Yz250f modified hp/torque #'s to shoot for National caliber

tzmike
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437
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2/22/2014
Location
Warwick, NY US
12/21/2019 11:45am
Doing a privateer 250 motor and was wondering what the gang here has achieved in actual Dyno hp/torque #s I can use as a general guideline to compare this completed motor against. A 249cc stock bore n stroke. It's a 2018 BTW
Thanks in advance and you all enjoy the holidays !
(I'll then hit the tech section for more info/questions)
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avidchimp
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3985
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Thousand Oaks, CA US
12/21/2019 12:11pm
About tree fiddy.
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tzmike
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Warwick, NY US
12/21/2019 12:12pm
Treefiddy is damn good for a 2fiddy
kzizok
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AS US
12/21/2019 12:28pm
Thanks for the advice/feedback/replies gang!

Thanks in advance!
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12/21/2019 1:06pm
My bike built by twisted with a full mod motor, built trans, and a bunch of stuff made 50
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The Shop

yz133rider
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8/1/2013
Location
Avondale, PA US
12/21/2019 1:40pm
Id get a 450 if i wanted to race nationals without support. A stock 450 with a-kit would be durable and competitive.

Where as a 250f will take endless maintenece and massive money to be even in the same ball park as the top 20. Engine is everything in that class.

450 would leave it more up to conditioning, rider, and give you half a chance of lasting the whole season.
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12/21/2019 1:45pm
This idea that you have to have a mod motor to do well (qualify) at an outdoors in the 250f class is being perpetuated by people that aren’t paying attention.

Majority of guys can not afford a 250 race motor, and additionally the maintenance along with it. Therefore they just go for it on stock motors with pipe and race gas. It works every weekend. Hell some guys don’t even show up with aftermarket exhaust.

With that being said- 50hp is a quality benchmark. Don’t need it. But that’s the built number.
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yz133rider
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Avondale, PA US
12/21/2019 1:50pm Edited Date/Time 12/21/2019 1:51pm
This idea that you have to have a mod motor to do well (qualify) at an outdoors in the 250f class is being perpetuated by people...
This idea that you have to have a mod motor to do well (qualify) at an outdoors in the 250f class is being perpetuated by people that aren’t paying attention.

Majority of guys can not afford a 250 race motor, and additionally the maintenance along with it. Therefore they just go for it on stock motors with pipe and race gas. It works every weekend. Hell some guys don’t even show up with aftermarket exhaust.

With that being said- 50hp is a quality benchmark. Don’t need it. But that’s the built number.
If you show up with an exhaust and that's it on a 250 youll be buried on the start, drug down each deep straight, drug up each hill.

With a 450 and suspension, clutch etc you'll be way closer and 100x more durable then a 250 with the same $ invested.
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Falcon
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Menifee, CA US
12/21/2019 1:50pm Edited Date/Time 12/21/2019 1:51pm
Build a strong, reliable motor and equip the bike with great suspension, then get your rider down to 160 pounds or less.
12/21/2019 2:01pm
yz133rider wrote:
If you show up with an exhaust and that's it on a 250 youll be buried on the start, drug down each deep straight, drug up...
If you show up with an exhaust and that's it on a 250 youll be buried on the start, drug down each deep straight, drug up each hill.

With a 450 and suspension, clutch etc you'll be way closer and 100x more durable then a 250 with the same $ invested.
450 class is twice as competitive.

Yeah you’ll get beat on the start. By riders that are going to beat you anyway.
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tzmike
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Warwick, NY US
12/21/2019 2:12pm
The rider is right at 160
50 hp is mindblowing
I appreciate all of your comments. The rider has a lot to think about here. At 50hp. I agree that requires way more maintenance to keep it from grenading. The project will be tamed down thanks to all your insights.
Thanks all. Again enjoy the holidays !
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12/21/2019 2:28pm
150sx will Dyno at 45, good for 2 rounds before they suspect it. fan favourite of it matters
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yak651
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8/26/2006
Location
Appleton, WI US
12/21/2019 2:31pm
yz133rider wrote:
If you show up with an exhaust and that's it on a 250 youll be buried on the start, drug down each deep straight, drug up...
If you show up with an exhaust and that's it on a 250 youll be buried on the start, drug down each deep straight, drug up each hill.

With a 450 and suspension, clutch etc you'll be way closer and 100x more durable then a 250 with the same $ invested.
450 class is twice as competitive.

Yeah you’ll get beat on the start. By riders that are going to beat you anyway.
I know you race the nationals and trust your opinion, but I would question your 450 class being 2x as competitive. Way more "supported" riders in the 250 class, and after the top 15-20 in 450s the talent drops. Take a local rider in WI, Nathan LaPorte, in '18 he qualified for just about every national he tried in the 450 class. In '19, I think he was riding better but was trying to race in 250 class and I'm pretty sure he didn't make many of them. Just my opinion, but if I was a privateer I would be trying the 450 class.
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LowBidder
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6/21/2019
Location
Bossier City, LA US
12/21/2019 3:25pm
Just like qualifying for Lorettas, easier to make it in A classes. Guys qualify for A all the time that would never make it in B.
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Kenman
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24
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1/28/2014
Location
New Castle, DE US
12/21/2019 5:05pm
Don’t bother. The 250 class is ridiculous. Had a motor built by a top builder with a capable rider who weighed 125lbs. Wasn’t even close to the pro circuit / geico / star / jgr guys. Same rider moved to the 450 class, and got multiple top 15’s with a stock 450, A-kit, race fuel and an ignition. Save your time building a time bomb. It’s LESS of a waste of money to go 450.
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ledger
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3678
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Location
TN US
12/21/2019 9:50pm Edited Date/Time 12/21/2019 10:09pm
kzizok wrote:
Thanks for the advice/feedback/replies gang!

Thanks in advance!
Overplayed like an ESR YZ 325 number T-7. You're so welcome !!
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resetjet
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2225
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3/16/2012
Location
Tampa, FL US
12/22/2019 2:58pm
I would have thought more from a factory bike as stock these days is 42hp. But i guess thats an 18% gain which is crazy respectable.
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Momus
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CD
12/22/2019 8:34pm Edited Date/Time 12/23/2019 4:36am
resetjet wrote:
I would have thought more from a factory bike as stock these days is 42hp. But i guess thats an 18% gain which is crazy respectable.
These 250 MX engines are already quite efficient so there are not big gains in torque to be had - torque x RPM = horsepower-so the only way with a given fuel to make significantly more peak hp is to rev the engines higher. The Kawasaki engines that Cosworth developed for Dixon in the UK to race in the GP's several years ago were being run to 16500 RPM for around that 50 peak hp with good range. Maintenance was high and the parts that needed replacing in general we're very special: try DLC coated pistons and con rods made from almost unobtainable, high strength, high purity steel normally reserved for F1.
50 hp from a 250 is 200 per litre; not a high figure with some sports bikes around that. Moto GP is around 60 per litre with good reliability. The Cosworth engineer who designed the modifications to the Kawasaki says that 80 hp would be possible if the motors could be reliably revved to well over 20000 RPM, probably 22000, 23000.
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