how to raise max RPM's

I typed a whole page, hit send and lost it all. This is my short version. To raise the rpm range the piston speed must increase.

Stock KZ650: @ 12,000 rpm's
62mm x 54mm

40 Cubic Inch (162.5cc per cyl.)

4,252 FPM

70.866 FPS


KZ650 with a 810cc Kit: @ 12,000 rpm's
69mm x 54mm

49 Cubic Inch (202.5cc per cyl.)

4,252 FPM

70.866 FPS
(the same FPM & FPS, as a stock KZ650)


KZ650 with a 810cc kit & a 1/4" stroker crank (6.35mm) @ 12,000 rpm's.

This comes out to be 901cc's.
69mm x 60.35mm

55 Cubic Inch (225.25cc per cyl.)

4,752 FPM (500fpm or 12% over stock)

79.199 FPS (8.33fps or 12% over stock)


Now I wanted to take it, alittle further. @ 14,000 rpm's

5,544 FPM (792fpm or 30% increase, over stock)

92.399 FPS (13.2fps or 30% increase, over stock)

I guess my next question would be, can a GPZ head flow enough to feed this motor? And what size carbs would it take?

kzz1p wrote:

I typed a whole page, hit send and lost it all. This is my short version. To raise the rpm range the piston speed must increase.

Stock KZ650: @ 12,000 rpm's
62mm x 54mm

40 Cubic Inch (162.5cc per cyl.)

4,252 FPM

70.866 FPS


KZ650 with a 810cc Kit: @ 12,000 rpm's
69mm x 54mm

49 Cubic Inch (202.5cc per cyl.)

4,252 FPM

70.866 FPS
(the same FPM & FPS, as a stock KZ650)


KZ650 with a 810cc kit & a 1/4" stroker crank (6.35mm) @ 12,000 rpm's.

This comes out to be 901cc's.
69mm x 60.35mm

55 Cubic Inch (225.25cc per cyl.)

4,752 FPM (500fpm or 12% over stock)

79.199 FPS (8.33fps or 12% over stock)


Now I wanted to take it, alittle further. @ 14,000 rpm's

5,544 FPM (792fpm or 30% increase, over stock)

92.399 FPS (13.2fps or 30% increase, over stock)

I guess my next question would be, can a GPZ head flow enough to feed this motor? And what size carbs would it take?

i figured out years ago that according to dear ol dads formula it takes around 930cfm and change to feed a healthy 496" bigblock,so i say play it safe and put a 1050 dominator on that 650 and let her rip.dont forget progressive linkage to get it rolling! :laugh:

PLUMMEN wrote:

kzz1p wrote:

I typed a whole page, hit send and lost it all. This is my short version. To raise the rpm range the piston speed must increase.

Stock KZ650: @ 12,000 rpm's
62mm x 54mm

40 Cubic Inch (162.5cc per cyl.)

4,252 FPM

70.866 FPS


KZ650 with a 810cc Kit: @ 12,000 rpm's
69mm x 54mm

49 Cubic Inch (202.5cc per cyl.)

4,252 FPM

70.866 FPS
(the same FPM & FPS, as a stock KZ650)


KZ650 with a 810cc kit & a 1/4" stroker crank (6.35mm) @ 12,000 rpm's.

This comes out to be 901cc's.
69mm x 60.35mm

55 Cubic Inch (225.25cc per cyl.)

4,752 FPM (500fpm or 12% over stock)

79.199 FPS (8.33fps or 12% over stock)


Now I wanted to take it, alittle further. @ 14,000 rpm's

5,544 FPM (792fpm or 30% increase, over stock)

92.399 FPS (13.2fps or 30% increase, over stock)

I guess my next question would be, can a GPZ head flow enough to feed this motor? And what size carbs would it take?

i figured out years ago that according to dear ol dads formula it takes around 930cfm and change to feed a healthy 496" bigblock,so i say play it safe and put a 1050 dominator on that 650 and let her rip.dont forget progressive linkage to get it rolling! :laugh:

I think we will need two!

sorry no close ups!

hardr0ck68 wrote:

I just don't dare to post new questions, as it seems some folks have become tired of my constantly asking "why?, why?,why?,why,?" :laugh:

Why, why , why, is what were all here for! Fire a way my friend!

You can make any HP bike streetable with gearing changes!
Think transmission when you get where you want to be with HP, its the hidden jewel!

Cheers.



