The faster I go, the higher the engine can rev? By FACE PLANT FOR LIFE (Read 510 times)

[FACE PLANT FOR LIFE]

So here is an odd question, whenever I'm on my scooter, it seems like my RPM is limited to about 6-7k when I'm going between 0-55 KPH, but as I reach 60 KPH, the engine RPM picks up to what sounds like 8-9k until I reach 70 KPH. So, what exactly is it about this speed that let's my engine get a bit more power out of it?

[Bashan]

It's called a power band Fern Face. It's when the factors of air, gas, and compression all come together in their optimal design parameters. The air is flowing just right for the gas being delivered and the combustion chamber is getting all it needs. We humans call it "hitting our stride". When you hit that RPM band where everything is coming together it's like the engine kicks in nitrous. It's more apparent in a two cycle. We'd crack the throttle on a 2T three cyclinder Mach III Kawi and if you were in the lower RPMs it would make a bogging sound and kind of pick up speed. These things would wind out man, if I remember red line was 12K, maybe higher. When the tach hit about 9K you hit the power band and you better be hanging on buddy boy because that front wheel wanted off of the ground...big time. And of course it handled like crap so here's this screaming banshee between your legs, the front wheel is trying to get off the ground, and it keeps trying to do a high speed wobble.....god that was FUN!! It doesn't look that fast does it? For a while the 500cc was the fastest production bike in the world. Two of my buddies had them...I had an 800cc Beemer at the time. Here's the Kawi:

[cyborg]

could be any number of factors,,,,carburetion can be and issue here,,with a slightly weak midrange ,then when you get past a certain rpm you can get whats called "inertia charging" where the mass of the charge can slightly overfill the cylinder and make more power,,,,most of my engines i designed the intake charge went supersonic at 6500-7000 rpm with a huge surge in power till rev limit,,,and not alot of people know the roar of the intake at a point in the rev range is actually the charge breaking the sound barrier,,,mini sonic booms as it were,,,i love that sound,,,so is there a nice roar when this happens?

[Alleyoop]

No that is the way it supposed to work, that means his cvt is setup right. The rpms when you first start off should go to around 6-7k then as the speed catchs up with the rpms the rpms should then start to climb even higher PERFECT SETUP when that happens.
Alleyoop

[Bashan]

I agree with what you guys are saying but I still say the GY6 hits a RPM band where it likes everything that's going on and becomes more efficient. It starts pulling harder and sounding more aggressive. Now, it's not as apparent on a 4T and especially a GY6 with a CVT because the engine is always seeking an ideal RPM via the CVT. I've spent many hours watching a tiny tach while winding it out, there is a optimal power band. Depending on the particular engine (each has it's own personality) and particular setup (cam/carb,etc.) around 6,500 it starts pulling better up to about 8,000 and then it's diminishing returns after that. Now the 300i is a different animal. It gets a kick in the pants about 6 and pulls hard all the way up to 9K. That's when the tach goes into the red area. But there's a white line at 9.5K and I'm thinking that's the rev limiter. I haven't made it past 9K and probably won't. But every engine, even your lawn mower has a power band.

This engine gets real happy around 3K to 4K. Every engine is different but every engine has a power band.