Before and After Dyno Comparison

[crashcourse]

I've been waiting a long time for this. I finally got the bike back on the dyno! I did an initial dyno run a few months ago as a baseline before I started doing any modifications. The attached .pdf file shows the results. The bike is a 1981 Special. It previously had no modifications. Over the summer I changed from the stock exhaust to a 2-2 system from Gordon Scott Engineering, and that is the data marked as "Modified" in the chart.

You'll notice that peak power has hardly changed, but there is a big boost in mid-range torque about 4200 rpm, and I am especially excited to see the boost in torque from 2800 to 5000 rpm, which is where I do most of my riding. Peak torque has moved up a bit from where it was, and the curve is definitely less smooth, but it rides great and sounds awesome.

I neglected to get any pictures or video on the dyno, but this video gives an idea of the sound.

 

[rahndo]

So, do you think it was worth several hundred $$?

 

[crashcourse]

So, do you think it was worth several hundred $$?

I think, if I were to do this over, I would have gone with a cheaper system. Nothing against Gordon; he did great work. But he doesn't sell finished pipes: getting them chromed cost more than I originally budgeted. I know there are other options out there besides chrome, but I wanted to keep the stock look.

Gordon delivered on a stock look with improved mid-range torque, which is exactly what I asked for.

 

[scabber]

You did the right thing the pipes look and perform great. The cheater systems wont be half as nice as those or fit as well.

 

[jd750ace]

Your dyno sheet seems to support the often offered notion here, and what my butt dyno tells me, it's relatively pointless to run a stock XS over 5000 rpm or so. That thing goes to sleep. Don't know what the pipes cost you, but that is a significant torque shift to right where you need it. That's a good buy in my book. Don't know about chroming cost, but the performance shift is real nice.

 

[crashcourse]

Scabber, that's what I suspected but can't prove. The reason I didn't go with Mikesxs was they claim a "performance" part but have no data to back up that claim. The performance boost is certainly where I want it. Maybe I'm just too cheap to really dive into performance motorcycle mods.

 

[scabber]

The dyno report is very interesting. What other modifications did you do before you put the new exhaust. I would try a bigger main jet since it is lagging top end.

 

[crashcourse]

I didn't do any other modifications; just the exhaust. How much bigger on the main jet would you suggest?

 

[scabber]

I would try a 135 to start with and a 45 pilot . That should work well with the exhaust.

 

[weaselbeak]

"Your dyno sheet seems to support the often offered notion here, and what my butt dyno tells me, it's relatively pointless to run a stock XS over 5000 rpm or so."

While torque wasn't doing much by 5000 rpm, HP was climbing well all the way to 6500. That doesn't count as a positive above 5000?

 

[jd750ace]

I say that because torque was falling off far steeper than the HP rise. On my SV this equates to making a shitload of noise without much acceleration. It still pulls up there, but if you pause with the throttle just after the torque peak, then whack it open from there, the acceleration is a bit lackluster compared to what you got across the plateau that IS the torque rise on the SV. My Road Star is similar. Even though the torque is sloping down easy, the HP is creeping up, and it pulls decent. If the torque falls off a cliff and the HP is just on a sedate upward climb, another ratio is better benefit to making hay than pulling that gear out the top.
Torque equals acceleration in the real world most of us ride in.
Not saying it won't pull, just not a very satisfying pull in my book. That's a very happy chart to me. I'd be very happy with that torque profile for the way I use the bike.

 

[crashcourse]

I may be able to run it on the dyno again after putting in the larger main jets. I'd be curious to see if it helps with that torque drop-off.