Originally Posted by (sp?)
STP - standard temperature and pressure, e.g. a value corrected for temperature and altitude.
these runs were taken one evening after JohnJen, Javarilla and I had just done OVADs on our bikes. I don't have the stock data but do have an RPM correlated graph.
Once upon a time I lusted after a R1200S...had a special order in with BMW...desposited $1,000...waited three months for delivery..then was told that BMW had cancelled all special R1200S orders since there were too many in inventory....Dealer was great and had no real part in it; BMW never hinted they were going to cancel... Dealer gave me my $1,000 back...I turned around and bought my '07GSA...in my opinion a much better bike than the S for me...
OK...long way around for these points...while researching my R1200S I got heavy into adding an after market exhaust...here is what I found:
#1 Very expensive; very,very expensive
#2 Perhaps a slight 3-4 Hp increase at higher Rpms
#3 The torque curve had a flat spot relative to stock in mid-Rpm range [see above]
So for a sports bike it was a toss up...for a GS or GSA used off road it was not what I personally want...why:
#1 I have all the Hp and torque that I could want or use
#2 The torque I wanted was in mid-range not at higher Rpms
Soooooo....I have found that exhaust systems, ignition mods, fuel control mods are only of benefit if they fit your special needs...discussing them is like discussing which oil is best! Lots of opinions..
If you want to put on a cool looking and sounding exhaust...go for it, it is your bike, do with it what you want to
Dean's Hp vs weight is a good one; on a race bike this would make sense..... weight is especially of interest for me when that weight is carried up high above CG, where the muffler is mounted.....but I have just shed 27 pounds
of weight by going to soft luggage [Ortlieb] and benching my BMW aluminum "adv" boxes..and again I have got way more Hp/torque that I could ever need or learn to use...but reducing weight and especially wt. above the CG will accelerate the development of my riding skills...skilled riders of GSAs can carry a huge load and still make the bike dance under control over tough off road terrain...I can't yet but that is my goal.
If you can overlay the stock vs custom exhausts curves...most manufacturers have this on their web sites, but doing your own dyno test has more validity...check out where and when the advertised advantages occur compare that to where and when you most frequently use the Hp/Tq.
To paraphrase a producer of off road riding skill training DVDs "the best accessory you can add to your bike to improve your skills is gasoline"
Ps...You measure torque and calculate Hp from that @ Rpms...torque rules!