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Why aren't big bikes ever 2t?

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Diggs
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PostPosted: 18:48 - 15 Jun 2007    Post subject: Reply with quote

Check out this KH!!!

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hmmmnz
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PostPosted: 18:49 - 15 Jun 2007    Post subject: Reply with quote

Jack_Cheese wrote:

To be honest, i can only see one major downfall. Sure, the engine would burn less oil, be quieter and potentially be more reliable. But it would still need an expansion chamber to reduce emissions. The design of the 2-stroke engine means that the exhaust port is open while the piston is at the bottom of it's stroke, and inevitably some fuel will be lost through this gaping hole in the side of the bore.

another way round it would be to pressurise the mixture beyond atmospheric pressure using said supercharger, and inject it after the piston has gone past the exhaust port. There would be no increase in performance from this, but it would keep the engine clean and help the 2-stroke keep on living.

The thing is, new engines like this just aren't 2-strokes. A proper 2-stroke has an expansion chamber, burns gallons of oil, a powervalve blade in the exhaust and a full top-end rebuild can be done in under an hour. A new complex engine wouldn;t be the same, all the magic appeal of the 2-stroke would be lost.

Jack


did you have a look at the page?
it runs with a standard exhaust system, with no need for an expansion chamber as it has a rotary valve system on it,
http://www.sixstroke.com/images/discvlv_ff.jpg
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Wafer_Thin_Ham
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PostPosted: 18:54 - 15 Jun 2007    Post subject: Reply with quote

Svedebo wrote:
But imagine a bike like the R1 but in 2t. If it's already basically sneeze and you risk a wheelie...Wouldn't a high performance 2t be insanely fast and torqueish?


Insanely fast yes. In it's powerband.

Torque outside of the powerband would be non-existant.

Think RS250 x 4.

That would give you 220 bhp, with the lower weight off a 2t motor, 155kg dry should be achievable. Cool
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Kickstart
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PostPosted: 18:58 - 15 Jun 2007    Post subject: Reply with quote

Jack_Cheese wrote:
Previous attempts at big 2-strokes have lead to problems with overheating problems. The old kawasaki 750 triple was notorious for destroying the middle cylinder IIRC.


Quite a few 4 strokes have had similar issues.

Jack_Cheese wrote:
But it would still need an expansion chamber to reduce emissions.


You can happily run a 2 stroke without an expansion chamber (they are a comparitively modern refinement on 2 strokes, developed by MZ). Best way to reduce emissions is direct fuel injection. Relying on an expansion chamber might help at some revs but will make things worse at other revs.

All the best

Keith
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bish777
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PostPosted: 01:07 - 16 Jun 2007    Post subject: Reply with quote

Heat is more of an issue in strokers, the 4 stroke cycle allows more time for heat to disperse-overheating is more of a result of poor design than inherant flaws in the 4 stroke system.

However you may NOT want to get higher power outputs.

If you have a 1000cc 2 stroke and a 1000cc 4 stroke, you could have the same power output and run the 2 stroke at much lower RPM-much lower wear on bearings. Also if you go the supercharged route you can use valvegear much like a 4 stroke (or the slave piston thing on the '6stroke' motor). Doing it that way means that there is no need for an expansion chamber.

have the inlet port in the cylinder wall as in old two strokes, just have the exhaust ports in the head a'la 4 stroke, the induction supercharger can also help blow burnt mix up the exhaust as it fills the cylinder. This also avoids the need for direct injection.

I reckon a supercharged lower RPM stroke would be torquey, smooth and economical.
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gazzabo
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PostPosted: 02:16 - 16 Jun 2007    Post subject: Reply with quote

The old Yam RD 500 LC was a fast 2 stroke bike . but in them days the brakes , tyres and suspension was not up to it .
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Jack_Cheese
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PostPosted: 08:34 - 16 Jun 2007    Post subject: Reply with quote

hmmmnz wrote:
did you have a look at the page?
it runs with a standard exhaust system, with no need for an expansion chamber as it has a rotary valve system on it,


Sorry, i missed the link. I'll use it as mental hangover food. Thumbs Up Laughing

Edit: Just visited the site, and it is rather interesting, some cool ideas and concepts there.

I can't stand looking at engines from a physics point of view, the numbers melt my brain Sick Thumbs Down
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lilredmachine
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PostPosted: 09:13 - 16 Jun 2007    Post subject: Reply with quote

Quote:
If you have a 1000cc 2 stroke and a 1000cc 4 stroke, you could have the same power output and run the 2 stroke at much lower RPM-much lower wear on bearings. Also if you go the supercharged route you can use valvegear much like a 4 stroke (or the slave piston thing on the '6stroke' motor). Doing it that way means that there is no need for an expansion chamber.

