With a lighter flywheel, your pistons are doing all the work to keep the crank in motion. You need way more midrange and top end, then with a heavier flywheel.
Texasstar said:..... Did you listen to the engine in the first video with the lighter flywheel. It did not pull near as hard off the line and then when came on the pipe it was like it was on a rev limiter..:started spattering like it was out of fuel...backed off the throttle and it let me proceed but could not give it full throttle.
you hit the nail on the head...our dyno guy said it was worthless to use a sniffer...we need to go to BB’s dyno who understands two strokes.teazer said:A heavy flywheel helps to maintain the energy once it has been created, so for example at high revs it may just want to keep going where a lighter flywheel might allow it to run out of breath.. B U T a lighter flywheel takes less energy to build that inertia and also less total vehicle weight to accelerate so it should accelerate harder.
On a street bike a heavy flywheel can sometime be an advantage but on a drag motor you need to use what you have and that's power at higher revs. Check the torque and power curves from a dyno run and see where you need it to rev to. DOn't run it way into the red just because that seems like the way to go. It isn't. It is really important to rev it to the right moment and then change to keep it in the meat of the torque curve.
Make the most of what you have and keep looking for more. Reed valves can help at low to mid range by reducing blow back and so improve volumetric efficiency. More gas stays in the motor and that also raises the effective compression ratio.
You could also run the pipe and port numbers through Bimotion and MOTA or even EngMod2T to make sure pipes and ports are matched. Then add in all the timing advance and compression she'll stand. Make sure the squish clearance and width provide the target MSV at the revs you want to run. Too low, tighten it up. Too high reduce the width or thickness.
If all that overpowers your ignition system start looking at a more powerful CDI system, but first try changing ignition timing on the dyno and plot the results to get the best result.
Ask BB to design and machine a billet torroidal head. Add extra transfer and exhaust ports. No shortage of things to try.
And back to the flywheel thing. If it's missing and breaking up, that's not the flywheel inertia but fueling or spark issues. Did I mention getting it on the dyno again with a sniffer? If your local dyno guy wont sniff a two stroke pipe, get an Air-fuel meter and Bosch sensor and log the results, even if you just get a video of the A:F and revs and look at the dyno charts and manually check the A:F.
This doesn't make sense. If the goal is to tune for a lighter fly wheel, which is better for drag applications, then all of your other data will be off.Texasstar said:We will use the heavier flywheel for now until we can address advanced tuning like methanol carb tuning , toroidal combustion chambers, Et al.
Oh don’t worry this will make sense and we will tune for the lighter flywheel later. No doubt. There are too many variables that need to be addressed first. Chassis set up and air shifter are first on the list. We have a brand new 1/8 Drag strip 5 miles from my home.irk miller said:This doesn't make sense. If the goal is to tune for a lighter fly wheel, which is better for drag applications, then all of your other data will be off.
Isn’t 5250 rpms the magic number for max torque?Sonreir said:As a corollary, once you have your dyno information, you'll want to compare that to your gear ratios. The goal is to have as much torque going to the rear wheel at any given time. You should be able to calculate when the drop in torque at higher RPMs matches up with the same rear wheel torque values at a higher gear and lower RPM. On NA four strokes, you usually just take it to redline, but FI and two strokes are a different beast.
I don’t know why I had that stuck in my head...thought all our max torque numbers were under that.Sonreir said:No, that's the point at which the horsepower and torque are the same (due to the formula for calculating horsepower, which is just force over time).
In gasoline engines, torque changes over RPMs based on the volumetric efficiency of the engine at a given RPM and throttle setting.
I see why BB has a dyno in his garage...for the dark arts of two stroke tuning.teazer said:That's true, but there is also the element of time availability and sometimes we have to stop and make what we have work before embarking on the next step along the path of development.
Exhaust sniffing is interesting. We had a situation once with a Factory Pro eddy current dyno run on a 4 stroke where CO and CO2 levels looked normal and unburned HC levels were really high. What is was really telling us is that what burned was in the correct proportions but we had a lot of raw fuel going down the tailpipe. That was because we were using Primary (2 stroke) type needle jets which result in large fuel droplets and we needed to break that down and atomize it better to increase surface ares to be able to burn more of the fuel we were feeding it.
On a 2 stroke the churning through the crankcase adds turbulence and improves atomization but we still have unburned fuel and oil to confuse the simple sniffer on a Dynojet and its operators. The simple approach is to measure A:F and plot those against power/torque to work out what makes the most power and then tune for atmospheric changes to that empirical A:F target.
It's like looking at plugs. What should they look like? The answer is that they should be clean and after that they should look like they do when you make most power - whatever that looks like on your motor.
BTW, power and torque are the same. A Dyno measure torque (twisting action) and converts it to power using a simple formula. Where the dyno may suffer is its ability to read RPMs. On a more modern digital ignition that's easy to do, but our old noisy ignitions can complicate that.
Bill said John Magee (sp) built the pipes and he is a protégé of Blair but I couldn’t find any reference to him. He works for Mclaren now.teazer said:Who gave you that name? Was that a BB reference to Henry who built a 136HP reed valved street H2 or someone else? Who built those pipes? Andrew Walms (WTF pipes) builds amazing pipes for Kawasaki triples that snake all around the place. There are a couple of guys building amazing Denco replica pipes but I don't know their real names.