 discs each actually may be hurting your mid-range and top end, but you'd know from seat-of-the-pants experience. I'd think a 2-2, at 441cc/cylinder pipe, would probably give you better usable power at around 4-5 discs each. Experiment and let us know what you find.

Nadim Dao
10-20-2009, 09:57 AM
I'll keep you posted in a month or so..Tks again.