2 Strokes Down Under

Gday lads,

I've been watching this forum for awhile and thought I'd register. My name is Liam (obviously) and I'm an avid motorcycling enthusiast. Alas I have not owned a 2T road bike however, I had and still do have a desire to custom build my own NSR500 in coming years, siamesing two NSR250's together. My most recent bike was a 2009 Honda CBR1000RR Repsol, bought new but had to sell it for family commitments. I am however looking to buy an RM250 dirt squirter as of yesterday, which will give me my bike (and blue smoke) fix.

I have a few questions for the legends and larrikins alike if you would be kind enough to welcome me aboard. Love the forums guys.

Cheers.

Welcome Liam!

We're are mostly 'heavy smokers' around here, but its great to convert new 2 stroke fans to our obsession.


Cheers, Markus.

Cheers Markus,

I've always been a massive fan of strokers, I've ridden a few. They don't come close to overall performance of the modern Superbike, but the feeling of thrust and sheer excitement in riding a stroker is too damn exciting, plus they are generally easy to fix.

Liam wrote:Cheers Markus,

I've always been a massive fan of strokers, I've ridden a few. They don't come close to overall performance of the modern Superbike, but the feeling of thrust and sheer excitement in riding a stroker is too damn exciting, plus they are generally easy to fix.

You might be surprised how good a well sorted RGV250 or RS250 will compare to more modern bikes. Yes, your top end rebuilds are fairly straightforward, no cams / valves, etc. to worry about

Also, they are now becoming unique and collectable.


Cheers, Markus.

wheels999 wrote: You might be surprised how good a well sorted RGV250 or RS250 will compare to more modern bikes. Yes, your top end rebuilds are fairly straightforward, no cams / valves, etc. to worry about

Also, they are now becoming unique and collectable.

Without a doubt, my dream bike is actually a Honda RS250W replica (I know you meant Aprilia ).

True they are. It's a shame that no one has bothered to make them create less emissions. I'd think it would be quite easy TBH.

Its been done already with snowmobile two stroke engines, sealed crank bearings, very low emissions. But Honda would rather sell four strokes to you.

The emissions from a small 2stroke in the grand scheme of things are really not that bad anyway. It's all a load of rubbish.

Completely agree there guys. Not only on Snowmobiles but also Marine outboards. I don't know why they couldn't just seal off the intake track from the induction to the crankcase, and the crankcase to the inlet port. Have two separate injectors, one that sprays a mixed fuel at the crank and piston from underneath with a simple fuel pickup at the bottom, and the actual inlet just have an injector spraying straight fuel into the cylinder. Yes I know that complicates things with EFI and a few extra bits and pieces, but it would improve drastically the efficiency and performance quite significantly IMO. Maybe I should modify a small 100 cc two stroke with my idea then scale it up.

Liam wrote:Completely agree there guys. Not only on Snowmobiles but also Marine outboards. I don't know why they couldn't just seal off the intake track from the induction to the crankcase, and the crankcase to the inlet port. Have two separate injectors, one that sprays a mixed fuel at the crank and piston from underneath with a simple fuel pickup at the bottom, and the actual inlet just have an injector spraying straight fuel into the cylinder. Yes I know that complicates things with EFI and a few extra bits and pieces, but it would improve drastically the efficiency and performance quite significantly IMO. Maybe I should modify a small 100 cc two stroke with my idea then scale it up.

Not another one DFI/EFI on a OEM bike is a fairytale and it isn't easy. You can do it with a LINK system and at the end of it you will have something that performs as well as a carby. Not as good as perfectly jetted carby even.

Why not mate, they have fuel injected 4 strokes. Why can't that technology be put across and a separate lubrication system be employed for the moving parts?

Injecting fuel at the intake does not cure the issue of your fuel charge leaving out the exhaust port before the port is closed.

The only way to fix this is injection direct to the combustion chamber at the right time, which requires very high pressures.

That's correct for a current exhaust port and intake port as it is in a 2 stroke cylinder.

If you could lower the Exhaust port closer to the crank shaft, meaning that the expanding fuel doesn't discharge til almost the end of the stroke and then once it is expelled and piston is on its way up past the lowered exhaust port, sealing the port and removing the vacuum and scavenging effect, then an injector can inject the fuel required for the combustion. Kinda hard for me to explain.

Liam wrote:Why not mate, they have fuel injected 4 strokes. Why can't that technology be put across and a separate lubrication system be employed for the moving parts?

2 strokes are not 4 strokes. Before you start banging on about jet ski's and sleds, jet ski's are on or off the throttle and sleds have a CVT which means they are never at part throttle or off the pipe.Just like a boat.

Direct injection won't go over about 9000 rpm.

If you could lower the Exhaust port closer to the crank shaft, meaning that the expanding fuel doesn't discharge til almost the end of the stroke and then once it is expelled and piston is on its way up past the lowered exhaust port, sealing the port and removing the vacuum and scavenging effect, then an injector can inject the fuel required for the combustion. Kinda hard for me to explain.

I don't think you have a accurate overview of the the two cycle engine. That is because your missing the blowdown period, without that vital small part of the cycle two strokes don't work very well at all. Next is the engine needs the scavenging of the pipe to work properly. Unless you have a whippersnipper.

2TInstitute wrote: 2 strokes are not 4 strokes. Before you start banging on about jet ski's and sleds, jet ski's are on or off the throttle and sleds have a CVT which means they are never at part throttle or off the pipe.Just like a boat.

Direct injection won't go over about 9000 rpm.

I don't think you have a accurate overview of the the two cycle engine. That is because your missing the blowdown period, without that vital small part of the cycle two strokes don't work very well at all. Next is the engine needs the scavenging of the pipe to work properly. Unless you have a whippersnipper.

What is a "Blowdown period 2T"?

Uh... don't make uncle Lozza angry now, sounds like he's run out of condensed milk