Found this while looking about .
06-10-2009, 12:29 PM
Please,
NO change in the outer surface of the crankwheels in a 2 cycle engine will show one bit of power increase OR decrease..
Crank MASS does affect vibrations FELT as well as polar moment of inertia,
changes to crank mass can deaden vibration and SLIGHTLY effect response to CHANGE in rpm,that means both up and down rpm swings.
Reducing crankwheel diameter WITHOUT like changes to maintain crankwheel to case clearance will lower case compression and create large pools of unatomized fuel that will cause fluctuating fuel curves.
In 23 yrs of 2 cycle work No gain has been made in texture of the surface as crankwheel rpm is very very slow and will NOT cause ANY pressure change in the cases.
IF it did would it not be exactly the same as supercharging a 2 stroke? how well does that work
IN THE REAL WORLD THAT IS<<<<!!!
supercharged 2 strokes have always had an exhaust valve OR have been designed with an extremely low BMEP so as to NOT make enough scavenging to effect the LOW pressure boost of the supercharger.
Changes to the shape of the OD of the wheels (full circle vs pie cut )......
Pie cut cranks may look like they FLOW to the transfers of a case fed engine better at near bdc timing but ,,,,,,
The real FELT change is in the POLAR MOMENT.. mass being equal, the gain in acceleration is due to the moment of inertia,,,,,nothing else..
Sorry if I burst the hopes of some newbies,, welcome to reality !! LOL:eek:
I can elaborate further if this ever comes off a dyno showing ANYTHING LOL
2 questions for you guys to ponder.
1. how do we measure transient power changes ?
2 will I notice anything from it ?
I'll check back in and see how we do..:beer;
Gus
06-11-2009, 03:08 PM
Transient power is the correct term for {rate of acceleration }.
The dynomometer testing we are accustom to reading is either swept up in the rpm range at a predetermined rate or decelled ..
Water brakes, eddy current brakes, hydraulic brakes,, these are all basic steady state methods of testing the power output of an engine.
When we make changes that alter the throttle response and or an engines ability to accelerate a given mass we have to do a transient laod sweep to quantify this.
Track dyno's or rear wheel dynomometers, These are using a fixed known mass with a fixed known moment of inertia.
When using these types of dynomometers, we are calculating the time to accellerate the engine from a specifeid rpm to another specified rpm.
The change in time from baseline tuning to modified tuning is hopefully quicker, this would read as an increase in transien horse power.
Land and Sea has a neet unit tha bolts directly to the crankshaft in place of the drive clutch, This fixed mass is the WHEEL that we are accelerating.
Bob designed the wheel to closely match the inertia of a std 121 tracked sled . With this WEIGHTED WHEEL we are not turning the track, just a weight on the end of the crank.
This is true to life real inertia testing of the ENGINE only.
This is THE ONLY real accurate way to quatify changes to responsiveness in the engine..
Well,,,,, short of the old seat of the pants method or jackstand whacking !!!
The dynomite computer will spit out the results to you at a rate of 200 samples per second..
These fiqures are not power figures, but acceleration fiqures..
This is why a superflow test at dynotech will not show changes or could show lower power output from a say,,,,,, reed cage or intake boot that really wakes up responsiveness..
the big reason you see companies like Boyesen and Steve Tass stay away from dyno's is unless the product shows a steady state power increase it won;t sell... EVEN if your e.t drops a full tenth !!!!!!!
The long winded story is about over for now,,
Gus:D
