why dont they make...?

[Brewskiz3]

why dont they make a dirtbike that is

(direct efi)

Isolated crank so it acts like a 4 stroke bottom end.

2 stroke

with power exaust valve and a blower

that would eleminate the need for mixing. no more lubing the crank with mixed gas, plus it would stomp a 4 stroke for power and it would have 2 times the snap plus it could rev to the moon

[Alex_YZ450F]

Because Four strokes create more revenue.

[Brewskiz3]

interesting. i h8 those h0's

[enduro4231]

why dont they make a dirtbike that is

(direct efi)

Isolated crank so it acts like a 4 stroke bottom end.

2 stroke

with power exaust valve and a blower

that would eleminate the need for mixing. no more lubing the crank with mixed gas, plus it would stomp a 4 stroke for power and it would have 2 times the snap plus it could rev to the moon

I'll tell you why. They don't want to spend the $$$$$$$$$$ developing it when they could just spend it improving current designs. Anyway what's the big deal with mixing, and the crank becing lubed by the premix? Mixing takes 2 seconds and I've never had a crank fail.

[JohnnyOfast]

So how are you going to lube the top end?

You did say a 2t top, thats why its mixed to begin with, crank just came along for the ride.

You would still be mixing.

(funny, I was thinking of this recently but couldn't come up with a way to lube the 2t top end.)

[Honda80]

thats a good idea..but itl sadly never happen

[EuroFreak]

It's been done-Skidoo Semi-Direct Injection for Seadoos and Skidoos meet the 2006 emissions and get much better gas mileage than the 2T competition w/lots of power. Suzuki used a location specific oil injection in the '70's on all thier street two strokes. Made for less oil used but was a little more complicated casting.

A blower works better on a street bike or sled because of the weight and bulk but you could put one on anything. Don't think it would be very useful on a dirtbike.

Honda's 2T was very promising as well-wonder why they shelved that project?

[frncsc]

why dont they make a dirtbike that is

(direct efi)

Isolated crank so it acts like a 4 stroke bottom end.

2 stroke

with power exaust valve and a blower

Because turbo/super charging is prohibited according to FIM rules.

[Brewskiz3]

So how are you going to lube the top end?

You did say a 2t top, thats why its mixed to begin with, crank just came along for the ride.

You would still be mixing.

(funny, I was thinking of this recently but couldn't come up with a way to lube the 2t top end.)

but then why dont 4 strokes have to mix? hmm

because engine oil lubes everything

since the 2t doesent have a valve train other then a powervalve setup

so you wouldent need to mix, im not sayin that mixing is a big deal it would be rad if that was a top idea

[enduro4231]

You would have to have a fair sized oil resevoir with it constantly being burned off.

[CBus660R]

Well, an engine like this does exist. Big diesel marine engines are 2-strokes with a blower and an isolated crankcase. http://people.bath.ac.uk/ccsshb/12cyl/ The problem with this design for dirtbike applications is you lose 2 big advantages of the current 2-stroke design. The 1st is that it's a compact engine, the 2nd is that it's a simple engine to work on.

[I_Sneebarted]

but then why dont 4 strokes have to mix? hmm

because engine oil lubes everything

since the 2t doesent have a valve train other then a powervalve setup

so you wouldent need to mix, im not sayin that mixing is a big deal it would be rad if that was a top idea

What he means by "not being able to lubricate the top end" is that although the crank would be lubricated, the cylinder wall and rings would not.

Even if you had a piston design like a 4-stroke (oil holes, oil rings/wipers, ect) it still wouldn't work. In a 4-stroke, the ports are overhead thanks to valves... on a two-stroke however, the ports are casted into the cylinder wall. This would allow some oil to get squirted out the exhaust port every time the piston went over it, and would require you to constantly add oil to account for what is being lost.

So, basically... you will always need pre-mix.

[Britishbikes]

Detroit Diesel used to make a two stroke engine very similar to the one you described, except it was a diesel commercial truck engine. I have never driven a truck with one, but they were V-8's with a roots type blower. They have a distinct sound and were once pretty common in class 7 amd 8 trucks. A friend of mine said they had a quick throttle response and lots of torque. I don't know why they were discontinued; I have never heard anything bad about them. Looking into this design would be a starting point; you might find some limiting factors which would preclude its use in a high performance gasoline application.

I have a feeling that the new direct injection for gas engines would work here, Bimota worked on a direct injected two stroke streetbike in the 90's but they could never get it to run without fuel delivery glitches and then they gave up. Perhaps the newer injection is better. You have to remember that a two stroke engine spinning 13k would require an injector to cycle about 4 times faster than in a four stroke passenger car engine and about 12 times faster than in a heavy truck engine. This was one of the problems for Bimota.

Another thing I have thought about is that since a two cycle engine almost has to have the exhaust and intake strokes happening at the same time, it would be little advantage to have the extra weight and expense of a blower because any attempt at actually supercharging the cylinder would just blow most of the charge out the exhaust port. You would never have more power than a regular four stroke running one atmosphere (15.8psi) of boost, even if the breathing was 100% efficient. So it would make more sense if you already are going to spend money on a blower, to run an intercooler and blow a regular four cycle engine at about 20psi or more.

If all you want is to not have to premix the oil and gas, you know older two stroke streetbikes and dualsports had a separate oil tank and a little pump to mix the oil for you, so that when you filled up at a gas station you just put in gas. Lots of two-cycle outboard engines have a similar feature.

You're not the only one to dream of how to pressure oil the bottom of a two stroke and supercharge the top. So far the only productive way to force a two cycle to make lots more power is with NOS, at least that I have seen.

[CaptDan]

why dont they...

Chrysler messed with that idea for a while...

http://www.allpar.com/neon/stroke.html

...and Orbital had something similar...

http://www.banksiafdn.com/page_assets/Case2003_Orbital.pdf

[CBus660R]

I forgot to mention that the diesel engine in GM's mdeium/heavy duty trucks back in the 30's till ??? was a 2-stroke with a Roots style blower. It was known as a 4-71, 6-71, or 8-71 depending on whether it was a 4, 6, or 8 cylinder motor. You ever hear about hotrods from the 50's having an 8-71 blower? Guess where it came from.