ESE's works engine tuner

[190mech]

Thanks guys!An adjustable stop will be added..Flettner,Thats a 47mm scooter cylinder,I got the idea from your belt drive porting tool you posted here a while back..

[2T Institute]

A fantastic way to make a mess of a good cylinder. fail to see how you get any control with that contraption

[Haufen]

What you can do with any carb, large or small, is to shorten the inlet tract as much as possible. This may allow you to close the disc earlier, giving a more civilized engine behaviour, and still maintain decent crankcase filling at high revs.
Or you could go the opposite route: increase crankcase volume, increase inlet tract length, and leave the inlet disc out altogether: 24/7-inlet. But then you will need some sort of hinged reed to enable starting. And I don't think anybody will manage to get decent carburation in both the reed-phase and the 24/7-phase; It will take fuel injection to get both phases right.

As the 24/7 concept has been successfully tested on a kart engine in the meantime, can you comment on the experience which has been gained, Frits?

Was fuel injection really necessary?
Which factors is it worth paying attention to / is the system sensitive to (crankcase cr, intake length, pipe? etc) if one were to have a go oneselve?

[Frits Overmars]

As the 24/7 concept has been successfully tested on a kart engine in the meantime, can you comment on the experience which has been gained, Frits?

I am not at liberty to say any more about it than I already did here, Haufen. You may want to search for 'Modena' and 'Roland Holzner'.

Was fuel injection really necessary?

OK, this is a question I can answer because it was obvious for all the world to see that the Modena 24/7 uses the normal homologated 30mm Dellorto carb.
My fears that injection would be necessary were not confirmed. The Modena runs fine with a carb, notwithstanding the fact that they also have a working injection system on the shelf.

Which factors is it worth paying attention to / is the system sensitive to (crankcase cr, intake length, pipe? etc) if one were to have a go oneselve?

The 24/7 system depends on the pipe even more than a conventional inlet system does, but the pipe itself does not need to be altered.
Crankcase volume, inlet length and carb diameter all play a role; none of those values are critical, but their combination should yield a suitable Helmholtz frequency.
The most practical way to go about this would be to start with a fairly big crankcase volume and a fairly small carburettor, vary the inlet length and see what happens.

[breezy]

"The 24/7 system depends on the pipe even more than a conventional inlet system does, but the pipe itself does not need to be altered."

Frits, do you think that the amount of power gained by the exhaust system used as it is today,could be better used elsewhere, on a 2 stroke engine, to produce better results? what are your thoughts on piston dwell at bcd, are there any rules which are a must in terms of minimum/maximum?

[jasonu]

Poor man's angle porting tool;Thought you all might try making one for small cylinders,
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Now that is in the 'spirit' of bucket racing!

[TZ350]

Modena KK1 EFI engine.

[Flettner]

Frits, I guess you are right, there is more to this discovery than we might think. If this is what I think it is, then there will also be some VERY interested fourstroke customers, ones that might race in GP class! I can see why you NEED to keep a lid on it.

So, this IS the game changer? Are we witnessing the end of the fourstroke? Time to change back to the twostroke in GP's as the emission rules no longer apply! Run this in California as much as you want, cleaner than a fourstroke (race engine)! Imagine pistons that never wear out. Good on Ryger.

[Frits Overmars]

Frits, do you think that the amount of power gained by the exhaust system used as it is today, could be better used elsewhere, on a 2 stroke engine, to produce better results? what are your thoughts on piston dwell at bcd, are there any rules which are a must in terms of minimum/maximum?

One remark in advance, which regards not only the above question but all questions: unless I say otherwise, all my answers concern conventional engines; they may or may not be valid for the Ryger engine, so don't go jumping to conclusions.

Breezy, a good exhaust system triples the power of a racing two-stroke. How would you use that power elsewhere? By driving a compressor for example? It would help but it's not allowed in most types of motor sport. And in case you mean the amount of energy contained in the exhaust gases: I don't see a way of utilizing that other than in the exhaust pipe.

