I will be starting on an experiment next year to see if I can fit a small turbo
to the NSR. Of course this would mean that I loose the beautiful exhausts but
it would be interesting. The only problem I can see at this moment is the carbs.
Does anyone know how much pressure these carbs can take? the best option is
to try and get throttle bodies but its going to be hard to get a size under 40mm.
I already have the right size turbo, just needs reconditioning then a pipe would be
custom built. Any information on these carbs would be great.
This project is just for testing and seeing if it is possible to turbo a NSR motor.
I dont think you will get much of a response since so few people have done what you are trying to do. Others will wonder why bother.
Is this a university project as it woudl be preferable to use a dyno test cell?
I have had a little involvement in turbochargin (landrovers). A lot of 4T turbo converisons run a suck through carb since trying to pressurise carbs not designed for it is difficult - steve burns etc. The Renault 5 used a pressurised carb IIRC. You will need to make sure all vents are also at the same pressure and run a fuel pump referenced to pressure. An potentially easier option is to use a plenum chamber with the standard carbs inside - effectively a pressurised carb enveloping airbox, with sealed cable entries etc
If you are only doing it for proof of concept then you can use an engine in a test stand, and run low boost pressure like 1/3 bar. Low pressure like this makes your life easier as you may just be able to pressurise the fuel tank and use easy to fabricate parts like sheet alloy for the plenum chamber or may be even fibreglass. Start out with low boost (1/5 bar), a couple of head gaskets and monitor the EGT and see what you can develop. Above a certain boost pressure you may not need inlet reeds. I guess crank seals would be good upto 2 bar boost. Dont forget extra cooling - both for the water and the turbo oil. An electric turbo oil pump may be OK for bench proof of principel tests, but I would want a mechanical oil pump for anything more serious.
It might be cheaper to use an RGV engine as parts are more readily avaiable in the UK.
Post up any pictures!
Good luck, Vincent _________________ NSRless again...
I'm just a private owner with 3 NSR motors. I have a friend with all the facilities to turbocharge just
about anything. They are into drag racing. They have turbocharged a Vespa 250cc 2-stroke for
interests and they got the little bike to work with the turbo after not to much time and money spent.
I will certainly keep this project updated and make use of your information. For now I am still
doing a little research on making the motor work as fast as possible. I'm looking to make maximum
power at 1bar boost, anything higher I think would mean making more work for yourself. But lets see
what we can put together and if we can make the motor reliable running on a turbo setup.
I don't know if it'd be worth the bother. It could be done but I don't think you'd improve the performance by that much. The problem with a crankcase scavenged two stroke is that the exhaust gases are still escaping when the piston is on it's way down and taking in fresh air/fuel mixture. This means that some of the air/fuel mixture escapes out the exhaust port and by turbo/super charging you're forcing more in AND more out. Sure, the pressure waves in the expansion chambers push a lot of it back in but the chambers are only tuned to do that at a certain rev range (read power band). Anyhow, carbs and turboing ARE a bad idea - very troublesome to fit an intercooler (without one the engine is prone to detonate) and you end up with fuel atomisation problems.
Another point to consider is the crankcase seals on boost and if they could take it.
Certainly though turbo/supercharging a two stroke IS a GREAT idea but it would require a rework of how a crankcase scavenging two stroke works, namely, doing away with it and going to a valve system similar in function to a four-stroke. Direct fuel injection and variable valve timing are high up on the priority list too. How I envision it working is when both valves are closed, air and fuel are forced in to the cylinder. Piston travels up to TDC and fires forcing the piston back down on its power stroke and the exhaust valve opens. Some spent gases leave due to pressure. Shortly after, the inlet opens _while the exhaust is still opened_ but only air is forced in to the cylinder to evacuate the last of the exhaust gases (as remember, we are missing an exhaust stroke to push out the spent gas) and to aid in cooling. Shortly after, the exhaust valve closes, the pressure builds in the cylinder and fuel is forced in, leaving as back where we started.
I think this is similar to how the old diesel supercharged two-strokes operated. No need for expansion chambers, sadly, as no spent fuel is escaping but it would be a highly efficient engine if someone got it to work. I'd say it'd be easier to play around with a banshee motor as parts are more common and cheaper, and either way you go you're sure to shag a cylinder and maybe a rod occasionally experimenting and we don't want fewer parts available to go around
Other interesting concepts on how to get valves operating is using a servo operated open pipe that has a hole cut in the side of it like a flute (someone mentioned somewhere that Norton used this design early on). The flute hole would line up with the exhaust port to allow gases to leave. This would eliminate energy spent lifting valves against springs and friction on cam shafts and turbulence. Best to have the inlet valve in the top of the head as in a four-stroke so that air can be forced in the top evacuate the exhaust sooner. Two stroke exhaust port position could be retained.
Anyway, just some ideas I had. Seems if your friend has the setup to do serious work you may as well take advantage of it and do something really impressive. Fuel injection is the way to go if there is any chance of seeing two strokes out side of museums in ten years but fuel injection without a different means of scavenging seems to be wishful thinking. _________________ MC21 Honda NSR250. TYGA 300 conversion.
I've seen pics of a 3 cylinder turbo banshee. They use a single common expansion chamber (big enough to fit you head inside) with the turbo connected after the expansion chamber.
I liked reading your post shyster, I can totally picture how a valved turbo two stroke could be very a efficient and powerful engine.
You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum You cannot attach files in this forum You cannot download files in this forum