YZ454: I have a question.

You can put a 426 rod on the 400 crank and go with the 426 bore .And if you really want power stroke it to.


With those mods, how much power are we talking? I took my bike to Stroker performance to get a quote and one of the wrenches told me to put a 426 crank in my 99 YZ400 with a taller cylinder to stroke it to 440cc's. Sounds almost like what you were suggesting. How reliable is this set up and how much of a power increase is there?

I know one thing they did to the 426 was beef up the clutch. I would think that this may be the weak point in the set up your talking about unles you went with a Hinson clutch setup. Cooling the bike may be another concern, depending on the type of riding you do. Something else to consider is for the money your talking about, you could pick up a new 426. Food for thought...


02 YZ426

99 YZ400 (for sale :) )

If it's gonna be that much, I'll buy a CR or KX500. It's a Glamis (Sand Dunes) bike and I want more power but not at the sacrifice of reliability or the cost of a new 500. :)

Hey, as much as I swear by my 4 stroke, if your just going to be at the dunes, go with a CR500. Nothing jumps on top of the sand like a 2 stroke 500. For the money you're looking to invest in making your YZ into a grenade with 2 wheels, you could buy the CR, a paddle, and still have your YZF for the dirt. just a thought.

Jeff Bailey suggested you do what I did. I wanted a YZ400 so bad when they came out that I couldnt stand it. Then I raced one up Oldsmobile hill at Glamis. My prom date turned out to be a pig, so to speak. My 1988 CR500 had 20 bikes at the top on that 400. Then we swapped bikes, my 500 beat me to the top by about 25 bikes, all the while the front numberplate and controls, not to mention my face and helmet, were being sandblasted to nothingness by big red. The CR500 is king of the sand plain and simple. If your duning primarily, sell the blue one and buy an old red one.

what about the kx500? lol. why the cr(i ride a cr250) not the kx? ive never seen a kx500. what do they compair?

Sorry been gone,but a good hp gain on stock motors is 1hp per 10cc.My 454 is more than that it was the first 1 built and tested by yamaha team riders.As for breaking parts go ' I blame the riders for most the time .This bike has not broke any thing in side the motor and its a 98.But i have buiding and racing 4 strokes for 30 years even in the pro class be for it was cool. But to get to the point yes the 426 rod will fit right on YOU DONT HAVE TO PUT A LONGER BARREL ON TO STROKE IT.call powroll.Or shorten the rod.And the stroke works better than a bore any time in the dirt.

Sorry I mean you don't have to shorten the rod to do it.

I hate to ruin your day but at about 300cc about even between 2 and 4 srokes in 1985 I built a 660cc yamaha with trick every thing and to this day it's never be beat in the sand any where.This is a dirt bike that can do 105+ and not work hard at it. I have raced at that speed in the sand years a go.Now days it just sets in the shop ,just to old to ride a dirt bike that dammed fast.To put it this way it was cloked at 90mph shifting out of third with two more gears to go.

Thanks for the replies everyone. If I can have stroker or someone build me a stronger reliable motor for this bike, I'd like to go that route. My YZ will just out handle the big two stroke in anything tight. I need the reliability because I ride revving the snot out of the bike. I run with the big boys out there and would like an easier time of keeping up. I am hoping for 55 horsepower at the rear wheel but if that figure isn't feasable, I'll go back with a two-stroke. I just love the look on peoples face after they get taken for the ride of their lives by someone on a thumper! :)

The only difference between the 400 rod and the 426 rod is the diameter of the piston pin. But that would allow you to run a 426 cylinder (which bolts right on a 400 case). The 426 cylinder can eqasily and reliably be bored 2mm over and that gives you a 444cc motor (A.k.a. the "450 kit"). Thumper Racing had a batch of that sized pistons made (97mm bore) to fit the 400 rod. I got the last one and have had it for a few years now. It hasn't been apart since I originally put it together and has been stone reliable and brutally strong. I do have to be quite deliberate with the clutch and not abuse it or it will cook it in about 10 minutes if I'm not careful. The clutch that is in there now has been in for over a year of hard riding (and that's with Mobil 1 15w50).

Too much horsepower is just enough.

I will tell you that a 55hp two stroke is a big ? And that is 1 dyno rhe factory would like to have. A 55hp two stroke time bomb.

If you want that much power, what about Methanol? I know it works wonders on two smokes, especially in the sand. It also runs cooler than regular fuel, which would help fight overheating. It has some bad side effects though. Like, toxicity, and it corrodes aluminum. So drain the carb after every ride, and don't run the bike in an enclosed garage or trailer. And don't sniff the fumes!!! I was wondering if anyone has tried this stuff on Thumpers?

Methanol is burned twice as fast as gasoline. Besides the fact that it's alot of work to run (I.E. draining the carb and using after run oil), my ride time would be severely limited.

YZ454: You mean a 55HP four-stroke is a time bomb? Honda and Kawasaki both claim around 64hp for the 500 two strokes. Looks like I'm gonna have to go back to pre-mix to get what I want.

Yes they can claim all kinds of hp numbers.I tell you what if you want to run a 55hp two stroke you better have a factory parts truck to .Let me tell you in the 80s rick johnson and 1 other rider where running detuned flate track motors that honda claimed to have 85hp.Thy were in cj motocross frames.And were claimed to only put out 65hp.

454, umm.. I'd be willing to stand behind the 55-60 HP rating of a stock CR500, and a KX500. I think that's a pretty accurate rating. Also, what is a Honda CJ frame out of curiosity? I know that Rick Johnson and David Bailey raced the 500 nationals with production based CR500s with quite a few HRC parts in them, but rewelded stock CR frames. If I'm not mistaken they had 5th gear blocked, HRC cylinders, works showa suspension, disc brakes, and works swingarms.

You must have one of those dynos that take hp from the wrist pin like the factorys have for there ads.And yes they did ride big 4 strokes at carlsbad.And did'nt want to ride them every day the power put for the dirt was to much and made for hard bike to ride.

Are you saying that RJ and DB rode 4 strokes at the Carlsbad USGP? I know allot of people that rode big 4 strokes back in the day ( ATK's 630 HRC kitted Honda XR600's, and built TT 600's) and the power was anything but hard to manage. Very powerful, Very tractable, and best of all very easy to manage ( much like our YZ400/426 F's are today. The big disadvantage they had was the weight they carried. As far as I understand the weight was the only thing about them hard to handle. Are you sure your not accidentally inserting "4 stroke" where you meant to put "2 stroke" ?



All I want is 55hp at the rear wheel as well,but all I have been able to manage is 53. I have a 426 bored to a 440, I also have a stroked motor to a 440, but I like the power of the big bore. I have done the 426 rod on a 400 crank thing,and I even have a 416 cylinder and piston for that set up if you are interested. At 416cc there is no need to beef up the clutch, as it will take the extra hp. I will sell the parts cheap if you are interested. Lawdog

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