how to turbocharged 2 stroke ????

[bjhines]

quote: "to me i call a "true" blower the kind that mount on top of your engine with carbs/ or FI. forcing air and fuel"

 

now you are getting into 2 more subcatagories of superchargers...

 

positive displacement compressors vs axial flow/centrifugal compressors

 

The "tuned pipe" on small 2 cycle engines is an acoustic compressor...

 

You are also bringing up draw through vs blow through intake configurations... don't forget diesels are direct injection they just have a compressor and a plenum... no throttle plate... NO NOTHIN... so they really don't count in this particular context...

[Guest camaroboy383]

hello im new here and actually the only reason im here is to reply to this thread....i was searching for info on turbocharged 2 strokes and stumbled across this thread.....i am actually about 4 months into a turbocharged 2 stoke in a snowmobile...i have posted gobs of info and pictures of the fabrication in a thread on a snowmobile web site....this is mainly directed to WARRENP,,,but anyone else feel free to check it out....the web site is WWW.JOHNDEE.COM YOU WILL HAVE TO CLICK ON GENERAL DISCUSSION,,,THEN TECH TALK,,,,,,, MY THREAD IS TITLED TURBOCHARGED 521 FORMULA PLUS..... all parts were fabricated by me...i have at least 8 months worth of research ive done invested in it,,,and i cant even count the hours.....i read earlier in the post about the rotary valve engine,,,,this is what i have and supposedly it is the best donor to turbocharge....the rotary valve actually opens and closes the intake ports like a 4 stroke....no reeds in these engines....also the expansion chamber must be before the engine or it just will run like crap...the engine needs the reverb of the expansion chamber for it to operate properly.....anyway if you get a chance check out my thread on johndee.com good luck with that project,,,if you need any info let me know,,,id be glad to help....

[ndeli55]

stop using detroits as a basis for a argument that 2 strokes can be turbocharged or supercharged. they are a completley different beasts, they don't rely on the piston to create the bulk of their compression, that comes from the blower, and turbo combo, hence the need for forced induction to work. basically the air/fuel mix is forced in through holes on the side of the piston that correspond with holes in the cylinder jacket creating a cleaning and charging cycle in one, plus diesel fuel needs a much higher compression ratio to ignite, another reason for the use of forced induction.

 

now im not saying it can't be done, in fact i believe it can, if the turbo attaches after the expansion chamber and the chambers size and taper takes into consideration not only the extra restriction created by the turbo but also the false sense of greater cubic displacement created by the extra charge in the cylinder. would take ALOT of research but could be viable.

[MoNkEyT88]

Camaro boy..

 

Any old 02 sensor hooked up to a wide band isn't going to show you anything. They are narrow band sensors You need a wide band 02 sensor for accurate tuning.

 

As far as tuning goes, you can forget the wide band, because so much fuel is going to pass through the cylinder unburnt because of the boost that its going to read way off anyway.

 

A 2 stroke actually has over 100% volumetric efficiency. If you want a turbocharged snowmobile, I'd suggest getting a 4 stroke motor, as you will not waste so much time for minimal at best gains.

[TravRMK]

Turbos flat out work on two strokes! Snowmobiling is one of my passions, and while my sled isn't turbocharged, I know several people, including my uncle who own turbo two stroke sleds. The engine design is totaly different than a four stroke, and you can't think that what applies to a four cycle will apply to a two. The pipe on a performance two stroke is verry important to the power, how much, and where in the rpm range it is created. I won't get into the design of pipes, but I will say, that there have been some missinformation in this thread about them, and the two cycle engine. My uncles 700cc Polaris twin cylinder two stroke makes 250 horsepower, and is scary powerful. His stock NA engine made 127.5. They work, and work well. It is a bit more complicated than a 4 stroke though.

[TravRMK]

I belong to another online forum for snowmobiles. My sled doesn't have a turbo, but it has nitrous oxide injection. Some people think that nitrous will blow up a two stroke, and won't work like it does on a 4. Here are a couple of pictures from that forum of a few of the hundreds I know of. Some of them are self lubed, and others use automotive turbos with an electric oil pump, and a small oil tank, from T3's to evo takeoffs, GT28's etc. There are alot of turbo four stroke yamaha Apex's, and RX-1's also (they have an engine similar to the Yamaha R1 bike) Alot of them are pushing 250-400hp.

