Different CCs for BBKs By Alleyoop (Read 2,297 times)

[Alleyoop]

Very confusing on the BBKs:
Some 61mm BBKs say they are 165cc, some 61mm say they are 170ccs, some 61mm say they are 171.3,

Some 62mm BBKs say they are 175cc, some 62mm say they are 177.?cc.

What is the correct cc displacement for them if anyone knows or
does the actually displacements vary?
Alleyoop

[rapidjim]

I will have to look around for the formula to figure displacement. I do know piston stroke is used to figure it, so if you don't know the stroke you can only get close.

Jim

[rapidjim]

Here you go the long way

divide piston size by 2 (61mm/2 = 30.5 then convert to centimeters(move the decimal point over a place) = 3.05

multiply by stroke converted to centimeters (58mm= 5.8)

displacement equals 1/2 piston size in mm converted to centimeters multiplied by itself multiplied by stroke in centimeters multipied by "pie" 3.14

or

3.05 * 3.05 * 5.8 * 3.14 = 169.41713 cc

Now here is the easy way

Reference www.buggydepot.com/buggy-tech-center/150cc/Yerf-Dog-Blade-GY6-Buggies-Parts/16#gy6_calc

61mm standard stroke (58mm) = 169.5 cc

61mm oversize stroke (60mm) = 175.35cc

62mm standard stroke (58mm) = 175.11 cc

62mm oversize stroke (60mm) = 180.14cc

63mm standard stroke (58mm) = 180.8cc

63mm oversize stroke (60mm) = 187.04cc

So the info I got before that I gave to you over the phone Alley was not correct. I corrected the person that gave me that info.

Jim/Owner
Rapid Repair

[Alleyoop]

Jim,
Fantastic!! Great info and explains it very clearly. Would be nice to be able to put in a stroker but that means shaveing more off the case): Which would probably make the case to thin and could crack.

Now is there also something that also calculates the HP created for each?
Alleyoop

[rapidjim]

Damn I love research!!!!!!

First off lets get one thing straight before some decides to argue my figures or my definitions.. There is basically two types of horsepower, Indicated Horsepower and Brake Horsepower. Basically Indicated Horsepower is a mathematical equation that calculates, under ideal conditions, what an engine should produce for horsepower. Where, Brake Horsepower is the actual power that an engine produces, tested on a dyno. Now if an engine is built correctly and has the right compression it should produce between 80 and 88 percent of the indicated horsepower.

Indicated Horsepower can be used to draw comparisons of what percentage of power increase could be expected from increasing bore and/or stroke.

First off the formula for calculating Indicated Horsepower (IHP)

Multiply the area of the cylinder by the length of stroke in inches and that product by the number of revolutions per minute then divide by the constant 10000 for two-cycle or 13400 for four-cycle engine, the result will be the I.H.P.

Cool Huh?

IHP = ( bore(inches) * stroke (inches) * RPM ) / 13400 (4 stroke)

150cc GY6 has a piston diameter of 57.4 mm and a stroke of 58mm

First we need to convert to inches, One Inch = 0.0393700787, for our purposes we will round off to 0.03937. So, diameter of a 57.4 mm piston is 2.2598 inches and the stroke is 2.2835 inches.

Now we need to figure the bore (area) of the piston. Area = 3.14 (pi) * diameter or
Bore = 2.2598 * 3.14 or Bore = 7.0958

Now using a constant of 6500 RPM we can figure IHP

IHP = (7.0959 * 2.2835 * 6500) / 13400 or IHP of a 150cc GY6 is 7.8599 or 7.86 IHP

Using a 59mm piston

IHP = (7.2937 * 2.2835 * 6500) / 13400 = 8.08 IHP ( 2.73% gain over stock)

Using a 61 mm piston

IHP = ( 7.5409 * 2.2835 * 6500) / 13400 = 8.35 IHP ( 5.87% gain over stock)

Using a 62mm piston

IHP = ( 7.6646 * 2.2835 * 6500) / 13400 = 8.49 IHP ( 7.43% gain over stock)

Using a 63mm piston

IHP = ( 7.7882 * 2.2835 * 6500) / 13400 = 8.63 IHP ( 8.93% gain over stock)

Jim/Owner
Rapid Repair

IHP reference, Loetzer's Hand-book, 9th Edition

[Alleyoop]

Jim,
That is Great!! But little disappointed at the numbers. If I understand it with a 62mm BBK the gain is NOT even 1 more HP or am not understanding the numbers:)
Alleyoop

[rapidjim]

That is what the figures say. Now keep in mind there are alot of other factors that determine power and speed, not just IHP. IHP does not take any other factors into play just bore and stroke. When dealing with a small motor 7.43% gain is not a bad thing.

Jim