...Think long/tall first gear... CSR... I can use first gear on my KZ to kill any speed limit here. 2nd gear launches are a blast!

I hadn't even thought of running a stoker kit.

With a 6.5mm stroke what size spacer would be needed under the jugs?

I hopped on falicon's web page, and I could swing it. The 810 kit and and porting on the head will have to wait a year...as the $1000 for the stroke, then the $600 for the supercrank and I am guessing around $500 for the rods will be about $500 over budget on their own for this years mods.

I would think a set of carbs in the area of vm28's or bs34's would feed it; it is only a 901cc the z1 was fed with vm26 right? As for the head it can be fitted with 36mm intake valves and already has 30mm exhaust; the same as early kz1000's.

Certainly something to speak to falicon about when I get them on the phone.

I guess my only concern is, for $1500 the price is getting pretty close to DIY turbo. I want to run FI, so I would be half way to a turbo when that is finished...then all I would need is a combo of parts ment for the turbo 750 and aftermarket goodies.

Increasing length of stroke increases the piston speed during each crankshaft revolution, and thereby reduces maximum sustainable rpm.

For example, the long-stroke (under-square bore-to-stroke ratio) v-twin Harleys have a relatively high piston speed, and operate at lower rpm's.

Whereas the Japanese bikes mostly adopted shorter strokes (square or over-square bore-to-stroke ratio) with a relatively slower piston speed, which allowed operation at higher rpm's.

As understood way back in the peanut gallery. :lol:

Good Luck!

hardr0ck68 wrote:

I hadn't even thought of running a stoker kit.

With a 6.5mm stroke what size spacer would be needed under the jugs?

There are many different ways of stroking stuff. That part is up to you to figure out!

I hopped on falicon's web page, and I could swing it. The 810 kit and and porting on the head will have to wait a year...as the $1000 for the stroke, then the $600 for the supercrank and I am guessing around $500 for the rods will be about $500 over budget on their own for this years mods.

I would think a set of carbs in the area of vm28's or bs34's would feed it; it is only a 901cc the z1 was fed with vm26 right? As for the head it can be fitted with 36mm intake valves and already has 30mm exhaust; the same as early kz1000's.

speed. Are the intake ports bigger then 29mm's? It may only be a 901cc, but it will have alot of piston
Certainly something to speak to falicon about when I get them on the phone.

I guess my only concern is, for $1500 the price is getting pretty close to DIY turbo. I want to run FI, so I would be half way to a turbo when that is finished...then all I would need is a combo of parts ment for the turbo 750 and aftermarket goodies.

Buying a turbo is only the start, then you need the motor to go with it (unless you only run a couple pounds of boost)Bolting on a turbo, isn't a one of a kind motor!

As for FI, it sounds good. It's not just as simple as everyone thinks. You could wear out a new motor, just getting it dialed in. Maybe in a few years, they will have, the buggs out of it.

everything costs money! :laugh:

Patton wrote:

Increasing length of stroke increases the piston speed during each crankshaft revolution, and thereby reduces maximum sustainable rpm.

For example, the long-stroke (under-square bore-to-stroke ratio) v-twin Harleys have a relatively high piston speed, and operate at lower rpm's.

Whereas the Japanese bikes mostly adopted shorter strokes (square or over-square bore-to-stroke ratio) with a relatively slower piston speed, which allowed operation at higher rpm's.

As understood way back in the peanut gallery. :lol:

Good Luck!

Different engine builders seem to have their own opinions on the subject. I know this much, stroking blows the torque through the roof.

Japanese bikes do have higher rpm's, but it doesn't mean they have power in the upper rpm range. With these bikes we are not talking about a chevy size piston, like the Harleys.

Patton, have you looked at the piston speed for a KZ-810cc with a -1/4" stroke?

It is 44CI., 3,752FPM and 62.5FPS, the CI goes up but everything else goes down.

Myself I don't care so much about the rpm's, but you are adding 225cc to the motor or 1.5 cylinders. Thats a racers dream come true. Very streetable depending on compression ratio an

PLUMMEN wrote:

everything costs money! :laugh:

My answer is, most people don't think about, they will be spending $2000 or $3000 on the motor, before they buy the turbo. That may be for only round one! A turbo sounds great, but how many average street riders, can really handle a turbo?

Plummen at your age and skill level, with a slick and wheelie bar, do you truely think you could handle a hot turbo bike? I couldn't, I would find some younger guy with skill's.

Wouldn't 69mm Bore x 60.35 Stroke, still be over square?