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Stelvio996

Boring/Stroking WR450F to 475cc

8 posts in this topic

With the new AMA/ISDE rules, Class 3 requires that 4 strokes be over 475cc. I'm trying to find anyone that is familiar with kits that can get to 450 to 475. I appreciate any and all help.

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I would start with Thumper Racing in TX.

Ride fast - take chances.

Chad

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I think you're gonna be pushing it. That'd make the water jackets

really thin...if you gotta ride Class 3, you may want to consider

orange...

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Thumper Racing has a proven kit that was tested by Dirt Bike magazine last year and was very well received. :thumbsup:

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Thanks for the responses.

I checked Thumper Racing's website and they don't show a 450 to 475 kit. The website may need an update I'll call or e-mail them.

I understand about the reliability issues. At last years ISDE in Brazil, Stefan Everts won on a 505cc Yamaha. I guess I could call him. :thumbsup:

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YZF

WISECO makes 2mm oversize kits for the older models of YZ400 and 426F plus the new 450. For those models we have kits ranging from 420,444, and 472cc with two choices of compression ratios; 12.5 and 13.5:1 We also have 2mm high compression kit for the YZF250 that makes it 262cc and 13.2:1 This kit doesn't seem like a big displacement change but it makes a big difference in throttle response and offers a "more of everything" power increase. Our kit price with boring, NICOM plating, piston and gasket kits is only $350 Compare that to RPM's $2,300 300cc package. Our kit is 40cc smaller (about the size of an RC car engine) and $1,950 less expensive.

>> http://www.eric-gorr.com/services/fourstroke.html

470CC - YZ 450F BIG BORE KIT 2003-2004 (Bore 97mm)

New dyno of torque and power for Stock

and Max Power coming soon.

images/Kit-yzf490cc.jpgimages/Kit-yzf490cc.jpg

Stage one: $450.00 Uncoated piston and top end gasket kit.

Stage two: $495.00 With Xtreme piston and gasket set.

Stage three: $670.00 Head porting, with Xtreme Piston and gasket kit (with valves removed, valve seals not included).

Stage three: $745.00 Head porting, with Xtreme Piston and gasket kit (with complete head, this includes new valve seals).

Stage four: $1045.00 Head porting, with Xtreme Piston and gasket kit (must have complete head, this includes new valve seals, springs and intake / exhaust Hot Cams ).

490CC -- YZ 450F BIG BORE KIT 2003-2004 (Bore 99mm)

Stage one: $500.00 Uncoated piston and top end gasket kit.

Stage two: $545.00 With Xtreme piston and top end gasket kit.

Stage three: $720.00 Head porting, with Xtreme Piston and gasket kit (with valves removed, valve seals not included).

Stage three: $795.00 Head porting, with Xtreme Piston and gasket kit (with complete head, this includes new valve seals)

Stage four: $1095.00 Head porting, with Xtreme Piston and gasket kit (must have complete head, this includes new valve seals, springs and intake / exhaust Hot Cams).

>> http://www.maxpower-engines.com/bb-yamaha.htm

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for SM the AMA rules for open bikes required the OEM displacement to be within their requirements.

Be very careful.

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