Turbocharging carbureted petrol 2 stroke engines

[Luth]

Hi, please remain on topic, we speak about turbocharging 2 stroke gas engine carbureted. The primary question is if the picture set up can really do more hp than the naturally aspirated. Gas mileage is not important we speak only about hp gain between the same set up with and without a turbo.

 

[bluechipx]

Hi, please remain on topic, we speak about turbocharging 2 stroke gas engine carbureted. The primary question is if the picture set up can really do more hp than the naturally aspirated. Gas mileage is not important we speak only about hp gain between the same set up with and without a turbo. View attachment 269436

I'm with you all the way on this one, I was wondering where things were starting to go myself.

 

[Luth]

Online I have found a research(?) conducted by some Indian students on the 2 stroke turbo but there aren't many details.
In this research carb is blow trough and there is not an expansion chamber.
Is not the set up of the previous image I have attached but can help us to understand something.

Here the link of the research:

https://www.academia.edu/37091140/Turbocharged_2_Stroke_Single_Cylinder_98_2cc_Si_Engine

(but we're is the turbo oiling system in this research? )

IS this research valid?

 

[Luth]

I'm with you all the way on this one, I was wondering where things were starting to go myself.

Yes the question simple

For example:
Turbocharged 2 stroke (reed valve, or piston port) carbureted: 5hp

Turbocharged 2 stroke (reed valve, or piston port) carbureted: hp?? More or not??

Same engine same parts not turbo and with turbo (just carburetion setting properly for each set up)

 

[Luth]

We can understand this, this thread is really costruptive and interesting!Luth

 

[Tom.G]

...costruptive...

And obviously rather creative!

 

[Luth]

Anyone have seen the Indian research I've posted? What do you think about it?

 

[bluechipx]

Anyone have seen the Indian research I've posted? What do you think about it?

I read it and it looks like they are blowing through the original carbs. The picture wasn't clear enough to see if they had a way to pressurize the float bowls with boost pressure. If they weren't they would get bad results.

 

[Baluncore]

Anyone have seen the Indian research I've posted? What do you think about it?

Couldn't download it without giving access to my address book. So no go.

 

[Luth]

Couldn't download it without giving access to my address book. So no go.

Don't download it you can just watch it online. Download it is required only if you want do it!

 

[Luth]

I read it and it looks like they are blowing through the original carbs. The picture wasn't clear enough to see if they had a way to pressurize the float bowls with boost pressure. If they weren't they would get bad results.

Yes its not detailed. But seems they have made some conclusions.I don't understand if it is a valid research or not.

 

[Baluncore]

IS this research valid?

No.
They claim to have designed their own turbo. But the unit pictured on the first page is a commercial unit with a manufacturers tag. There is no mention of balancing a turbo. There is no picture of their turbo installed on a bike.

They claim to have a waste gate on the exhaust manifold to limit the charge.

There is so much that appears to be imagined in this paper.
Maybe the Prof needed to be lead author on another publication, so he got a student to write it.

 

[Luth]

No.
They claim to have designed their own turbo. But the unit pictured on the first page is a commercial unit with a manufacturers tag. There is no mention of balancing a turbo. There is no picture of their turbo installed on a bike.

They claim to have a waste gate on the exhaust manifold to limit the charge.

There is so much that appears to be imagined in this paper.
Maybe the Prof needed to be lead author on another publication, so he got a student to write it.

Like I suspected! Completely agree with you on this! thanks Baluncore.
So there are no details. I'll try to search again around the web but there is nothing at all. Bluechipx reported his positive experience (thanks again) but to understand we need more detail.
There are some sled guys forum that speaks about it but some say it work and give hp and other not.
Here 2 YouTube interesting video link the first about the impossibility to turbocharge a 2 stroke the second is the Rotax E-tec turbo 2 stroke. One the opposite of the other.

(but it is an EFI not carbureted like I mean)

The video of the impossibility in supercharging two stroke:


The video of a 2 stroke turbocharged available on the market (EFI not carb)


In the second video is possible because the fuel injection is done after the piston cover the exhaust post. But in a carbureted 2 stroke motor how can it work?

