engine mods by pro-circuit

[cantrell24x]

guys

At a new west tennessee track the othe day I realised quite quickly that my stock 125 was not capable (with me on the seat) of clearing this nice 70' or so uphill triple. since then I have been very interested in engine mods and pipes for my 2002 yz. I talked with the phone answerer at PC and he gave me their prices and basically told me nothing other than that they do some head work and some porting. My first question is. Has anyone used PC for engine mods recently and what was the result? Second, there are programs available for determining the hp of a two stroke engine with unbelievable flexability for different porting and pipes etc. Has anyone used any of these programs to do your own porting and engine mods? Sorry for rattling on, just a little more. Ive heard that most pipes in america are designed for stock porting. but PC sells the same pipe for its modified engines as it does for stock. That was my first ??? when talking to the phone guy. So should I even change from the stock pipe? I am looking for more power everywhere not bottom or top. Is it true that to gain power in one area you must give it up in another? ok sorry for the long post but it seems like everytime i learn one thing I think of two more questions. Maybe I should start by learning how to ride faster!

 

[MX145]

I sent my '02 YZ125 head & cylinder into Pro Circuit for some mod's. I requested for more mid to top end performance since that is where I ride the bike at. I was impressed, as well as my brother, which also owns a '02 YZ125. There was a significant gain as well as response. My bike now seems to also have more bottom end than his even though that wasn't what I was specifically looking for. Be prepared once you get it back to be able to gap the rings to the specified clearance (not hard, but requires a few tools). You will also have to get new needles, jets, and run race gas. Recently I've been running my bike at our local test track and indoor arena-cross and the performance has been top notch. I haven't been able to run it on an outdoor MX track yet, but I'm positive it will perform even better there. Last fall, at one of the outdoor tracks they have an uphill double that once I lowered my rear sprocket teeth it made a huge difference. I was able to then hit it in 5th wide open instead of 4th/5th with some bog. If you haven't already changed the gearing, I would go for that with a new required chain and see if that helps any. I raced last fall on a stock '02 YZ125 with only a change in handlebars and rear sprocket/chain and did pretty well considering there wasn't any aftermarket acc. or performance products for the all new redesigned bike. I even had to make my own black backgrounds since those weren't available at the time. Now you can get almost anything for them. These bikes RIP !! and you can make them haul BOOTY!!

I don't know of any programs for you to use in order to port the '02 YZ125 motor for your specifications. I leave it up to the guys that do it everyday.

If you leave your engine stock, I would recommend a new reed cage/rad valve rather than a pipe & silencer. You will get better performance off it for your money than an aftermarket pipe & silencer. If you go for the mod's then you might want the pipe & silencer and maybe even go with the reed cage/rad valve as well. It really all depends on what you are looking for. The stock pipes are really good nowdays it seems. I was happy with the overall performance before all the mod's I have done and now LUV it. I can't wait to ride.

 

[spanky250]

I haven't used PC, but FMF did my current bike, and I'm sure the results would be similar. They gave me an off-the-shelf, cookie-cutter job that was obviously tailored to pro-level riders, with no regards to the type of poer that I requested . The performance increase was dramatic, but I ended up with a hard-hitting power delivery that actually made the bike harder to ride in many situations. If I had it to do over again, I would have sent my engine to Eric, where I could have gotten the power tailored to my conditions and preference.

Just my $.02;)

 

[hoosierf]

Tom Morgan racing did a buddies' 1999 YZ125. He turned it into a mini 250. He did tailor the engine to his riding style based upon some questions they went over. The bike was phenomonal when he was done. Check with them.

 

[MX-727]

I've had Eric do two engines and a head for the third bike. Eric will talk with you and figure out exactly what you want. He will let you know exactly what he is going to do. The reason I only had the head milled on the third bike (02 YZ250) is Eric didn't feel that the bike needed to be ported and he only milled the head due to my high altitude and desire to run VP C12. Rather than take my money for work he knew I didn't need, he was upfront and honest. Heck, talk to him, what have you got to lose? Plus you just might save a bunch since Eric doesn't overcharge for his work.

 

[cantrell24x]

mx 145 Do you run a rad valve with your PC mods? I was considering that but when I talked to the phone guy at PC he said they recomend stock reads. Its just a feeling but I got the impression it was because the reed manufacturers recommend stock pipes, if you know what I mean.

 

[MX145]

No, I don't run a rad valve with the PC mods, atleast not now. I bought a Boyesen RAD 33-G valve but have not used it. When I talked to PC and gave them all the spec's of what I wanted done and the parts I'll be using I included the rad valve in the list. When I spoke with the motor technician, he also stated that they don't recommend the rad valve - the stock carbonfiber reeds would actually perform better in my application. Maybe if I was going for more bottom end, or overall performance, the rad valve would work better in that situation. I currently have my Boyesen rad valve up for sale. If it doesn't sell and I have the time to experiment - I may put it on and see what it does. It may make it even better or may make it unmanageable. I do know the rad valves work, even better than a pipe & silencer combo on a stock motor. Alot of racers swear by bolting on the Boyesen rad valve and pipe/silencer for a low cost yet high performance enhancement. If I didn't have the engine mod's that is where I would be.