# Small Engine Turbocharger (Is it possible)



## kcmillin (Apr 13, 2011)

I am contemplating making a turbocharger for my Tiny inline 4 cylinder. I have seen superchargers and blowers in model engine size but not turbochargers.

So my questions are.

Has this been done for engines with less than 1 Cubic Inch displacement?

What would I have to to to the carb to stop the compressed air from blowing the fuel backwards into the fuel line?

Also, what type of RPM's are we talking about with an impeller less than 1" diameter? I understand that extremely high revving components are a whole different game, perhaps out of range of the average model builder. I don't want tiny impeller pieces in my face and body so please talk me out of it if you feel this would be unsafe. After all, there is probably a reason I can't find one.

Kel


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## Sparticusrye (Apr 13, 2011)

If you find any information on this I would be interested.

I haven't found any info on one being used in small dispalcements. In theory it should be possible. If attempting it then possible adding a way of loading the turbine of the turbo in order to prevent excessive RPM. Not sure what kind of RPM you would see in a 1" turbine, 100k maybe?, but you would need to take that time to balance the rotating assembly. Adding a ring in the machining process to the back of the compressor and turbine would allow you to file off small amounts to balance each component. Not sure what kind of design you were thinking. With high RPMs a good set of bearings would be needed, lubrication might be an issue to where the Tiny 4 doesn't have forced lubrication. I've got a lot of ideas floating around in my head towards this topic just not sure where to start.

For the fuel blow back its hard to say as your probably gravity feeding at the moment. Could simply increase the height of the tank to increase head pressure, but the turbo pressure will vary with engine speed. Might not even be an issue with an engine this small.

Sorry I'm not more help. Just really interested in the turbo idea on a small IC engine.

James


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## mu38&Bg# (Apr 13, 2011)

Small turbos are problematic. I have a Borg Warner KP-31 compressor wheel I bought years ago with the intention to build a small turbine for model aircraft. It was, and I think still is, the smallest available for a turbo at 31mm diameter. The compressor map spans 140,000 to 300,000 RPM. Efficiency ranges from 50 to 73%. These are used for engines in the 1L, 60HP range. As turbo machinery gets smaller RPM must increase to achieve any sort of pressure and volume to surface areas mean more friction loss. Pretty soon you have a turbo that doesn't accomplish anything.

Positive displacement is the only practical arrangement for something this small.

Greg


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## kf2qd (Apr 13, 2011)

HIGH RPMs and heat. Those are the things you would have to deal with. An very low efficiencies. And very low volume through the engine.


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## kcmillin (Apr 13, 2011)

Thanks for clearing it up guys. I think a turbo might be a little out of realm. To make it functional and safe it would probably look a little out of proportion to the engine, although I already have a near comically proportioned distributor :big:

Thanks again.

Kel


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## Diy89 (Apr 14, 2011)

Funny how it is... I was just in a local hobby store that does a ton of rc car-truck stuff. One thing that caught my eye was this rather large truck with an OS .21 glow engine with a supercharger. It was belt (o ring) driven from the crank and was rather large, almost the same size as the cooling fins on the engine head. 
The store owner commented that tuning was a real pita with the blower, as it tended to have only one sweet spot. 
Of course, it is two stroke,nitro-glow fueled, high reving with a very basic carb.

Personally i think you should try it. I really rather doubt you will end up with a compressor or turbine wheel that has enough mass to do real damage should it explode. If i were to think of building one, i would start with something like a flow meter turbine (stainless) or a micro turbine from a dentist instrument and adapt from there. Use the fuel to lubricate and cool the bearings, and pull air thru rather than blowing thru the carb. 

What do you have to loose?


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## FIXIT (Apr 14, 2011)

To try and answer your origanal question fuel supply.

the only carburetter/ turbo engine i have come across is the MG metro and that fuel system uses a high flow/pressure fuel pump with a separate variable pressure regulator that holds the fuel pressure 4 PSI above boost pressure and the SU carb is completely sealed with 'o' rings and lip seals on the throttle shaft.

I hope that gives you in-site to the problems !  'fuel injection maybe !!'


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## Longboy (Apr 14, 2011)

That would be a tough one, a mini turbo. It would put a machinist at the top in developing such. An alternative would be to make a faux turbo. The looks without the function. You could make the plumbing, impeller housing, impeller and possibly get the turbo whine without a need for timing, octane, heat & boost control issues. No chance of damaging your engine with just a redo of the intake/ exhaust circuits. Since most model engines are dynamic displays and not workhorses, there would not be any sustained load where even a viable mini turbo engine would be hurt. Some of these engines are over engineered and may survive under several minutes of boost pressure............but the question is: Would I risk my multi cyl. model I took months/ years to create to have this uniqueness. Smoking a hole in a piston that can be replaced is one thing. Blowing the bottom end out means you now have a 15 lbs paperweight. If you ever see at a show these model supercharged V-8's driving a dynamo at more than half throttle, that would be a testament to load bearing capacities but a big time risk.


