[Technique] BRC (Superkart)

Hi pfraider, I am not rich enough to buy a Luyten kit or another for the Honda 125 rs of my Driver. I preferred to invest in a dyno (Rotronics) and soon buy TFX equipment to make myself development. I have three PCB pressure sensors with their supply. My project is to make statements in the exhaust, intake, crankcase and combustion chamber.

Ridley, if you start measuring pressures in the exhaust pipe, you'll go crazy. Pressures vary at any point in the pipe at any moment and you can't distinguish what you are looking at. Pulses moving in different directions will locally enhance or reduce each other and one centimer or one millisecond later their values may be totally different. You cannot draw any conclusions from these measurements. The same goes more or less for pressures in the intake duct.
On the other hand cylinder and crankcase pressures can be very useful.

Too late, Frits, I'm already crazy but I'll certainly follow your advice. Thank you for your intervention. What's that? :
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Frits, knowing that the internal temperature of an exhaust system determines the speed of pressure waves, it would be possible to create a stinger with variable geometry? Does the internal temperature can change very quickly?

ridley a écrit:

Too late, Frits, I'm already crazy but I'll certainly follow your advice. Thank you for your intervention. What's that?

It is a test pipe with pressure transducers (only useful if you want to know the mean pressure in the pipe), thermocouples (very useful if they react quickly enough, which you can promote by removing their stainless steel and ceramic protection) and lambdasondes, otherwise known as Air/Fuel sensors, that are also quite useful.
In theory lambdasondes won't work in the oily exhaust gas of a two-stroke; in practice they work fine if you make sure they are heated properly before you start the engine, and if you don't put them too close to the cylinder, where they would be hit by cold unburnt mixture that is sucked into the pipe.

ridley a écrit:

Frits, knowing that the internal temperature of an exhaust system determines the speed of pressure waves, it would be possible to create a stinger with variable geometry? Does the internal temperature can change very quickly?

Jan Thiel and I have been considering such a device. Just below the power band there is a huge collapse in the torque curve of a competition two-stroke. It is caused by the positive exhaust pulse that arrives at the cylinder too early and messes up the scavenging. I sketched a simple tailpipe-device with which you can considerably weaken that pulse when it is not wanted. Like so:
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Left is the end cone of the expansion pipe; red is the calibrated venturi. When the blue arm carrying the yellow venturi-holder swings to the right, the venturi-holder forms one closed cone together with the surrounding end cone.
In the sketch the venturi-holder is moved to the left by the brown bowden cable. Now the exhaust pressure can escape through the big circular gap around the venturi-holder.

When you see such ideas, you realize what a pity that they stop 2strokes in GP...

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What was the disadvantage of the 22mm crankpin?

The Aprilia RSA has one and it is very light! 120mm long.
Made from very special French steel.

We went with the 20mm pin and connecting rod for the decrease in reciprocating mass. At the same balance factor, the 22mm set up broke parts! The 20mm is running really well. Unlike Aprilia GP, I have to maintain a budget by using available components.

a 110 mm conrod seems a bit short for your 150cc engine!
In my opinion a short stroke engine needs an even longer conrod
than a square engine. Have you tried a longer one?
I would suggest 120 or 125.
Do you have your conrods made in Italy?

Jan,

My con-rods are made in Italy. So yes, we can test longer rods. I have seen the longer rod benefits in an engine that has a gearbox, but also a slightly narrower power band. The 150cc engine we have is a fixed gear class, so width of curve is important.

Riley
You had a motor kart 125 ICC under construction, the project always is current or was abandoned? Have you of the details, Photo and cuts of this motor to show us? If this is not too indiscreet...

