YZ144 getting close to 45 hp

[harrperf]

Just finished tidying up a motor for a kid who is chasing loretta's this year in california (schoolboy 2 bike).

I put a lot of time into the exhaust port and tried a few things I hadn't made work yet on previous builds in hopes to chase down some more ponies.

Well - on avgas we are getting close, with vp 4.4 or mrx02 it would be over 45 but that's not a realistic comparison for most people..
 

Im tickled pink on the results and cant wait to try even more things yet ?

 

 

Edited April 26, 2014 by harrperf

[SmokinJoe90]

Looks like a good curve wonder how long the top end will last

[450DK]

Which exhaust-system are you running on this build? 

 

Kim

[nickmell]

Is this with the long rod stroker or stock length rod?

[Bruce372]

Have you got a stock motor on that dyno to reference?

[BRM]

Have you got a stock motor on that dyno to reference?

 

Exactly what I was about to ask.

[harrperf]

Is this with the long rod stroker or stock length rod?

 

The long rod is not a stroker....it's a long rod - which is a common mis conception but think about it for a second and it will make sense.  Our long rod motor runs the same length rod a large amount of the current kart motors do.

The long rod produces huge gains from 5k up - almost 2lb/ft more torque through the curve than the non long rod - but peaks slightly earlier in the rpm range.  it's a faster engine around the track by a mile but doesn't make more peak hp as we have it set up.  If I chase down more rpm on that set up, it will produce more power but iMHO it's slower that way around a track.  Most riders want to come off the turn around 8k - and that's where you start your "area" under the curve for acceleration

And this is the non long rod - run of the mill 144.  Requires minor case modifications anyone can do if they have a dremel (mostly clearance for 144 piston) - and ignition box.  Without the box it's at 42.  The run shown is an fmf fatty, but a stock pipe performs very similarly on this motor package.  The PC continues to perform poorly for me - its down about 1 horse across the curve only after the ignition curve is changed to suit the PC pipe vs the fmf or stocker.  

 

I've attached a stock chart.  I finally got my hands on a brand new bike off the show room to test, which performed the best I've had a stocker do to date, as all other stockers have been rebuilt new but "old" motors.  I've heard from some gp guys that old cases lost power for them after 10-15 hours which I find weird - but I can say with every other stock motor we've tested being in the 33.5-34 range when totally freshened - I can now see it being possible.  The stocker shown is on slightly better performing gas (vp110).

 

[yamaha7442]

Thats Wicked !

[nickmell]

The long rod is not a stroker....it's a long rod - which is a common mis conception but think about it for a second and it will make sense.  Our long rod motor runs the same length rod a large amount of the current kart motors do.

The long rod produces huge gains from 5k up - almost 2lb/ft more torque through the curve than the non long rod - but peaks slightly earlier in the rpm range.  it's a faster engine around the track by a mile but doesn't make more peak hp as we have it set up.  If I chase down more rpm on that set up, it will produce more power but iMHO it's slower that way around a track.  Most riders want to come off the turn around 8k - and that's where you start your "area" under the curve for acceleration

And this is the non long rod - run of the mill 144.  Requires minor case modifications anyone can do if they have a dremel (mostly clearance for 144 piston) - and ignition box.  Without the box it's at 42.  The run shown is an fmf fatty, but a stock pipe performs very similarly on this motor package.  The PC continues to perform poorly for me - its down about 1 horse across the curve only after the ignition curve is changed to suit the PC pipe vs the fmf or stocker.  

 

I've attached a stock chart.  I finally got my hands on a brand new bike off the show room to test, which performed the best I've had a stocker do to date, as all other stockers have been rebuilt new but "old" motors.  I've heard from some gp guys that old cases lost power for them after 10-15 hours which I find weird - but I can say with every other stock motor we've tested being in the 33.5-34 range when totally freshened - I can now see it being possible.  The stocker shown is on slightly better performing gas (vp110).

 

📎Screenshot (103).png

O ok I Thought you said the long rod was run with a stroked crank also, I miss understood. Is It possible to run the long rod crank with ported 2mm cylinder set up for a stock crank? Im working on rebuilding a 05 I have and just got my cylinder back from plating so I dont want to go through it again to get it ported for the long rod but if its possible to use my cylinder with it I may be interested.

[DirtRider500R]

I'm impressed. And talk about a skinny power band 

[harrperf]

O ok I Thought you said the long rod was run with a stroked crank also, I miss understood. Is It possible to run the long rod crank with ported 2mm cylinder set up for a stock crank? Im working on rebuilding a 05 I have and just got my cylinder back from plating so I dont want to go through it again to get it ported for the long rod but if its possible to use my cylinder with it I may be interested.

 

 

Ported 2mm cylinder set up?  

 

It is possible to run a long rod lower half with a "normal" top half.

 

[nickmell]

Ported 2mm cylinder set up?  

 

It is possible to run a long rod lower half with a "normal" top half.

O sorry, I meant ported  2mm bore cylinder.. So since its possible to run that cylinder with it what kind of power difference would there be between the long rod set up and a stroker setup, what is the price for the rod kit and spacer plate, and what other mods have to go with it?

[harrperf]

O sorry, I meant ported  2mm bore cylinder.. So since its possible to run that cylinder with it what kind of power difference would there be between the long rod set up and a stroker setup, what is the price for the rod kit and spacer plate, and what other mods have to go with it?

 

 

the long rod adds huge torque.  i dont know what's been done to your current cylinder, but if the transfers weren't raised to much and the exhaust was raised some - it's a good candidate. 

I've attached what a stock 125, then a modified cylinder, then exact same modified cylinder on our long rod set up looks like.  The torque curve is the telling difference - a new yz250f makes 40 horse for me, but we all know a 40 horse 125 isnt' even close around the track - it's the additional torque early in the curve that makes the 250fs faster.

 

[Marten]

How long rod do you use? 110mm from Ktm or

the long rod adds huge torque.  i dont know what's been done to your current cylinder, but if the transfers weren't raised to much and the exhaust was raised some - it's a good candidate. 

I've attached what a stock 125, then a modified cylinder, then exact same modified cylinder on our long rod set up looks like.  The torque curve is the telling difference - a new yz250f makes 40 horse for me, but we all know a 40 horse 125 isnt' even close around the track - it's the additional torque early in the curve that makes the 250fs faster.

 

📎Screenshot (106).png

[Robbyg91]

Can someone explain what a "stroker" crank and long rod is?

Or how they work?

With a long rod is the head modified to let the piston travel up further?

[Bruce372]

very impressive, i remember when suzuki copied the ktm long rod engine back in 2004, the RM125 was still a little weak, but a real wolf in sheeps clothing once it was worked a bit.

[1987CR250R]

Can someone explain what a "stroker" crank and long rod is?

Or how they work?

With a long rod is the head modified to let the piston travel up further?

 

A stroker crank increases the displacement of the engine by increasing the stroke.  A long rod has a longer connecting rod and increases the amount of time the piston spends at the top and bottom of the stroke but does NOT increase the displacement of the engine.  A spacer is usually added underneath the cylinder to accommodate the added length of the rod while still allowing the use of the stock piston.  Moving the wrist pin closer to the crown is another option but requires expensive custom pistons.

[Johnny_On_The_Spot]

Very cool.  Can you display avg power and torque for those 3 graphs?  That really shows power under the curve well.

 

Have you played with any of the Athena 125cc Factory kits with a long rod setup?

[MXRider72]

I think that bike makes as much hp as my 250. I want to ride it. 45 hp and sub 200 pounds? Awesome!

[ah665]

That would be a fun bike to ride, for sure (as the stocker already is). Great numbers on your build!