In my never ending quest for a high HP dirt bike, I would like to know how much HP has been extracted from Yamahas engine. Big bore kits, stroking, whatever. All is fair game in my book. Even turbo's. Has anyone past the 50RWHP mark?
Ask Ty Davis. when he exceeds the 50 hp level ,the bike blows up. Most mere mortals cannot handle 50 hp in the dirt anyway. there is a practical limit to how much hp is too much where dirtbikes are concerned.
A stock VOR 503 produces about 51 rear wheel HP. A KTM 520 about 52. The new VOR530 is going to beat that by about 5hp AND have a wider powerband. The VOR Supermotard itteration make even more. Bet both the big Husaberg and Big Husky make over 50 but I don't know for certain. Any of the big bore 2- strokes can put over 50 at the rear wheel! I think the VOR motor only weighs about 60lbs. I heard part of a discussion about building a bike for Pikes Peak and that was the number that came up when they were being compared to the old Rotax motors. I can check if your interested.:)
(Bet some of those mfg's would sell just a motor if you were going to build a bike...I know one that would):D
( You can find big bore two strokes cheap surrounded by motorcycles! LOL. Those Honda CR's can be made to crank out big HP reliably....and what about that Service Honda deal? Isn't that effectivly a plateform to build the Extreemly High HP dirt bike in a modern chassis?):eek:
Far from it. You already started another thread that is addressing the two-stroke versus four-stroke issues. Feel free to rant and rave to your heart's content in that thread. Just don't expect to take a thread asking a legitimate question way off-topic to serve as a vehicle for your personal agenda.
Love them or hate them, I could care less. Just try and stay on topic. :)
Thanks for the replys. Rich, I was hoping you would shed some light on this subject. I really like riding Yamaha's big bore, I think the bike is exceptional. however I do desire quite a bit more power. Might be a good candidate for a turbo! A 9 to 1 piston for that bike would be a real oddity.
Chris - To answer your question. With the stock valve area I believe the 400/426 engine is good for about 50-54 reliable sustainable crankshaft horsepower using standard leaded race fuel. Going to bigger bores and longer strokes will fill in the area on either side of the torque peak but the small valve area is a bit of a limiting factor. I think it's possible to raise the peak horsepower revs with changes to the appropriate hard parts, but IMO there is little use in doing this with the existing valve area. Lots of people are selling "big valve" mods but I've yet to see evidence that they flow substantially better than the OEM setup. If you are looking for big peak horsepower numbers look for a four-valve engine with valve area in the 32-34% of bore area range. If you want an engine with a BIG wide table top flat torque curve then the 5 valve Yamaha is IMO the best starting point.
If I were interested in doing a project like you suggested I would look to the 600 Rotax engine. The good flat track tuners can get HP numbers well within the range you are looking for and they can do it with a high degree of reliability. You can purchase an engine for a reasonable price. OEM and performance parts availablility is exceptional and general knowledge of the engine's quirks is excellent. There is a huge used market for these engines as well.
I dynoed my bike, stock standard. It is a 2002 KTM 520exc. Put out 47 RWHP. Changed the jetting, put a new end cap on the muffler and repacked it.
Now puts out 54 RWHP.
It was stated from one professional rider, can't remember who, that 55 RWHP is about optimol. Any more would be unusable.
I would of been happy with 47 RWHP, but the way it made power was crap. Now the tourque curve is as flat as a 12yo;)