2 stroke-4 stroke

[bigbore]

I love 'em both.My biggest problem is the unfair rules that make competition virtually impossible.It makes me sad to see the smokers leaving the market little by little.My CRF450R is a hoot to ride as is my YZ465.I'd love to see modern big bore smokers available at less than 8-10K.But that's unlikely to happen.....sigh.

There's a lot of child like "hater" foofoo going on around here wasting bandwidth.We should be sharing info on the care,feeding and use of our smokers instead of posting I hate four strokes garbage.Let's celebrate our wonderful smokers and share info instead of wasting time posting crap.Make this a good board.

P.S. Flaming me away from the board would be a mistake.

[JohnN]

Big Bore - I totally agree!

We should be talking about the care, feeding and promotion of the two-stroke. As has been mentioned before I don't hate four-strokes, but I do think that the lopsided rule has "convinced" people that they "had" to have a four-stroke. Even though in some cases they wouldn't have chosen it over the two-stroke except they felt they had to on order to be competitive.

All voices are welcome here.

No one will flame anyone because if they do, their post will be deleted. Do it enough times and you will be banned from the site.

As I mentioned when starting this forum, I don't want bullies ruling the roost. This forum is for fans of two-strokes. To be a fan does not mean that you have to hate anyone or anything.

[JETZcorp]

Brilliantly said.  Although I do not like four strokes in a dirt bike role, I appreciate them as an engineering accomplishment.  It's that unnecessary complexity that makes it fun to watch them work.

But, that's not why I will defend four-stroke fans (or sympathiers) against abuse.  Above all other beliefs which I hold (no really, ALL of them), I feel that everyone deserves to speak their mind, regardless of how out-numbered or unpopular their view may be.  We can't allow ourselves to drum out dissenters, because that is a path void of discovery and wearing a sticker reading, "made in N. Korea". As the line goes, we must keep our minds open, butnot so open that our brains start dribbling out.

[Recovered]

I don't "hate" four strokes in a literal sense. I hate what has happened. I hate how it happened. And I really hate WHY it happened.

That being said, I have spent a huge amount of my life with four strokes. IMHO, in single and twin cylinder applications, a two stroke will always be better than a four stroke, no matter how "modern" they say it is. Once you get into triples and more, the two stroke loses its appeal, because there is a lack of room for expansion chambers.
So wait...maybe I do hate four strokes..........

[JETZcorp]

Well, Evinrude and all those outboard dudes have done very well with big, six-cylinder two-strokes which don't have, and presumably don't need expansion chambers.  They're destroying the 4T competition in power and weight as it is.  Whatever they're doing, I see no reason why it wouldn't work in a Dodge Neon.

[Recovered]

I have seen but not studied those out. They could be viable....but it will be a hard sell to the millions who think of them as "smokers"

[JETZcorp]

It might be, but in the outboard motor community they've proven very popular.  They appeal to a market that remember the good old days of two-stroke power, and when they're told that two-strokes are now just as clean, and are in fact used by the guys who patrol Lake Tahoe against "over-polluting engines" they buy into it pretty fast.

I think in the car market, which is made largely of "average people," they will have never heard of a two-stroke and it can thus be marketed as new, small, powerful, and clean.  By the way, here's an interesting bit of trivia, which I think I picked up from one of the ye olde articles on this site.  Orbital makes a lot of the injector technology for these outboards (though not Evinrude, if I recall) and they have received interest in varying degrees from automakers like GM, Chrysler, Ford, Toyota, Nissan, etc.  Honda isn't on the list, even though they have more "history" with two-strokes than any of the others.  Hmm...

There are exceptions, of course.  My friend's family up in Canada bought this monstrous, anemic Yamaha four-stroke outboard for their boat.  At one point, I saw a guy running a Mercury Opti-Max (clean, DI two-stroke) with the same power but with half the size.  I pointed out that he was running a two-stroke, and the reply was, "Yick, I can almost smell it from here."  I couldn't quite bring myself to correct them, but in hindsight I should've.