 

[bluechipx]

FWIW, I bought a Haltech electronic fuel injection system for my Mercury outboard. I had the dealer come over and he had me bring it up to various rpm's under full load on my dyno while he monitored his instruments and set up the fuel curve. $1000 system (still have it, anybody interested?) With equal boost as carbs you could give it any fuel mixture you wanted but it never worked as well as Mikuni draw through carbs did for some reason. Go figure. Maybe I just got lucky on my first attempt with the draw through system because nothing I changed afterwards did anything but decrease performance, sometimes by a lot.

 

[Baluncore]

I took a look at the two stroke engines used in the chainsaw equivalent of a drag race, the (Stihl) Hot-Saws competition. Engines are limited to a single cylinder, of any capacity. They must have a tuned exhaust and a chain guard.
The limit is how much weight and power the operator can control, not the maximum power from a standard capacity engine. That partly explains why hot-saws are not turbocharged, although one competitor is named "Turbo".
Turbo lag may also be a problem. An assistant has one minute to start and warm up the competitor's saw. The three competition cuts can then be completed in less than 6 seconds.

It is easy to lose sight of the bigger picture while focused on the technical challenges of turbocharging a two stroke engine.

 

[Luth]

I took a look at the two stroke engines used in the chainsaw equivalent of a drag race, the (Stihl) Hot-Saws competition. Engines are limited to a single cylinder, of any capacity. They must have a tuned exhaust and a chain guard.
The limit is how much weight and power the operator can control, not the maximum power from a standard capacity engine. That partly explains why hot-saws are not turbocharged, although one competitor is named "Turbo".
Turbo lag may also be a problem. An assistant has one minute to start and warm up the competitor's saw. The three competition cuts can then be completed in less than 6 seconds.

It is easy to lose sight of the bigger picture while focused on the technical challenges of turbocharging a two stroke engine.

Interesting! Yes, I think turbo lag maybe more evident than a turbo 4 stroke, a correct tuned pipe maybe reduces a bit this problem. Two stroke (50cc 100cc 125cc 250cc) have a different power and torque curve than a 4 stroke and also in n/a the low rpm often have a "naturally lag". The low rpm are not the "strong point" of these engines.

Here another video about a 125cc 2 stroke turbo carbureted tested on the bench.


Maybe real results or fake?

 

[Luth]

Nobody is interested anymore?

What a pity it was an interesting topic.

 

[Baluncore]

It is certainly an engineering challenge, and an entertaining novelty for the spectators.

It is interesting that when double the power is needed from a two stroke engine, it can be achieved with a turbocharger. But that is really only justified when the rules of a sport specify a maximum engine capacity, and there is a competitor who can benefit from more power than a tuned inlet and exhaust could provide.

Unfortunately fuel costs and emissions rise to the point where it would not now be approved for regular use. If it became common, the rules of the game would be changed to level the playing field.

 

[Luth]

It is certainly an engineering challenge, and an entertaining novelty for the spectators.

It is interesting that when double the power is needed from a two stroke engine, it can be achieved with a turbocharger. But that is really only justified when the rules of a sport specify a maximum engine capacity, and there is a competitor who can benefit from more power than a tuned inlet and exhaust could provide.

Unfortunately fuel costs and emissions rise to the point where it would not now be approved for regular use. If it became common, the rules of the game would be changed to level the playing field.

Yes, but mine is just a simple test to understand if really a two stroke turbo can produce more power than the same aspirated.

 

[Luth]

50cc 2 stroke do a complete cycle anytime so could be correct match a turbo used in a 100cc 4 stroke?

 

[Luth]

50cc 2 stroke do a complete cycle anytime so could be correct match a turbo used in a 100cc 4 stroke?

Noboby know this?

 

[jack action]

50cc 2 stroke do a complete cycle anytime so could be correct match a turbo used in a 100cc 4 stroke?

Yes, but "could be" are the appropriate keywords.

