View Full Version : 1998 Road King

04-07-2009, 04:47 PM
I switched to your 2:1 Supermeg exhaust system in order to decrease sound while riding at freeway speeds. After a 600 mile test ride this weekend I am happy to report that the sound level is much improved. Now I have a question about MPG. I have a 1998 Road King with the following mods: Arlen Ness intake, Magneti Marelli throttle body bored from 38mm to 42mm, Andrews ev27 cam, S&S VFI closed loop system (replaced Harley's computer), your Super Meg exhaust with oxygen sensors, no head work, stock displacement. My dealer told me to use 18 discs with a closed end cap so that's what I installed. Seat of the pants tells me that my performance is essentially the same as with my old V&H system. Unfortunately at a cruising speed of 75 MPH in 5th gear, my fuel consumption went from 39MPG down to 29-30MPG. Curiously, when I increased my cruising speed to 80MPH in 6th gear (Baker 6 speed) my MPG improved to 33MPG. Would a decrease or increase in the number of disc help my fuel consumption concern? If so, which way and how many? I know this is would just be a ballpark answer for you but I have no access to a dyno with a sniffer so anything you can tell me would help. Thanks!!

04-08-2009, 07:25 AM
Hard to say for sure, only guessing, but figuring in higher gear it is probably turning lower rpm-mileage increases vs. lower gear and higer rpm? I would have to guess that at the higher rpm, it is dumping fuel and running rich, hurting mpg?

Typically we will just run all 20 and go from there, try putting two more in and see what it does for mileage and how it runs.

04-08-2009, 10:53 AM
Thanks, I'll give it a try.

04-08-2009, 11:16 AM
Keep us posted.

05-20-2009, 04:48 PM
Excuse the delay in getting back to you. Things are improving but I'm still looking for a little more mileage at freeway speeds. I installed two extra discs per your suggestion bringing the total to 20. I also made a slight modification to my base fuel map. This past weekend I put on 800 miles of mixed interstate and rural speeds. At speeds averaging 60 -65 mph in 5th gear I got 44 - 47 MPG (yeah). At 80+ mph in 6th gear my mileage dropped to 37 MPG. I am going to tweak my base map again, just a little, and try a cruising speed of 75 MPH in 6th and see what I get in terms of mileage. The addition of the two discs did not appreciably change the volume so cruising speed noise is still ok. The changes did not noticeably alter engine performance at the low or the high end, the engine still pulls strongly through out the RPM range. Thanks for your assistance - I'll keep you posted. As before, if you have any other suggestions I would appreciate them. Thanks!!

05-21-2009, 07:31 AM
Sounds pretty good, only thing I can suggest is to look at what RPM the motor is turning at those specific speeds to adjust fuel delivery?
Otherwise, go ride the snot out of it and enjoy the good weather.