For what it's worth, this friend is in the market for a dirt-bike, and because I'm the one who got him into it, he's looking for a '77-'82 Husky 250.

[juliend]

I think multi cylinder 2 strokes will become more feasible after we see more done with forced induction on the 2t engine. The drawback to this (imo) will be the requirement of some sort of camshaft and a more 4t style exhaust valve. If the exhaust port is closed, then the forced induction can replace the scavenging affect that the pipe offers. We can still get the same sort of performance, but in a much more efficient way. I'm really looking forward to these type of engine designs in the future!

[bigbore]

An exhaust valve is not needed for forced induction on a two-stroke.Port timing and a pipe designed for that application will do the job nicely.After all one of the reasons two-strokes make more power is the fresh charge comes in under pressure via crankcase compression.It's a forced induction already and a good pipe will enhance that.

[Recovered]

I agree that these new designs have potential. I'm more worried about the here and now, and sadly 97% of the still existing 2 stroke market has no idea how to tune one.

I'm thinking about a book................some of which is already written

All that said, a boat is somewhat different than a motorcycle, in that it has a relatively narrow power band. You can size a pipe to work with a small expansion chamber, or without one at all.

As far as I am concerned ALL Otto cycle internal combustion engines NEED a scavenge cycle. I'm not going to go through it here but it is so important that 4 stroke guys spend countless hours and dollars studying this phenomenon. And for good reason. It broadens the powerband for one....

[juliend]

An exhaust valve is not needed for forced induction on a two-stroke.Port timing and a pipe designed for that application will do the job nicely.After all one of the reasons two-strokes make more power is the fresh charge comes in under pressure via crankcase compression.It's a forced induction already and a good pipe will enhance that.

Agreed. I did not mean to say it was necessary. It will be a lot easier to have several 2 stroke cylinders without the need for several expansion chambers though.

[Recovered]

An exhaust valve is not needed for forced induction on a two-stroke.Port timing and a pipe designed for that application will do the job nicely.After all one of the reasons two-strokes make more power is the fresh charge comes in under pressure via crankcase compression.It's a forced induction already and a good pipe will enhance that.

Agreed. I did not mean to say it was necessary. It will be a lot easier to have several 2 stroke cylinders without the need for several expansion chambers though.

That's exactly my point. I love what the expansion chamber brings to the table. I don't like how much space it eats up.

[bigbore]

Four-strokes do have a scavenge cycle.It's called overlap.

[Recovered]

Four-strokes do have a scavenge cycle.It's called overlap.

Exactly.

[JETZcorp]

If we could go back to the bit about forced induction, someone said that the two-strokes de-facto forced induction helps it against four-strokes.  Not really.

When a 4T takes in air, it takes in the engine displacement of gas, then the valve closes and the engine goes to work.  With forced induction, gas is pushed by the turbo- or super-charger as well as being sucked by the piston, so you get more gas in that 450cc or whatever of space.  With a 2T, the piston pumps the engine displacement of gas into the cylinder, but some of it escapes out the exhaust.  The expansion chamber helps - but does not fix - this problem.  Additionally, before closing off the transfer ports, the piston starts pumping air back into the crank, further reducing the charge.  Thus, a classical 2T gets less air per power-stroke than a naturally-aspirated 4T, and a lot less than one with a supercharger.

In 2T diesel designs, even though the engine has a supercharger, it's referred to as a scavenging pump, because you're substituting the supercharger for that extra pair of strokes.  This doesn't mean that it's not an improvement, however.  If you go forced-induction, you can lower the exhaust port, giving you a longer power-stroke and less fresh charge lost in the scavenging process, resulting in higher compression and more power-per-stroke compared to a classical two-stroke.  The problem, of course, is the weight of a supercharger on a bike.  In an outboard motor or a car, it doesn't really matter as much, which is why I think Evinrude-style DI two-strokes should be the future of multi-cylinder internal-combustion.

Incidentally, this new configuration with the changed exhaust port placement may make the expansion chamber unnecessary, which would be quite convenient for a V12 2T.