F3 barrels VS Stock well modified Vs R etc etc

[TwoStroke Institute]

So you are saying that the

Main 189° Duration
KIPS 185° Duration
T1 120° Duration
T2 123° Duration
T3 116° Duration

and what to do with the expansion?

On piston speed if the Aprilia peaked at 13,000 the shorter stroke KR will go to 13,300 is this factored in?

My calculator gives open ATDC
Main 85
Sub 87
A 119
B 117
C 121

I doubt a KR crank would handle 13,000? Peak at 11,500-12,000 would be good enough. How the cylinders/crank handle that nobody knows.

[fred]

ive got one in my left kr1 barrel now,it`le be on shelf in a few weeks,but if you want to sell it to me ? just to keep the pairing

[TwoStroke Institute]

.... weld a hump in the exhaust duct.....

Like this?

What's the idea around that then?

It isn't a 'idea' it's a trick used by most manufacturers. the trick is that a small duct volume only allows gas at high pressure and velocity to escape. Which is just after ex open only, fresh cool intake charge cannot force it's way out of (for want of a better word) choke point.
As Frits pointed out when I asked him, what does the connecting tube from a tyre valve to a pump look like? Is it 100mm ID or is it about 3mm ID? If it were 100mm in dia the pump would never force air into the tube, only vary the pressure in the connector.
A step at the bottom also kicks up the plugging pulse

[KR-1R]

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ah but that analogy is flawed...of course the pump would flow through the 100mm connector, because the reservoir in the pump is at higher pressure than the current tyre pressure (differential) and the one way valve that stops it reversing. AND IF THE 100mm CONNECTOR WAS LONGER IT WOULD JUST TAKE LONGER (LIKE PUMPING UP A TRUCK TYRE WITH A SMALL PUMP.


looks more like the 'D' port heads and header pipes used on Superbikes (ZX7R etc) to narrow and more evenly flow 'VECTORS' in the exhaust cross section AROUND THE TIGHTEST BEND....

put your finger tips on one hand on corresponding hand's tips to form an 'O' with your thumbs BETWEEN HANDS - now push your thumbs up so the 'O' opening becomes more sausage shaped - thus the flow in the sausage cross section is more even than the flow in the centre of the 'O' and the outside of the 'O'

see Mircon Serpent header pipes - some other pipes such as Akrapovic, Moriwaki have 'D' welded in the pipe (that matches the port in the head)


"YOU CANT BLOW A NOTE ON A TRUMPET WITHOUT LIPS"
^^^ but lips are like a restriction/orifice

you homework tonight is to press the head of your P3nis firmly against a small empty soda bottle opening - how much do you think will flow - very little - your bladder is only relaxing (not exerting pressure) and the pressure soon builds (air in a decreasing volume space) inside the bottle that will overcome the pressure inside your body - its hilarious - you have completely relaxed your full bladder and the flow just stops
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neck size of the bottle may vary between individuals

[dave32]

[quote="TwoStroke Institute"]Have you understood pit-lane? What makes the HP is blowdown area or if you don't have area, blowdown time, and lots of blowdown time AND area makes even more HP. Why worry about the mystical F3 stuff when you can transpose from the pinnicle of two stroke design?
With a Stock rod in mm from TDC
Main open 26mm
Sub open 27

A Transfer 40mm
B transfer 39.5mm
C transfer 40.75

Leave the transfer ducts as they are and weld a hump in the exhaust duct.
the whole point of my post wasnt "whats the best way to mod a KR1 barrel"?,more out of curiosity as to what was done to the F3 spec KR's porting wise.
Just thought it would be interesting to have the facts on what the factory did to "improve" so to speak

Interesting thoughts on the EX duct,as used on h***a RS's and late Kit spec TZ's,has it been tried on the KR?Would it not restrict the motor unless the rest of the ports and pipe design were taken into account?
Cheers for the replies

[KR-1R]

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F3 main jet 180 !!? on a 32:1 mix of A747
F3 pilot jet 48

[TwoStroke Institute]

D shaped headers are different all togethher. With the connector it does do the work, The one way valve is forced open by a increase in velocity, no matter the pressure in the tube you can always squeeze a little more in.

[dave32]

Have you tried the Duct mod then Lozza?
Is it definitely worth doing?
how does the lower edge "kick up" the incoming gas if its a square edge with no lead,doesnt it weaken the pulse,kinda like hitting a brickwall (or a curb )

[TwoStroke Institute]

Yes welded up a few previously hogged out ducts(no names mentioned ) made way more mid but no dyno to conforim as it was on a vintage mx. About the time I learned about this I had a kx65 to do, one before I had hogged the duct out, this just left it but widened the outlet at 3 and 9 o'clock to make a oval, left the step top and bottom. Went much better mainly mid range, got out of the gate really well and had bags of top end.
In the end I have stopped worrying why it works, either a oval outlet with a step to a round pipe or a oval to round flange beats a matching outlet/pipe.
Have a pair of VJ23 cylinders that will be dynoed.

[mj43]

Piccy I posted is of my barrel. The step will be drilled and tapped to allow an extender to be fitted that will go in to the expansion. This is because I do not know what is the best length.
Also I am toying with ports with a twist. I have noticed that ports, T2 twirl the flow on outlet. A total least they do on my engine....

[TwoStroke Institute]

The extender sounds like a fantastic way to heat the freash intake charge. To do it properly it needs the oval to round flange.

[KR-1R]

KResurrect...


finally found a JHA pic

although I think would act like a restrictor on the exhaust side rather than if it was the same oval in cylinder



when they ported the SP barrels I think it was 4 or 5mm raise the exhaust
I took this with a grain of salt
although still to confirm the 56mm YZ125/TZ125 with peak about 12,000
has exhaust heights around 24/25mm

I think MJ was after broader power and reduced load on road bike crank so lower revs