HP question...

[04'400ex'er]

My brother bought a used YFZ with a RE National motor in it. The receipt was provided with the sale, and read $3600 including the exhaust.
The head is engraved RE and the receipt is the same as mine was when I ordered their exhaust, so this motor is legit.

When he got it, He could pull me by about a bike length, and that was all. We couldn't figure out what was wrong with the bike, so I called Rossier. They told me their piston (near 14.5:1 JE) was only good for around 16 hours before it needed a rebuild, so we immediately blamed this.

Last month, we took the bike to SandTrax, a local engine builder, and had the piston replaced with a milder piston which we could use pump gas with and would not have a reliability issue with. He also had the crank mod done and some other small things, totaling out around $1100.

SandTrax put this bike on the dyno, and surprisingly it only pulled 49.8 HP. The torque curve was huge, and gave a nice seat of the pants feel, but the HP is still too low for a national engine.

I'm not sure if anyone else has had this issue with Rossier, and I am very pleased with their exhaust, but the motor is not as potent as it should be.
Anyone have any ideas???

[#17YFZRACER]

it looks like an 05, is it?

[04'400ex'er]

Originally posted by #17YFZRACER
it looks like an 05, is it? Yes sir... does it matter?

[#17YFZRACER]

it would still have the 439 in it. does it feel low on power when your riding (sluggish)? might just be a low dyno:confused: hows the clutch?

[04'400ex'er]

Originally posted by #17YFZRACER
it would still have the 439 in it. does it feel low on power when your riding (sluggish)? might just be a low dyno:confused: hows the clutch? It's not the clutch, it feels pretty strong when you get on it but the power pulls smooth all across the board.

The torque is there, and on the track this bike will run with any of them, but it just seems like it should post bigger numbers than this on the top end.

When you say 439 I am assuming you are speaking of the 439 grind Web Cams? Why would you say it has those particular cams?

[daddio]

'04 -'05 YFZ motors came stock 439cc's. It would have to be stroked (or an '06 crank installed) or bored oversize to make 450cc's.

[#17YFZRACER]

what he said^

[leveldrummer]

dont take too much stock in the numbers that a dyno produces, look at the curve, you want it to peak fast and stay up, which is what it sounds like yours is doing.

the bike might be geared down to pull harder and have a lower top speed.

im not familiar with national motors, but with most high end builds, they need to be rebuilt some what often, it could be that the engine is just slightly worn and a little loose. or it could be that the engine is built for a strong take off, and not a high top speed.

[jim_beam_racer]

well you could get more top end if you got a web cam ground for top end if you would have got that motor from rossier and it was set up for flat track i dont see why it wouldnt go fast enough

its the port job.... that motor will run with the pros how much hp do you think they have? most pro mx bikes only hit 52hp! cuz of the gearing!


what do you want to run mx or what?

[04'400ex'er]

Originally posted by leveldrummer
dont take too much stock in the numbers that a dyno produces, look at the curve, you want it to peak fast and stay up, which is what it sounds like yours is doing.

the bike might be geared down to pull harder and have a lower top speed.

im not familiar with national motors, but with most high end builds, they need to be rebuilt some what often, it could be that the engine is just slightly worn and a little loose. or it could be that the engine is built for a strong take off, and not a high top speed.
I believe the bike is geared pretty low now that you mention that, I know it's lower than stock. I never thought about that affecting Dyno numbers.

When we got the bike, it wasn't running but a bike length ahead of my R. I called rossier and talked with them about the engine, and they told us the top end needed a rebuild every 15 hours, and that is what we blamed all of this on. Thats why we put a lower compression 3 ring JE in it, for reliability issues. The new motor (JE and oil mod) still doesn't impress, I think the gearing is the next route to take.

And to the guy talking about the 439, I know what your talking about now. It had the big bore cylinder and piston in it, which were removed and put back to a 439, because they didn't make a piston that size which would take pump gas. So that's for sale BTW.

Its going to be an occasional MX bike, more of a dune and just aggressive trail bike. I was under the impression that most of the pros were touching in the upper 50s and close to 60.