Can You Turbocharge a 62 cc Two-Stroke Engine?

[oldunion]

How would you go about designing a turbocharger for a small 62 cc two stroke engine. I have heard of two stroke snowmobiles being turboed, and i understand the concept of a turbo well so it seems plausible.

Bolt a small turbo in the passage of the exhaust port, then somehow have it turn a turbine on the intake side. would this turbine be before or after the air/fuel mixture? Also, the exhaust port and intake port on the complete opposite sides of the engine, so... plus how would you tune a carb to a turbo?

 

[GENIERE]

Possible but difficult; on a 2-stroke, the exhaust port is open while the fuel-air mixture is forced into the cylinder. With a turbo you would blow a lot of the new charge out the exhaust pipe. Besides the horrendous fuel consumption there would be little pressure increase and HP gain. The exhaust could be tuned to provide an immense amount of backpressure enabling use of the more dense charge, but the engine would only run well within a very small RPM range.

Adding fuel injection and an exhaust valve I think would be the more feasible method. Of course that would cost several thousand dollars to do. Where you mount the turbo is the least of the problems.

If I recall, some folks in Australia are working on it.

...

 

[oldunion]

link to the aussies?

 

[GENIERE]

Here you are:

http://www.banksiafdn.com/page_assets/Case2003_Orbital.pdf

 

[Cliff_J]

Awesome link Geniere! Not sure how they keep the engine lubricated but now its similar to a 2 cycle diesel where the exhaust port timing and backpressure would not be as critical but still need to be managed for the turbo to work optimally. Maybe more along the lines of a Miller cycle camshaft for 4 cycle turbo applications.

 

[GENIERE]

Awesome link Geniere! Not sure how they keep the engine lubricated but now its similar to a 2 cycle diesel where the exhaust port timing and backpressure would not be as critical but still need to be managed for the turbo to work optimally. Maybe more along the lines of a Miller cycle camshaft for 4 cycle turbo applications.

Yeah- How do they lube it? I think piston engine development is about a far as it can go except for small incremental improvements. We need the chemists to come up with a super oxidizer to mix with the fuel at point of injection. Mayby like the German's T-Stoff and C-Stoff. Perfectly safe at 500 meters.

 

[glorybe]

Although this may sound wrong at first the exhaust pipe in a two stroke engine actually functions as if it is a cam shaft. In other words the shapes and length of the exhaust pipe will control the flow of the exhaust gas which in itself places some control over the intake mixture. Therefore a turbo charger will severely mess up a two stroke with the exception of some large diesel two stroke engines with limited power ranges.
But what can be done is a super charger! The basics involve a multi cylinder two stroke engine as one intake port really needs to be open at all times. It also helps to have a large intake air chamber after the blower so that the intake can be regular and smooth. You will also need a really good electronic fuel injection system as well as a custom ignition system.
But after you spend a fortune the question of why will leap out at you. Two strokes can be built to make more power than you would ever want to use without super chargers. Further what power they do make can be made really suddenly. Anyone who ever operated the old Kawasaki H2 750 three cylinder two stroke can tell you that the acceleration from zero to 100 mph was insane. If one wanted a straight six could be built by joining two of those engines in line. And you can easily drill them out to take larger pistons and racing crankshafts are still in the wild for these beasts. Such an engine would be about the same length as a four cylinder in most small cars. With full race expansion chambers people will hear you coming for several miles. I know first hand.

 

[Breuklen]

I once turboed a lambretta 80cc scooter.I used a small european ford turbo a friend had sittin in a junker on his lot.Its hard to discribe.It sucked & scared the heck outta me at the same time! the amount of time it took for the turbo to spool seemed like for ever.But when it finaly hit boost levels,that little scooter thought it was herculese.I wore holes in my boot toes when it stood straight up at 50 mph.I didnt think it was going to do anything.It was about 1,000 rpm short of its stock redline and then, Blastoff! I thought I was going to die.It lasted a week before it turned to schrapnel.I really never got to know how fast it could go cause it took so long for the turbo to spool.I believe if you could find a tubbo small enough,it would spool up much faster and would have better results than I did.Also,you would need a long intake manifold between the turbo and intake.It helps store boost pressure for a broarder powerband with a large turbo that dosent spool so fast.Another thing is 2 strokers are horrible @ making boost pressure at lower rpms.Too much duration during the scavenge cycle.The faster the piston opens & closes the ports the faster the boost pressure builds.
Speaking of kawasaki h2s.I have several.2 will be turned into a v6 arangement with a shorter stroke crank,Direct fuel injection & a crank driven super charger. Weeee!