 

[Baluncore]

50cc 2 stroke do a complete cycle anytime so could be correct match a turbo used in a 100cc 4 stroke?

There are too many words missing. I could not understand the question.

 

[Cope]

FWIW, I bought a Haltech electronic fuel injection system for my Mercury outboard. I had the dealer come over and he had me bring it up to various rpm's under full load on my dyno while he monitored his instruments and set up the fuel curve. $1000 system (still have it, anybody interested?) With equal boost as carbs you could give it any fuel mixture you wanted but it never worked as well as Mikuni draw through carbs did for some reason. Go figure. Maybe I just got lucky on my first attempt with the draw through system because nothing I changed afterwards did anything but decrease performance, sometimes by a lot.

bluechipx, what Haltech system did you try? After 40 plus years of having a hobby of trying to prove that 2cycle engines love boost, and can reach unreal HP numbers, I have arrived at the fact, that to reach the highest horsepower number, whether Turbo, Supercharged, or Nitrous, EFI is a must!

My choice of poison has been Kawasaki Triple engines 750cc. I started with draw-thru carb turbo in 1973 and followed into nitrous in 75. Still have everything I've tried and still build nitrous engines for a friends drag bike.

We are spraying , folks that make our nitrous system claim, is the equivalent to adding 285 HP to the engine! With the only issue being we have reached the mechanical limit of the transmission.

Sorry, back the the question, what did the Haltech run? I have been in contact with them and didn't find them too reassuring that my investment would be supported. I have already built mechanical fuel injection for these engines, but realizing that the most important aspect of fuel delivery to a 2cycle, is the understanding of its cyclic fuel curve, EFI would be the ultimate.

This site is an answered prayer for a very old, retired, 37yr Fireman, 35yr machine shop welder and guy who always hated to be told something couldn't be done.

Thanks
Cope

 

[bluechipx]

I'll find the Haltech in a day or so and give you the model, I bought it from Tom Earhart out of Gun Lake MI. He would be the guy for questions about it. What were you running the 750cc triple in? The 700cc snowmobile I have with a turbo was in a multi-state grass drag and was running the unlimited cc open fuel class. He made it to the final race with one other competitor. Up until this last race he used a hob switch to turn the nitrous off at 15 lbs of boost, just for a little help at the starting line. Then he would run 35 lbs of boost and at that boost level the crankshaft was only good for 2-3 passes. For a important final race for 1st place, a decision was made to disconnect the hob switch and run the nitrous for the full pass. Unfortunetly it was a bad decision, he burned it down at half track. I have never run it past 25 lbs of boost which the original owner said would good for the long run, never hurting it at that level.

 

[Cope]

I'll find the Haltech in a day or so and give you the model, I bought it from Tom Earhart out of Gun Lake MI. He would be the guy for questions about it. What were you running the 750cc triple in? The 700cc snowmobile I have with a turbo was in a multi-state grass drag and was running the unlimited cc open fuel class. He made it to the final race with one other competitor. Up until this last race he used a hob switch to turn the nitrous off at 15 lbs of boost, just for a little help at the starting line. Then he would run 35 lbs of boost and at that boost level the crankshaft was only good for 2-3 passes. For a important final race for 1st place, a decision was made to disconnect the hob switch and run the nitrous for the full pass. Unfortunetly it was a bad decision, he burned it down at half track. I have never run it past 25 lbs of boost which the original owner said would good for the long run, never hurting it at that level.

The mechanical injected engines were run in 3/4 midgets, until they cut us back to 600cc, at which time I learned the 42mm throttle bodies I built still worked on the reduced sized engine. It only took one more season and the UMRA completely outlawed even the560cc engine.

The 750 made 168HP at 9,000 and the 560 made 144HP. As for the nitrous engines, they have been for drag race motorcycle 8.40s@ 162mph with a robust 225lb rider LOL For your sled, not knowing what kind of nitrous system he was running, I wouldn't think he would have used that large of jets for take off, and if that's true, 99% of the time a nitrous meltdown is caused by fuel shortage, pressure too low, lines too small (usually black plastic lines fail).