[a6t8vw]

Very impressive snow machine

[Guest camaroboy383]

i agree with travrmk,,,although a 2 stroke is a different world than a four stroke,,,i beleive a turbocharged 2 stroke could work well....also as far as unburnt fuel in the pipes,,,,the fuel that is unburnt in the pipes does not stay there,,,,,it is burnt off by exhaust fire in the expansion chamber,,,its not like the fuel just runs out the exhaust.....and my 02 is in the down pipe way far away from the expansion chambers....i highly doubt the 02 sensor is going to sense raw fuel and give me a bunk reading.......the 02 is there for reference,,,it is not like on a vehicle where it is actually controling my air/fuel ratio..... it is just to give me an idea of whats going on.....i beleive with the proper tune,,,,a turbo can give gobs of power to a 2 stroke as stated by travrmk,,,,his uncles machine gained twice the power with a turbo.....thats nothing to sneeze at......also there is a company who produces small turbo's for 2 stroke snowmobiles,,,,and they sell for like 3 grand....obviously if there is a company who produces them and installs them then the idea is not that far fetched....

[Tony D]

Two Strokes take to turbocharging very well.

As for the comments about Detroits, they have 17:1 CR in the 71 Series and that is definately enough to start compression. The blower in the Detroit is there to scavenge the cylinders, and the Turbocharger is either altitude compensation or power boosting. A Detroit V871-T will have a blower for idle scavenging, and once turbo boost comes up sufficiently to scavenge the cylinders in many cases the DDEC Controller will disconnect drive to the blower to allow the turbo to continue the scavenging function, as well as going to positive pressure (in some cases 45psi+) for engine power boosting. In the old days a simple pressure control anneroid connected to the fuel rack would twist and allow more fueling comeing from the injectors...but now the peizeo injectors and the DDEC controller will control that much more efficiently.

 

Talk that a Two-Stroke can't be turbocharged is simply foolishness.

 

Just an FYI, the Snowmobile Mr. Unser got busted on when he trespassed in the national park was a turbocharged two-stroke with well above 200hp. They have been selling turbokits for Snowmachines for YEARS.

[Tony D]

I have also heard of opposing piston, 2 stroke diesels that had cranks at the top and bottom of the engine with separate pistons at either end of each cylinder. When the pistons were all the way apart, they unshrouded an intake port at one end and an exhaust port at the other. Thus the pistons themselves worked like valves. These engines also use some type of turbo or supercharger to force air into the cylinders.

 

That would be an Ajax engine, or on a ship more than likely a Fairbanks Morse.

 

Most Two Strokes do NOT use Reed Valves. They use either Rotary Valves or Piston Porting.

 

And this is why they are totally suitable for forced induction.

 

Even with reed valves in the intake as the 'anti-reversion' device, the exhaust is invariably piston-ported, and works fine in turbo service.

 

But Ajax and Fairbanks Morse use the opposed piston, common combustion chamber design. Another which is bitchenwickedcool to watch in operation or even to look over from a design standpoint is the "Deltic Engine" which has THREE crankshafts which are linked via gearing to a central shaft running through the center of the DELTA configured engine block (think of those common combustion chambered engines, set up so they configure a triangle, with SIX pistons at any given time being able to give power to any of the three crankchafts...) I think you can find Deltic Engine information on Google... It's worth a look if you want to see a reaaaaallly cool engine design!

[TravRMK]

OK, in a nutshell this is how a tuned pipe on a two stroke works in laymans terms. There is more to it but this is just so you can understand the principles. First the pipe is made up of several parts, and altering any of these will change the power output, as well as the powerband. The header(the part that bolts to the cylinder) The diffuser (taper towards the belly), the belly (the fat part of the pipe), the reflector(the taperd cone part at the end of the belly), the stinger (the small pipe at the end of the cone that goes to the muffler).

The tuned pipe opperates on sound, and pressure waves. sice the engine has no valves, just ports in the cylinder walls, there is some unburnt fuel that exits the exhaust ports into the pipe with the exhaust, but the unburnt part exits after the burnt fuel. when the exhaust hits the reflector(cone) it pushes back, forcing all the unburnt fuel back into the cylinder just before the piston closes the exhaust port craeting a supercharging type of effect. They are tuned for opperating temperatures. Generally snomobile exhaust is tuned for a certain RPM (narrow) because they opperate in a narrow band well (CVT transmission), and more power is attainable this way, and with the CVT there are not many drivability concerns.

[TravRMK]

One other thing, All modern high performance two strokes use reed valves on the intake. Ski Doo (older Rotax engines) were the only ones that used the rotary valve. Turbos don't care about the reeds. Stiffer ones are necessary for higher boost though. You can buy stiffer carbon fiber ones these days, but in the 80's when my Uncle started messing with turbo sleds they just stacked two sets of reeds. Trimming the second set for the desired stiffness.

[Tony D]

One last item, to say there are no 'supercharged' diesels that actually boost pressure to do more than scavenge the cylinders is also plain wrong.

Early stationary engines, as well as several mobile engines used gear driven suprechargers to boost engine performance. Some of the Cooper GMV series produced before 1940 used huge contrifugal compressors as an engine boosting device. Many of the mobile engines used compound roots blowers for higher pressures which were gear driven, or crankshaft driven straight off the crankshaft.