 

[Breuklen]

You have 2 systems that work with carbs,draw through which the the carb is placed on the intake scroll of the turbo.This system is good because it it keeps temperatures of the intake charge lower because the turbo sucks air and fuel charge through the turbo keeping things cooler.The down side is maintaining consistent air fuel ratio as boost increases.As boost pressure increases the fuel mixture gets leaner which means you have to jet or adjust your carb for the rpm & boost pressure your going to run at. Blow through is a little better at this because you can use a carb with a float bowl and pressureize it by pluming the float bowl vent into the pipe or air box going onto the front of the carb after the turbo.The down side to this is hotter intake temps,Its a long trial and error process getting the float level height set correctly.

 

[n72.75]

This man offer some insight:

http://www.sdrm.org/roster/diesel/emd/scavenge.html

 

[Breuklen]

Thank you.thats just what i was thinkin for my v6 h2.Im movin a little tward a whipple charger.thay are a little more efficient,compact & lower air charge temps. making the cases and crank will be fun.

 

[FlexGunship]

Yes, you'd be better off using a "supercharger" as opposed to a "turbocharger." There are two principle concerns (both of which have been mentioned here) with regards to turbocharger operation:

• exhaust flow volume
• oiling of the turbo bearings

Quite frankly, with a small two-stroke engine you just won't make enough gas to spin the turbine wheel enough to get the impeller up to speed. Yes, you could size your turbo to match, but then you're talking about tiny amounts of compression... fractions of a pound per square inch.

All turbos require external lubrication. Either for a journal bearing or ball bearing.

A supercharger, however, can be made with sealed lubricant gear boxes and does not rely on exhaust flow for operation. A roots-style would probably work fine. It is essentially two meshed helices.

 

[Max Power Man]

Ive always wanted to turbo charge a two stroke but as it seems the way to go is Supercharging! I have a Suzuki T350 Twin which i intend to supercharge! Would it work if I was to modify one cylinder into a Supercharger and use it to boost the other would this work.

 

[wmazz]

Assuming this is a G62 mounted in some sort of large scale airplane, the real issue is power gained vs increased weight.

A vane style (like an air-tool, die grinder, impact, etc.) super charger, is another avenue, and well suited for a two-stroke.

To minimize charge loss, reduce the width of the exhaust port, exhaust tract diameter, decrease T1 port duration, and increase the negative T1 port angles.

But in my opinion, converting the engine to a rotary-valve induction, combined with an exhaust system that only scavenges would be better.

 

[chkneater]

Turbo charging a two cycle is out of the question. The exhaust needs to remain unrestricted in order for the chamber to clear effectively and even then a turbo is not going to pressurize the chambers enough to produce significant power gain versus the weight gan.

Super charging MAY seem like a good alternative, howver you're going to end up with a crappy power band at about 3-4000 rpms., which is OK for diesels who need good torque but not horsepower, after that it will crap out since superchargers gear exponentially, i.e. more acceleration=more boost. More boost equals wasted energy since you have to remember that the exhaust port is open at BDC, all your extra boost just goes out your tailpipe.

On the other hand, and I'm not self promoting here, (ok maybe I am a little), I have devised a way to provide the right amount of boost without wasting energy in the end. It will scavenge the CC and remove most exhaust (you need SOME backpressure from the exhaust) and also pressurize the cylinder more so than what the normal two cycle crankcase can pressurize it.

I can't go into any more details than that since I have a patent pending on this design. Suffice what I am saying into a 200 HP engine you can carry around with one hand!

If you wish to help on this project, please feel free to contact me. I need all the help I can get, but trust me, I am not a greedy person, anyone that wishes to contribute and help (not necessarily money wise)
I will reward 10 fold, and that is a promise.

 

[chkneater]

Superchargers are overkill for two cycles. Waste of time, waste of money, waste of flesh. Yes, if you just want to go fast and burn your engine out after two hours go ahead. Why anyone has cornered themselves into thinking that turbo/superchargers are the only way to positively aspirate is beyond me.

This isn't the 60's anymore, we have much better technology, and the two cycle is by far the best, simplest, and most powerful engine that hasn't even begun to see it's potential yet. The four cycle is dead, so stop thinking in terms of applying four cycle technology to something that is far supreme to those crappy paperweights. 100 years of technology and we still think of improving a crappy design instead of improving a wonderful design.

Two cycles= two moving parts (excluding bearing and externals like distributors)

Four cycles= Over 600 moving parts conspiring to break on you at any moment.

