99 KX 144 test (Eric Gorr vs. RPM)

In 99 my friend and I each purchased 99 KX 125. Since the bike is such a dog, we both decided to get the big bore kits. I decided to use Eric and my friend went with Rick Peterson. When I first received my cylinder back from Eric, I didn't really notice any changes except for the larger bore. My friend’s cylinder was different. RPM turned down the cylinder base and also had a different cut in the head. He also used a two ring piston in his bike. Once we both had a chance to break the motors in, it was time to switch. My friend and I are very similar riders (5'7" ht., 160lbs) with identical riding styles. Both bikes were faster than stock, but had different power. The RPM motor had low and mid power not much better than stock. The top seemed good but had a tendency to over rev. Eric Gorr's motor had more power everywhere. It pulled from bottom to top. It was definitely a noticeable difference. It was a much more useable motor. Even a novice rider could figure this one out. Can anyone explain why this is? What was RPM trying to accomplish by cutting the base down and changing the squish band so dramatically?

Another point I would like to make is the turnaround time and price difference? RPM was twice as much and twice as long. Need I say more?

Eric,
I appreciate the time you take in actually R&D bikes to maximize Hp, instead of just punching out a big bore to create more ponies.

I am considering a 02 YZ 125 (instead of the 02 KX) for next season. I plan on the Eric Gorr 144cc for the bike. Is the YZ 144 better than KX 144? If so, by how much? What is the hp difference between the bikes?

Also as an added note, my friend purchased the 167cc kit from RPM for his 01 KX 125. He didn't learn much from his prior mistake. The bike seems faster than my 01 KX 144 Eric Gorr motor, but only very slight. The $1600 price tag doesn't seem justifiable. He wasn't very happy with the result and now plans on selling the bike to switch to a YZ or KTM. If I purchased the bike (since it has minimal use on it) is there anything I could do to make this engine more useable? It just doesn't seem like the larger displacement is being maximized in terms of power. Is it a porting/timing problem? Why doesn't this bike rip? I can tell you from experience that a 01' RPM 139cc YZ is faster than an 01' RPM 167cc KX. That's a difference of 28cc. It just doesn't make sense. Also, the 167cc seems like too much motor for the 125 crank. The price is right to purchase this bike, but I need to make it run at its max. level. Will porting or anything make a difference? Or should I just scrap the whole idea and purchase a 02 yz 125 and add the Eric Gorr 144cc kit? I would really appreciate some sound advice and input.

What I meant by noticable changes was that RPM had cut the cylinder base dramatically and the squish band looked much different than stock. Both cylinders had noticable porting work, but this is typical. I was attempting to point out the visible changes without the use of a micrometer to check the difference. I didn't have the ability to hold them side by side until after they were bolted on.

In regards to the comment on sending the whole engine, I think it depends on the bike. I had sent EG a 99 and 01 KX 125 cylinder for the 144 kit and only set the head/cylinder/power valve assembly intact. I never sent EG the whole engine. I may be wrong (someone feel free to correct me) but I think on the YZ's (maybe other bike too) you have to send him the whole motor.

By the way, a month turnaround time is nothing. RPM took 9 weeks for my friend and REP took 3 months to port my 98'. If your from CT then you have heard of REP.

I would still appreciate some more input from anyone on the 01' 167cc KX solution. Marcus.... I appreciate your reply

Thanks Eric for your response. Like always your post are very informative. I am very satisfied with your work, turnaround time and the cost. Furthermore, I also apoligize on the fact that you spent a majority of your post time on defending the 'uniformed'. That wasn't my orginal intent. I know your time is valuable and a large majority of us appreciate your posts.

I think that it would be more benefidal to reduce as much friction (friction equals loss of horsepower) as possibly on 125. I typically replace a piston on the 125 after 10 to 15 hours of use. I not concern about pinching pennies to reach 50 hours of use on a 125. Serious racers have new bikes by then anyways. As I stated before there was a big difference between EG and RPM mods on this particular bike. I was able to have an excellant opportunity of testing two bikes side by side. I hope my experience proved useful to others. Bottom line.... the Eric Gorr bike ripped much better than RPM's. End of story. Maybe other bikes have a different ending.

Another note I would like to make is that this is a 'Mods & Performance Forum'. If you want to complain about something then post it on the 'Flame Board' forum. This is not the place to whine and cry about what things cost or how long. Some of us use this as a very valuable resource. You must remember some of us race for a living and the information found in these forums are the difference between winning and dnf. Winning provides a paycheck. Even a monkey can figure this one out. Sorry to be so rude, but I had a point to make in the beginning so stick with it.