We use Speedtech Nitrous, car size nozzles and lines. they are the best, and more than helpful in anyway you need! I like to use wet style system (fuel supply dedicated for nitrous sys.) Dry systems have too much complication and avenues for problems. AS far as issues, we run more nitrous on a 2 stroke than anyone iv'e heard of. Full kit from starting line to finish, a quarter mile at a time. 2 1/2 lb. bottle per pass. No crank (welded pins and cryo-treated), piston or cyl. head problems. Average 5 runs a day, tear down just for a look, once every couple of months. The turbo bike, was always street tested and I have a 4gen. build almost ready, need to finish intake.

For those who care, figured out from the start in the 70s, no Physics, formulas or( the one I like) HE said it won't work! Chambers are a waste of time with a turbo. Keep the exhaust as short as posable, the closer to the exhaust port the better, and don't make the head pipes too big. Heat, velocity and pressure in the turbine housing of the turbo, will do the same job! For some other time, I'll tell you about a 750 with a supercharger on it. Have ridden the bike and even with a much too small carb, it was impressive. Another reason I want to get an EFI system found.

I started this life long love of 2 strokes in 1969 when I started out working on Mercury Marine engines and attended their schools at the factory in Fondulac.

Thanks for the time
Cope

 

[Mechnique]

I'll find the Haltech in a day or so and give you the model, I bought it from Tom Earhart out of Gun Lake MI. He would be the guy for questions about it. What were you running the 750cc triple in? The 700cc snowmobile I have with a turbo was in a multi-state grass drag and was running the unlimited cc open fuel class. He made it to the final race with one other competitor. Up until this last race he used a hob switch to turn the nitrous off at 15 lbs of boost, just for a little help at the starting line. Then he would run 35 lbs of boost and at that boost level the crankshaft was only good for 2-3 passes. For a important final race for 1st place, a decision was made to disconnect the hob switch and run the nitrous for the full pass. Unfortunetly it was a bad decision, he burned it down at half track. I have never run it past 25 lbs of boost which the original owner said would good for the long run, never hurting it at that level.

Hi Bluechipx, Came across you in two turbo posts and enjoyed your laid back and down to Earth explanations relating to how it was possible to turbo a 2 stroke. I wonder if you read this if you could contact me on the forum or via email ([personal e-mail address redacted by the Mentors]) It is in relation to turbocharging. Nothing ominous just a simple question on if one is using expansion chambers how are they placed into/at the impeller side of the Turbo?

 

[NOS_350x]

Is there any way to add pictures? I currently have a turbo drag atv and several others have made successful turbo 2 stroke quads,

There is also one supercharged one that was never quite finished. If I can figure out how to post pics I’ll show y’all. There was quite a few questions but the basics of it is, adding pressure to the intake adds power, it’s simple don’t over think it about the exhaust being open, you still get the same rate of gain as you do with a 4 stroke.

A standard engine pulls vacuum on the intake side, by keeping the boost at 0 psi you get a gain because the engine isn’t working to suck the air in. At 15psi of boost you double your hp, at 30 you double it again, these same ideas work on a 2stroke

 

[bluechipx]

When I told a motorcyle dealer that had a turbo on his bike, that I made OVER double hp at 14.7 psi boost he sneered and said I broke the laws of physics. I told him to visulize a 500 ci engine with a small lawn motor carb on it that would be running in a very high vacuum and making very little hp, now ad a turbo and crank the boost up to a whopping zero psi (but no vacuum) and watch the hp quadruple or more! I still don't think he got it for some reason due to the look on his face.

 

[StianM]

Just signed up here after googling a little regarding my next project. And lots of guys here with practical experience, but a few logic flaws that made me sign up here. As an petrolhead, engineer and flawed two stroke motorbike racer(I was a coward in the corners) I do have the practical experience with tuning high performance two strokes and I understand the physics behind it.
Some here talk about back pressure and how an engine needs it to work. That is simply not true and are conclusion based on observations you do not understand.

An engine thrives when it has a low back pressure that helps extract the exhaust. An high back pressure will restrict engine power.

