Exhaust valve timing..?

[John]

More to think about?

If the spring is pre-loaded it will take more power to compress it hence a higher RPM to open the exhaust valves. How will this affect the engine characteristics though? Will the power band be leaner or more aggressive?

Changing the spring to a weaker one will make the exhaust vales open earlier. How would that change the engine characteristics?
 
I am lost with two strokes; and a lot of beer doesn?t help?

Interesting thread though and a wonderful forum!

//John

[GDubb]

All this talk is reminding me of the centrifical (?) clutch on my gas powered R/C truck. You lighten the three clutch shoes so that the weight of the shoes doesnt carry them out to make contact with the clutch bell untill they are spun at a higher RPM... therefore the engine is making more power before it is sent through the drivetrain to the wheels.  I think a heavier spring would slow the whole process evenly(higher rpm to open, but open at the same rate of speed) while lighter balls or steeper ramps? would cause the exhaust valve to hesitate opening until higher rpm is reached but sort of slamming the exhaust valve open creating more of a "hit" with the power band.  

I could be totally wrong and far off base... just a little brainstorm I had when I realized this was all sounding like the clutch on my R/C truck. I really dont have any  real life experience or knowledge with KIPS valves so hopefully this is of some assistance and not just a waste of space on the thread.  

[YUNGGUNNAZ]

never a waste.there is always something in thought that can be put to use.i would say you're probably on track with heavier spring  bringing on harder hit.boy what a ride that would be! now how would it act thru the bottom range?what if we changed the number of teeth on plastic gear to spin it at a quicker rate.if we could find one.does a kx125 or 250 have same number of teeth.these should spin at faster rate or open quicker.man,now i've got to pull my cover off my 250 and 125.

[mun]

Mayby 2 dyno picture more explain better than i able write english.

[YUNGGUNNAZ]

does it apprear that valve begins to open at around 4300-4400 and maybe climbs on pipe around 5300 are so.what would you say the reason for decrease in power with valve open constant?timing of power curve vs. type of pipe involve or not burning of as  much fuel charge cleanly.where did the other 2. hp go from previous graph?interesting.there is a performance gain here somewhere in tuning of this valve with other mods. include in the equation.

[John]

Mun,

Got it! These are nice graphs, thanks Mun!

Looks like the exhaust valves are starting to open at 4500RPM's and are fully open at 5500RPM's. There goes my theory of "never half-open"...

When you did these tests, did you increase the rews quick och slowly?

Do you agree with my interpetation?

//John

[doordie]

You can use a extern spring attached between KIPS-wheel and  cylinder, it?s very easy to "TEST" different springrates and see what?s happens.
After that can you test with preloaded stock spring or buy
a KX250 spring.
My own test will be with my third kx500 to get so much torque as possible,
spreaded for so long rpm-range as possible.
(fourstrokes beware)

Recept:    
Gnarly pipe with extension part
Powerblade
D-shaped carb.
Flywheel weight
High compression(wide squish)
Low exhaustport
Reshaped scavening ports
Modified KIPS


//doordie

[YUNGGUNNAZ]

great.now we rolling.we'll say openning 4500.fully open @5500.now if we open it earlier @oh 3800 say will the power now spread more smoothly, at a  greater efficently, maybe peaking a little more hp.
doordie, 1.5" added to head pipe should help torgue on gnarly.

[mun]

where did the other 2. hp go from previous graph?

Previous is with 490 main and this is with 500 main.
We start Slechten pipe with 500 main (57hp), what i use on tarmack. It's badly too rich on inertia dyno!!! (You can't find best jetting on inertia dyno! It has not enough braking to burning all fuel that you neet on track.)
Then 480 (65hp) and 460 (66hp), which was best of tested. But more smaller can be better, no time. Then MuN-pipe, start 490 (72hp) > 500 (71hp), no other . Powervalve testing (i quess again) we make with MuN-pipe and 500 main jet.
I remember that "powervalve OFF" mixture was very very rich.
This dynoing happend almost 5 years since and i don't remember all exactly. Some of those difference can be of dynos tolerances. Motor temp and pipe temp (it's most importing), ...

Looks like the exhaust valves are starting to open at 4500RPM's and are fully open at 5500RPM's. There goes my theory of "never half-open"...
When you did these tests, did you increase the rews quick och slowly?
Do you agree with my interpetation?
//John

John, your theory about "never half-open" is right. Please don't shut me, because i don't remember sure. If someone can take cover plastic of cylinder, so that KIPS moving arms is seeing. Raise rpm slovly and check what arms making. I'm so sick than i can't do now that. I last start my KX summer 2004 .
This dyno was PekkaP's Fuchs-dyno, http://www.pekkap.fi/fuchs.htm. That is acceleration, or inertia dyno. Pekka raised rpm slowly to 4000 and then wide open. We dynoing KX only one evening. If you want better results you need own dyno and eat and sleep in dyno room .

Remember: My old -86 KX500 have KIPS only side exhausts, not in main exhaust.

There all rest dyno graphs:

[doordie]

Mun,you have a different carburator (mikuni 40mm) than we other so the jetting is not the same.
I?m up to 205 mainjet with ovalbored Kehin (39mm) at the same hp(70+) as you.
Hope you will get better soon Markku!
This test with KIPS should be done on a water or oil braked dyno for best result.

//doordie

[YUNGGUNNAZ]

have set up date with Ms. Dyno for the sat. after xmas.its at a friends harley shop(he races top fuel kaw)for suppose to be 65.00 hr.but its likely going to two hrs. for that.we get to talking and trying things and you know.will be trying 3 pipes,keihin carb,44 lectron,stock flywheel,lighten one,ignition timing and of course exhaust valve washers,springs.sounds like three hrs.uh.anything else i should maybe check if time allows?

[doordie]

YUNGGUNNAZ,

Different intake valves,stock or aftermarket(vforce,Radvalve),maybe borrow someones if you don?t have.
You should have O2-sensor to adjust right jetting (A/F-ratio).
A good chain and easy rolling tire.
 
//doordie

[YUNGGUNNAZ]

ok. got a stock intake,vforce and mossbarger w/spacer on hand.his dyno setup should have o2 sensor wand or something i guess.will change tire to either street or enduro thread.we were going to do it today but it would have been a rush getting everything together.although i have the 99 already down to replace some trans. gears.he wanted to show me a VICTORY on the dyno but did'nt have time.boy this is going to be fun!oh might as well take some thermal wrap for pipes to see results.gonna get my money's worth.

[Brett]

I would try each item one at a time only otherwise you will get lost, then wack the best of each option on and hopefully not go backwards.  The thing i would like to see is a simple before and after reed block spacer as there has been much discussion on this and i would like to see if much top end losses.

[YUNGGUNNAZ]

the spacer deal was another thing i was looking at also.i'll try each pipe, carb combo first starting with stock reed cage and either pro circuit or dyno-port up pipe i have.after plug chop,i'll change cages and carbs.getting the best pull with each after proper tune up.i'm looking for the most hp,torque #'s out of each combo.keeping curve in mind.will document each setup(jet,timing changes,temps,a/fr,etc.)