40mph speed secrets revealed

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Humsuckler

Humsuckler

New Member
Jul 28, 2009
457
1
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Ontario
ah! i didnt envision it a a long taper cone my mucho ap-oligo to you mofrere

that pipe is going to work great i think. is it set up for midrange top end?

looks like it is gonna be friggin shweet (make sure you put a nice stinger on the end of that and run it mufflerless of course, wouldnt want to lose any power on that monster!

on a side note, i never even clued in to the fins untill it was mentioned, you could run into an issue there, perhaps you can ratrod up an air catch and direct it down?
 
F

Foximus

New Member
Sep 28, 2009
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Orlando
Vertical fins cool better for slow moving engines, especially at idle. Horizontal cools better for fast moving engines.

30mph is still considered a slow moving engine.
 
G

gberry50

New Member
Jun 16, 2009
20
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0
snowflake,az
that's a lot of work for just 40mph Im already there with minor piston port matching
and a very good expansion chamber Im hoping the new reed valve set up will get me to a 28 tooth rear sprocket and 50mph!
 
foureasy

foureasy

New Member
Jul 9, 2009
478
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tucson
this motor hasn't actually run yet, but since it is a true 79cc motor, i imagine it shouldn't run too bad. where did you get your very good expansion chamber?
 
foureasy

foureasy

New Member
Jul 9, 2009
478
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tucson
thanks, gearnut. but apparently gberry50 thinks i should simplify, i rode simple in the beginning and it sucks.
 
T

thehatchninja

New Member
Feb 26, 2009
5
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Columbia, SC
Was the spacer under the jug just to space it up some, or is it an adapter? 40mph doesn't seem too difficult, but this motor is sure to run for a lot longer than most.
 
BarelyAWake

BarelyAWake

New Member
Jul 21, 2009
7,194
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Maine
thehatchninja said:
40mph doesn't seem too difficult...
Click to expand...
With these small engines there's a wall at about 35mph caused by the combination of a lack of torque and escalating wind resistance. The drag ratio involves some very messed up math where the resistance is squared... making every mph past 20ish harder and harder to get.

"Assuming a more-or-less constant drag coefficient, drag will vary as the square of velocity. Thus, the resultant power needed to overcome this drag will vary as the cube of velocity."

>.<

I hate math - but suffice to say physics isa ***** - it boils down to pretty much if ya wanna go twice as fast you'll need at least four times the power (more actually, a lot more as the effect is exponential - but ya get my point lol). With the speeds foureasy is already achieving it'd be actually far easier to gain significant speed by reducing resistance (like an aerodynamic shell) than tweakin' the motor any more. Honestly to get more speed he'd prolly hafta double his displacement at least, and that would only gain about 1/3 more speed... if that.
 
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Humsuckler

Humsuckler

New Member
Jul 28, 2009
457
1
0
Ontario
you have a ten mil stroker happytime? you are my hero.... haha (no, seriousley, all you need is a top notch crankshaft assembly and you have it made!)
 
Bikeguy Joe

Bikeguy Joe

Godfather of Motorized Bicycles
Jan 8, 2008
11,837
252
63
up north now
BarelyAWake said:
With these small engines there's a wall at about 35mph caused by the combination of a lack of torque and escalating wind resistance. The drag ratio involves some very messed up math where the resistance is squared... making every mph past 20ish harder and harder to get.

"Assuming a more-or-less constant drag coefficient, drag will vary as the square of velocity. Thus, the resultant power needed to overcome this drag will vary as the cube of velocity."

>.<

I hate math - but suffice to say physics isa ***** - it boils down to pretty much if ya wanna go twice as fast you'll need at least four times the power (more actually, a lot more as the effect is exponential - but ya get my point lol). With the speeds foureasy is already achieving it'd be actually far easier to gain significant speed by reducing resistance (like an aerodynamic shell) than tweakin' the motor any more. Honestly to get more speed he'd prolly hafta double his displacement at least, and that would only gain about 1/3 more speed... if that.
Click to expand...
Fo'sho'! Gear up and streamline if you really want to see a mile a minute. Also, pay up your life and medical insurances.
 
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