99 WR400 Dyno Tuned -- The results are in...

Ok, I see William's point making sense to me, the fact of a jet not being a fixed oriface I cannot agree with. Jetting in based on an air/fuel mixture, a larger vacuum will pull more air, thus to retain the correct mixture will need more fuel.

2 vacuums sucking a pile of dirt: a small 1/4 hp hand held and a 3 horse shop vac. Both pickup the dirt for 20 seconds, if tge nozzle (jet) is the same the larger will pickup more of the dirt? Ok, good with that. But to maintain a ratio of dirt to air the same as the smaller unit, you need to increase the size of the hose, otherwise it'll just choke at the opening. Again, only so much can be pulled through that opening at a time.

Whatever, it's not worth going back and forth over, but I can definitely see how a too open airbox can cause a much larger than normal jet needing to be used.

And a dyno run is based off of the moving of a drum, the better the grip, the stronger the connection, the more recorded HP. A simply worn tire on a sportbike can read 3-5 hp lower than a fresh tire will.

Mike

not to derail.

but i cannot imagine he would have seen that much more power with a street tire vs knobby.

that bike is pretty stout 41hp and 29ft lbs isnt anything to shake a stick at considering its stock bore and stroke..

what did the bikes make from the factory- 37-39hp if that.

This is the first time I have ever heard of anyone dyno'ing with a knobby!

Everything I have even seen about dynos tells me if you don't have time to put a street tire on the wheel don't even bother to dyno but I understand where you were coming from with your testing.

Nice bike and good job.

not to derail.

but i cannot imagine he would have seen that much more power with a street tire vs knobby.

that bike is pretty stout 41hp and 29ft lbs isnt anything to shake a stick at considering its stock bore and stroke..

what did the bikes make from the factory- 37-39hp if that.

I would think more than that. The YZ400 was made to go head to head with 250 2 strokes at the time which made 45+ hp. And at that time I'm pretty sure the WR was exctly the same bike as the YZ, even same cams, only the exhaust cam timing was different, which most everyone switched to YZ timing anyways.

I would think more than that. The YZ400 was made to go head to head with 250 2 strokes at the time which made 45+ hp. And at that time I'm pretty sure the WR was exctly the same bike as the YZ, even same cams, only the exhaust cam timing was different, which most everyone switched to YZ timing anyways.

i have no doubt it made in the 45 neighborhood but thats at the crank im sure.

for that matter the 426 was rated at 47hp and mine worked over made 47hp- 39ft lbs at the tire(and this was with a head gasket that was leaking when the bike was under a load)

But to maintain a ratio of dirt to air the same as the smaller unit, you need to increase the size of the hose, otherwise it'll just choke at the opening. Again, only so much can be pulled through that opening at a time.

That's sound logic... if you were running into the peak possible fuel being sucked through a jet. Have you seen the size of even a 170 jet? You can move far more fuel than nescesary through that... howver on a WR400

Where you are incorrect is believing that jets are always at peak capability. That is not the case.

Where you are incorrect is believing that jets are always at peak capability. That is not the case.

????? Really? The main jet would be fully submerged in fuel, it will always suck based on engine suction and pretty much at maximum flow based on throttle position. The only time the main jet comes fully into play is at 3/4-full throttle, pretty much maximum suction of the engine, right? Intake suction time is based on intake cycle of the valve train.....what am I missing.

One of us isn't understanding something or was fed wrong info. I do understand that jetting isn't always according to a book, and motors you think may need more fuel don't always, but for some reason 2 identicle sized cabrs hooked up to a 500cc engine and another hooked up to a 400cc motor would call for the 500 to need more fuel and a larger jet in my book.

OK, I'll take your work for it as no one else has chimed in with an agurment one way or another.

Mike

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