How big'n engine should I get? A calculator for deciding

GoldenMotor.com

Nipash

New Member
Jul 31, 2011
22
0
0
Washington
I got started in motorized bicycling back in 2011 by buying a 66cc Happytime engine like everyone else and mounting it on my bike. The website described it as the rolls-royce of bicycle engines but this wasn't exactly what I'd call...... accurate. So, anyway, I had to find an engine that had a bit more power and reliability for my use. Instead of just guessing how powerful an engine to get and then hoping it would work, I thought there had to be a better way. So, using the detailed equations from Build your own Electric Motorcycle and the internet, I built a calculator that will tell you how powerful an engine you should get based off of different criteria:


The calculator was built in Excel 2007 but is supported in Excel 2010 and a version is included for Excel 97'. It is pretty "self serve" as basically what you do is fill it out like a form and then below you get the amount of Horsepower required. There are explanations for each value and the values are divided into categories like: Speed and Acceleration, Bike and Drivetrain, Aerodynamics and Rolling Resistance. There are also suggested values for each value as some of the values you have to enter are difficult to figure out. Finally, at the bottom there is a list of common engines and it will tell you if they will provide the required power or not. The equations are quite complicated, and I put them in with the best of my ability, but I'd reckon it is a little conservative in it's estimates (Carroll Shelby said: "Too much is just right"). I posted it here for others to use and critique, so please respond! The calculator is attached below:
 

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rustycase

Gutter Rider
May 26, 2011
2,746
5
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Left coast
OK N, it sounds wonderful...

example, please!

and which powerplant did it advise for yourself?
(pls enter ur specs and IF the program presented what has proven to be an astute optimization.)

and Carroll Shelby... lol
a 427 Cobra is abt the only car I'd really like to have.
(I still remember that Honey West program on TV.)

It was claimed they had more brute torque than anything ever built.
I don't doubt it.

My built Z-28 would just get up and go sideways if the driver was not cautious with the throttle, and it was a small block...

what I mean to say is, too much is just that. un-manageable.
Control, IMO, is far more important than brute HP.

lol
but that's all my opinion.
based on experience! :)

Best
rc
 

The_Aleman

Active Member
Jul 31, 2008
2,653
4
38
el People's Republik de Kalifornistan
The "comment box" for the Gear Ratio has a bit of a misnomer in it. You put in "20x for 2-stroke, 10x for 4-stroke". Being 2- or 4-stroke isn't going to matter there, what will matter is how high you have to spin the engine to get usable power out of it. A reg ol chinagirl 2-stroke and a Huasheng/GXH50/Titan 4-stroke can use the same ratio, they have similar rev ranges and powerband. The optimum for either is around 17-18:1 in single-speed config. Of course a pocketbike 2-stroke will exceed 20:1 and a HF 212 will be closer to 10, but that's an extreme comparison.

Just food for thought I guess. That's a pretty nifty app!