Michel

ridley a écrit:

Too late, Frits, I'm already crazy but I'll certainly follow your advice. Thank you for your intervention. What's that? :
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it's from an SAE paper where they could rapidly change every part.
my opinion is that with such an amount of steel, there is a huge thermal momentum.

hi Steph, and a big lack of resonence

Frits my queries, with the 270 / 90 firing order, in you experienced opinion would the torque produced be equal to or greater than that of an inline as per the current BRC, FPE, DEA, PVP and what if a 180* firing order was to be considered, given the kart world considerably differs from that of a bike is this torque query I've raised relevant ?
we would be talking same cylinders, rods, bearings, g-box etc in each configuration as per the information provided by yourself an many others upon the great ( GP 125 All that you wanted to know thread )

I have read your topic BIG BANG and I probably do not fully understand it, I get the reduced stress to the tire, g-box etc, Here's where I'm confused or lack the knowledge to asses accurately.
If we have less torque as with differing firing orders of a twin cylinder engine this may provide a better control of the applied throttle / drive grip but how does this effect high rpm wide open throttle 6 gear drive as I'm assuming that the torque of both cylinders firing together is needed to push a kart through the aero elements at 240 / 250 kmh

The energy is still produced, but it's frequency has changed. Some say it gives the tires more time between larger pulses to grip the road surface. In a straight line it may be faster as the decreased loading may produce slightly less frictional losses due to bending. Grip off of the turns in lower gears I doubt will be as good. Component life of the drivetrain will be longer.

RAW a écrit:

Frits my queries, with the 270 / 90 firing order, in you experienced opinion would the torque produced be equal to or greater than that of an inline...

You must distinguish between the average torque value that is developed during a crankshaft revolution, and the peak torque values that can be ten times as high as the average. The average value is what accelerates the vehicle; the peak values cause stress peaks on clutch, transmission and tires.
The average torque produced by all types of firing order is identical (assuming the air box can cope with suction from multiple cylinders firing simultaneously), but the peak values are highest for a single cylinder engine (or a 0° multi).
Contrary to common belief the peaks are almost as high for a 180° firing order, and a whole lot lower for a 90° firing order, as I tried to explain in the Big Bang text  http://www.pit-lane.biz/t1461p32-technique-moteurs-motogp .

Citation :

...given the kart world considerably differs from that of a bike...

As far as torque fluctuations and their effect, there is no difference at all.

Citation :

...If we have less torque as with differing firing orders of a twin cylinder engine...

We do not have less torque; we only have higher or lower peaks.

Citation :

I'm assuming that the torque of both cylinders firing together is needed to push a kart through the aero elements at 240 / 250 kmh

The torque of both cylinders together is needed. But firing together or not does not alter the total amount of available average torque.
And to put an end to this story: What we need is torque at the driving wheels. Crankshaft torque values are meaningless in themselves; you have to take crankshaft rpm and total gear ratio between crankshaft and wheel into account.

Riley Will a écrit:

The energy is still produced, but it's frequency has changed. Some say it gives the tires more time between larger pulses to grip the road surface.

I say the larger pulses are more likely to break the grip. And once it is broken and there is sliding between rubber and road, the friction coefficient drops and the subsequent 'relaxation' of the force has to be considerable before the grip can be restored, so the average force that can be transmitted, suffers.
An even force without any peaks offers the most grip and furthermore a rubber compound that is not exposed to peak forces, can be softer and grippier.

You see, the designation Big Bang is completely misleading. A Big Bang engine's torque fluctuations are smaller, not bigger than those of a 'screamer'. The name stems from the engine sound. Cylinders firing at 180° produce a pleasant (I think) musical tone, whereas cylinders firing at 90° / 270° produce a rougher sound.
The ultimate screamer would be a four cylinder engine firing one pot every 90°. That would give a really smooth torque and a lovely sound pitch. Honda built one, but top rider Mick Doohan didn't like it, so that was the end of it.

Thank you Frits, I'm getting the picture now

Mick Doohan went back to the screamer engine in 96-97, due to Mick believing less people.....well Alex Creville to be exact couldn't ride the NSR as fast without the big bang motor.