Speculation about turbocharged two-stroke singles.

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

Owen_N

Well-Known Member
Joined
Dec 26, 2021
Messages
239
Reaction score
12
Location
Kawerau, New Zealand
This is about the crankcase-charged variety.

I have found that the record output for a turbocharged 50cc is still around 20 hp.

This seems rather low, as that is about the same output you can get using a tuned pipe and no turbocharger.

What factors would affect slow progress in gaining more power?

1) The available turbochargers are for larger engines, - typically the VZ21 turbocharger, which can be used for 200-800 cc sized four-stroke engines.
2) The pulsing action of a single cylinder exhaust is not efficiently used by the turbine scroll.
3) The compressor housing is not matched to the desired flow rate and pressure. This can lead to stall and surging if draw-off is insufficient.
4) current examples seem to be mounted after the expansion chamber, and tend to lose pressure from the exhaust and suffer from the effects of chamber pulses.
5) aftercoolers are not used. This affects mixture density on the induction side.
6) The sheer heat generated overheats and seizes pistons.- speculative-. two-stroke engines have a precarious thermal balance, and it doesn't take much to upset it.
8) The crankcase cycle limits gas flow through the engine, especially if the tuned pipe is not drawing mixture through as well.- is this true?

Could a non-chamber system work well by emulating a lower speed engine without a pipe, and just increasing mixture density?
These engines normally only make a quarter of the hp of a tuned race engine.

Can design factors for turbine and compressor scrolls be adjusted to improve output?

If the engine runs at 4 bar, will it generate a net 4x amount of power?

How much does running the exhaust at an elevated pressure reduce the output?

This would be assisted by using aftercooling, and alcohol fuel for detonation resistance, and some internal cooling.
Is the 4-stroke cycle inherently better suited to taking advantage of a turbocharger?

Given examples from the race world, it looks like turbocharged engine output is really only limited by the strength of the engine, and a 1600 cc engine when turbocharged can make more power consistently
than a 3.5 litre race engine in Formula One. This is in the region of 1000 hp, or 31 hp for 50cc .
More for a drag-race engine.
 

lohring

Well-Known Member
Joined
Aug 6, 2011
Messages
425
Reaction score
151
Crankshaft scavenged turbocharged two strokes have been built. The secret to supercharging two strokes is to raise the exhaust back pressure along with the intake pressure. Since the increased back pressure occures around bottom dead center, there is very little negative work. Today's small turbochargers could work with 50 cc two strokes. Below are some pictures. The four cylinder 800 hp engine is one of my favorites.

Lohring Miller

DSC_0528.JPG turbotwostroke.jpg GT0632SZ turbo.jpg
 

Attachments

  • Garrett GT0632SZ.pdf
    844.9 KB · Views: 66

Owen_N

Well-Known Member
Joined
Dec 26, 2021
Messages
239
Reaction score
12
Location
Kawerau, New Zealand
Crankshaft scavenged turbocharged two strokes have been built. The secret to supercharging two strokes is to raise the exhaust back pressure along with the intake pressure. Since the increased back pressure occures around bottom dead center, there is very little negative work. Today's small turbochargers could work with 50 cc two strokes. Below are some pictures. The four cylinder 800 hp engine is one of my favorites.

Lohring Miller

View attachment 135831 View attachment 135832 View attachment 135834
I recognise the middle one. It is from the Budfab streamliner, 2008. good for 144 mph, or 230 kph, record, and has reached 150 mph (240 kph).
I think it is still around 20 hp, though.

Does it use the Garret turbocharger? What price are those? I bet they are a lot more than the VZ21, but probably much more efficient.
There is a more recent example of an engine like this, on YouTube, about 2014, but it doesn't seem to have been developed to this extent, or followed up on.

I can see why the expansion chamber is desirable. This allows more power for less pressure, and less thermal and mechanical load.

I wonder whether the limit is heat tolerance of the engine, or turbocharger performance?

If the turbo is too small, then you are rpm-limited. If the turbine scroll has too much volume, then you will not reach peak rpm and throughput.

I have seen layered twin-scroll housings which supposedly work better with a pulsating input, but I don't know if just reducing the width or other scroll dimensions would have the same effect.