Re dwelling: a short con rod will cause a higher piston acceleration near TDC and a lower acceleration near BDC, so the piston will dwell longer around BDC.
Assuming the cylinder remains unchanged, a shorter rod will increase angle.areas. For example, The Aprilia RSA has a blowdown angle.area of 14322°mm² and a transfer angle.area of 109969°mm². If we replace its 120 mm con rod with a 100 mm rod (17% shorter), the blowdown angle.area becomes 14609°mm² (2% more) and the transfer angle.area becomes 113119°mm² (2,9% more). The drawback is that the short con rod causes more piston friction and costs crankcase volume.

[husaberg]

One remark in advance, which regards not only the above question but all questions: unless I say otherwise, all my answers concern conventional engines; they may or may not be valid for the Ryger engine, so don't go jumping to conclusions.

Breezy, a good exhaust system triples the power of a racing two-stroke. How would you use that power elsewhere? By driving a compressor for example? It would help but it's not allowed in most types of motor sport. And in case you mean the amount of energy contained in the exhaust gases: I don't see a way of utilizing that other than in the exhaust pipe.

Re dwelling: a short con rod will cause a higher piston acceleration near TDC and a lower acceleration near BDC, so the piston will dwell longer around BDC.
Assuming the cylinder remains unchanged, a shorter rod will increase angle.areas. For example, The Aprilia RSA has a blowdown angle.area of 14322°mm² and a transfer angle.area of 109969°mm². If we replace its 120 mm con rod with a 100 mm rod (17% shorter), the blowdown angle.area becomes 14609°mm² (2% more) and the transfer angle.area becomes 113119°mm² (2,9% more). The drawback is that the short con rod causes more piston friction and costs crankcase volume.

I know this is heathen talk.

Frits say if we deal in gas it changes states m3 and velocity changes from atmosphere the carb to the crankcase to the cylinder.
What we seem to need is the gas actually effectively compressed before it enters the cylinder that way more mass can actually be burned. I can't recall but is the volume mixture drawn in to the cylinder each revolution of the RSA only actually what is contained in the transfers.

Blown down (as far as I am aware) is measured as the time and area prior to the pressure equalizing between the cylinder and transfers to allow the flow into the cylinder is that correct?
So a higher rate of primary compression would (all things being equal allow) allow the same port timing to actually produce more blowdown time area.


I had a wee play looking at hugely variable exhaust port durations and a pipe calculator it looks to me from the quick look that the ex pipe could be made to function over a huge range of engine speeds.

yes I know this is 60's talk, but with advances in ex port variable timing, fuel injection and port shapes, reed valves surely maybe there is actually some room to improve.
I am not simply suggesting a smaller crankcase just a variable size with a higher delivery rate likely remote to minimise heat sink.
I think this can be achieved without the wet crankcase set up we have now so the flow restrictions and oiling cooling issues encountered in the 60's would not be an issue.
Also is there not pressure waves still present in the exhaust when the exhaust port is shut?

Also do the supercharging rules actually really cover the creation of a vacuum rather than positive boost pressure?

Yes I say all of this fully aware that the later RSA made less power when they had crank stuffers fitted.

[senso]

Modena KK1 EFI engine.

Wow, only 50cc of oil in the gearbox?

[Frits Overmars]

Frits say if we deal in gas it changes states m3 and velocity changes from atmosphere the carb to the crankcase to the cylinder. What we seem to need is the gas actually effectively compressed before it enters the cylinder that way more mass can actually be burned. I can't recall but is the volume mixture drawn in to the cylinder each revolution of the RSA only actually what is contained in the transfers.

That depends on how you define the transfers. They are not only the ducts in the cylinder but also the sweeping curves in the crankcase. In any case it is not a matter of mixture drawn into the cylinder, but of mixture drawn through the cylinder. Some of it stays there, some of it exits and then comes back, some of it may be lost, especially at revs outside the optimum range. By the way, I like the distinction you make between mixture mass and mixture volume.

Blown down (as far as I am aware) is measured as the time and area prior to the pressure equalizing between the cylinder and transfers to allow the flow into the cylinder is that correct?