 

[chkneater]

Assuming this is a G62 mounted in some sort of large scale airplane, the real issue is power gained vs increased weight.

A vane style (like an air-tool, die grinder, impact, etc.) super charger, is another avenue, and well suited for a two-stroke.

To minimize charge loss, reduce the width of the exhaust port, exhaust tract diameter, decrease T1 port duration, and increase the negative T1 port angles.

But in my opinion, converting the engine to a rotary-valve induction, combined with an exhaust system that only scavenges would be better.

Reducing charge lost by reducing the width of the exhaust port will create a smelly bomb. How would fresh air enter if there is burnt gas in there? And then you have to deal with the soot accumulation inside the cylinder which would build up quickly. There are far many variables other than what kind of turbo/super to use. You must consider how the fuel/air mixture will be introduced, HOW the exhaust will excape BEFORE the fresh air begins to enter, and the HOW to keep that pressurized air before the piston is returning to TDC. Any type of mechanical means of induction that relies on the mechanical motion of the engine will fail bar none. Except in the case of diesels

 

[chkneater]

Ive always wanted to turbo charge a two stroke but as it seems the way to go is Supercharging! I have a Suzuki T350 Twin which i intend to supercharge! Would it work if I was to modify one cylinder into a Supercharger and use it to boost the other would this work.

No, you'd fracture your connecting rod since one chamber is producing significantly more power than the other. The non-charged cylinder wouldn't keep up and either burn out altogether or most likely throw a rod if not entirely fracturing your connecting rod. This doen't mean some bonehead hasn't tried it and had some succes with it, but give it time, he won't be enjoying it for very long.

 

[chkneater]

This man offer some insight:

http://www.sdrm.org/roster/diesel/emd/scavenge.html

This design defeats the entire purpose of two cycles. Yes it does have only two actually cycles, however your relying on FOUR stroke technology to do that! Why do you thnk that 4 strokes limit at about 6-8000 RPM? Because of valves. It takes energy to move those valves, and those valves move at the same rate regardless of engine speed. The original designs of two cycles had it right the first time, however EFI wasn't available at the time. Valves not only waste energy, cant' vary timing, but as wear happens the timing gets effed. This diagram was ridiculously simplistic.

 

[chkneater]

How would you go about designing a turbocharger for a small 62 cc two stroke engine. I have heard of two stroke snowmobiles being turboed, and i understand the concept of a turbo well so it seems plausible.

Bolt a small turbo in the passage of the exhaust port, then somehow have it turn a turbine on the intake side. would this turbine be before or after the air/fuel mixture? Also, the exhaust port and intake port on the complete opposite sides of the engine, so... plus how would you tune a carb to a turbo?

The turbines on both the exhaust and intake side are connected directly. You'd have to route a hose from the intake side of the turbo to the intake. Any snowmobiles that were turboed were most likely 4 cylinders (aka wastes of flesh). Even with a supercharger you're are going to waste as much boost as it creates so it is pointless.

IF you used a turbine, it would be placed b4 the air/fuel mixture, since it's the flow of air that determines how much fuel to send. Better yet, just get EFI. The comp. will monitor the air coming via the mass airflow sensor and automatically adjust ignition timing as well as the fuel mixture. Like I said tho, all that boost is just going out the exhaust tho.

If this is something that REALLY interests you I have a two cycle design that deals with all these problems, so if you know of anyone that might like to help develop this, I am not a greedy person and would be willing to have all the help possible.


BTW, engines that have valves ARE NOT TRUE TWO CYCLE!

 

[bluechipx]

Can't easily turbo a two stroke? Wrong,wrong, wrong! I am a two stroke nut and have been for decades. I also thought that turbo'ing a two stroke couldn't work because it would simply blow through the exhaust port, wrong! About ten years ago I was at a snowmobile grass drag and the class was open fuel, anything goes. I noticed a sled with a turbo at the end of the exhaust stinger. I asked if they had done some major port moving or installed valves. The answer was no to all, it was basically a stock motor with turbo added. I replied that it can't work, to which the driver asked if I just arrived there. I said yes and he said to be at the starting line in ten minutes. I just about crapped when he left the line with well over double the original horsepower! I have since bought that very sled and expiremented with a turbo on a two stroke mercury four cyl. on a hydroplane. The motor I was using on the hydro was dyno'ed a shade over forty HP and good for 80 mph on a good day. I simple adapted turbo on the 40 hp motor made 85 hp on the very first dyno run and easily bumped to 100hp. Once you realize that it works, you can began to figure why. If anyone is interested or doubts this, I'll go into the simple explanation.
Dixon

 

[brewnog]

IF you used a turbine, it would be placed b4 the air/fuel mixture

No, the turbine (extracting work) is on the exhaust. The compressor goes on the inlet side, but can be placed either up or downstream of the point at which the fuel is metered, depending on the fuel injection system used.

since it's the flow of air that determines how much fuel to send.

