View Full Version : Dyno Tuning Question

09-11-2009, 03:42 PM
Hello Folks, My bike is a 2004 HD Super Glide with SE air cleaner, Power Commander and 2-1 Supermeg. Presently, I'm running 21 discs with closed endcap, following one of Dynojet's MAP recommendations, but fuel consumption is way up. Exhaust is looking sooty and bike runs sluggish at lower speeds, especially from a stop and low-speed roll-on. I'm planning on getting a dyno tune done soon and the prospective tuner says the number of discs will not really affect the tuning (I'm assuming up to a point). He says to use the number of discs that give the desired sound level and then he does the fuel tuning from there. Is he being truthful or should I look for another tuner? Thanks.

09-11-2009, 04:26 PM
Your tuner is correct in one respect, if your happy with the sound, leave it and let him tune it properly.
From what you described, it sound fat down low, whcih is typical with an 'off the shelf' MAP or jet spec, better to err on the rich side vs. the lean side.

You can fine tune with the discs, but again, from the sounds of it, it needs more than fine tuning?

Let him run with it.

09-11-2009, 06:18 PM
Your tuner is correct in one respect, if your happy with the sound, leave it and let him tune it properly... http://www.zxforums.com/forums/images/smilies/plusone.gif I second that.

Your tuner sounds wise, because he knows what most matters to riders: how they want their bikes to sound and better power. So based on the sound you desire on the Supertrapp, he'll adjust the PC map accordingly for optimal a/f ratio & power. Many factors go into tuning correctly and it sounds like something's amiss with your current PC map. It isn't matching the flow characterstics of your air filter, exhaust and atmospheric conditions (altitude, humidity, etc). When he's done, you should experience better throttle response, more power and better MPG.

09-14-2009, 12:18 PM
Guys, thanks for your prompt replies, I appreciate the input! I'm thinking of trying 18 discs, as that amount seems to be about average and I won't mind the reduction in decibels from the 21 I'm presently using. I've got another Supertrapp muffler which seems very restrictive but very quiet (maybe the Silent Series?). Is there any use in trying that muffler or will I lose much of the performance gain compared to the Supermeg? I'm trying to keep the muffler "noise" issue in mind. Thanks again.

09-14-2009, 01:33 PM
You say this other muffler seems very restrictive & quiet. What are you basing your observation on? Have you swapped out these mufflers with your current muffler and tune/combination? The same muffler is going to sound different on an 88 vs a 103. You need to compare apples to apples.
Run a broom handle up the inlet. If it only goes 1/3-1/2 the into the muffler, it has a mechanical baffle which quiets the exhaust and restricts the flow. This type of core will generally not allow you to realize the full potential of your upgrades.

09-14-2009, 04:05 PM
You got it right on! Only thing I changed was the two mufflers on the same bike, same tuning. The one with the mechanical baffle, as you call it, sounded much quieter than the other and "seemed" more flow restrictive. When I removed the cores, the mechanical baffle was obvious on the one muffler while the other had a straight-through design. Admittedly, these sound and flow observations are without any mechanical measuring devices. Your last sentence suggests I use the straight-through core to realize the full potential of my upgrades. Thanks for your advice and I apologize for my confusion and ignorance.

09-14-2009, 04:54 PM
Nothing to apologize for, you're correct, the straight through core will perform better.