4-stroke engines do not seem to be limited in boost pressure or output, in the same way as two-strokes.

Is it just that the developers do not want to build a special engine to take the extra heat and load, or some other factor?

If you just make the engine beefier- say use more 125cc parts, clutch, gearbox, special barrel with longer, heavier piston for more skirt cooling,
add intercoolers, maybe water injection??

You also need an oil circuit for the turbocharger.

It would be cheaper to build an engine, or several, like this, than to run a whole streamliner record campaign. - Maybe everyone runs out of money and interest before they get to the point of seriously diminishing returns.

I am sure the Budfab team spent some time on wind tunnel development, to get such good results.

Personally, I would like to pursue naturally aspirated engines, based on fairly cheap, but water-cooled engines.

I am sure they are good for over 20 hp without spending a lot of money- the most expensive part is getting the Nikasil redone.

I wouldn't go to the extent of going record-racing in a totally other country, though.

There are not many places where you have 10 miles of totally flat track to do runs on.

Running on salt must be more "draggy" than tarmac, but the Budfab seemed to do quite well on not a lot of power.
 

lohring

Well-Known Member
Joined
Aug 6, 2011
Messages
425
Reaction score
151
The tuned pipe is a no moving parts turbocharger. It's possible to get over 50 hp from a 125 cc engine with it. Jan Thiel estimated that a single cylinder 50 cc engine could develop 30 hp and a two cylinder 50 cc engine could develop 39 hp. I believe some Dutch tuners have exceeded 30 hp with a tuned pipe engine. Quickdraw gets close to 8 hp from a 26 cc engine. Small timing changes can raise this to 10 hp. Turbochargers really come into their own at high altitudes like Bonneville and snowmobiles. Turbocharger efficiency sets the power possible for small units.

Larger engines can be built with any combination of power from the engine versus the turbine. Electric motor boosted turbos have also been used. However, turbines are simpler, lighter, and more reliable for large power plants. That's why large aircraft and naval ships use turbines. Only where fuel economy is critical are turbocharged two strokes used in large ships.

Lohring Miller
 

Owen_N

Well-Known Member
Joined
Dec 26, 2021
Messages
239
Reaction score
12
Location
Kawerau, New Zealand
The tuned pipe is a no moving parts turbocharger. It's possible to get over 50 hp from a 125 cc engine with it. Jan Thiel estimated that a single cylinder 50 cc engine could develop 30 hp and a two cylinder 50 cc engine could develop 39 hp. I believe some Dutch tuners have exceeded 30 hp with a tuned pipe engine. Quickdraw gets close to 8 hp from a 26 cc engine. Small timing changes can raise this to 10 hp. Turbochargers really come into their own at high altitudes like Bonneville and snowmobiles. Turbocharger efficiency sets the power possible for small units.
<snip>
Lohring Miller
I am interested in the 30+ hp from a tuned pipe.
These people don't seem to publish on the internet. Were they pre-internet results?

When was Moto GP changed over. I seem to remember 2011 was the last year for 500s.
When did 125 GP racing cease?
When did 50cc GP finish? - that hasn't been around for a while.
I will look up Jan Theil.
If you compare 50cc and 125cc output vs rpm and volume, 27 hp looks quite possible from a 50.
It is looking like he has about 20 hp as a first cut, but yet to be verified on an engine dyno.

This seems to depend mainly on the pipe design,
as there is not a huge amount you can do with the engine part beyond what has been done.


- refinements on power valves, cavity resonance in the crankcase area- the resonant inlet tract with no valving has not been fully developed yet.

Mr "2StrokeStuffing" seems to be fairly cutting-edge. It is a pity than he has switched attention to the supercharged 2-stroke, so we don't get to see
what can be done with natural aspiration. I think they will come out even eventually, but the supercharger gives a wider power band.

Using a Roots blower, and massive effective inlet-exhaust overlap, is not very efficient.

