YZ450F vs YFZ450 engine...

[troyfisher123]

Can somebody elaborate on the differences in the engines? I know there is something with the exhaust cam, the displacement is different. Is it the bore or stroke that is different? What is it that gives the bike engine the 7-9hp advantage? I know the number varies on who you talk to, but I know it is a fair amount. I won the bike, and a friend has the quad, and we're curious as to what exactly the differences are. In detail preferably. Thanks!

[RaptorRacer888]

You might have to register to see the post, but it is worth it, its a detailed post of the differences of the YFZ and YZF motor. Its a YFZ rider converting his engine to YZF dirtbike specs.

http://www.bluetraxx.com/phpBB/viewtopic.php?t=82395&highlight=

[grayracer513]

The displacement, bore and stroke are the same, at least on the current models. The YFZ is an electric start, so it uses a different left crank axle, but the crank is otherwise the same. The crankcases are unique to the bike on all 3 of the different 450 models, although, more WR parts will interchange with a YFZ than with a YZ. The YFZ 5 speed is a closer ratio gear set than the WR450 is. I'm not certain as to whether they can be interchanged, but I'd like to know that. As far as the difference in power, I would imagine that the YFZ uses a cam similar to that in the WR, and I know that the OEM exhaust is a restriction to the power output.

[troyfisher123]

The quad engine was 439cc (until the 2006 model year), and the bike version is 449cc. So either the bore or the stroke has to be different. From what I hear, the '06 quad had the exact same engine as the bikes do now.

[Spadman450]

Yamaha Website….YFZ450 Features:

Liquid-cooled, 439cc, 5-valve, DOHC, four-stroke with titanium valves features 95mm bore and 62mm stroke (vs. 63.4 on a WR or YZ) delivering, broad torque curve (for instant hook-up) with high over-rev capacity and crisp, linear throttle response.

I would also like to know if the YFZ transmission would bolt into either a WR or YZ....

Transmission WR [YZ] (YFZ)

Primary Ratio 62/22 2.818 [62/22 2.818] (62/22 2.818)

Chain Drive 50/14 3.571 [48/14 3.429]

1st Gear Ratio 29/12 2.416 [27/14 1.929] (29/12 2.416)

2nd Gear Ratio 26/15 1.733 [25/16 1.563] (27/14 1.929)

3rd Gear Ratio 21/16 1.312 [23/18 1.278] (25/16 1.563)

4th Gear Ratio 21/20 1.050 [21/20 1.050] (23/18 1.278)

5th Gear Ratio 21/25 0.840 [N/A] (21/20 1.050)

Sorry the columns format does not line up, but use the brackets to decifer.

Notice the YFZ ratios are the same as the YZ with a WR 1st gear ratio.

Does anybody out there know the answers????????

[grayracer513]

Notice the YFZ ratios are the same as the YZ with a WR 1st gear ratio.

It's sort of the opposite approach I was hoping for, which would have been the YZ 4 with an extra on top. This is the YZ 4 with one underneath. But it is a wider spread than the YZ426 5 speed, and closer than the WR. It shows two different part numbers for the shafts than the WR does, but all 4 bearings are the same, and they use the same clutch boss.

You could gear the bike 15/47 and get a stock overall low gear ratio and add over ten MPH on top.