- Mon Jun 10, 2019 7:57 pm
Hi TZ, bloody brilliant work mate.
Sorry, I haven't been keeping up to date with your project, but what you have achieved has been said by many "2 stroke gurus" to be impossible, due to the weird airflow through a two stroke engine. If you were over here, I wouldn't let you buy a beer for the day, perhaps two if you're lucky!
My project is making slow but steady progress, I have finally finished reconditioning the bottom end of the NSR250 and am prepping it for FI conversion. I have installed two barbs in the top part of the crankcase for the pressure transducers. I'm not sure if it really requires two, but I've installed them anyway? The engine has two distinct halves, so has basically a crankcase per cylinder. I was thinking of just using one half as the master and the other half as the slave, using the master's timings but delayed by 90 degrees (90 degree v twin). I'm still going to initially only control the fuelling, leaving the ignition and powervalve to the Zeeltronic ignition unit.
I have also installed an external air inlet into each of the A ports, controlled by one way valves. This is following on from your's and other's conclusions that at low revs, the exhaust gases are flowing freely back into the crankcases. The idea is by placing the air inlets within the A ports, as the piston descends it can also suck on fresh air and I'm hoping will stop most of the exhaust gases flowing down the transfers. As I mentioned earlier this has been done in the past. One guy did this to his KTM crosser, where he had to seriously lean out his pilot jet making the engine at low revs crisper and more responsive. I will in the future look at controlling the flow better with some air solenoids. But, for now the current method will be a direct feed from the sealed airbox. He was using a 1mm jet to control the flow, but said it wasn't really required as each time he made it bigger, the better it got. By the time the engine's pipe starts working the crankcase will be providing the majority of the air to the cylinder. So, as you've said even with a slight increase of pressure past BDC with the TPS reading 0%, the Speedy can be made to ignore the readings.
Clearly the high vs low pressure comparison works, but I can't get my head around only using 3 interrupts for taking the readings? For my engine, which uses crankcase reed valve induction and using the same cylinders as yours. The transfer port timing is symmetrical regardless of the revs, opening at 118 degrees ATDC (62 BBDC) and closing at 242 ATDC (62 ABDC or 118 BTDC). So shouldn't there be more interrupts around the opening/closing times?