Diesel or Petrol, the designs were interchangable. Many stationary engines were designed to run on Diesel, and where you normally would have a diesel injector, operated off a lobe on the cam...you have a 'gas admission valve' which opens a third valve allowing gasseous fuel to be admitted to the intake tract for combustion.

 

Hell, to think of it, I've owned at least two 2-Stroke Cars in my lifetime. A Suzuki Cervo, and a Suzuki Jimny Jeep. For the market, they both were stellar successes in my eyes. I had nary a problem with either vehicle. The Jeep Ate Clutch Cables every 25K km, and both the cars needed spark plugs to be changed on a regular basis. Other than that, run the hell out of them and they just kept going and going and going...

 

I sold the Jeep and bought a Twin-Charged Suzuki Alto. It had a Roots Blower, as well as a Turbocharger, ran some ridiculous amount of boost, had a redline like a sportbike and sequential shifting. A screaming 550cc's of DOHC Microcar. And no, I was like 120# lighter then so I had no problem fitting in the car.... Man, that Alto was a hooot to drive! LOL

 

 

I digress...

[Guest camaroboy383]

man i would love to meet your uncle and talk turbo sleds....i cant wait to take this thing for its first ride....about the stacking reeds though,,,did it have any effect on (off boost drivability?????)also how was he acuiring extra fuel on boost??? so he didnt run into a lean condition......just curious so i can cover all bases....

[Guest camaroboy383]

tonyd,,,its funny how you mentioned the deltic engine......not alot of people will know what you are talking about.....well the only reason i know anything about the deltic engine is because i am a model engine enthusiast,,,im sure youve seen like a 1/4 scale conley v8 made by gary connely......(miniature v8 engines that run)....anyway i found this guy,,his name is clen tomlinson,,,,he actually either is done with by now or is still engineering a replica deltic engine that has 18 cylinders, and 36 pistons...he shows arcitectural drawings and the engine it self in various stages,,,,,,he actually made the turbo and the supercharger also.....these guys are talented......check out this link it will bring you right to clen tomlinsons napier deltic engine......... very cool like you said to look at the tech drawings and engine it self.......also read the page there are lots of interesting information...... http://craftsmanshipmuseum.com/tomlinson.htm

[TravRMK]

I believe on the older carbed sleds they ran a boost activated hobbs switch that powered an electric fuel pump that went to a couple of power jets. Todays EFI powered sleds are much easier as you can buy programable EFI boxes and use the stock injectors for added fuel. Before that I remember them talking about running pressure to the float bowl, and to the top of the slides, they found out that under boost the throttle didn't want to close, so they pressurized the top of the slide as well. The power jets was a better setup.

[Guest camaroboy383]

i dont know if you checked out the link to my forum on johndee.com...but anyway that is how im running my set up is with a pressure hobbs switch that turns on at 2psi and activates a fuel selenoid which is hooked to the pressure/boost/intake box with nitrous dry shot fogger nozzles,and is run off an electric fuel pump,,,its nice cause the large aray of jets out there makes the nozzles easy to tune...i figure i jet large and let it be rich on boost then just tune down till i get a nice air fuel mixture....me and my buddy were talking about that same slide issue,,,and i was figuring if they dont want to close on boost ill just put some stiffer slide springs in the carbs....but yes you need to pressurize the overflow vents so they dont blow fuel all over the place on boost..... i just used some 10/32" pressure fittings and tapped into the boost box,,,then just slid the over flow vents onto them....worked mint.

[TravRMK]

I would look into the power jets, they are simple and effective. To add or subtract fuel is as easy as turning a knob. See attatched instructions. Most of the added fuel is added through the main jet because of the added pressure in the bowl, and any additional through the power jet. I think you will need to tap into your carb cap to keep the engine from hanging while under boost. A stiffer spring would not help as much, and since the pressure on the top of the slide would be equal to the underside it acts as if naturaly aspirated. You DO NOT want your sled to keep going when you need to stop, or let off! If you look closely at the picture of the cat turbo below you can see the 1/8" lines tapped into the top of the carbs that come from the pressurized airbox.

[TravRMK]

One other thing, make sure you double up each pipe spring (two springs everywhere there was one). Do you have any EGT guages? If not, you may want to try and find some, as the learning curve is huge, and pistons melt pretty easy. Also what are you going to do for clutching? I assume you know that what was in there before isn't going to cut it with boost.

[Tony D]

And now I show this thread to my wife...who was thinking I was insane for wanting to make a belt-driven centrifugal supercharger for the Minibike!

 

She now realizes there is a complete subphylum of diseased individuals for which forcing more air into engines is something that they 'just do because'!

 

What got her was the Cat Photo. She realized it was the same sled her dad has back in Michigan, and since she has run it around a bit and knows it's characteristics...and knows what the Turbo Z runs like compared to her N/A 260Z...well she put 2 and 2 together and came to the 'Diseased Sub Phylum' Conclusion.

 

I concur, what about you, doctor? LOL