RSl25 Race Tips

By Mike Himmelsbach


 In our efforts to constantly improve the horsepower output of my Team Himmelsbach Racing RS125 Honda my dad and I started researching different exhaust pipes their costs and what can be expected from them.

 We managed to get two aftermarket pipes in our possession . One was a Moto Liberty "B Kit" replica that retailed for $950 without a silencer, The other was a Jolly Moto pipe distributed by Morgan Racing that retailed for $1015 and came with a carbon silencer and a spare carbon silencer. Moto Liberty and Morgan Racing both claimed that their pipes produced more power than stock pipes. Moto Liberty claimed an increase of about 1 horsepower from around 9000 rpm on up, while Morgan Raring was more bold, predicting a 1.5 peak horsepower increase while producing about 1 horsepower more from 9000 rpm on up.

 Here is what we found when we ran the pipes on the dyno. All the dyno tests were run on a Dynojet Model 150 dyno at Blackmanís Cycle, using my 1995 RS125 Honda. Engine configuration and parts were changed between the first test and the second one as part of our ongoing efforts to improve our racing program, but in each case thc aftermarket pipes were tested against a stock pipe. My father, Bill Himmelsbach, long time two-stoke tuner and 250cc Grand Prix racer, handled all the responsibilities of operating the dyno.

 In the first test (Round l) we ran the stock pipe against the "B Kit." replica pipe offered by Moto Liberty. Moto Liberty claimed we would see approximately a 1 horsepower increase over the stock pipe all throughout the useable powerband. but. we didn't. get that result. Thc Moto Liberty pipe was equal to the stock pipe in some respects and lacking in other areas.

 The Moto Liberty pipe produced higher peak horsepower by +0.4 bhp and slightly better peak torque by +0.4 lbs.-ft.. The horsepower averages for the two pipes between 10,000 rpm and 12,250 rpm were identical at 37.11 bhp. The torque averages varied by only 0.0 l with the Moto Liberty pipe producing a 17.53 lbs.-ft, average while the stack pipe produced 17.52 lbs.-ft. average torque between the same range.

 We also looked at the time it took to accelerate from a certain rpm range to another. The time it took thc stock pipe to get from 10,000 rpm to 12,250 rpm was 0.l-second less than it took the Moto Liberty pipe to accelerate from 10,000 to 12.250 rpm.

After running the Liberty as well as the pipe builder to get some tuning help for the pipe in order to see this promised l horsepower gain. The builder gave me the complete engine set-up used to design and test the pipe. This set-up was totally different than ours, so we changed our bike to meet his engine set-up specifications. But when we did that and re-ran thetests, the bike made less power, so we went. back to our original engine set.-up.

 So which one is better, the stocker or the Moto Liberty "B Kit" replica ? After trying both pipes on the track, I elected to go with the stock pipe to start the season.

 After the disappointing results from the first pipe tests. I did not have much hope for the Jolly Moto pipe end I had prepared myself for another $1000 loss. But to my surprise, the Jolly Moto pipe from Morgan Racing lived up to the hype and performed well.

 The Morgan Racing pipe out-performed the stock pipe in most categories. Peak horse- power was higher by +1.4 bhp and the peak torque was also higher, by +0.7 lbs.-ft,. The horsepower average for the two pipes between 10,000 rpm and l2,250 rpm also favored the Morgan pipe by +0.92 bhp, an almost one full horsepower increase; the torque average increased by +0.43 lbs. ft.

 The stock pipe was slightly better thanthc

Morgan pipe in terns of acceleration time from 10,000 rpm to 12,250 rpm, by 0.02-second.

 We raced with thc Morgan Racing-distributed pipe for the first time at Summit. Point Raceway during the WEBA National Challenge Series event. The first time out on the track the bike immediately needed a smaller rear sprocket to compensate for the higher straightaway speeds. One noticeable characteristic. of the pipe is that. it has dramatic burst of power at 10,250 rpm as you cansee by thc dyno chart, it jumps seven horsepower in 750 rpm. This boost of power is good if you are at or above 10,250 rpm but the. bike will just fall flat if you are under it, making the bike a little more temperamental for the rider. The pipe worked well during thc entire weekend. We ended up on the top of the podium and the bike was faster than ever before.

 We used the Jolly Moto pipe from Morgan Racing for rest of the 1997 WERA 125cc Grand Prix National Challenge Series and won thc Championship.

 More information is available is available from Mike Himmelsbach at Team Himmelsbach Racing. (215) 529-4332: Bill Himmelsbach at Blackmanís Cycle. (610) 965-9865; Mickey Hunt at Moto Liberty, (972) 242-6440; and Will Morgan at Morgan Racing, (508) 867-6295. RW