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## Ken I (Apr 14, 2011)

Have to agree with longboy - why risk your model - surely you are not really looking for more power ?

Having had the experience of cranking 448 H.P. out of a 2.0 L Opel engine I can tell you it was a long painfull process of breaking things. A constant process of finding the next "weakest link".

As regards fueling it - fuel injection is pretty much mandatory - trying to boost a carb is full of problems - although I think a simple venturi system will work - but of course this only has one "sweet spot" as pointed out in an earlier reply.

Full throttle control requires all sorts of sophistication and even with fuel injection the fuel pressure has to be moderated by the boost pressure otherwise it leans out KABOOM.

Faux turbos for appearance only is probably the way to go.

Ken


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## Chaffe (Apr 14, 2011)

Turbocharging is something im very familiar in full sized practice. If the turbine and compressor wheels were accuratly machined from the solid then they would need not be balanced. As in full sized practice a wastegate could be incorporated into the exhust housing to regulate boost pressure/turbine speed. Carburated setups in real life include the renault 5 gt turbo and the the metro "a" series turbo, both pressurise the carb fuel bowl and use a fuel pump. This is not nesesary as you could use your excisting carb and suck through it from the inlet side of the compressor, and so it would function perfectly normal, with the increased bonus that the turbo would be cooled by the air/fuel mix. To actually make boost would be tricky, but as mentioned a demonstrational turbo would be easy, the bearings are very simple and a drip feed would probably suffice for a model. I think you should try it! the turbo could be tested with a compressor piped up to act as exhaust gasses, to prove any posible failure points prior to fitting to the engine, or even never fit it just make a model turbo! that in itself would be rewarding enough! hmmm thinking i might do something myself now.....


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## Ken I (Apr 14, 2011)

Carburettor to turbo inlet is a pretty good receipe for inlet plennum explosions.

Unpressurised inlet mixture is frequently ignited by flame leakage from the inlet valves - however boundary effect cooling and the relatively low flame speed inhibit this to negligable levels -apart from the odd "WHOOMPH" during cranking (the cycle being slow enough during cranking to permit flame propogation).

This problem becomes significantly worse with boost - doable but not desireable.

All my negative comments aside for the moment I think a miniature turbo would be a cool idea.

Ken


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## Chaffe (Apr 14, 2011)

yes, as a seperate project i think a small turbocharger would be excellent! I would make one and use it as a keyring!


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## Ken I (Apr 14, 2011)

Now that really made me chuckle.

Ken


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## Chaffe (Apr 14, 2011)

i already have ideas running through my head!  :big:


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## Foozer (Apr 14, 2011)

Days ago, back in the 70's I took a turbo setup off a corvair spider and rigged it onto a Vega 4 banger. Worked, too bad the ol Vega engine was justa step below junk. 

Would look nice as a model, tho getting it to function I do not think is gonna go. Turbo relies upon the exhaust heat to increase the air speed. Do not think a small model will generate the high exhaust temps or at least survive for long with 1000 degree plus exhaust temp.

Perhaps a paxton type belt driven centrifugal charger? Would have the challenges of a turbo in building.


Robert


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## mu38&Bg# (Apr 14, 2011)

In my opinion, at this size a turbocharger won't work without some serious design study. Turbo design is a full college education itself. There have been very small turbine engines built in universities and a few private firms. Most have not been practical due to low efficiency. They operate at 500,000 to 1,000,000 RPM.

The truth is to make more power with a tiny engine like this there are much more effective means. Improving intake and exhaust geometry, valve train, and increasing piston speed is where I would begin. OS made fourstrokes for RC cars that ran 22kRPM with 4.4cc displacement. Aftermarket development of the head yielded a useful RPM range through 26kRPM and almost double the power output.


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## steamer (Apr 14, 2011)

Ageless engines sells they're engine plans with a turbo super charger.  ( a aircraft style mechanically driven impellor wheel).

They claim it helps with fuel mixing ...but does little, if anything else.

Perhaps Ron Colonna will pipe up and tell us about his Novi engine?......Breaker breaker ...you got your ears on Ron?

Dave


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## narrowgauger (Apr 15, 2011)

Hi Guys

would have thought that the far better direction to take would be via a belt driven supercharger instead of a turbo.

simpler design and progressive in performance, with the added benefit that the compression ratio can be varied.

have fun
Bernard


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## Chaffe (Apr 15, 2011)

narrowgauger  said:
			
		

> Hi Guys
> 
> would have thought that the far better direction to take would be via a belt driven supercharger instead of a turbo.
> 
> ...


Certainly in real life turbo's are better than superchargers in my experience, thats why we see soo many turbo diesel and performance petrol turbo cars, the turbo makes for better fuel economy when off boost, and makes for higher torque accross the board when in boost as the peak boost can be reached low down and maintained until the redline, unlike a supercharger that starts low and rises. As for simplicity, i think its six and two threes personally, but certainly agree that centrifugal chargers in this small scale will have little or no benefit and posetive displacement is probably the only "real" way to go. In saying that someone should make a small turbo as it seems no one has had experience of this yet


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