Correct. Blowdown should be finished by the time the transfers open, but it takes a certain time.area and if this time.area has not been reached by the time the transfers open, the exhaust gas just abuses the transfers as extra exhaust ports.

Maybe we should be more aware of the ambiguity of blowdown. It starts at the angle where the exhaust begins to open, but where does it end? It should end at the opening point of the transfers, but at low revs that is more blowdown time.area than we need, and at high revs the blowdown may carry on past the opening point of the transfers. Usually we take the opening point of the transfers as the end point of the blowdown because we have no simple way of knowing at what crank angle the cylinder and transfer pressures are equal.

So a higher rate of primary compression would (all things being equal allow) allow the same port timing to actually produce more blowdown time area.

You're thinking in the right direction but I'd like to rephrase your thoughts. Blowdown time.area is the product of port timings and port areas, divided by revs. If you don't alter the cylinder, the blowdown angle.area and time.area stay the same, irrespective of crankcase pressure. Blowdown should allow the cylinder pressure to drop to the level of the transfer pressure just before the transfers open. So a higher crankcase pressure means that the cylinder pressure does not have to drop quite so far.
In other words, a higher crankcase pressure requires less blowdown time.area.

looking at hugely variable exhaust port durations and a pipe calculator it looks to me from the quick look that the ex pipe could be made to function over a huge range of engine speeds.

That's right, but for real power you cannot vary the exhaust timing too much; it has to be about 180° effective or you'll get no true resonance.

Also is there not pressure waves still present in the exhaust when the exhaust port is shut?

Yes; that is the main reason that the exhaust timing has to be about 180° effective for true resonance; we want superposition of the old and the new +pulses.

Also do the supercharging rules actually really cover the creation of a vacuum rather than positive boost pressure?

They cover both; the variation of the crankcase volume during one crankshaft revolution should not exceed the permissible cylinder capacity, so both suction and primary compression are coupled to piston displacement. In addition, any mechanical device that creates positive boost, is forbidden (an exhaust pipe does that, but it is not considered a mechanical device).

[breezy]

One remark in advance, which regards not only the above question but all questions: unless I say otherwise, all my answers concern conventional engines; they may or may not be valid for the Ryger engine, so don't go jumping to conclusions.

Breezy, a good exhaust system triples the power of a racing two-stroke. How would you use that power elsewhere? By driving a compressor for example? It would help but it's not allowed in most types of motor sport. And in case you mean the amount of energy contained in the exhaust gases: I don't see a way of utilizing that other than in the exhaust pipe.

Re dwelling: a short con rod will cause a higher piston acceleration near TDC and a lower acceleration near BDC, so the piston will dwell longer around BDC.
Assuming the cylinder remains unchanged, a shorter rod will increase angle.areas. For example, The Aprilia RSA has a blowdown angle.area of 14322°mm² and a transfer angle.area of 109969°mm². If we replace its 120 mm con rod with a 100 mm rod (17% shorter), the blowdown angle.area becomes 14609°mm² (2% more) and the transfer angle.area becomes 113119°mm² (2,9% more). The drawback is that the short con rod causes more piston friction and costs crankcase volume.

Thanks for your reply Frits, my thinking with the exhaust is that returning waves pushing fuel back into the cylinder from the fuel held in the very hot exhaust port/ header, would be less volume and less hot than he cooler fuel introduced into the cylinder via the inlet system, and that the exhausts pressure waves , which" triple power ",via the exhaust port wouldnt be any different via the inlet system? (closely resembling tz250 plenum system)
with this in mind if the dwell at bdc could be extended/controlled better filling of the cylinder would be achievable...... i had also thought maybe more control over exhaust ports opening and closing would greatly improve the cylinder filling,.... on a conventional 2 stroke engine.....

[FastFred]

Wow, only 50cc of oil in the gearbox?

It looked like it in TeeZees post, but no, the leading digit of the left hand number was obscured.

[breezy]

Wobby, is their any part of the conventional 2 stroke engine cycle which would concern the terms "choked flow" or "positive choked flow"?