I do not notice any loss of low end torque doing this mod. If fact the opposite is true; there is better pulling power than before all through the range. I too was apprehensive about modifying the exhaust thinking that there would be a trade off somewhere along the power range, but in fact the mod has increased the power throughout the entire range. I too figured Yamaha had done their homework to figure out exactly the right amount of back pressure needed when designing the exhaust the way they did, but that turns out not to be the case. I think Yamaha was more focused on creating a fool proof spark arrester that would pass all the government regulations rather than being focused on creating an exhaust that metered out the correct flat torque curve with a minimal amount of noise. The bottom line from my experiments is that the stock exhaust is way too restrictive for this engine. It is so restrictive that it basically nullifies any tuning effect of back pressure on the power curve. The restriction and back pressure is so great with the stock pipe that it does not come close to the threshold of where you can tune the exhaust with too little or too much back pressure. Plain and simple it is plugged up so bad in its stock form that it would be like running a marathon and trying to exhale out of only one nostril of your nose, with your other nostril plugged up and your mouth closed. Even with the 1 + ½ hole I ended up drilling in the exhaust, which is almost like running an open pipe without the spark arrester in it; the power curve is only enhanced with no ill effects to the low end power. The way I can really tell about the low end power increase is when I go up long incline hill and I am able to pull one higher gear than I usually would, even with the new 16 tooth countershaft sproket I installed. I can also tell by riding on flat ground and choosing two gears higher than what I would normally do, allowing the engine to lug down low and then opening up the throttle. With the stock pipe I would feel very little increase in power if I lug it down that low and then open the throttle up. I would normally need to gear down to get an increase in power in that situation. With the exhaust opened up I can open up the throttle and get more pulling power without having to go down a gear. I do suspect there is even more power gains to be had by increasing the intake flow through the airbox and rejetting the carb to run richer. Yamaha probably figured the intake airbox volume specifications taking into account the limited exhaust flow, and the ability for the engine to only require that limited intake of air, so there are probably gains to be made there for sure. I will report back as my progress toward XT225 Nirvana continues.