Thread: Question for the mechanically minded

Is it possible to supercharge or turbo charge a 2 stroke or is there something in the 2 strokes design features that doesn't allow it ?
I was having a conversation with a mate today about the annual beach race we have here for motorbikes .
The " King of the Beach " always goes to one of the big 500cc bored out 2 stroke motor cross bikes running methanol and that have been highly modified just for the beach , long swing arms , big expansion exhausts etc .
They go at a hell of a speed , close to 200kph at the end of the straight .
I was saying to my mate the only way you could maybe beat them would be turbo or supercharge a similar bike .
He said he thought it couldn't be done because they are 2 strokes .
I have no knowledge of these things .
Is it possible ?

Ken

Are there engine size restrictions

There are different classes , but the big race at the end of the day is the one that everyone wants .

Here's a link I found , its a few years old , and the fastest bikes that year were either out due to problems or the riders injured .

https://m.youtube.com/watch?v=ntlkHLpy0NQ

Ken

I don't think it is physically possible to turbocharge a conventional (ports) 2 stroke motor

The poor old "commer knocker" three cylinder six piston two stroke diesel truck engine was supercharged and turbocharged

Anything is possible

Detroit two stroke diesels were supercharged IIRC. You would see the bastard things for miles at sea as they were the big black cloud of smoke on the horizon.

Yes possible.
big marine diesel two strokes will not run (or extremely poorly)without a supercharger or turbo as they have no bottom end pressure (being common bottom end)to push charge air into the cylinders.
usually a hydraulic supercharger is run on start and idle and is switched off as load comes on and the turbo winds up and provides boost off its own accord.

Spanners will correct me if I am wrong on any points here I am sure its been well over ten years since i had anything to do with a wartsilla and it wasn't my dept.

Your common "crosser" single cylinder two stroke uses bottom end pressure to push charge air into the cylinder and reed valves to contain the pressure, "tuned" exhaust expansion chambers are designed to work in a rpm range.

As exhaust bursts out of the cylinder the velocity and mass of the gases(mass/velocity effect think leaning into a strong wind and any loose clothing being pulled behind you) it pulls fresh charge air into the cylinder and exhaust and the exhaust charge air is thrust back into the cylinder by a pressure wave returning from the big to small taper of the exhaust, so charging the cylinder with more than its share.
all this works on resonance/harmonics.

As a very very general rule.

Stiffer reed valves more top end, dual or light more bottom and mid at the expense of top.

exhaust. once again very generally, long skinny tapers top end short fat taper bottom mid.

turbo or super charger is really something that would have to be designed into the port timing, intake and exhaust, or even run an exhaust valve to have any real benefit.
not impossible but for any real gains the engine would have to be designed around forced induction.

nitros oxide on the other hand :thumbup:


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Originally Posted by kiwijames

Detroit two stroke diesels were supercharged IIRC. You would see the bastard things for miles at sea as they were the big black cloud of smoke on the horizon.

The silver series detriots 8v53, 8v72 and 8v96 ( fuel pincher) were supercharged and turbocharged

Tomoana freezers has two V16 detroits as back up generator engines

I used to service them when I was a diesel mechanic for Ballie Farmers Motors

http://youtu.be/19eQBQep-sc

The supercharger is coloured blue and sits in the top centre of the engine.

Originally Posted by 7mmsaum

The poor old "commer knocker" three cylinder six piston two stroke diesel truck engine was supercharged and turbocharged

Anything is possible

My old man used to have one of them to cart his dozers,used to have to get into deep reduction low low crawler gear to get up around tight corners when the tires of the lowbed were scuffing and sucking power.

Originally Posted by 7mmsaum

The poor old "commer knocker" three cylinder six piston two stroke diesel truck engine was supercharged and turbocharged

Anything is possible

Commer TS3 - Interesting design ...

But back to the original question I still don't see how you can turbocharge a conventional 2 stroke (ports only no exhaust valve) petrol motor effectively unless possibly it was designed with that intent from the start

Google 2 stroke turbo and you get a Yamaha increasing its horse power nearly double, and a Vespa or something that became unrideable

Is there any rule about having to be a two stroke? A 4 banger opens up a whole world of other possiblities, albeit quite expensive ones!

Mate of mine turned a tl1000 into a quad for the open class of dash for cash a few years back, that was an awesome beast!

From what little i know about it the trick seems to be to stay as close to stock on the motors as possible, all the blokes that have turned up with heavily turboed and nitroused bikes spend most of their time trying to get them to start/run or they blow up on the first gear change.

Goes to the op where you say normally gets won buy just a bored out 2 banger, keep it simple!

I've been doing a bit of local homework here about these bikes and the multiple champion is a guy called Mick Hansen . He owns the local Honda dealership and his fully worked Honda CR 500 will do over 200kmh , produces 93 hp at the rear wheel , and runs low 10 sec passes at the local drag strip when he takes it out for a bit of fun .
Maybe a turbo or supercharger would just make it more dangerous than it already is

Ken

The problem stems from the boost pressure always trying to push the reeds open and pushing crankcase seals out.
Would need to flipflop double seal it..
If you really wanted to do it, then a 800 seadoo jetski engine with its rotary valve timing would be the best way to start - 110 hp factory and variable heigh exhaust ports.
A 4 stroke seadoo engine with a ecu flash and bigger blower puts you well over 300 hp. Slipper clutch and tie your nuts to the handlebars!
There were kits made for the banshees and most people fitted RZ350 engines to them as they were same same but with electronic power valves.
There is a good reason that they didn't sell heaps of them and are no longer made.
If you can run a 4st, a road bike engine puts you waaaay ahead to start with.