Possibly fine tuning the rotary exhaust valve will give some improvement, but a valving system with less lost volume could be even better.
4 valve head, cams, poppet valves??
<edit>
I had a look at you reference.
1) why is 1983 used as a limiting date?
2) I say a Kreider engine mentioned which used a different barrel unit and a grafted-on 6-speed box.
This seems to be going beyond the date limitation??
3) 53.9hp looks like the limiting hp figure for 125s at 13,000 rpm.
Is this metric or imperial hp? 746w vs 735w metric.

4) Why is short-stroke disc valve mentioned?
I would have thought that "square" dimensions are best for porting.
even at 39mm stroke, you can go to 19,500 rpm before you reach 25 m/s average.

Possibly this should be reserved for your top overrev, so 17,850 sounds like a good spot for maximum power.
Disc valve seems to be better than even quite large, light reed valves. (40 hp vs 53 hp)

5) I need to find some more detailed descriptions of successful pipes.

- I suppose this discussion can be moved back to "unusual two-stroke head design", though this feature has been shown to be not that important
for lower-revving engines.
 

lohring

Well-Known Member
Joined
Aug 6, 2011
Messages
425
Reaction score
151
Jan Thiel retired long ago. With minor exceptions, two stroke development stopped with the Aprilia. My favorite site for the current state of the art is in the ESE engine works tuning section under Buckets in Kiwi biker. It will take days to get through it. Another valuable tool is EngMod2T. It is a low cost engine simulation program. Below is a spread sheet that gives a starting point in engine and pipe design.

Lohring Miller
 

Attachments

  • JanBros 2-stroke 1.2.pdf
    537.8 KB · Views: 219
  • JanBros 2-stroke 1.2.xlsm
    4.8 MB · Views: 40

Owen_N

Well-Known Member
Joined
Dec 26, 2021
Messages
239
Reaction score
12
Location
Kawerau, New Zealand
Jan Thiel retired long ago. With minor exceptions, two stroke development stopped with the Aprilia. My favorite site for the current state of the art is in the ESE engine works tuning section under Buckets in Kiwi biker. It will take days to get through it. Another valuable tool is EngMod2T. It is a low cost engine simulation program. Below is a spread sheet that gives a starting point in engine and pipe design.

Lohring Miller
sounds quite narrow -
[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 1) (Locked) - Page 14 (pit-lane.biz)

Frits Overmars has some interesting numbers on port layouts here.
I am not sure whether they are a "real engine", as the exhaust seems very wide. at 4x 65 degrees.

However, 6 identical transfers and no boost port seems interesting.
The AM6 engine has 6 transfers plus a boost port, but no supplementary exhaust ports.

Vertical timing of 192 degrees about bdc, Exhaust; Transfers 130 degrees, about bdc, and exhaust floor up a little from bdc?
exhaust floor up 104.5 from tdc sounds narrow-would that only be for the side row of e ports. - that is 20 degrees wide, and above the transfers.
If I want a real piston, then about 165 degrees of exhaust in 3 blocks sounds ok, as 48-65-48, and a bit closer to the transfers.
I need to get Engmod2t and try it out.

The 360 degree skirt may be beneficial, but I think I would have to design and make my own- later version, maybe.
Using fine threads and winding the skirt on, does not seem very secure. It is low mass, though.
Using steel bolts into bosses on the skirt is secure, but heavy. Possible heat transfer problem to the top bearing??
 

lohring

Well-Known Member
Joined
Aug 6, 2011
Messages
425
Reaction score
151
Look at the page below for some great information.


Lohring Miller
 

Owen_N

Well-Known Member
Joined
Dec 26, 2021
Messages
239
Reaction score
12
Location
Kawerau, New Zealand
We seem to be drifting a bit from the topic, but I want to discuss naturally aspirated performance two-strokes a bit more.
I should start a new topic, as the cylinder head topic is about my current series of air-cooled prop engines
The new topic can be "details of performance two-strokes"
 

Owen_N

Well-Known Member
Joined
Dec 26, 2021
Messages
239
Reaction score
12
Location
Kawerau, New Zealand
Look at the page below for some great information.


Lohring Miller
Thanks- got that. Now for some reading.
The tip about reducing CR on a pipe engine is interesting.
How low do I have to go?
is 8.0:1 ok for 95 RON? and a high-revving engine?
 

Latest posts

Top