Hypothetical question?

[noobster]

Hypothetically... If you had a 2 stroke and 4 stroke with the same max hp which would get better fuel economy? I think a 2 stroke 50cc and a 4 stroke 90cc may be comparable. Anyways hit me back, thanks. -Ryan

[Kenny_McCormic]

If you have two engines of the same displacement, bore stroke, and chamber design the 2 stroke will eat twice as much gas and maybe a hair more but it will make twice as much power and maybe a hair more compared to the 4 stroke.

Why? Because the 2 stroke every time the piston moves down power is made, on a 4 stroke you only make power every other time the piston goes down.

[Dac]

yeah, 2 stroke use twice as much gas. BUT 2strokes have so much power, that you can get just as much power at like 1/2-2/3s throttle.
so you save gas there by not having to hold it wide open.

[noobster]

Thank you guys for trying though you answered a question I did not ask. To Clarify imagine two engines one being a small 2-stroke and the other being a larger 4-stroke both making the SAME max HP(not the same displacement). Now which one would get better gas millage? In other words, which stroke style is more efficient in regards to gas vs. hp?

[Bear45-70]

Thank you guys for trying though you answered a question I did not ask. To Clarify imagine two engines one being a small 2-stroke and the other being a larger 4-stroke both making the SAME max HP(not the same displacement). Now which one would get better gas millage? In other words, which stroke style is more efficient in regards to gas vs. hp?

Chances for the better mpg are on the 4 strokes side. All 2 strokes have an efficiency problem with unburnt fuel going out the exhaust, hence causing lower mpg numbers.

[noobster]

Thank you. I was leaning towards that conclusion myself but I'm no expert when it comes to 2-strokes. All in all 2-strokes seem appealing because of the ease of rebuilding and low amount/cost of parts, but we'll see. Though whatever I do I think I'll shoehorn it in a spree just because I like the way they look
Shameless plug here, but if you would like to check out my <0.01$ per mile, 800 watt, 28mph, e-bike your welcome to at electricky.googlepages.com (no www.). I'm asking these questions because I need something that can be quickly refueled/recharged, my bike is great but it takes about 2 hours to charge for a 25 mile trip

[Kenny_McCormic]

Thank you guys for trying though you answered a question I did not ask. To Clarify imagine two engines one being a small 2-stroke and the other being a larger 4-stroke both making the SAME max HP(not the same displacement). Now which one would get better gas millage? In other words, which stroke style is more efficient in regards to gas vs. hp?

Chances for the better mpg are on the 4 strokes side. All 2 strokes have an efficiency problem with unburnt fuel going out the exhaust, hence causing lower mpg numbers.

Direct fuel injection solves that issue, the bottom end is like a 4 stroke and in a non consumable oil bath, the intake air is blowing into the jug with ports just like normal intake ports but they connect to a turbo or blower instead of the crank, all that is blown is air. Nothing but air comes form the exhaust.

When the piston starts upward travel the second the piston closes off the intake ports a small head mounted fuel injector similar to a diesel injector injects a pre calculated computer controlled amount of fuel. Near TDC it lights with a spark plug and works like an normal 2 stroke.

There ya have it a 2 stroke as efficient as a 4, Im pretty sure some Italian scooter companies are now using this technology.

[Bear45-70]

Thank you guys for trying though you answered a question I did not ask. To Clarify imagine two engines one being a small 2-stroke and the other being a larger 4-stroke both making the SAME max HP(not the same displacement). Now which one would get better gas millage? In other words, which stroke style is more efficient in regards to gas vs. hp?

Chances for the better mpg are on the 4 strokes side. All 2 strokes have an efficiency problem with unburnt fuel going out the exhaust, hence causing lower mpg numbers.

Direct fuel injection solves that issue, the bottom end is like a 4 stroke and in a non consumable oil bath, the intake air is blowing into the jug with ports just like normal intake ports but they connect to a turbo or blower instead of the crank, all that is blown is air. Nothing but air comes form the exhaust.

When the piston starts upward travel the second the piston closes off the intake ports a small head mounted fuel injector similar to a diesel injector injects a pre calculated computer controlled amount of fuel. Near TDC it lights with a spark plug and works like an normal 2 stroke.

There ya have it a 2 stroke as efficient as a 4, Im pretty sure some Italian scooter companies are now using this technology.

Every 2 stroke outboard made since about 2002 is using Direct Fuel Injection( DFI) technology. It is very true, DFI solves the 2 stroke's problem. However even the outboard manufactures and the likes of Briggs and Stratton and Honda also know that on small displacement engines, that is less than about 50 CID, DFI is way to expensive to build compared to 4 strokes. Hence the move to 4 stroke for all small engines in this country. I ought to know, I worked thru the 7 year change over period from old 2 stroketechnology to DFI and the smalle 4strokes in the outboard industry.

Actually a DFI squirts the fuel in even before the exhaust port closes, but not long enough before for any of the fuel to escape out the exhaust. I spent several weeks with both Mercury and Johnson/Evinrude factory schools learning about and tinkering with DFI engines.

[Kenny_McCormic]

I bet it could be done mechanically.

[Bear45-70]

I bet it could be done mechanically.

If it could be done mechanically, don't you think by now at least one of the manufacturers would have found a way to do it? The problem is you can't just use the same fuel charge at all engine speeds. That's why the computer is needed. Also this happens fast, that little piston in a less than 2" stroke engine at 8000+ rpm doesn't give much time to squirt the fuel in because you don't have the full stroke distance available to use. You need to cover the exhaust port before the fuel gets to it.

[Kenny_McCormic]

Fuel pump driven by crank, higher rpm=higher pressure, and the 57chevy had mech fuel injection as an option. Many high performance engines were mechanically injected before integrated circuits go cheap.

[Bear45-70]

Fuel pump driven by crank, higher rpm=higher pressure, and the 57chevy had mech fuel injection as an option. Many high performance engines were mechanically injected before integrated circuits go cheap.

Yeah there sure were. They were not that efficient and were expensive and didn't work well longevity wise. Diesel don't even use that system anymore. You think maybe there was a reason for that stuff to not become standard production equipment on the standard cars? A $2 or $3K injection system on a $200 dollars scooter is ridiculous and you have now jacked the price of a new scooter to a minimum of double the cost.

[noobster]

Single cylinder turbo 2 stroke diesels have a one lobe camshaft and a single exhaust valve, similar to a 4 stroke in operation, in the combustion chamber. The charged air is sent through the uncovered cylinder port at the bottom of the power stroke pushing the exhaust out of the open valve at the top of the combustion chamber while simultaneously positively charging the cylinder once the exhaust valve shuts but before the compression stroke of the piston covers the intake port. There is also a preignition cup with a injector recessed into it like in many diesels. Quick question, I have access to a dyno and smog test equipment at my college because we serve as the local California referee, could I tune a 2-stroke for maximum fuel economy on that equipment?