I have a question for the mechanics in this forum not all the kids and quacks showing up lately. On the subject of h.p. Air in this forum has a 426ex with 39mm carb. race cam dmc pipe etc. etc. and he can run with the ds650 until top end on long drag races. Other than power to weight ratio how does this work? What I mean is a 426 vs. a 650 and it's close? How do they guage engine size with h.p? Why or how can a 426 produce similar h.p. to a 650 yet be so much smaller in engine size? Last question. All this leads me to think that a modified 400ex to a 480 or 500 (how ever big is possible whith the stock engine)with all the extras like carb,cam, filter, pipe etc. would probably bring it close in h,p to the new yamaha raptor and be able to outrun a ds650, Right? Your input is appreciated.

 

well one thing for sure, the bigger the motor, the more power it will make. one thing is that while that 426 might run close to a DS650, it is on the edge of what the motor might have been designed for. It will stress more parts out on the motor, whereas the 650 was designed to make that power, reliably. Dont get me wrong, hondas are very reliable but when you start pushin the limits on what the projected power they were designed for, you start losing reliablity. Puttin a race cam, you basically reving the engine more, more revs per minute than before, so more wear and tear occurs at a more rapid rate. On the other hand, if you mod a raptor or ds650, dont expect a modded 426-480ex to be even close to one of these bad boys. Like they say in the automotive world, theres no substitute for cubic inches. hope this helps somewhat

 

Actually, I've heard it as "There's no replacement for displacement".

You answered the question very well, but I just wanted to add one thing on power:weight ratio. Power, weight, and acceleration are very closely related. a 3000 pound vehicle with 300 horsepower will accelerate at the same rate as a 6000 pound vehicle with 600 horsepower, theoretically speaking. There are always many other variables to consider such as aerodynamics and traction, but for the most part this holds true.

So, a stock DS650, which weighs about 610lbs with a 150lb rider and puts out 40hp, will run side by side with a modified 400ex that weighs about 520lbs with a 150lb rider, if it's putting out 34hp ( 520/610 X 40 = 34 ). You can see how any weight difference in the riders can also make a big difference. If the DS650 rider were 200lbs and the EX rider were still 150lbs, the EX would only need 31.5hp to keep up.

 

Look at the gearing. a stock 400 runs at a 2.57 Ratio (i Think) and he is running his 400 at a 300. Thats low,low bottom end and not enough top end. the higher the ratio the lower the top speed. Airs bike is impressive and its fun to watch banshee and bomb owners expressions when they are beat by a 400. One bomb owner would go back to camp and strip components off to try and beat him. He finally went home.