Why supercharging a 2stroke doesn't work?

[Z.hb71]

So I know that you can't supercharger our engines (don't come at me with Detroit deisels), but can someone give me a really in depth explanation? I think it's related to port timing? And FYI, I'm not even thinking about doing this, I want to just leave this here so if a newbie comes along looking at those rb innovations superchargers that don't do anything, they can get a nice explanation.

 

[cbaker65]

So I know that you can't supercharger our engines (don't come at me with Detroit deisels), but can someone give me a really in depth explanation? I think it's related to port timing? And FYI, I'm not even thinking about doing this, I want to just leave this here so if a newbie comes along looking at those rb innovations superchargers that don't do anything, they can get a nice explanation.

NO!

 

[Z.hb71]

NO!

No what? I know it doesn't do jack Im asking for a detailed explanation not stating the obvious

 

[Seandonato73]

The biggest issue is keeping the charge in the cylinder and not having it blow out the exhaust. If there were exhaust valves to control the exhaust cycle it would be rather easy. But we don't have that. It would take very precise timing to get good gains in our engine design. Going to a hybrid valved design would yield good power. As of right now there are no rc engines that use this type of system. I'm sure there are gains to be had with the rb system but I would think most would be realized only at high rpm as the port opening / closing speed is very fast.

 

[Z.hb71]

The biggest issue is keeping the charge in the cylinder and not having it blow out the exhaust. If there were exhaust valves to control the exhaust cycle it would be rather easy. But we don't have that. It would take very precise timing to get good gains in our engine design. Going to a hybrid valved design would yield good power. As of right now there are no rc engines that use this type of system. I'm sure there are gains to be had with the rb system but I would think most would be realized only at high rpm as the port opening / closing speed is very fast.

thanks!

 

[Turbokevin81]

A supercharger is belt driven from crank speed, Now a turbo is driven from exhaust gas so unless I am missing the gist of it. The supercharger could work.

 

[Seandonato73]

Has nothing to do with how its driven. It has to do with how its ported/valved. It's been done and will be done, just not the mega power adder its claimed to be. Most of your fuel air charge under that amount of pressure would blow out your exhaust port before the piston would close it off. To circumvent this, you would need a very small exhaust port timing window, or some sort of exhaust valve. For the sake of debate in the rc 1/5 scale engine it isnt practical. If we want to dive off into other 2 strokes then yeah it makes perfect sense. But as most of them either have valves and/ or are not piston valved engines it's a moot point for this discussion.

 

[Z.hb71]

Has nothing to do with how its driven. It has to do with how its ported/valved. It's been done and will be done, just not the mega power adder its claimed to be. Most of your fuel air charge under that amount of pressure would blow out your exhaust port before the piston would close it off. To circumvent this, you would need a very small exhaust port timing window, or some sort of exhaust valve. For the sake of debate in the rc 1/5 scale engine it isnt practical. If we want to dive off into other 2 strokes then yeah it makes perfect sense. But as most of them either have valves and/ or are not piston valved engines it's a moot point for this discussion.

Yes, what he said. There has been a turbo 2 stroke scooter engine, I'm sure you can find it on the internet. I think it made 26hp, so it can be done but it'd impractical.

 

[Turbokevin81]

ok

 

[Seandonato73]

From what i know the turbo is doable on multi cylinder 2 strokes. You still cant run much boost but the turbo acts like it's own valve by putting back pressure on the cylinder. It's not the gains that were used to in the 4 stroke world but It is noticable. Google arctic cat triple 600 turbo.

 

[Seandonato73]

Good luck....

 

[Clubin]

Snowmobiles do it with success. The reason they work if because they are direct injected.

 

[Seandonato73]

2 strokes none that I know of the new 4 strokes yes.
Ok went and looked it up, I'm still correct. No mass produced supercharged 2 strokes (gas) the rotax is turbo charged and has "advanced valves intake track" so besides being full blow efi, there is valving ti help it along. Which goes in turn to why it's not a total fuel pig. As I've said before. Super charging/ turbocharging sends a lot of the boosted charge out the exhaust pipe. Wasting fuel and power. They work best at very high rpm, giving you a narrow peak power band. If there is a variable exhaust valve, similar to what Yamaha did back in the day, you could boost low and mid range power. Now we just over complicated the fek out of a very simple design. Added a bunch of weight and still didnt reap any major benefit. Make it a true valve exhaust 2 stroke and Bob's your uncle. But realize your now dependent on the supercharger for all induction as you wouldnt be using/ needing the crankcase to do the breathing for you. Turboed 2 strokes have had some mild success due to the turbo half acting like a valve keeping back pressure on the engine. This half works because it limits the scavenging effect of the engine, but allows more of the pressurized air fuel mix into the engine. Direct injected engines again are a bandaid for poor engine design. This again over complicates what is a simple engine, as it need for sophisticated electronics for it to function properly.
I'm not against this idea, I've been looking I to it for years. The few guys that did it with any amount of decent out come almost all admit it wasnt worth the expense to get a bit more power out of. With @Kovid45 porting abilities he should easily be able to get better gains and fuel economy without a super charger to muddy the mix. Now if you really want to super charge a small engine, go get one of those ryobi 4 strokes or a stihl 4 mix and have at it. They would be rather I impressive boosted. (And done even get me started on turbo dynamics on single cylinder engines)

 

[Polar_Bus]

Many have tried none have succeeded with 2 stroke forced induction hp gains . Same with NOS . The physics of forcing a mixture into a ported 2 stroke cylinder just doesn't work well. The best way to sick 2 stroke HP is big bore / stroker kits and running Alcohol.

 

[Seandonato73]

Funny you mention strato engines. If it ever clears customs I'll be getting my first. I like the idea of using them in conjunction with using the exhaust as as second I take port at tdc, this would (in theory) fix my biggest female dog about supercharged non valved 2 strokes.Loosing fuel air mix to atmosphere for no reason other then getting peak rpm power. There is however an issue posed with superheating the charge where pre detonation may become a concern. (Again would have to be a trial and error sort of thing)
the I am familiar with 2 stage reeds, we ran them in our dirt bikes, and race boat. It would take a bit to figure out the right combination (as mentioned)
there were a few blokes trying something similar in old triumph engines. (No success I assume do to their blog not being updated in years now) but hey I'll mention this. If you figure it out, and it works really well, and is reliable, and well packaged I'll be the first to rescind any negative vibes I've put out.