2000-01 Honda CR250 Race Engine Build Pt3 (Final)

[dogger315]

OK, this is the last post on this engine build and will cover the top end.

The top end has recieved a lot of attention. The cylinder recieved "robust"
mid and up port work from Tom Morgan, who also machined the cylinder
head.




As planned, this engine is on a race gas only diet. I'll be using Renegade
SX2 race gas which is a leaded, oxygenated fuel worth 2 to 3 additional
horsepower over VP C12.

The piston is a Wiseco single ring GP model which is nearly identical to the
Honda HRC works piston. Here is a picture comparing the Wiseco to an OE
Honda piston.


And here is a picture of an HRC piston. Notice the HRC is cast instead of
forged like the Wiseco. You can see the identical windows in both.


The piston pin is a works HRC item. Lighter and stronger than OE. I also
had the pin REMed to match the crank pin.


Here is a picture of the piston installed.


Cylinder installed.


I finished the assembly with a VForce 3 and a Keihin PWK S with a power jet
and throttle position sensor.



You may have noticed the stator is missing. I made a last minute change
when I was fortunate enough to get my hands on a new works HRC stator
assembly. It hasn't arrived yet - so no pictures. I'll still be using a Vortex
IC and a custom harness to integrate the PWK S with the Honda electrics.

So, this one is pretty much done and ready to drop in the 2009 CRF250R
frame when it's finished.

dogger

[eprovenzano]

Dogger all I can say is WOW!    You done good...   

[Lolerbabop]

Oh come on.. Not the crf chassi.............. 

[dogger315]

You done good

Thanks!

Not the crf chassi

I know, a purest would use an 02-07 CR250 chassis.  Remember, this build is supposed to produce the
companion to my CR500 (2008 CRF250R) for a matched set.  I plan to use the same graphics and
everything else, just the numbers and backgrounds (Black on White) will be different.

dogger

[eprovenzano]

Remember, this build is supposed to produce the
companion to my CR500 (2008 CRF250R) for a matched set.

Ok, Ok I'll give that one to you as you know some of the best things in life come in pairs...    

[Lolerbabop]

Let me rephrase that. "Oh noeeee not the alu frame again....  " 

[Recovered]

SWEET CR500 dogger can't wait to see the CR250

[scotty dog]

That is so nice, you put together a sweet looking piece of machinery dogger, they are going to look so good together, top job

[dogger315]

Thanks!  Now that the motor is done, I'm getting some of the other components started.
I finished the brake assemblies yesterday.  I had TCR build me a pair of wheels using
their Red anodized billet hub, Excel spline drives and DID Dirtstar rims.  I'm doing the
subframe and airbox mods next.  Pro Circuit came through again by swapping a long
body shock for the short body that comes with the SSF "works" suspension.

I'm hoping to wrap it up sometime in the Fall.

dogger

[scotty dog]

lookin forward to it 

[cnrcpla]

It looks great    I can't wait to see the rest of the bike though

[Jeram]

nice motor.

one question though.

if you intend to get the exta hp of running racegas im guessing your running a very high comp motor and a custom short/fat pipe (cooler EGT)

a friend tested elf moto 124 (124 octane, $14/liter) on the dyno without the above and found that it made no more hp than pump gas


looking forward to seeing a vid of it running.

[dogger315]

a friend tested elf moto 124 (124 octane, $14/liter) on the dyno without the above and found that it made no more hp than pump gas

Yes, this motor has head the head milled and reshaped and has significantly higher compression.  The
race gas is necessary for the compression but the primary benefit is the lead content and oxygenation.
SX2's octane rating is only R+M/2 104 but it's been boosted with 5.5% oxygen.  Also, don't under
estimate the value of lead for a two stroke.  You remember what happened after the AMA adopted
the FIM fuel rules and banned leaded gas.  The works 125s were at an immediate additional
disadvantage to the 250fs as a result.  The gas I used before Renegade was VP MR-2.  This was
VP's "witches brew" that burned your eyes and nose and cost $25/gal.  The octane rating was only
98, but it really woke up a modified engine.

TMR recommends an FMF fatty pipe and shorty or ti-2 silencer for this combination.  That's what I'll
be running.

This is not my first time around with this engine.  I ran pretty much the same back in 2000-01. 
Those were the stoutest CR250 engines I ever raced, so naturally I wanted to duplicate that
same engine for my "ultimate" CR250 project.  I was really stoked when I found out TMR was
doing two stroke work again on a limited basis.  This motor is a close cousin to the motors he
built for Blackfoot Honda back when they were a Honda support team.

dogger

[Jeram]

a friend tested elf moto 124 (124 octane, $14/liter) on the dyno without the above and found that it made no more hp than pump gas

Yes, this motor has head the head milled and reshaped and has significantly higher compression.  The
race gas is necessary for the compression but the primary benefit is the lead content and oxygenation.
SX2's octane rating is only R+M/2 104 but it's been boosted with 5.5% oxygen.  Also, don't under
estimate the value of lead for a two stroke.  You remember what happened after the AMA adopted
the FIM fuel rules and banned leaded gas.  The works 125s were at an immediate additional
disadvantage to the 250fs as a result.  The gas I used before Renegade was VP MR-2.  This was
VP's "witches brew" that burned your eyes and nose and cost $25/gal.  The octane rating was only
98, but it really woke up a modified engine.

TMR recommends an FMF fatty pipe and shorty or ti-2 silencer for this combination.  That's what I'll
be running.

This is not my first time around with this engine.  I ran pretty much the same back in 2000-01. 
Those were the stoutest CR250 engines I ever raced, so naturally I wanted to duplicate that
same engine for my "ultimate" CR250 project.  I was really stoked when I found out TMR was
doing two stroke work again on a limited basis.  This motor is a close cousin to the motors he
built for Blackfoot Honda back when they were a Honda support team.

dogger

IMO an FMF fatty pipe will be too long for a high comp motor.

P1/T1 = P2/T2

(a higher comp motor has a higher internal pressure, therefore when this expands to atmospheric pressure in the pipe the temerature drops to lower than for a std motor, slower pulses means your pipe is now tuned for lower RPM, so the bike will sign off earlier.)

but if your only concern is having a strong bottom end and potent mid range than you should be a really great combo!

[Stusmoke]

Wow Dogger... Just wow. I thoroughly enjoyed reading this threads and I may have drooled a little.

Heres a totally unrelated question but one I want to ask anyway: How exactly does a clutch work? I've never properly understood it.

Good work, I can't wait to see the look on the fooper troopers faces