KX500 Port timing lift numbers with compression.

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KX500 Port timing lift numbers with compression.

Post by Sandblaster » Sat Jul 01, 2017 11:27 pm

You did the best port cleanup possible using Team Green cylinder specs....
You even did a few tricks that Team Green didn't...
Oh goodie... that's a start :o
Want more power?
You need to up the compression and change the port timing...
More power on top requires more cylinder lift but you will loose some bottom end :cry:
This chart is to give you a rough idea of what your in for.
The reason I say a rough idea is because every KX500 is a snowflake... They are all a little different.
Get a degree wheel to get it right..
Sometime in the last year or so Cometic added several new thicknesses of aluminum available for spacers.

Available Thicknesses: .010, .016, .020, .025, .032, .040, .047, .050, .063, .080, .100, .125, .160, .188, .217, .250, .313, .375, .500, .625

No need to check all of these but here is what sort of lift numbers you can expect from these stacks of gaskets and spacers.

.020 base gasket = 187 degrees of exhaust port timing

(2) .020 base gaskets + .020" aluminum spacer = 190 degrees of exhaust port timing

(2) .020 base gaskets + .025" aluminum spacer = 190.5 degrees of exhaust port timing

(2) .020 base gaskets + .032" aluminum spacer = 191 degrees of exhaust port timing * SPECIAL * I really like 191 for the best all around performance.

(2) .020 base gaskets + .040" aluminum spacer = 191.5 degrees of exhaust port timing

(2) .020 base gaskets + .063" aluminum spacer = 193.5 degrees of exhaust port timing 14.27:1 for peak hp and torque

(2) .020 base gaskets + .080" aluminum spacer = 194.5 degrees of exhaust port timing

(2) .020 base gaskets + .100" aluminum spacer = 196 degrees of exhaust port timing

(2) .020 base gaskets + .125" aluminum spacer = 197 degrees of exhaust port timing

(3) .020 base gaskets + .040" aluminum spacer + .080" aluminum spacer = 198 degrees of exhaust port timing

Another issue you will run into is the higher the cylinder sits, the more you need to shave the top down to keep your correct squish.
Then, you also have to change the combustion chamber to to get your compression back because you have less trapt volume 8-)
If bikes are for kids I'll never grow up.

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Re: KX500 Port timing lift numbers.

Post by Sandblaster » Sun Jul 02, 2017 2:25 am

Say hello to my little friend :lol:

KX GURU RACING KX500 PORT TIMING NUMBERS 101.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 101.jpg (423.57 KiB) Viewed 7928 times
KX GURU RACING KX500 PORT TIMING NUMBERS 102.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 102.jpg (375.99 KiB) Viewed 7928 times

Start with the piston so that it just covers the top of the exhaust port...

KX GURU RACING KX500 PORT TIMING NUMBERS 110.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 110.jpg (414.36 KiB) Viewed 7928 times

Make sure that the indicator is lined up and record the starting number.

KX GURU RACING KX500 PORT TIMING NUMBERS 103.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 103.jpg (396.21 KiB) Viewed 7928 times
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Re: KX500 Port timing lift numbers.

Post by Sandblaster » Sun Jul 02, 2017 2:34 am

Rotate the crank backwards so that it goes all the way to the bottom of the stroke...

KX GURU RACING KX500 PORT TIMING NUMBERS 106.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 106.jpg (370.81 KiB) Viewed 7926 times

Then continue to rotate the crank backwards...

KX GURU RACING KX500 PORT TIMING NUMBERS 107.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 107.jpg (398.02 KiB) Viewed 7926 times
KX GURU RACING KX500 PORT TIMING NUMBERS 108.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 108.jpg (385.58 KiB) Viewed 7926 times
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Re: KX500 Port timing lift numbers.

Post by Sandblaster » Sun Jul 02, 2017 2:37 am

KX GURU RACING KX500 PORT TIMING NUMBERS 109.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 109.jpg (412.5 KiB) Viewed 7925 times

Continue rotating the crank until the piston is just covering the exhaust port again...

KX GURU RACING KX500 PORT TIMING NUMBERS 110.jpg
KX GURU RACING KX500 PORT TIMING NUMBERS 110.jpg (414.36 KiB) Viewed 7925 times

Record the number on the degree wheel, do the math to see how much the degree wheel rotated.
Easy... 8-)
If bikes are for kids I'll never grow up.

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Re: KX500 Port timing lift numbers.

Post by Sandblaster » Sun Jul 02, 2017 2:40 am

Oh... you don't need such a large degree wheel.
Most guys use one about half the size of mine...
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Re: KX500 Port timing lift numbers with compression.

Post by Sandblaster » Mon Dec 25, 2023 9:36 pm

Well... Today I dropped in a 6mm stroker..
That's a radical change in port timing... :lol:
These numbers are approximate but close enough for what I needed to see..

.000" base gasket = 190 degrees of exhaust port timing..
.075" total lift = 194 degrees of exhaust port timing..
.095" total lift = 196 degrees of exhaust port timing..
.125" total lift = 198 degrees of exhaust port timing..
.145" total lift = 199 degrees of exhaust port timing.
If bikes are for kids I'll never grow up.

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