predator engine, easy way to remove governer

[Frankenstein]

Those of you who have done this, what seems like a reasonable top rpm for the 79cc? Like the speed you would cruise at without reservation?

Well it's listed at 3600 rpm max on Harbor freight, but it also mentions that the max torque is 3 and a half ft/lbs at 2500 rpm. That would indicate that above 2500 you start getting less power. If I was to build a bike I would try to get my gear ratio to match my ideal cruise speed at that rpm.

If I was to go with a multi gear set up then it wouldn't matter too much as long as my highest gear gets the speed I want at that rpm, and the lowest gear is capable of climbing the steepest hill I expect to encounter.

 

[butre]

Well it's listed at 3600 rpm max on Harbor freight, but it also mentions that the max torque is 3 and a half ft/lbs at 2500 rpm. That would indicate that above 2500 you start getting less power. If I was to build a bike I would try to get my gear ratio to match my ideal cruise speed at that rpm.

If I was to go with a multi gear set up then it wouldn't matter too much as long as my highest gear gets the speed I want at that rpm, and the lowest gear is capable of climbing the steepest hill I expect to encounter.

just less torque past 2500, not less power. remember power is a factor of torque and rpm.

I wouldn't cruise past about 4500. remember they're designed to be dead reliable and run for hours at a time under heavy load at 3600. max rpm will be naturally limited by valve float. just try not to let a valve touch the piston.

 

[butre]

this is what a typical dyno sheet looks like, in this case for a corvette Z06

notice how torque tops out around 4700 RPM while power keeps climbing all the way to around 6300

 

[Street Ryderz]

Displacement 79 cu. in
Torque 4.5 ft-lb
Max. Speed 3,600 RPM
Shaft Diameter 5/8 in.
Shaft Rotation CCW
Shaft Length 2.4 in.
Shaft End Tapped (Diameter (in) / Threads Per Inch) 5/16-24 UNF
Air Cleaner Type Foam
Fuel Type Gasoline
Fuel Tank Capacity 1.58 qt.
Fuel Filter Yes
Oil Capacity .37 qt.
Lubrication System Splash

Low Oil Shutdown Yes
Start Type Pull
Ignition System Transistorized Magneto
Governer System Yes
Number of Cylinders 1
Bore Diameter 2.13 in.
Stroke 1.5 in.
Compression Ratio 9.1:1
Muffler Yes
Spark Plug Use NGK BP6HS or Champion L92YC
The Canadain version says 4.5ft-lb at 3000 in the manual that comes with engine! and 3hp thats pretty darn good output for a geared setup!

 

[Cozmik Mezzenger]

I was using an NGK BR4HS plug. Why is the NGK BP6HS preferred or recommended?

 

[Cozmik Mezzenger]

If you are going to be racing using this engine then you will need to get an aluminum flywheel so that it can withstand the higher RPMs you can get with running without a guv'nor and with larger volume carbs and exhausts. I read somewhere that a stock flywheel can fly apart at higher than recommended RPMs. Imagine a piece of flywheel embedded into your leg, or worse! :-(

 

[Street Ryderz]

The NGK BP6HS is deeper into the chamber and not as hot!

 

[Cozmik Mezzenger]

The NGK BP6HS is deeper into the chamber and not as hot!

Why are those desired characteristics? Is cooler better? Why is that? And what does "deeper" do for performance?

 

[Street Ryderz]

Cooler is better at keeping the operating temp where it should be and less chance of pre ignition,detonation.Also deeper in the combustion chamber will help to get a more efficient full burn!

 

[Cozmik Mezzenger]

Cooler is better at keeping the operating temp where it should be and less chance of pre ignition,detonation.Also deeper in the combustion chamber will help to get a more efficient full burn!

Thank you. I will give it a try!