What your experiencing when you remove the exhaust off an 4stroke is a loss of bottom end power because of increased back pressure. An exhaust system Transports pressure and sound pullses that translates into a low pressure on the exhaustvalve. What this exhaust system is removed the atmospheric pressure will act on the exhaust valve creating a backpresure. When you move on to 2strokes understanding how sound and pressure works with the dynamics become even more essential. How do you guys think honda got 200hp from its NSR500 20+ years ago? The design is to my knowledge still an secret to this day.

An blower on a two stroke would work just as well as an turbo since there is no extra backpressure needed, but efficiency could become lower but with and wider powerband. Maybe a blower setup would produce more power at an better efficiency because you could throw the reedcage away and get rid of that resistance.

For the exhaust I would just throw the original expansion chambers and fit larger ones. The exhaust volume would be larger so I would think a that you should design the chambers according to cylindervolume*atmospheres. So if running 3 atmospheres of boost on a 50cc you should use chambers from a 150cc to obtain max results.
How much boost you could run would simply be limited by the pressure spike from the reflecting wave.

 

[StianM]

Some bloke trying to get a two-stroke to run on renosance alone without valves.

This guy prove parts of my claims. He has understood how a two stroke works.

Sadly he later looses it because of lack of theoretical understanding of engines.


The first thing he do make perfect sense. He gets the engine to run without an valve removing the losses there is in the valves.
For he's brute force concept it will work, but he is now fighting against the pressures instead of making them work with him ending up using a lot of power to run a blower who's fighting pressure waves.

https://www.snowmobile.com/blog/wp-...ris-two-stroke-turbo-patent-US20200182139.pdf

Looking at this patent from Polaris indicate that they use some different dimensioning of pipes that what is normal on naturally aspirated engines like myself have thought, but this could be purposely misleading to prevent copies.

 

[Dustyballs]

With a two stroke engine the pressure in the pipe determines how fast the pressure wave travels up and down the length of the tuned chamber forcing the blow by back into the chamber n/a it effectively super charges itself. This can be tuned with the length of pipe. Longer pipe returns later, power at higher rpm, shorter pipe the opposite. The added psi of turbo charging will make this pressure wave travel faster. possibly so fast that the power band is moved out of the engines operating rpm. So I think a much longer chamber in the pipe would be needed to make the engine still have the two stroke power band we all know and love.

 

[Dustyballs]

Also the power band would change rpms as boost psi ramps up. Possibly if you could slowly raise the boost psi you could create a very wide progressive power band.

 

[Paanch]

Yes it's what I mean. The mistery is that thing seems work! But if we look the 2 stroke working process seems impossible. The return wave in the exhaust can put back the fresh charge expelled from the cylinder but if this fresh charge is boosted also how can it work? The gif picture is exactly the same engine principle of what I said. You can see carb Reeds and the ports open at the same time. Imagine to put a turbo at the outlet of the pipe.

Anyone can explain how a turbo can work on this?
View attachment 269184

Because the turbine side also increases back pressure equally. You guys seem to forget that part of the equation. If you use a turbo setup where the exhaust pressure can be regulated to not exceed boost pressure by too much you should be able to contain a bigger and denser mixture. Another thing is that an intercooler in this case will likely massively increase the performance too. Since a cooler charge is a denser charge. Means more mass at the same pressure. Which also means more power.

 

[CLatch]

Here's a shot of the assembled Merc with the Aerodyne turbo.View attachment 269366

Man, I NEED to do this with an inline 6. If you still look at these forums please get back with me.

 

[CLatch]

The mechanical injected engines were run in 3/4 midgets, until they cut us back to 600cc, at which time I learned the 42mm throttle bodies I built still worked on the reduced sized engine. It only took one more season and the UMRA completely outlawed even the560cc engine.