The air mass flow rate is the same either side of the compressor.

BTW, engines that have valves ARE NOT TRUE TWO CYCLE!

Rubbish. Valves are employed on heaps of "true" two stroke engine designs.

 

[chkneater]

Rubbish. Valves are employed on heaps of "true" two stroke engine designs.

Rubbish, my opinion is valves on two strokes are for idiots who have had strokes.

Yes, the air/fuel RATE would remain the same, the amount of FUEL is dictated by how much AIR makes it to the engine, so why you felt you had to correct me when I was making the same point as you is weird. The RATE (14.7:1 ideally) stays constant, but if more air goes in, more fuel goes in. Thanks for paying attention.

Look, the entire point of using two cycles with the four cycle tech we have now is for them to be more powerful and efficient than four cycles. It's not enough that they are small and cute anymore. Putting valves on two strokes is a waste of weight, inertia, time, effort, flesh...

Poppet valves may be in use everywhere as you say, but they are inefficient, wasteful, and cause loss of momentum with the reciprocating mass, so stop talking about poppet valves~! The issue I am trying to deal with, that all the die hard stubborn in their ways fools keep bringing up with petty semantics, IS can/and how do you positively aspirate a two cycle engine (without poppet valves) using existing two cycle designs?

I say that Yes, it can be done. I think you could probably use a turbo, though supercharger would be less restrictive on exhaust. Superchargers have their obvious disadvantages on top end power, which is where two cycles are generally the best.

Now I WAS interested in what Dixon was saying about the turbo'd sled. I'm interested to know how much boost was achievable, what kind of fuel injection if any (port or CFI?), have you attempted any port manipulation on the exhaust side, and have you tried supercharging or inner cooling (probably not too effective on a snowmobile, but still good to know). Also, have you tried any types of lubrication to help seal the main bearings and hold more pressure? (like axle grease or something?)

 

[chkneater]

Have you attempted any changes to the ports or done anything to help the crankcase hold pressure? What psi's can you get?

 

[chkneater]

No, the turbine (extracting work) is on the exhaust. The compressor goes on the inlet side, but can be placed either up or downstream of the point at which the fuel is metered, depending on the fuel injection system used.
.

I think what I was referring too with that question was that the placement of the compressor in the intake would be different if it was carboreatted or EFI. If it was carbureatted then it would need to be after the carburetor or else it would blow into the venturi jets, but if it were fuel injected you could place it before.

 

[bluechipx]

First off, reeds ARE valves, but I'm not here to argue minor language issues. Anyone that gets this far in this thread and feels two stroke turbocharging isn't practical, follow along and you, like myself will have an OMG! eureka!, moment shortly.
On my way home from seeing a basically stock 700cc snowmobile with a turbo run with the biggest and baddest stuff out there, a four hour trip, I was forced to rethink my thirty-odd years of thinking the charge would simply blow through the last to close exhaust port. At first I thought possibly the gain would come from getting a super clean, no residual exhaust, fresh charged cylinder, but with no real boost. But that wouldn't account for the doubling or possibly tripiling of the horsepower. BTW, the racer that I bought the machine from said he ALWAYS had much more top speed than his competition, but it sometimes took a bit of catching up. Grass drag snowmobiles are dynamite off the line and the race is only five or so seconds long, so holeshot is critical. In my later projects of putting turbo's on two strokes, there is a bit of delay in throttle, but it's minor. I had a friend that choose the nitrous route against my smaller displacement turbo in the hydroplanes, and in an even start from a slow float, (thirty MPH or so) he would get about a twelve foot, one boat length jump before I began coming back. Also, his nitrous was great on accel., but didn't have much effect on top end, probably less than one MPH. The turbo was unbelievable for both accel and top end. It would quickly push the designed for 75-80 MPH hydro past 100 into high speed handling problems, so I never really saw what it would be good for top end. Also the motor was designed for forty HP and was really being pushed at one hundred HP.
Back to the "why it works" basics. Try to clear your head of the blowing though the exhaust with no boost for a second and ponder the fact that it REALLY DOES WORK. See if it hits any of you with the jaw dropping effect it had on me when it hit me. I almost had to pull the car over to the side of the highway and compose myself. I'll get back and give you the answer tomorrow about this same time, so this is your one last chance to see if you can get it on your own once you know it works. Hint, it is not rocket science but simple basic logic that will make you feel like you should have seen it long ago. But who am I to talk. I was thirty plus years of getting it wrong.
Dixon

