Yz290f = Yz269f ?

holeshot

Crazy Russian
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#1
I just received the latest issue of Dirt Bike, where they test the Thumper Racing YZ290F. The only modification they make to the engine is sleeve and bore it for an 80mm piston in place of the stock 77mm piston. Sorry, but this brings the displacement to 269.4 cc.
An 83mm piston would bring the displacement to almost exactly 290cc, but I doubt if they could get the piston weight within 3 grams of the stock piston weight (as stated in the article) with this large an overbore (if such a bore is even possible without interfering with the water jackets in the stock cylinder).To make matters worse, they call it the YZ300F on the cover, to further puff it up.

I've heard of fuzzy math, but this destroys Dirt Bikes credibility IMO.

I was about to venture into what they said about using Mobil 1 in four strokes, but thankfully, Mweissen has it covered in another thread in this forum.

Not that I believe in anything I read in a magazine........:confused:
 
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#2
I called Thumper Racing to inquire about the kit. The piston size was mis-printed by Dirt Bike. They offer two different kits: 1) 290cc/83mm Wiseco/ sleeve. 2) 280cc/81.5mm Wiseco/replated cylinder. Pistons from Wiseco are due in the next week or so. If you want an eye opener, try calculating the compression ratios! It must be close to 14.5:1, unless they've found a way to raise the cylinder or lower the piston!

Mark
 

holeshot

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#3
That makes more sense. :cool:

It'll be interesting to read the posts from DRNr's (the real people) when they install and report on the overbore kits.
 
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#4
I dont like dirt bike mag. I subscribe to MXA an dirt rider , they are the only ones I trust to give me info. I was looking at the 125 test in all three mags and dirt bike differed in info from MXA and dirt rider
 

penguin

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#5
I was looking at the 125 test in all three mags and dirt bike differed in info from MXA and dirt rider
So DB mag has gotta be wrong? Dirt bike mag as been around a lot longer than the other 2 rags. MXA is in love with anything blue and Dirt Rider is a big apparel catalog :p

BTW: I subscribe to all 3, there is some info in all of them sometimes.
 
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#6
DB sucker

How about the 14,000 RPM Yamaha Screamer on last months cover? That was POWEROLL proto ? and they took photos at BBR,s open house!!
SSDBS how about as believable as the national enquirere:confused: