Kx500

[endurohero]

I have just finished most of the engine mods I have come up with useing TSR design programs and have just ran it up on a super flow dyno. Ihave ended up with 63hp @rear wheel,but I have no yard stick to compare to.The spread of torque to horsepower is 850rpm. Is this good or is there room for improvement.

 

[LJW]

At what RPM was peak HP?

 

[endurohero]

unfortunatly the dyno's rpm pick up was inconsistent at best , so peak hp was read @6850rpm , but its anyones guess if this is fact.

 

[LJW]

What modifications were made?

 

[cujet]

That sounds just about right for a nicely tuned big bore 2 stroke. In my mind, the 62 RWHP mark is about perfect for a 500cc 2 stroke in terms of power spread. I owned a 70RWHP CR5 and it was too peaky. Of course the big CR does not use a power valve and that skews the relative results.

In addition, turning a big bore to the higher RPM's that are required for big HP results in shorter engine life.

Chris

 

[LJW]

Originally posted by endurohero
unfortunatly the dyno's rpm pick up was inconsistent at best , so peak hp was read @6850rpm , but its anyones guess if this is fact.

Without accurate RPM data, it's impossible to calculate horsepower.

 

[motometal]

good point, isn't hp calculated using torque, rpm, and a constant?

 

[marcusgunby]

Ive been to a dyno that didnt use a pick up,and it can use rear wheel speed

 

[gwcrim]

good point, isn't hp calculated using torque, rpm, and a constant?

The constant is 5450. Notice that TQ and HP always cross at this RPM.

Without accurate RPM data, it's impossible to calculate horsepower.

I second that emotion.

How was it determined that the pick up was 'inconsistant'? If the graph went all squiggley at high RPMs that could have been caused by something else like ignition noise.

 

[endurohero]

The dyno used rear wheel speed to calculate torque and hp.with 14/42 gearing, the run starts @45 mph then full throttle acceleration to 105 mph.My understanding of this calculation of hp is done through how long it takes the weighted drum to reach the high specified speed from the low specified speed. So engine rpm can be used as a comparator in case of tire slip , because tire slip is unlikely under 135hp/250lbs dirt bike a comprimise had to be met. as for mods done I am in the middle of moving my house and shop my home computer is missing so i cant give definate specs only what i can remember and i have slept snce then so here goes exh 87deg trans 118deg all exhaust boost ports sharpened rads maximun width and raised 1mm , Trans #5 ports widened to max roof angle 10deg rear hook angle reduced to send gases toward front side of mains,mains widened closest to exhaust 1.5mm gases redirected toward front side of opposite #5 ports with 0deg roof angle with mains opening .4mm before #5 ports. boost port angle changed to 55 deg directing gases sligtly ahead of spark plug.Intake side changed very little in area and boyesen ports opened up only to removed massive casting flaws. Exhaust port outlet diameter matched to Pro circus desert pipe,stk carb

 

[Rich Rohrich]

Originally posted by gwcrim
The constant is 5450. Notice that TQ and HP always cross at this RPM.

The constant is 5252.

horsepower = (torque x RPM) / 5252

 

[gwcrim]

The constant is 5252.

Dang numbers always come around and bite me! :(

I'm no good at horse shoes or hand grenades either.

 

[Rich Rohrich]

LOL :)

 

[David Trustrum]

Most modern Dynos like the industry std Dynojet use wheelspeed & calculate time to accelerate a drum of given weight.

Sounds like a useful toy. I have a friend who is building a road registerable KX500 (which in NZ is quite possible) c/w larger brakes & RGV250 mags. Sadly he has been super slack as of late -- ‘cause I would love to have a ride. :aj: