a thinner version of you grumph!!!!!!!!!!!!
a thinner version of you grumph!!!!!!!!!!!!
riding history into the future since ages ago.
Plugged the numbers in where?
You may also want to take another look here, regarding your mean area: https://www.kiwibiker.co.nz/forums/s...post1131055378
Come to think of it, maybe a more fundamental explanation may be in order:
Blowdown angle.area
Blowdown angle.area is not simply the total blowdown area multiplied by the total blowdown angle. It is the sum of a lot of small area steps, multiplied by the time during which each of these steps is open.
For example, let us assume that the exhaust port is a simple rectangle, 40 mm wide, that it opens 1 mm further for each degree of crankshaft rotation, and that the total blowdown angle from the point where the exhaust port is beginning to open till the point were the transfer ports are beginning to open, is 30°.
Then the first degree of exhaust opening will open an area of 40 mm x 1 mm = 40 mm², and this area will be open during the whole 30° of blowdown period. That first area thus has an angle.area of 30° x 40 mm² = 1200°mm².
When the crankshaft turns 1 degree further, an additional area of 40 mm² is opened. This second area will be open during 29°, so its angle.area is 29° x 40 mm² = 1160°mm².
Repeat this calculation for each crank degree until the end of the blowdown phase, and add all the angle.area values; that will give you the total blowdown angle.area.
In reality this calculation is complicated by the fact that not every degree of crank angle gives the same port height difference, and even more complicated by the fact that the exhaust port is not a simple rectangle. But you will understand the principle of angle.area.
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Transfer angle.area
Let us assume a transfer port with a timing of 130°.
When you turn the crank 1º past Transfer Open, a certain area of port, say A1, will be exposed. I don't know or care what that area is, that's for you to measure.
That area of port A1 will be open for 130º. The angle.area for this area A1 is = 130 x A1.
Turn the crank another 1º and an additional area of port, A2, will be opened.
This additional area A2 will be open for 128º. The angle.area for this area is = 128 x A2.
The next degree of crank rotation will open Area A3 which will be open for 126º and its angle.area will be 126 x A3.
Keep going like this until BDC, then add up all the angle.areas you have calculated.
The total is the angle.area for that transfer port.
Here you go Neil.
If your MB40 engine is recent, you will have a narrower exhaust port and an accordingly smaller blowdown angle.area than the value shown in my picture.
These small methanol-burning engines have lousy carburation because the fuel is not sucked in by the air flow passing through the carb, but pushed in by means of exhaust pipe pressure exerted on the fuel bladder. Big globs of fuel enter the engine with no time at all to evaporate, so the mixture will be anything but homogeneous;
it will vary from very rich to very lean all over the place.
In order to get anything like a decent burn speed the mixture needs pre-heating by means of mixing with spent gases, so a blowdown time.area that would be too small for a bigger engine, may work better in these small screamers. It took me quite some time to grasp this...
Dad fitted the Vanguard in the early 50's, replacing a 4cyl Chrysler. He worked at a big Standard dealership. The engine block was rescued from the rubbish bin, it had thrown a rod out the side and had been replaced under warranty. The block was patched, the rest was usable. It was pretty high tech at the time, most midgets still ran Model A, V-8 60, Jeep, Studebaker's & JAP V-twins. They quickly discovered it's deficiencies for racing. First problem was the valve spring retainers, these were a stepped ring with a slotted hole to fit into the groove in the valve. Uniquely, the longer outer 'retaining' spring was quite soft and the inner was the strong one. Clever idea for easy assembly & quiet operation, but highly likely to spit out the retainers and drop valves when revved. Early crankshafts were soft and needed nitriding to prevent journals going out of round. The cylinder head has a large water passage over the gap in the liners between 2 & 3. The gasket is only supported by the top edge of the liners and is prone to blowing out there. Although not officially sponsoring the car (except the 'under the counter' parts, especially new big end bearings, every week) the Dealer did send reports to the UK and many things were rectified by the time the Triumph versions were released (except the head gasket issue). The Vanguard was eventually replaced with the ubiquitous grey (side-plate) Holden 6 cyl.
I think I've discovered the cause of the big end bearing problem, which is good, I'm rebuilding this version of the car from original parts.
cheers, Daryl
Thanks Frits, that explains a lot more. Yeah the fuel delivery is really bad, and efforts to make it better a atomisation for the effort did not deliver any more power. Part of that could be that when it does get a better atomisation, then requires a larger blow down more approaching that of the petrol engines. Something that we did not try and so may have missed the boat on that testing series.
Neil
When I first arrived in NZ in 1966, (51 years ago, - still can't believe it!!) - I had never seen either Motorcycle speedway or Midget Car racing and I remember that the Holdens were starting to gain control - that was way before the VW's (or derivatives of) had taken over and I was hearing the name "Offenhauser" a lot. I was told that their cylinder blocks and heads were 1 piece castings - what happened to the Offenhausers?
I never did get to see one.
Strokers Galore!
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