Killer bee exhaust duration

James clive Sun Oct 10, 2021 5:50 am

Any one know the correct exhaust duration in terms of crankshaft
Rotation for a GENUINE Killer bee i need this in degrees as measures
In thou can vary too mutch
Any helpers
Thanks
James clive

crankbndr Sun Oct 10, 2021 1:06 pm

I can do that give me about a week.

balogh Sun Oct 10, 2021 6:18 pm

I guess the old stock KB had a No.1 cylinder with an additional booster port added to each bypass port...the same design that COX Int'l and Exmodelengines sell as aftermarket TeeDee049 cylinders. I remember from one post by Brad aka 1/2A Nut describing the tuned pipes that the exhaust duration of such cylinders is 160 or so degrees..

crankbndr Sun Oct 10, 2021 7:26 pm

Found some spare time this evening so, the piston starts to open the top exhaust slit at 111 degrees and closes back up at 244 degrees.
At TDC there is 10 thousands SPI, at BDC the bottom exhaust slit is open 1 or 2 thousands. In other words most exhaust exits the smaller top slit. I used a new KB piston and cylinder and real KB crank. Rod and ball socket tight.

crankbndr Sun Oct 10, 2021 8:10 pm

Shouldn't these numbers be symmetrical. 360-244=116. Im off a few degrees somewhere.

gkamysz Sun Oct 10, 2021 8:59 pm

That's about what I get in CAD in measured parts, 134° duration. Tolerances can add up, but I have no idea if they controlled these tighter than others.

1/2A Nut Sun Oct 10, 2021 11:57 pm

Andras, there are no stock cox engines at 160.

List of what I am aware of thus far not counting for variances between engines:

KB .049 / 134 per Greg
TD .049 / 140
TD .010 / 150
TD .020 / 130 per Mattes
XLS .15 / 150
ASP .12 / 150
AP .09 / 150
Norvel AME .06 / 150
Picco .8cc / 160
Picco .8cc / 165 Mels version
Fuji .05 / 160
CY .06 / 160
AP .06 / 160
SH-.07 / 170
Sirio .09 / 160
Norvel .074 / 160
TT GP .10 / 160
GS Pro V.12RR / 170

Found this on the net:

James clive Mon Oct 11, 2021 12:51 am

Thanks all for your input
Only thing is we seem to measure thing's differently although both are correct
Crankbndr gives me exhaust opening at 111 degrees this threw me for a moment till I realised he has measured open In in degrees after top dead
Centre whereas exhaust timing is usually measured in degrees opening before bottom dead centre still works out at 138 degrees which is right on taking
Into account variations in deck height e.g. surestart measures 140 which is what bernie modifies to produce td cylinders ie removing centre bar and increasing depth by approx .0131 which after initial run and settling in gives spi of .027
Thanks all for your input very helpful
James clive

balogh Mon Oct 11, 2021 12:55 am

Thanks, Brad,
I was under the impression that the formula you once gave me to determine the Profi Tuned Pipe length for a given engine speed was related to COX engines, but I checked again and you mentioned it was for Fuji engines:

".05 car engine Fuji or a Sportwerks engine:
160 deg timing so center of piston to reflection zone varies on opinion
always best to find the average rpm spread to select unloaded state
with any given props selection I will us a 4x5NE / 137 mph at 29k

- 1675(wave speed) x 160(timing) ÷ 9.5 (pipe length) = 28.21k rpm
- 1675(wave speed) x 160(timing) ÷ 8.5 (pipe length) = 31.53K rpm"

Now I tend to understand why my TD engines did not jump speed with the tuned pipe: I should have changed the formula to 140 from 160, i.e. the real opening duration degree of TD049?

James clive Mon Oct 11, 2021 5:53 am

Has always been my understanding for high speed motors
Such as profit etc exhaust duration should be around
180 to 189 degrees thats if you want to go fast
James clive

1/2A Nut Mon Oct 11, 2021 7:01 am

Yes Andras 140° for the TD .049 should get you in the ball park.

Example - Nano X: 1675 x 140° ÷ 7.5" MRP = 31.26k rpm
Requires prop unloaded state to reach 31k or better for pipe sync function.
Flight Tested: HQ carbon 4x4.5 unloaded to 33.1k down wind.

Example - Cox competition grey 4.5x4 with a TD .049
Set header length for a MRP of 9.4" with the .8cc Profi pipe.

1675 x 140° ÷ 9.4" MRP / mean reflective point = 25.2k rpm
Good for a low drag / weight RC speed plane. Pipe should provide
working boost anything past 25k unloaded.

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Killer bee exhaust duration