Ok so yesterday i was out ridin w/ my buddy and this guy w/ a 400ex pulls up and wants to see how his bike would do against mine so we lined em up and we raced about 6 times switchin drivers and still pretty much the same result, i got smoked by at least 4 quad lengths. My motor must really be in need of a freakin rebuild or i need to invest in a different kind of bike cuz that was just sad. Oh yeah btw the 400 only had a white bros. E-series slip on......

 

If its the same engine since 1985 you might need new rings. Do a compression check first though.

There's no replacement for displacement. If you had your 350 stroked to a 400, you'd smoke him.

Gearing is also another consideration. You've changed your tires. Did you change the gearing at the same time. Are both the same speed at the top end or do you start gaining?

 

I'm pretty sure that this bike sat in a garage for about 15 years cuz some kid flipped it and his parents made him park it. About the gearing and tires, as for mine i have it geared at 14/40 and his was geared at 14/38? w/ 20" tires. Our top end is close to the same but man his just out-pulled mine through the gears. Some of the ppl i've talked to have said his is the fastest 400 they've ever rode and its stock cept for that pipe, factory glitch maybe? Anyway i'm definantly gonna spend some money on gettin the motor rebuilt w/ a cam and 10:5:1 comp. piston just cuz i hate gettin beat by somethin thats not much bigger than mine.

 

Your stock 350X had 22" tires with 13/40 gearing with a gearing ratio of 3.08

The 14/40 gearing gives you a ratio of 2.86 which would make you faster on top end if you still ran 22" tires.

So with the 20" rears and 14/40 gearing you are probably about 2-3 mph slower on top end but have a little better take off.

0.22 gearing ratio difference

The diameter of a 20" tire is over 6" smaller than a 22" tire.

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With my 200X I run stock 22" tires with stock 12/40 gearing in the winter and 20" tires with 13/38 gearing in the summer. 3.33 gearing ratio

I chose the 13/38 gearing just so I could use the same drive chain and my 200x is WAY faster with my summer set-up. About 6-7 mph faster! 2.92 gearing ratio

0.41 gearing ratio difference

Hope this make sense....Sidewinder sprockets used to do the figuring for you if you purchased sprokets through them.

Jeff

 

If you feeling brave use this formula to figure speed, this is the formula that Sidewinder came up with and compared it to actual radar gun reading and it was very close.

SPEED = P x T x S x r x 3.1416 x d x 60 x 0.08333 x 0.0001893

P = primary drive gear ratio (crankshaft to clutch)
T = trans gear ratios (first through fifth/sixth…just one ratio at a time, do just the top gear ratio if you want top speed!)
S = secondary gear ratio(number of rear sprocket teeth divided by the number of front sprocket teeth)

R = engine rpm ( if you want top speed enter the rpm at the rev limiter)
D = tire size (actual, for example all 22” are not the same height)


Different tires grow in size differently at different speeds but it a good formula for gearing changes if you have the time to do the formula.

Jeff

 

If you just want an easy way to beat that 400EX just put 5 lbs of air in you rear tire! I bet you WIN, you would be suprised on what a difference a little air makes.

Jeff

 

Well i've been lookin around for information on hop-up parts for my motor and i think i've picked out what i'm gonna put in it. I'm gonna start off w/ a 11:5:1 wiesco, a mild cam from webcams, install an extra oil cooler & buy super scoops. Non motor things are gonna be a new hi-flite red desert seat, 18" holeshot mxr4's, and gear it to 14/38. How much more power am i lookin at here over stock w/ just a slip-on? I'm sure its gonna be a night and day difference because my motor feels so worn out right now its not even funny. Oh and another question, am i going to have to put in a new clutch to handle the extra torque and power? Thx.