The 750 made 168HP at 9,000 and the 560 made 144HP. As for the nitrous engines, they have been for drag race motorcycle 8.40s@ 162mph with a robust 225lb rider LOL For your sled, not knowing what kind of nitrous system he was running, I wouldn't think he would have used that large of jets for take off, and if that's true, 99% of the time a nitrous meltdown is caused by fuel shortage, pressure too low, lines too small (usually black plastic lines fail).

We use Speedtech Nitrous, car size nozzles and lines. they are the best, and more than helpful in anyway you need! I like to use wet style system (fuel supply dedicated for nitrous sys.) Dry systems have too much complication and avenues for problems. AS far as issues, we run more nitrous on a 2 stroke than anyone iv'e heard of. Full kit from starting line to finish, a quarter mile at a time. 2 1/2 lb. bottle per pass. No crank (welded pins and cryo-treated), piston or cyl. head problems. Average 5 runs a day, tear down just for a look, once every couple of months. The turbo bike, was always street tested and I have a 4gen. build almost ready, need to finish intake.

For those who care, figured out from the start in the 70s, no Physics, formulas or( the one I like) HE said it won't work! Chambers are a waste of time with a turbo. Keep the exhaust as short as posable, the closer to the exhaust port the better, and don't make the head pipes too big. Heat, velocity and pressure in the turbine housing of the turbo, will do the same job! For some other time, I'll tell you about a 750 with a supercharger on it. Have ridden the bike and even with a much too small carb, it was impressive. Another reason I want to get an EFI system found.

I started this life long love of 2 strokes in 1969 when I started out working on Mercury Marine engines and attended their schools at the factory in Fondulac.

Thanks for the time
Cope

Oh man, another great person to talk to about forced induction 2 smokes. This is an amazing thread, hope you guys can get back to me about the inline 6's.

 

[bluechipx]

Oh man, another great person to talk to about forced induction 2 smokes. This is an amazing thread, hope you guys can get back to me about the inline 6's.

What was the advertised HP of your inline six cyl?

 

[CLatch]

What was the advertised HP of your inline six cyl?

I've got the 115hp mid 70s mercs

 

[bluechipx]

Not the perfect engine for adding HP. The long somewhat frail crankshaft I feel was at the edge in stock form. Either a V-4 or V-6 is a much stronger unit. The small inline four cylinder Merc thast I used had the front half of the motor (crankcase) that supported the crank and took a lot of thrust from the firing cylinders and barely weighed a pound! I happened to have a solid billet block of 7075 aluminum that was just the size to make a real strong crankcase out of. Also the turbo was hard on reeds and and in stock form you had to almost completely tear the engine apart to get at thev reeds. My new crankcase had a much smaller internal volume and used pyramid style reeds that are almost external and easily changed.

 

[CLatch]

Not the perfect engine for adding HP. The long somewhat frail crankshaft I feel was at the edge in stock form. Either a V-4 or V-6 is a much stronger unit. The small inline four cylinder Merc thast I used had the front half of the motor (crankcase) that supported the crank and took a lot of thrust from the firing cylinders and barely weighed a pound! I happened to have a solid billet block of 7075 aluminum that was just the size to make a real strong crankcase out of. Also the turbo was hard on reeds and and in stock form you had to almost completely tear the engine apart to get at thev reeds. My new crankcase had a much smaller internal volume and used pyramid style reeds that are almost external and easily changed.

Was that done with a cnc? If so I have access to materials and the machines, and I can get one cranked out probably pretty easy. Would you happen to still have the files on it if it was cnc?

 

[bluechipx]

I'm an old school machinist, sine plates, rotary tables and such. When I was buying my first Hurco machining center when the owner of the shop I was dealing with stepped away, I asked the twenty some year old operator how difficult it was to learn how to operate it. He said he could teach a monkey to do it in a half hour which gave me confidence. Six months later I was still struggling nand could only do the basics that could be done from the machines console. When it gets into 3-D I'm lost. My younger brother uses one of the mastercams from a computor and sends it to the machine. I did take an old crankcase and cut it across the area where the connecting rod travels and duplicated the shape on a piece of graphite and EDM'ed the pockets (which aren't half rounds , but a somewhat unique shape). One day last fall I wanted to try out a EGT gauge when it was in the thirties and snowed the next day. I took it kinda easy, probably around 80 mph and had the strange feeling the hydro was getting a little high in the front so I didn't look at my gauge and kept my eyes on the river. The trim adjustment jammed into a position that caused way to much bow lift. A professional racer friend saw the picture and said 1/4" more bow lift and it surely would have blown over. It's fixed now and it should be perfect in the spring when I run it again.

