as Blah said, it is not just duration, it is easier to think of port timing as a camshaft on a 4 stroke with the exception that there are no valves and it all happens every time the piston goes up so "cam timing" comparisons go right out the window. Not all motors like the same amount of timing, there is a lot more science to it than that, other factors determine optimum timing and many of those are in the inherent design of the particular engine and its breathing capability so you can't just go off some rule that 2 strokes like this much port duration, it will be different on every engine.
Quote:
Originally Posted by whatrudoing25
Do u have any idea's what the durations should be increased too, around 180* for 11grand?
lol, i made a dyno out of an oil pump. a spring balance and some electronic gear, it was pretty unstable as an engine dyno thanks to all the vibrations. I have it in the "to do" box for when i make a bike dyno up, it will be much better i think. the engine dyno was good for putting a load on the engine for jetting and checking temps even if the torque readings were all over the place. honestly, i'd use a lap timer and just compare your own results, be sneaky and time other people as well (shhhh)
Quote:
Originally Posted by geezer
Alas due to loose tolerances even with hard dyno data results will still vary. What would be a good base line for evaluating mods? (In theroy) Maybe someone has the blueprint specs from the Blata bluebird motor. At least this would be a constant baseline to model from.
Good job on the dyno trial. Boy you have alot more gumption than I do.
Well a little back on topic. I just think a dyno chart would be helpful in when comparing a mod like the stroker crank. I know these little motors are a constant compromise, more on top vs. longer time getting there. In my case I'm 220 lbs in gear. With my current tune I can straight line 32.1 MPH. But on the track My top speed is about 26.5. About the same as everyone else. So RPM is not my biggest concern. The biggest problem is being able to get under someone in a corner. I can get a line and gain but usally endup losing on the exit. Now I know the best mod would be lose the girth (and practice more). But if the stroker crank (BBK, Reeds, Pipe, ect., ect.) would bring on torque earlier then I think I could live with the top end being a little flater. You know accelerate to a slightly lower topend slightly quicker should get my big butt around the track quicker. Now I know there is clutch and gearing mods to help this also. But that is just what I'm getting at. A dyno chart would at least give an idea where the power would be made.
What would your thought be on that. If your top speed were not realised on the track would a decrease in RPM mean alot if you got to the max speed of the track quicker?
Would the stroker be an proper application in this case?
Well, if you realy wanted to compare engines then the dyno thing i started would have partly done the job. All you need is peak torque and cylinder displacement to find the bmep*, basicly you can compare a tractor to a lawnmower with bmep, don't know how you could translate it to track times though. if you have a greater torque at the same displacement you have a higher potential to put more power down i guess, gearing would be a way to do this. My little baby is still getting the running-in treatment, wound it out a bit but not all the way and it got to 30.6 pretty easy (compared to before), that's with 250lb on it. It was trying to lift the front wheel..good cag, you can do it.. that's a good sign, definately a different beast now i raised the ports, put the central dome 13:1 head on and biggened the reed cage, oh and the pipe mods, and um the uni filter and the porting, lol, umm everything. It's not going to stay like this for long, i have that other reed cage and a very big walbro in the "to do" tray.
