How much Power?

650ed wrote:

TexasKZ wrote: 650Ed,
I completely agree with your point, though there is one thing that makes me suspicious of that particular chart.. The horsepower and torque lines should cross at 5250 rpm, not at 6900+.. As I understand, torque is measured, but horsepower is a calculation of torque across time, and because of the nature of the formula, torque and horsepower will always be the same at 5250rpm.

The charts is from the Kawasaki Service Manual. Because it does not use separate scale lines for the torque scale, it doesn't maintain a relationship between the hp and torque curves. In other words the torque and hp portions of the graph are both accurate, but they should be viewed as two separate graphs rather than being compared to each other within the same chart. I looked at several other performance graphs for different KZ models, and Kawasaki used the same approach in those. As a result, the torque and hp lines cross at various different places depending on the scale of the chart. If Kawasaki had used separate horizontal lines for the torque scale, they could have established a relationship between the torque and hp curves which would have made the charts a bit easier to use. Ed

Any chart simultaneously showing power in horsepower and torque in ft-lbs must cross at 5250. It is just purely math of units.

Any chart with those units and not crossing at 5250 is bogus. Not really any other way around it. Many magazines get that wrong, by the way, which is why magazine articles are not to be trusted blindly. If they get basic math wrong...

650ed wrote: No, at 5k rpm the bike is not going to take off like a rocket.

Ed is spot on. At 5k, the 550 wallows a bit with a bunch of throttle. You must downshift at least one gear, or two if you really want it to scream. Even at 6k, it'll be a little sluggish. The 500 will likely be very similar to the 550 since most internals are the same except for bore.

If you are getting 180 psi across all four, the motor is in pretty good shape. Even a gpz, with higher compression, is doing good with 180 across all four cyls.

Like Texas said, you may want to check the valve lash at some point. On the 500/550 motors, the first symptom you will get if the lash is too small, is the motor will stall or run really rough right after coming to a stop right after a hard, 20-minute, highway run. After a few minutes it will return to running fine. If that is not happening, you probably won't have to worry about lash yet.

If you decide to check lash, you probably want to read the warning in my sig.

Incidentally, I think that factory graph is wrong too.

The hp scale is 10 times the torque scale in kg m.

The crossover should happen at 7261 rpm assuming 1 hp is 33,000 ft lbs per minute (most common definition of horsepower).

If they are using metric horsepower, it would be slightly different.

loudhvx wrote:

650ed wrote:

TexasKZ wrote: 650Ed,
I completely agree with your point, though there is one thing that makes me suspicious of that particular chart.. The horsepower and torque lines should cross at 5250 rpm, not at 6900+.. As I understand, torque is measured, but horsepower is a calculation of torque across time, and because of the nature of the formula, torque and horsepower will always be the same at 5250rpm.

The charts is from the Kawasaki Service Manual. Because it does not use separate scale lines for the torque scale, it doesn't maintain a relationship between the hp and torque curves. In other words the torque and hp portions of the graph are both accurate, but they should be viewed as two separate graphs rather than being compared to each other within the same chart. I looked at several other performance graphs for different KZ models, and Kawasaki used the same approach in those. As a result, the torque and hp lines cross at various different places depending on the scale of the chart. If Kawasaki had used separate horizontal lines for the torque scale, they could have established a relationship between the torque and hp curves which would have made the charts a bit easier to use. Ed

Any chart simultaneously showing power in horsepower and torque in ft-lbs must cross at 5250. It is just purely math of units.

Any chart with those units and not crossing at 5250 is bogus. Not really any other way around it. Many magazines get that wrong, by the way, which is why magazine articles are not to be trusted blindly. If they get basic math wrong...

I agree that it is desirable for a chart to have the various measures calibrated so they map to each other and that charts are more meaningful (or at least easier to read) when this is done. However, that doesn't mean the measures in this chart are not accurate (in fact they are accurate); it only shows that the person making the chart designed it to be used as a separate chart for hp and torque since the scales of the two measures are not calibrated in a way that makes the intersection of the two curves meaningful. The person making the chart in this case chose to use the same set of horizontal lines for both torque and horsepower without trying to make the two curves relate to each other. Consequently, the chart MUST be read as one chart for hp and a separate chart for torque. The chart actually is accurate when read that way, but if you try to match hp with torque using this single chart it will not appear to be accurate because the lines for the torque curve were not calibrated to map to the lines of the hp curve. It's difficult for me to explain in words, but maybe the example below will help. Notice in the modified chart I took the same chart but moved the torque readings down two lines. The torque levels for any given rpm are still the same as they were on the original chart, but their relationship to the hp readings have changed. The torque levels shown per rpm are still accurate as are the hp levels , but again one cannot look at the intersection of the two curves (it has moved) and expect it to occur at the correct level because the scale for hp on the left side of the chart and the scale for torque on the right side of the chart are not calibrated to map the two performance measures to each other. The chart is still accurate for each measure, but it shows a confusing picture because most folks looking at the chart naturally assume the scales are in sync. Ed

ORIGINAL CHART


MODIFIED CHART

oh for christ sake buy a bigger bik e if you want to go faster

Oh shit, you are right.
I saw the 40 and 4.0 on the scale and assumed a 10:1 ratio. But you are correct, the scales are not a simple multiple ratio.

Sorry about that and making you do all the typing.

At 7261 RPM it does appear the actual value for torque and hp are at a 10:1 ratio as they should be.
Sorry Kawasaki for doubting.

Yes Ed, I see what you mean. If 40 lb-ft was on the same line as 40 hp, the lines would cross at the proper place. I guess it just offends my twisted sensibilities.

Downshift then nail it, 6th gear is OD, not for blasts. the 550 is plenty powerful, definitely not a slouch

No its defiantly isn't a slouch, but it isn't practical nor comfortable to keep the bike revving above 5k for extended periods of time on the highway.

Currently I have 16/48 sprockets going to replace them with new chain and 16/40

Stock airbox and new OEM Airfilter new airbox manifolds engine side age is unknown plan on replacing.
Stock jetting 90main/32pilot, airscrews about 0.75 turns out floats 3.5mm below the bowl casting, needle clip position unknown. Carbs synced.
Recently had valves adjusted almost time to do it again. doesnt die after highway use has fresh oil
has a 4-1 aftermarktet exhaust, I am not sure what brand but it isnt really too loud.

I dont really want to go faster, not that I wouldn't mind that but just to figure out if this bike should be good at highway speeds/ travelling.

I think you meant 16/38.

There is a speed/rpm calculator on my main site, but you have to download it and rename it to get it to work.

It was designed in the days of 55mph being the rule in the U.S., so it was fine for back then, but if you cruise at 80, a taller sprocket would be nice. If a 17 will fit, I'd probably try that. Going smaller in back puts a bit more tension on the chain than going bigger in front (for a given speed).

5,000 rpm @ 100kph is correct for the z500. If you expect to loaf along at low rpm while going 100kph you will need a bigger or different bike. The Z500 has pep at high rpm, but it has little power at low rpm; it was never intended to be a low-rpm highway cruiser. Changing the sprocket ratios isn't going to buy you much because if you change the ratio to a point where the bike is only turning 4,000 or so rpm at 100kph your hp will be too low to run properly at that speed. 5,000 rpm is just a tad more than half of your engine's redline - it is not by any stretch of the imagination stressing that motor, so my advice is that you simply accept the fact that the bike is engineered to run at that speed; it is not a low revving engine. Ed

Yes you are right I meant 38,

Crap I had this all backwards, I have a 40 rear currently and am planning on going to a 38 to correct it all.

I don't mind revving the bike, it is more the vibrations. through the handle bars and pegs.