Texasstar
Can't is a four letter dirty word
Rad to see all the attention to detail and massive improvements you have made.
Thanks Brodie!
Sent from my iPhone using Tapatalk
Rad to see all the attention to detail and massive improvements you have made.
You could. Or you could just learn t... I.. I can't bring myself to say it! Help me Teazer!!
I think the appeal of the rekluse is that they're a simple drop in install. But I'd be a bit concerned that the thickness of it would prevent the use of enough plates to hold firmly. I guess you could make a custom basket to suit an off-the-shelf rekluse along with a sufficient number of off-the-shelf plates. My son Kurt had one in a KX250F; seemed to work well enough.
Those guys with all the launch gadgets are running bikes with horsepower in the hundreds aren't they? I think it's overkill for a simple (but fast) Bul.
More wacky fuel system pics for you, Pat. First pic shows the solenoid valve that shuts off the gas supply from the small gas tank under the carb. A positive fuel shutoff is a rules requirement. Fuel from the solenoid goes to the two needle valves on the other side.
The tank is positioned so the top is about 20mm below the height of the idle discharge holes. No float bowl required so it's very simple.
View attachment 235550
Some carbs allow a separate feed for the idle discharge holes and the intermediate transfer slots. This is ideal as it allows independant tuning of the idle and off-idle up to about 1/4 throttle or so. That's what these two needle valves are for, one for idle, the other for the area in between idle and the startup of the main circuit. It's possible to get a very sharp and clean transition with this.
View attachment 235551
The needle valves are remote valves made for RC cars and boats. They give a nice fine adjustment and stand up to alky and nitro. A nice feature is the arm that gives a coarse adjustment when it's turned. This is an easy way of adding enrichment for cold starts without altering the fine adjustment. You can see the arm in the pic below.
View attachment 235552
The gas is a very small proportion of the total fuel flow but it helps get a little heat in the engine. The main (alky) supply runs from the tank shutoff through a pill and pill holder (to set the max flow) then through a throttle actuated barrel valve to the carb nozzles (two barrel carb). So again, there's no float bowl and it's a simple and rugged system. Pill changes can be made easily in maybe half a minute without spilling much fuel at all.
Unless you keep the revs really low, a single exhaust port with a 70% chordal width does not give sufficient blowdown time.area, but because of the reason I explained above, making the port wider will be even worse (large radii). You will either have to use a bridge, add auxiliary exhaust ports, or raise the timing of the single port to well above the 190° that is optimal for pipe resonance.
The Aprilia cylinder is extreme in that respect: the middle exhaust port is 38 mm wide (older versions were 40 mm wide) and there are huge auxiliaries but even so the middle port is raised to 196° and then it gets a large radius at the top. The radius makes it difficult to measure the timing but if you shove a piston ring in the bore until you can just see light between the ring and the bore, you will find an exhaust timing of 202°.
Don't try this at home, unless you want your engine to produce its maximum power at a mean piston speed of 23.6 m/s. But then your transfer time.area will probably be insufficient. And you know: if you raise the transfers, that will eat into the blowdown time.area.
Why does Aprilia use an exhaust timing that is too high for optimum resonance? It is a compromise: any lower, and the maximum torque will rise, but the reduced blowdown time.area will cause an early torque collapse and the product of torque times revs (yes, that's power) will be lower.
STA stands for Specific Time.Area. STA depends on rpm: the higher the revs, the shorter the ports are open per revolution. So I can only give you STA numbers if you specify for what rpm you wish to know them.
It's like this: a cylinder has port windows with a certain width and certain distances from the cylinder top plane to port roof and port floor. You can only express the window dimensions in millimeters and square millimeters (or in other funny length and area units that english-speaking folk still use).
Put this cylinder on an engine with a crankshaft with a certain stroke and a certain conrod length. Now you can also express the window dimensions in crankshaft degrees.
Now we can look at the angle.area concept (the point between angle and area indicates a multiplication; I make a point of writing it like this )
Let us assume a port window is 1 mm wide. Turn the crankshaft until the window is on the verge of opening. Its open area is still zero.
Then turn the crankshaft 1° further. Let's say the piston descends 0.5 mm, so the open window area is 0.5 mm height * 1 mm width = 0.5 mm² , and it has been open for 1°; that yields an angle.area of 1° times 0.5 mm² = 0.5 °mm².
Then turn the crankshaft 1° further again. That first 0.5 mm² open area has now been open during 2°; and as the piston has descended some more, there is now some additional open window area that has been open for 1°. Multiply all those pieces of open window area with the number of crankshaft degrees they have been open, all the way from initial port opening till port closing, and you get the total angle.area of the port.
But for gas flow it does not matter during how many crank degrees an area has been open; what matters is the number of seconds it has been open.
That is where engine rpm comes into play: twice the revs means half the time; angle.area divided by rpm is time.area. And if you divide time.area by the cubic capacity of the cylinder that has to be filled (or emptied), you have specific time.area.
You may have noticed that in previous posts I sometimes talked about angle.area, and sometimes about time.area. And hopefully now you understand why. When I talk about an engine, I use angle.area. When I talk about a running engine, I use time.area.
With the angle.area values I posted, you should be able to work out the specific time.areas for 13.000 rpm. And these are universal; if you manage to get the same STA values for an engine with any cubic capacity and any rpm, you're doing fine.
An Arctic Pat! Got a Harley gearbox to go with it?
I realize Boyesens are very commonly used from the factory, but I seem to remember Jan Thiel once saying that he found no evidence of flow through the reed during the transfer-open period. I'll see if I can find more on his testing.
Boyesen ports seem to me to have something in common with boost bottles - there is practically no reliable dyno data anywhere showing they do anything at all when added to engines that didn't originally have them.