205 Pound /Alum Frame/ Great Suspension

The story of the one that got away....

Wish I had never gotten rid of it...

In 2010 a dealer in Ohio had a surplus of brand new 07 CRF250R's.... And was selling them for $3999.... 

Suspension re valved for woods and lowered 1" (still tall for me)... Bark Busters.... Bigger tank off x model... Heavier flywheel off x model... And the host of anything and everything I usually do to my bikes...labor of love...

Light and wonderfully manuverable in the woods...

And a powerband that was bordering on Nirvana... Pure Joy...

It was my last personal project before I sold my dyno to my friend Christopher/Sredrum...

The bike dynoed in stone stock at around 33hp....

All of my engine mods , as is always my goal, were aimed at more power everywhere in the band...  Once you have to give up something to add somewhere else, I could care less, I'm out... Personal preference ...

I was still doing business with CP at the time and they made me a custom 14+ comp piston to my spec request...

Hot Cams stage 2 cam...

Sredrum bored the FCR to 41mm..

And I did HIgh Velocity Portwork  with epoxy fill... Floor and roof raised... Better SSR... And smaller than OEM port volume by 20%....

The bottom graph was the best of the stocker runs.... The rest are overlays of a bunch of the modded runs to show how consistent it all was...

Significant percentage gains everywhere in the band....  And no giving up anything until the rev limiter pulls the plug at 13k.... Couldn't have been happier with that set of mods...

Screenshot_20170804-050505.png

Next up....

What could I get from a 20cc bore kit?

Cylinder works made a 13:1 bore kit to make it a 270cc with a little less compression....

Bigger size engine even increased the velocity of the porting arrangement...

Torque Baby :)... My favorite...

Didn't lose on top....pumped up the midrange... All Good

So this is fully modded 14:1 250 vs same setup as 13:1 270...

IMG_20170808_075357.jpg

Edited by mixxer

So overall the gains were around 20ish percent in the low to mid...

Torque over 20ft lbs....

My best runs made just a heartbreak amount under 40hp... 39 and change...

But no weak spots anywhere...

Power plateau instead of power peak...

And sold it because I wanted xr like simplicity.... Actually traded it for 2 xr250s...

The 270 was getting over the 30 hp mark a full 2000 rpm sooner than the stock bike...  Power was responsive and linear.... And was over 30 hp for 5000 rpm... 

The difference riding the bike was even bigger than the Dyno graphs show... In the woods it was non tiring and a true joy to ride fast....

I'd still take a KTM 200 over it if I had to choose a full-size bike. Might be down a touch on peak horsepower, depending on the pipe and tune, but a stock engine can make about 22 ft/lb. of torque, it's lighter, easier to start, doesn't flame-out like many 4-stroke mx bikes do at low RPM, and about as reliable as it gets for a 'modern bike'. Just stirring your pot a little, hehe.

2 hours ago, mx4god said:

I'd still take a KTM 200 over it if I had to choose a full-size bike. Might be down a touch on peak horsepower, depending on the pipe and tune, but a stock engine can make about 22 ft/lb. of torque, it's lighter, easier to start, doesn't flame-out like many 4-stroke mx bikes do at low RPM, and about as reliable as it gets for a 'modern bike'. Just stirring your pot a little, hehe.

Here's the killer though....

I have dynoed a zillion 2 strokes and the peak HP/TQ readings sound good, but their graphs and bands really don't compare to a 4 stroke... The 4s have much more HP over a much wider powerband.... 

I built the bike in the graphs as my woods bike...

Have the carb taken to 43.5mm...

Make the ports match the carb... Go bigger on valve diameter... Get a real top end biased cam.... There is a lot left on the table with that more power everywhere tune....

4 stroke bandwidth is soooooooo much wider .... 

The one here has a heavier flywheel... I have always been a fan of wide torque curves and some flywheel inertia.... Racing 500 2strokes thru the gears was one of my favorite things to do with my killer setup 450x... Shift too early...didn't matter...torque everywhere... Hold a gear to long..didn't matter... No power fade to the rev limiter.... Just keeps walking away no matter what I do...

3 hours ago, mx4god said:

I'd still take a KTM 200 over it if I had to choose a full-size bike. Might be down a touch on peak horsepower, depending on the pipe and tune, but a stock engine can make about 22 ft/lb. of torque, it's lighter, easier to start, doesn't flame-out like many 4-stroke mx bikes do at low RPM, and about as reliable as it gets for a 'modern bike'. Just stirring your pot a little, hehe.

Yup 22 ft lbs of torque but at peak rpm. As soon as it drops off the peak power band she looses all that torque fast as Mr. Mixxer said. 

Yep, I realize that's peak power. Although there's quite a few mods that would increase and broaden the power similar to what you did to the 250F. I'm not saying you're wrong and I'm right. Just wanted to express my opinion, ha. I like the power curve of my XCW. Other than the off-idle torque, it's actually fairly similar to my 230F, but more everywhere else.

Mixxer, I'd love to try one of your modded bikes, especially this 250F if you built another.

I don't do much hill-climbing or power-robbing sand riding, so 30hp is usually plenty for me when I'm trail riding. Another 10+ HP doesn't hurt when you're at 11-13k elevation, though!

I have built a few yz250f/290s for friends in the past....

It's still on my wish list to do a 290 for myself... 

Maybe someday...

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