 

[CLatch]

I'm an old school machinist, sine plates, rotary tables and such. When I was buying my first Hurco machining center when the owner of the shop I was dealing with stepped away, I asked the twenty some year old operator how difficult it was to learn how to operate it. He said he could teach a monkey to do it in a half hour which gave me confidence. Six months later I was still struggling nand could only do the basics that could be done from the machines console. When it gets into 3-D I'm lost. My younger brother uses one of the mastercams from a computor and sends it to the machine. I did take an old crankcase and cut it across the area where the connecting rod travels and duplicated the shape on a piece of graphite and EDM'ed the pockets (which aren't half rounds , but a somewhat unique shape). One day last fall I wanted to try out a EGT gauge when it was in the thirties and snowed the next day. I took it kinda easy, probably around 80 mph and had the strange feeling the hydro was getting a little high in the front so I didn't look at my gauge and kept my eyes on the river. The trim adjustment jammed into a position that caused way to much bow lift. A professional racer friend saw the picture and said 1/4" more bow lift and it surely would have blown over. It's fixed now and it should be perfect in the spring when I run it again.

Well I'm a welder/fabricator by trade, not anywhere close to a machinist, only thing I can operate like that is a drill press lol. I was asking so I could possibly have the engineering guys at work do their magic and recreate that idea in 6 cyl form, because I know for a fact that reeds won't survive boost, and they're INSIDE the crack case so it makes it that much harder. I really do like the idea of easier access to Reeds and a different type being that there's only 1 oem style aftermarket Reed option for the towers, and it's Boyosen. And yes, looking at that picture looks like it wasnt far off from tipping! I bet it sounds amazing tho! I do however have a question about cooling.
Did you have to modify the factory cooling on the block at all? And how about the lower unit?

 

[bluechipx]

No cooling mods at all. In fact the one to one gear case off a 45SS johnson race engine (stronger than the "D" Merc) had such a big water pump in it the engine wouldn't warm up so I had to re-route some of the water back to the river to get sensible engine temp. I really hope you aren't planning on using the stock gear ratio fishing lower unit gear box. Instead use one of the speedmaster series units. When a new guy would get a hydro, on a budget, and try high pitch props on the fishing unit, a fifty hp Merc (44 cu in) would barely hit fifty. A simple change to a "quicky" or one to one racing style lower unit would jump the speed easily to 76-78 on the first try.

 

[bluechipx]

BTW, in order to match the block to the new crankcase and wind up with the crank bore being round and sized right I did the bore on a DeVlieg jig mill. Yours being 50% longer will be a little tougher. I could be wrong but I think when the engineering guys see what you are asking they won't be quick to agree, it's quite a job from huge block of aluminum into finish product. Let me know how it goes when you run it past them.

 

[CLatch]

BTW, in order to match the block to the new crankcase and wind up with the crank bore being round and sized right I did the bore on a DeVlieg jig mill. Yours being 50% longer will be a little tougher. I could be wrong but I think when the engineering guys see what you are asking they won't be quick to agree, it's quite a job from huge block of aluminum into finish product. Let me know how it goes when you run it past them.

I'm aware about the lower, was just curious of what kind you had in your pictures. I might use it for initial testing purposes but not permanently. Im not really familiar with outboard racing or racing products for outboards in general, this project will just be a hobby deal for me.
And Hopefully the engineers and machinists won't turn it down, I mean I do work for one of the top automotive blower companies in the US, and we have experimented with outboard stuff a while back but ended up sticking to inboard blowers due to market not being there. I doubt it was anything this old, but I also doubt the guys will be scared to do it.
Also, what size carburetors did you use? Going to try to get an idea of the amount venturi I need along with the jet sizes you used. I imagine a good starting point would be slightly bigger carb than you used at 3 total?

