Need opinions for a motor

[Fear250r]

Hey guys, here's the deal, I'm rebuilding my R and putting something bigger in it. I've been planning on a Duncan 305 PV, but wanted some opinions from everybody. I ride just about everything from tight/fast trails, sandpits and a little backyard track. My buddy is concerned because it's just a bigger piston and not a longer rod, any info on that would be great also. Ok, I'll let you guys go at! Thanks

[beak7707]

Why would he be concered about a longer rod? You do not need to stroke a 250r to get good power. Stroking is more for drag racing not all around riding. That 305pv would have plenty of power, I think you would be impressed with any of the bolt on cylinders. I'm no expert but I'm pretty sure you dont stroke pv motors anyways, I think I read it is not a good combination.

[custom R]

I just put a esr 310 kit with a 4 mill stroker crank to make it a true 310 and a good mid range port job and I do alot of the same type of riding you do. I only have a few hours on the motor since break in but so far I love it great low end power and pulls hard all the way up

[wilkin250r]

Are you considering a stroker? Or are you talking strictly about a longer rod?

If memory serves, I think all Duncan motors are set up for short rod cranks, but a simple spacer plate would allow you to use a long-rod crank. I certainly know that my own Duncan 340PV uses a spacer plate.


My 340 PV is a handful. I'll be honest, if it was just trails and recreational, I wouldn't go with this motor. 90% of my trail riding is at 1/2 throttle. and I'm a fairly aggressive rider. A little smaller engine (like the 305 you are planning) still might be a little much, or it might be just right.

Throw the sandpits in the mix, and the 305 sounds like the perfect engine for you. You don't want to be over-powered on the trails (like my 340) because it really is exhausting, but you also don't want to be under-powered in the sand pits. I think the 305 will give you the best overall package for all types of riding.

[Fear250r]

For some reason he thought the kit would use a longer rod and he thinks that simply using a larger piston will put too much pressure on the rod/bottom end. I told him I think Duncan knows what they're doing. Like you said is exactly what I was thinking, the 340 is too much, but I think the 305 would be fine.

Anybody else? I'm looking for anyone to compare Duncan to other companies, feel free to chime in with your thoughts, Thanks.

[morse250r]

i have a 310 pro x for trail
i had a 350 on a stock rod it was fine now i just went to a stroker 4 mm youll be fiine not to much stress 310 is a good motor fun get a good pipe esr 5 and a 38mm air striker

[Fear250r]

ok, I've been searching old threads all morning about my situation. One thing I've noticed is the countless good words about Neil at C-Leigh. What does everybody think about getting a blank cylinder, say a 310 or 330 and send it to Neil for the port work? Anybody know what he charges/turn around time is? Also, how about a phone number.

My biggest concern is that a port job from Duncan could be a "cookie cutter" job and is spending 2 grand at Duncan worth it basically. Tearing into the bottom end is no big deal, I just don't want to spend all sorts of money on something that wasn't really worth the money. Anyway, have at it and let me know what you think. Thanks

[bushwesl]

Neil is a Pro-X, CT, and ESR dealer. You can purchase your cylinder through him and it will have his porting.

[wilkin250r]

The longer rod certainly wouldn't be a bad thing. Yes, the short rod has more severe rod angles during the normal operation of the motor. And yes, those more severe angles will create more stress in certain areas. Yes, overall, it does create higher risk.

But is it TOO much stress? Heck no.

Lots of people have run big bore motors with short rod cranks without ever having a problem. I would say the condition of the crank, bearings, and overall lower end would have a much more significant impact on the reliability of your motor than the rod length.

[morse250r]

you can ask neil directly go to trx250r.net he has his own forum headling ? and a's

[312R1]

Originally posted by Fear250r
My biggest concern is that a port job from Duncan could be a "cookie cutter" job and is spending 2 grand at Duncan worth it basically. Tearing into the bottom end is no big deal, I just don't want to spend all sorts of money on something that wasn't really worth the money. Anyway, have at it and let me know what you think. Thanks


If you go with Duncan you wouldn't be getting a cookie cutter design..Loren does all the porting himself for the customer..To me it's worth it!

-Steve

[wilkin250r]

I don't understand why everyone is afraid of a "cookie cutter" port job.

Companies like Duncan or ESR, they didn't gain success and recognition by putting out crappy products, yet they still have their own "cookie-cutter" port jobs.


Do you know WHY they are cookie-cutter jobs? It's because they found a combination that puts out good, useable power and works well for the majority of riders. Most often, a companies cookie-cutter port jobs are the exact same as the one they put into their own racer's engine. They develop a package that works well, and they sell it.

The only time I would be afraid of a cookie-cutter job is if I was looking for something that was TRULY custom, designed for my own riding style specifically. Maybe for dune riding, I want higher than a mid-range, but not quite an all-out drag porting. I want a compromise in the middle, to shift my mid-range just a tad higher in the RPM range. But at the same time, if I want to go with something custom like that, to my own exact specifications, I'm going to be willing to pay for it.

[Fear250r]

Well, I had actually called Duncan, before Steve had posted and found out that Loren is actually still doing the porting himself, which made me feel a lot better. Anyway, due to financial issues I might have to spend less than I wanted. :mad: Oh well, I'm used to the BS at this point. So, I'm thinking of an ESR or CT cylinder, 310/330ish and having Neil @ C-Leigh do the port work, should cut the cost in half. I can always upgrade next year.

Anyway, I "think" that will be what I do, now if I could only get a hold of Neil, he's a tough one to catch! Well, if anybody has any comments/suggestions, feel free to chime in again and Thank you for everyones' responses.

[havinnoj]

Originally posted by wilkin250r
I don't understand why everyone is afraid of a "cookie cutter" port job.

Companies like Duncan or ESR, they didn't gain success and recognition by putting out crappy products, yet they still have their own "cookie-cutter" port jobs.


Do you know WHY they are cookie-cutter jobs? It's because they found a combination that puts out good, useable power and works well for the majority of riders. Most often, a companies cookie-cutter port jobs are the exact same as the one they put into their own racer's engine. They develop a package that works well, and they sell it.

The only time I would be afraid of a cookie-cutter job is if I was looking for something that was TRULY custom, designed for my own riding style specifically. Maybe for dune riding, I want higher than a mid-range, but not quite an all-out drag porting. I want a compromise in the middle, to shift my mid-range just a tad higher in the RPM range. But at the same time, if I want to go with something custom like that, to my own exact specifications, I'm going to be willing to pay for it.

Except when you use only 3 portwork designs to match at least double the riding type and dozens more riding styles.