 

[molitor]

I got to say man, this thread has gotten crazy. Other than that, the exhaust intake events don't last very long at all at 8k rpms. The boosted intake charge would definitely aid in flushing the dirty exhaust gases out. and there would only be boost for as long as the intake port was open. Once the piston passes the port on its way up to compress the charge, its basically static and super dense. I don't see why a compressed charge in a two stroke wouldn't be phenomenal. Basically a two stroke is undercharged in its normal state. It doesn't have much in the way of induction because it relies on the rapid expansion of the exhaust gases and a tiny smidgen of vacuum to draw in the intake charge. You could rock a two stroke with a ram air system and smoke people with top end power. Other than that, I just got to say, don't knock it till you try it.

 

[brewnog]

Stuff

Did you mistake me for someone else? All I picked you up on was your comment that valves aren't used on two stroke engines. They are (get over it), and either your incorrect terminology or poor description regarding classical induction systems.

 

[bluechipx]

Here is a picture of my first try with a turbo two stroke Mercury four cyl in line. The motor is 44 cu. in. and has an advertised HP of fifty HP, but a dyno shows repeatable and consistent 40-41 Hp in stock form on all of these motors I have tested.

 

[bluechipx]

Okay, here's where the mistake comes in about the common notion that a turbo will simply blow through a two stoke without creating boost in the cylinders. I have put a one way reed pressure gauge on a simple two stroke to check only positive crankcase pressure. At high RPM's the positive pressure in the crankcase was about 7.5 psi. The motor was not an expansion chambered motor, but a simple non tuned exhaust system. When the piston is down and both ports are open you have a gradient of 7.5 psi on the transfer or intake and pretty much zero on the exhaust side, so the engine will run fine with the 7.5 psi difference driving the fresh charge in and the exhaust out. For clarity, let's assume we are super charging for a moment. Now let's crank up the crankcase pressure to 27 psi. If the exhaust pressure was still zero, it would work like 99% of people think. Lots of wasted fuel/air blowing through the open exhaust port with minimal HP gains.
Now here's the catch. Let's put a butterfly in the exhaust system near the motor and put a pressure gauge between the exhaust port and the open butterfly. With the motor running as we slowly close the butterfly, a pressure will began to build in the exhaust area. We know if you continue to restrict the exhaust until you have 20 psi, the crankcase will still have 27, for a seven pound difference and the motor will still operate. Now as the piston, on it's upward stroke is just about to close the exhaust port, you will have 20 psi in the cylinder and the exhaust system up to the butterfly or restriction. That's 20 psi boost.
A turbo works like a natural restricter in the exhaust system and puts out more air pressure on the compressor side in psi than it restricts in the exhaust side. On a four stroke, this exhaust pressure is an unfortunate thing, but on a two stroke it is positively needed.
It is said the true boost of a two stroke should be measured between the exhaust port and the turbo because that's the pressure your cylinders will see as the piston closes the exhaust port.
There is another advantage to a turbo'ed two stroke. The pressure that is fed through the crankcase before the reeds, that normally would be bumped up 7.5 psi in the crankcase, is much greater than it normally would be. This is probably due to the fact that the outside boost pressure is feeding the crankcase at piston positions that would not normally draw fuel/air into the case.
As far as working out all the pressures in all the various places like carbs, crankcase and exhaust, the turbo seems to pretty much take care of all of it naturally. My first try of putting a cover over the exhaust side of the motor and slapping a turbo on it, then routing the compressor side back to the crankcase with a carb UPSTREAM of the turbo made over double horsepower on the first try on the dyno.
The process is simple, but there are a few catches. A carb likes to be drawn through, but it also works to blow through the carb, but either the entire carb must be under boost pressure or at minimum, the top of the float bowls must see boost pressure. There are advantages and disadvantages top both methods. Blowing through the carbs means leaving the carbs in stock location but fuel input pressure must be higher than boost pressure, but all this has been worked out by regulator systems. If you draw through the carbs, this puts the carbs quite a distance from the engine, so starting and idling suffer a bit.
I hope I have gotten the concept of the turbo on a two stroke clarified. I've had quite a few racers say that they still don't get after going through everyway possible to explain it. It seems to be a mental block type thing I guess. So, if you see the concept, welcome to the elite 1%!
Dixon