Dumb noob question

thxcuz

thxcuz

Active Member
I enjoy my motorized bicycle but I am totally ignorant when it comes to mechanics.
Can someone answer my question?
Does the cubic centimeters of an engine determine power or just size? Can different displacement have the same horse power? I have a 26 cc engine and can go 20+ on a flat stretch. I read that the solex and the amf roadmaster had 49cc engines and were much slower. But wouldn't the larger engine have more power ( or as my dad used to say "more Whomp to" "
Thanks
 
It depends on the engineering of the engine. Some engines are small cc, but extremely high horsepower. Take morini engines for example. 49cc, 11 to 15hp stock, depending on the exact model. My minibike engine, 98cc, maybe 3 or 3.5hp with the governor removed. Generally speaking, high horsepower engines dont make much torque unless geared properly, which is a little on the low side. Lower hp engines tend to have decent torque with slightly higher gearing. You can put a morini engine in a bicycle and gear it to do 65, but it will take forever to get there, and it'll be a dog on hills. My minibike engine is geared for 32, gets there pretty quick, and climbs hills pretty nicely. I wouldn,t gear my bike any faster because I would lose torque. I wouldnt gear it any slower because I would constantly be over-revving it trying to get the speed I want. So in short, it depends on what the engine is made to do, what rpm/horsepower it makes, and how you gear it.
 
you can have a 8hp 50cc engine and a 4 hp 100cc engine - its all in the size of carb / quality of exhaust / port work etc. etc. etc.

To answer your question simply I think that displacement does not correlate to hp as much as tuning and upgrades do. Then again theres the old saying "theres no replacement for displacement"
 
Comparing different engines is like comparing apples to oranges. You can't do it effectively. That said, if you have two identical engines, same induction system (carburetor, intake manifold), cylinder head, fuel, ignition, etc, and one has more displacement, the larger of the two will typically produce more horsepower. As was said, there's no subsitute for cubic inches, no matter what. The keyword for the above is, "identical engines" in every respect except for displacement.

Tom
 
My 5.7 liter '74 Nova was rated at 155 hp.

My 2.5 liter '06 Altima makes almost 200hp.......and uses a third of the amount of fuel to do it! With that being said, the Nova had a boatload more torque.

There are lots of tricks and engineering updates that can be applied to engines now.
 
A lot of it depends on the RPM range of the engine. Higher revving engines engines make a ton of HP and less torque (like the Morini or Tomos). Lower revving engines make less HP and more torque. A hi revving engine works well with an internal multi speed gearbox or jackshaft shift kit.
 
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