I reckon a supercharged lower RPM stroke would be torquey, smooth and economical.


so in an effort to make the 2 stroke more reliable and emissions friendly, you are going to take away everything that makes a 2 stroke a 2 stroke? you'll end up with something akin to a diesel to ride, with none of the excitement or aural appeal of an old school 2 stroke. And as jackcheese pointed out, you'll make them far more difficult to rebuild in the process.

just seems like people are so desperate to save 2 strokes they are prepared to do away with the characteristics that make them different to the superior 4 strokes we have now. what's the point?

the original point of the thread was why there are no big capacity two stroke bikes, and although no one has answered the question directly, reading through the thread does answer the question. the point of the big capacity hooners like the gixxer thou and the r1 is that they are exciting to ride, have high red lines and make a noise that makes the adrenaline flow. They aren't sold on economy or emissions results. i could imagine the tagline now, 'the new suzuki gtsv1000 2t, smoother, quieter, lower revving, a bit like a diseasal, you know you want one'.
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Last edited by lilredmachine on 09:27 - 16 Jun 2007; edited 1 time in total
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hmmmnz
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PostPosted: 09:26 - 16 Jun 2007    Post subject: Reply with quote

this thread is brilliant Thumbs Up

ill have a go at trying to answer the why arnt there any big smokeys

lubrication.

thats it, thats all ive got, oooh and excessive heat.
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Kickstart
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PostPosted: 10:28 - 16 Jun 2007    Post subject: Reply with quote

lilredmachine wrote:
just seems like people are so desperate to save 2 strokes they are prepared to do away with the characteristics that make them different to the superior 4 strokes we have now. what's the point?


Agree to an extent. Although not that some already diesel like 4 stroke is superior. Only major problem that cannot relatively easier be solved with a bit of design effort is the emissions due to the exhaust port being open when fresh mixture is in engine, and that can be solved with some effort on direct fuel injection (something the car industry is having to do with 4 strokes to get them cleaner).

If it really came to it you could seal the bearings in the bottom end and provide them with the own oil supply, just leaving lubrication of the bores as a minor issue.

All the best

Keith
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Old Thread Alert!

There is a gap of 2 years, 181 days between these two posts...

tvr321
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PostPosted: 21:44 - 13 Dec 2009    Post subject: Reply with quote

Quote:
Honda have always hated 2 strokes. They spent massive sums of money developing the oval piston NR500 GP bike is a failed attempt to keep up with the 2 strokes and in the end gave up and built a 2 stroke themselves.

Yeah, it was called the NSR 500 and it friggin' kicked arse!
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salty21
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PostPosted: 22:17 - 13 Dec 2009    Post subject: Reply with quote

Svedebo wrote:
I'm guessing a 20x50cc cylinder 2t engine wouldn't really be practical... 20 exhausts...What would that look like?


i think it's do-able Laughing

http://www.youtube.com/watch?v=6ratfuML9QA

and another one but only 24 cylinder Neutral

http://www.youtube.com/watch?v=ZEv5Z1HV6-0
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Flip
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PostPosted: 22:27 - 13 Dec 2009    Post subject: Reply with quote

Wow, this thread is only 2.5 years old.
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Alexio
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PostPosted: 22:38 - 13 Dec 2009    Post subject: Reply with quote

What about that new engine posted on here a few days ago about a wet stump 2 stroke that is lubricated like a 4 stroke? Basically, that would solve most of the problems.
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LordShaftesbu...
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PostPosted: 14:48 - 14 Dec 2009    Post subject: Reply with quote

http://en.wikipedia.org/wiki/Rolls-Royce_Crecy

http://upload.wikimedia.org/wikipedia/en/thumb/a/ae/Rolls-Royce_Crecy.jpg/300px-Rolls-Royce_Crecy.jpg
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chris-red
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PostPosted: 14:59 - 14 Dec 2009    Post subject: Reply with quote

A 2t large capacity bike would be too expensive to rebuild I would have though. I mean a decent 125 piston is 60 that means it would be at least 240 for new pistons on a 600 il4 say. Not to mention gaskets bearings etc. doing that every 10k miles will not be fun.
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ms51ves3
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PostPosted: 15:01 - 14 Dec 2009    Post subject: Reply with quote

chris-red wrote:
...it would be at least 240 for new pistons on a 600 il4 say.


A small price to pay for awesomeness Wink
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Kickstart
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PostPosted: 15:08 - 14 Dec 2009    Post subject: Reply with quote

Hi

Detune it down to 600cc 4 stroke levels of performance and you could probably avoid having to change the pistons often at all. People seem to get an NSR to hit 30000 miles on the original pistons, and scale the power up with the capacity and that would give you a 120hp 600.