 

[bluechipx]

In case anyone is still following this thread, I did a real stupid thing last fall and nearly died. I have a formula/champ style one person tunnel hydro with a moderate v6 2.5 liter mercury on it. They all have power trim and trimming the engine angle is critical for controlling the bow lift.

I was just going to go for a easy ride and never even told anyone I was doing it. It was just going to be a easy run so I wasn't even wearing a helmit (I know, stupidity!). I had the trim set very conservatively and gradually increased my speed as I was going from river to lake in near calm wind. A recovered and dried gps read 118 mph. At somewhere around 118 mph the bow lifted so rapidly that there was no time to trim out of it.

All I could see was sky when I tightly closed my eyes and put a deathgrip on the steering wheel. I knew this was going to be a bad one. After a few seconds I felt a hard jarring and opened my eyes to see I landed upright in the water, unhurt and not even wet! A quick inspection showed the rear cowling gone and a badly leaking gas tank which broke loose. I stopped the leak by tipping the tank and was afraid to disconnect any electrical contacts to prevent sparking and igniting an inch or more of gas in the entire bottom of the hydro.

I removed my shirt and soaked up the gas like a sponge. Apparently I did a complete 360 and landed in a headache producing thud. It was one hour before a friend in a jetski came to tow me back. Not one other boat came by in that hour.

I have never given up on any project but this time I am. The boat is shrink wrapped and I'll never drive it again. In fact I'll destroy it before I sell it unless a person can do some real convincing that they have a ton of experiance and I don't have to hear they either died or were badly hurt in it. Google 'tunnel boat blowovers' for some footage of accidents others had and you will see how lucky I was to walk away unhurt but somewhat smarter!

 

[Tom.G]

Sounds like a case of "Live and Learn."
Too often the first requirement is skipped.

 

[Kaseytoo]

When a 4 stroke engine is converted to 2 stroke, the cylinders are used at twice the rate, so it has an improved power to weight ratio, but with higher emissions. A 4 stroke engine has separate inlet and exhaust manifolds so it can be easily turbocharged.

For inducted air-fuel mix engines the maximum compression ratio is limited by the octane rating of the fuel. The effective compression ratio is the product of the cylinder compression ratio, and the air pressure boost ratio. Most engines without superchargers are designed for optimum compression ratio, so there is little room for improvement. You might need to change from gasoline to ethanol for a higher compression ratio.

Fuel injection overcomes the compression limit. There have been many fuel injected two stroke diesels with superchargers.

I have built a small 170 cc split single 2 stroke engine. I'd like now to supercharge it. Can you recommend what size and type I could use?

 

[Baluncore]

I have built a small 170 cc split single 2 stroke engine. I'd like now to supercharge it. Can you recommend what size and type I could use?

Firstly, piston material and so piston temperature will decide the boost limit. With two pistons close together, cooling is more difficult than single-cylinder engines with air-cooling, or multicylinder engines with water jackets.

Secondly, with higher cylinder pressures, the main bearings will need improved lubrication. That may be difficult if you pass pressure boosted air-fuel mix through the crankcase. Maybe you could charge the inlet port directly from the supercharger, SC.

The required SC capacity will depend on the optimum engine RPM, and the required boost. Estimate the boost factor. If the SC is driven by the 170 cc engine, then boost ratio * 170 cc * RPM = capacity in cc/min. Select an appropriate gear ratio for the SC.

 

[Kaseytoo]

Thanks for the reply. I'm hoping that with internal oiling, the exhaust piston can have direct oil cooling to cover that. ports will be direct from the s/charger and or then turbo if possble. The a radicall split single design offers opportunities not found in normal two strokes. (see att. as a possibility)
Peak revs can be to 5000 rpm when needed. It needs 850000 ccs per minute at that rpm. some roots types (300 and 500) models are available from China. would one of them be adequate. Mazda use one type with their new valved 2 stroke.