modern 2 strokes

[maxc]

I run a pretty wild 2-stroke motor in my drag snowmobile - 8.8 seconds for the 1/4 on tarmac. To hit that time it was a 3 cylinder 1000cc running 118 octane race fuel on Lectron carbs with a very high output MSD ignition, pushing around 450bhp. The dyno showed 285bhp at the crank on fuel before the progressive nitrous system hit. This year it will run on injected methanol with the new fully progressive nitrous to give at least 500bhp. It will run fully sequential injection and ignition via an Electromotive ECU. It uses case reeds with primary load from a MAP sensor, measured at the throttle bodies. A real plus with this system are the inductive coils, giving 40K volts over 60 degrees duration, perfect for the slow flame-front with methanol. The motor weighs 23kg and is pretty reliable - until it leans out, then instant destruction!

For a track car, it would be awesome with a heavier flywheel. I run with an HTG motor and have considered building something with an 1800cc triple motor from PSI - www.psipowerinc.com/34696.htm - an easy 600+ bhp with plenty of torque for relatively little money.

Another instance of an effective 2-stroke is the Aaen V4 motor used in the US for Radical-type circuit cars - www.aaenperformance.com/V4_racing_engine.asp

[chuntington101]

maxc do any of the 2strokes run boost??? just thinkng these things with a few pounds of boost could be real monsters!!!

thanks Chris.

[MTv Dave]

Maxc - your skidoo in your profile looks mad! As do the stats!

Now I know what these things can do, I'm really interested in getting a reliable setup over max output figures:
The car will be spend most of its life waiting in the garage. When it's ready I'd really like to be able to hop in and go for a spin once in a while and drive it to and from the track... If I have to play with the carbs everytime I turn the engine over, then it's more hardcore than I can handle. As I'm getting the vibe that getting the fueling right is critical for a stroker (I'm also getting into the lingo) it may be that I can't handle it.
I'm not going to be running a highly tuned engine, but I'm still worried if I go down this path I'll have a lot of extra work keeping it running on my hands but I'm really after building it then playing with it and just doing services and all the big & little jobs every 6 months with little to nothing in between...

[Pigeon]

MTv Dave said:

Pigeon said:

You can indeed get them running with EFI, and if you inject direct into the cylinder after the exhaust port has closed you avoid the problems with charge spillage.

Just checked out your profile - how's the luck going with the engines? How much do you think you'd have to sell one for to make it worh your while? How long do you think they will last - bwtween needing tuning and between going pop?

Problems with both time and space, but I am finally clearing some space to work on it and hopefully that will cause the time to materialise

It's not a money-making project, it's just something I'm doing because I feel like it. Once it's done I plan to publish the design details on my website so anyone can have a crack.

In any case, I don't think the market's there. Diesel bikes seem to be of interest either to the military, for whom it would likely be too complex, or to people like me, who like knocking things together out of what they can use, and generally don't have the money to buy a brand new engine which would undoubtedly cost many times the price of a secondhand three-cylinder diesel out of a Smart with some remapping work, or other similar readily-available alternatives. Perhaps once a few people have built my design the idea might catch on and create a market, but I'm not certain and I don't think I could go about creating a market from scratch off my own bat. If it does catch on I will be content to know that I have given the world something people like.

As regards tuning in the maintenance sense there isn't a lot to go out of tune. Hydraulic valve gear ought to maintain consistent valve timing over long periods better than a camshaft and diesel injection pumps tend to hold their settings very well.

Intervals between major overhauls ought to be comparable with a car engine, I would expect, certainly in the single-cylinder version. The use of indirect injection keeps peak cylinder pressures down and the two-stroke rather than four-stroke cycle means that maximum pressures can be lower for the same specific power output. And the AD1 has pretty massive bearings for such a low-powered machine because it's designed to go on for ever while being non-maintained by gorillas. The loads on the bearings and wearing surfaces will be comparable or lower to those in a car diesel engine.

For the V-twin it's a bit more difficult because of the need to fit two con-rods on one crankpin in the same distance between the main bearings. But here again, the AD1 has a pretty chunky cast-iron crank. The webs are quite thick. I ought to be able to get a steel crank made up with thinner webs and a wider crankpin, and also increase the diameter of the crankpin, sufficiently to keep the bearing loadings to reasonable levels.

The one thing that is worrying me a bit is cooling, as there will be much more heat to be dissipated than in the original. I can increase the cooling capacity of the barrel by machining off the cast iron fins and soldering on copper ones in their place, but the head is more tricky. It's an aluminium casting with rather more length than is desirable between the valves and the mating surface for the manifold, so there's rather too much chance for heat transfer between the exhaust gases and the head. And I want to fit twin turbochargers, one per pot, to improve efficiency by taking over duty from the supercharger once they spin up, and also to improve charge distribution. So the heat will be worse.

However, the head like this because the ports come out through the rocker gear which is on this side of the head. Since I won't be using the rocker gear I can cut a big chunk off that side of the head and make the ports much shorter. I can also replace the existing fins on the head with larger ones by means of Lumiweld, and add finning to the manifold joint area. Then it will be a case of riding up hills with thermocouples on the head seeing how they cook