And check the price of a couple of new cams and the pistons don't look so expensive Laughing .

One problem with 2 strokes is that most of the work in developing engines is for racing and for cars, both of which only really bother with cheap, easily understood and compliant with racing regs 4 strokes.

All the best

Keith
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chris-red
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PostPosted: 15:13 - 14 Dec 2009    Post subject: Reply with quote

Kickstart wrote:
Hi

Detune it down to 600cc 4 stroke levels of performance and you could probably avoid having to change the pistons often at all. People seem to get an NSR to hit 30000 miles on the original pistons, and scale the power up with the capacity and that would give you a 120hp 600.

And check the price of a couple of new cams and the pistons don't look so expensive Laughing .

One problem with 2 strokes is that most of the work in developing engines is for racing and for cars, both of which only really bother with cheap, easily understood and compliant with racing regs 4 strokes.

All the best

Keith


I bought a whole tt600 engine for the Cams it cost me 2.20 Laughing I have rarely heard of a camshaft going wrong. Think how much a set of il4 2t barrells would cost if a ring caught on a port. Upwards of 1000 I would have though.
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Kickstart
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PostPosted: 15:19 - 14 Dec 2009    Post subject: Reply with quote

Hi

Smaller ports for an engine detuned like that and there should be no chance of a ring snagging.

Cams do go reasonably often. Last bit of the engine to get lube so they get wrecked when people start engines and rev them straight away (or have a Kawasaki choke which mostly appear to have nothing between "stall" and "6000rpm").

Suspect really that the makers can get as much power as they want from 4 strokes. Make 1hp more than your opponents and you have won the brochure war for that year. 10hp would also win it but just cost you a load more development money and still be overtaken then next year.

All the best

Keith
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Smooth
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PostPosted: 17:20 - 14 Dec 2009    Post subject: Reply with quote

Power is nothing without control and, in reality, fast bikes do have more than enough power for most riders.

Of course, if somebody did produce a big 2 stroke in a relatively low state of tune, everybody would be firing up their Dremels and 'tuning' them.....


.....bang!

2-strokes would be seen as 'unreliable' again.



The emissions laws are very strict and getting stricter.
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Kickstart
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PostPosted: 17:25 - 14 Dec 2009    Post subject: Reply with quote

MC Bodge wrote:
The emissions laws are very strict and getting stricter.


An ironically something that a direct fuel injection 2 stroke has as a potential advantage.

All the best

Keith
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Itchy
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PostPosted: 17:33 - 14 Dec 2009    Post subject: Reply with quote

Kickstart wrote:

An ironically something that a direct fuel injection 2 stroke has as a potential advantage.

All the best

Keith


Didn't somebody make a 2 stroke that did not require 2 stroke oil?.

Far too many inventions I read about but never come to fruition my fave being sometime in 1999 I read about a chain which was made out of a hardened plastic that would never need lubing. It was supposed to revolutionise industrial machinery.
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Kickstart
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PostPosted: 17:39 - 14 Dec 2009    Post subject: Reply with quote

Hi

Would be quite easy to make. You need the oil for the piston and bearings. If you can compress the mixture without using the crankcases (which could just be done with a supercharger) then you can seal the crankcases and use conventional 4 stroke lubrication.

The biggest problem with a 2 stroke is that the exhaust port and inlet port are open for a long time at the same time (same is true of a high performance 4 stroke with a bit of valve overlap, but nowhere near as long), hence a load of unburnt petrol goes straight down the exhaust. However if you inject the fuel after the exhaust port closes then this problem disappears.

Trouble is that getting direct injection to work quickly enough is difficult. Some cars have petrol direct injection but they are 4 stroke and only need to inject fuel 3000~4000 times a minutes, while a performance 2 stroke will need it about 3 times as often.

All the best

Keith
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Itchy
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PostPosted: 17:53 - 14 Dec 2009    Post subject: Reply with quote

Kickstart wrote:
Hi



Trouble is that getting direct injection to work quickly enough is difficult. Some cars have petrol direct injection but they are 4 stroke and only need to inject fuel 3000~4000 times a minutes, while a performance 2 stroke will need it about 3 times as often.


Keith


Hold on there was a question I asked a bit ago where one carb could serve more than one cylinder, so why don't they just put two fuel injectors which share the inlet port side by side, I believe even the fire blade has two injectors per cylinder. Hence each fuel injector has a cycle as fast as it normally operates with the other injector halving its workload.

I always heard an arguement for injectors was that they were smaller than carbs.
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