Port or Big Bore or both??

[robwbright]

Guys:

I'm on 2002 RM 125. Only engine mods are Bill's Pipe and Silencer and Hinson Clutch. I hadn't ridden much in a decade and had never raced before two months ago. So far I'm running a consistent 2nd in open D class after 4 races and 6th or 7th in 125 C at different track.

$$ is an issue at this time.

I'm thinking of a port job and/or 134 or 144 kit. I guess my first question comes down to this:

1: If I get a port job done soon, will it be compatible with a big bore kit later?

2: How much HP gain from the port job?

3: After the port job, how much HP gain from the 134 and 144?

Finally, my father in law is a professional transmission mechanic, and amateur Modified Dirt Track racer and 125 Cart racer. He builds his own dirt track motors, complete with port and polish jobs, etc . . .

He says he can port/polish my 125 for my for free. As $$ is an issue, this is an attractive offer, but I'm a bit hesitant. I know he can do it on cars, but I dunno about bikes. Any thoughts?

By the way, his 125 motor was built (complete with O ring instead of gasket on head/cylinder) by Boyesen (yes, the Boyesen) and my father in law claims it dynoed at 45 HP at the motor. That seems about 5 HP too high from what I read here.

Anyway, any thoughts would be appreciated.

Thanks

Rob

 

[bclapham]

if you get the 144 kit from Gorr, the porting will be included. if you want more power accross the RPM range, you need more CCs. if you want the power in a different RPM range, then porting.

note- its easily possible to get crazy HP numbers by tuning an engine to rev to the moon. it wont be a good engine for MX tho, and you will need to rebuilt it every race.

i had a 2002 RM144, it was a good bike.

 

[Glitch]

I think you can only go .080 over(133) per regulations if you still wanna race. Any higher and I thought the bike was illegal? I think..

 

[robwbright]

bclapham:

Would you give me some idea of the difference between stock 02 and 144cc 02 as far as HP and ridability? Whch port job did you use?

And what about racing. I'm doing outlaw right now. Have no plans to do AMA but wouldn't want to give up the option either . . .

Thanks

Rob

 

[dirtbikr99]

Just as a thought, maybe if your bikes up for a new pistion and rings, just have your uncle do a port job on it and maybe a little more compression. That way you get some more power and save money that you can put to getting a newer bike in the future. Just a thought, but a 144 kit from eric gorr would be nice!!

 

[Eric Gorr]

45HP huh? Did you guys have a nitrous tank laking in the dyno room?

 

[robwbright]

Yeah I was a bit skeptical of the 45 HP as well - actually very skeptical! But he's raced for 35 years and it was at the motor, not at the real wheel. I wasn't there . . .

Neway . . .

 

[JustinC]

Eric or bclapham, have either of you guys ever ran a 144 on the dyno? I'm curious about what kind of numbers the 144's are capable of producing since I'm thinking about a yz144 myself. I'm actually more concerned with torque numbers over horsepower though, I'm coming off of a 04 crf250r and I'm kind of struggling with the 125, I miss the crf's ridability, I'm looking for a more easy to use powerband.

 

[steve125]

My YZ144 dynoed at 39HP. It's easier to ride because it has more power. But it's not trail bike torquey like the CRF 250. Personally I find that kind of power boring. The 144 is a blast to ride and it runs and revs like a full on factory works125. :cool:

 

[JustinC]

steve what other mods have you done along with the big bore itself? how is it the cyl. ported? any reeds, pipe, etc...?

 

[fastwes]

Rob,
If I were you I'd have my father in law port it. Raise the ports only 1/4 as much as his kart engine's ports and make sure the transfer ports match exactly left to right/in pairs. Raise the compression as much as your fuel allows. Go to a 144 later on if you don't like revving or other characteristics of it.
Wes Gilbert
Boyesen Precision Porting(Yes, the Boyesen porter)

 

[steve125]

steve what other mods have you done along with the big bore itself? how is it the cyl. ported? any reeds, pipe, etc...?

Justin still testing the final specs, but what won't change is the FMF factory Fatty and shorty. That pipe beat out the PC and stock pipe quite nicely on the track and dyno.

The cylinder and head are what you would call mid to top porting, not far off a shifter kart spec. Race fuel is a must with a min. motor octane of 105 needed.

Still testing a Vortex ignition and reed valves. So far a modified Boyesen Rad Valve (reeds included) is proving to be a front runner.

Thanks to a new piston design from Wiseco the 144 piston is within a few grams of the std piston. This allows the 144 to rev out like a 125.

 

[DOTdirtbiker]

Steve125, modded rad valve...

modded rad valve... I was wondering what the best valve would be for my cr500? Any idea Steve? What did You have to modify on the rad valve? I wanted to try Delta force3, but they don't seem to be available for the 500. I just wonder if I can make them fit (I guess not they must be larger than a 250's), or if the catalogue (DK's) I was looking in left them out. Guess I should contact Delta Force.

 

[JustinC]

thanks for your input steve, i really appreciate it. since i am a novice rider i don't think the type of porting you have would work well for me. i will see if maybe eric can do his "mo better" porting to my cylinder.

 

[robwbright]

Thanks for the posts guys. I sent Wes an email requesting more information. I think I'll take his advice since I'm short on cash . . .