yz450 for road racing - best gear set??

Hello All

I have just obtained a 2005 yz450 engine and would appreciate some sound advice. Can anyone suggest the best gear set for the 2005 yz450 for road racing/supermono?

See www.tigcraft.com

The YZ450 has 4 gears, and as per the other posts, i see that a wr or a yz426 5 gear set will go straight in, and i understand that the yz426 'box is the closest ratio box.

Here are my stupid questions:

1. Is the yz400 gear set the same as the YZ426?

2. Anyone ever heard of a 6 speed conversion?

3. Cams - can anyone recommend some for road racing

4. Anyone have experience of a big bore conversion/stroker kit, from a point of view of reliability, and actual power gain.



The YZ450 has 4 gears, and as per the other posts, i see that a wr or a yz426 5 gear set will go straight in, and i understand that the yz426 'box is the closest ratio box.

Your information is quite faulty. The 426 transmission CAN be installed, but only with a great deal of custom fitting and machine work. Remember that not one single part of the four speed (other than your odd thrust ring or circlip) interchanges with any of the 5 speeds.

Your only drop-in option is the WR450 trans. See:


The '06 YZ450 box is some 12mm too wide to work. Someone may have pre-prepped YZ426 transmissions modified and available ready-to-use, but not without work.

Regarding "stupid" question 1: No, the YZ400 is actually the same as the first YZ250F trans. The 426 is bigger and has slighty different ratios.

The ratios are:

---yz400f/ yz426f/ 06yz450f/ 05yz450f/ 05wr450f

1st 1.929-- 1.846--- 1.929---- 1.929---- 2.417

2nd 1.563-- 1.533--- 1.533---- 1.563---- 1.733

3rd 1.278-- 1.278--- 1.278---- 1.278---- 1.313

4th 1.096-- 1.091--- 1.091---- 1.05----- 1.05

5th .952--- .952---- .952----- .000------.840

Hello, a few yz450 supermoto bikes down here in Oz run the 400 gearbox in them to get a higher 5th gear. As was posted before it isn't a straight swap and requires the clutch basket, cases and selector drum to be machined. Once that is done and its not a major job for an experienced mechanic, the entire 400 gearbox is put in. The beauty of this mod is if you are required to replace any damaged or worn gears, it is a straight foward job from there on. Personally I would start with trying a different cog ratio as its much easier and can be swapped back at anytime. cheers

The 400 uses the same clutch that eventually went into the 250F, also, and I can't see doing that much work to put a smaller, weaker, clutch and trans in the bike, although it apparently works.

The 426 swap can be done, and as I recall, it requires one or two of the shift rail pockets to be deepened, one of the crankcases to be fly cut for clearance, and the grinding of a couple of thrust washers. IMO, it would be a much more suitable trans to use for a beefed 450.

When the search function is back up, look for some posts by spadman450, or PM him. He's done a lot of work with this kind of stuff for kart racing.

Hi all, just finished talking to the race mechanic who originally built the bike I was talking about in the above post. Asked about the 5 speed conversion he did on the 04 450 and he gave me a fairly detailed explanation of the conversion but unfortunately my brain isn't as sharp as it used to be, and I wasn't able to take it all in in one go. The clutch used is the 450 clutch, and this is achieved(if I understood him right) by machining the clutch basket. He said it was an easy mod for him to do and only requirred some basic machining, doesn't require using any inferior parts and for them achieved exactly what they were attempting to achieve in regards to SM racing. The bike was raced by there team in 04 season and was then raced by a privateer in the 05 Australian SM championships. The gearbox never had any issues. He did bring up the point that doing this mod is proberbly obsolete now that the 06 and soon to be 07 bikes have the 5 speed gearboxs and money would be better spent(cost them about 1000AU dollars) on saving for one of the newer models. cheers

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