[GP125] All that you wanted to know on Aprilia RSA 125, and more, by Mr Jan Thiel and Mr Frits Overmars (PART 4)

seattle smitty a écrit:

I thought he meant having the cylinder block and half of the case as a single piece down to where the case splits over the centerline of the crankshaft (Konig 4-cylinders were like this) .  .  .  .

Jan certainly did not mean a cylinder block and a crankcase upper half as a single piece.
That would be much too cumbersome when working on the cylinder.

Yes Sir, unitized would be a bear.

Unless Dremel can build me a better mouse trap, I'd have to send that port job to brokedown.

God guiding the handles, one good candle and a Dremel an' a chisel has always worked for me, but a man must know his limitations.


Hey, the pros DO still use a Dremel, right ?

No, that would be completely crazy!

Does anyone recall an engine which utilized both a cylinder reed and case reed intake system? I have heard rumors such engines have been made before however they were probably made before my time. If anyone can provide a specific example or recall how well they worked I would be very interested in learning more.

I'm pondering a big bore two-stroke design and don't think I can get enough intake area into the crankcase itself.

Oh, duh, I see now that he must have just meant get rid of flange bolts. (sigh!)

Paul Olesen a écrit:

Does anyone recall an engine which utilized both a cylinder reed and case reed intake system? I have heard rumors such engines have been made before however they were probably made before my time. If anyone can provide a specific example or recall how well they worked I would be very interested in learning more.

I'm pondering a big bore two-stroke design and don't think I can get enough intake area into the crankcase itself.

Case reed + cylinder reed ? Don't think so. But a combination of a classic cylinder intake without reed and a rotary valve has been made.
Puch made such an engine,   and became world champion with it in 1975 with Harry Everts,   the father of Stefan Everts.  
[Vous devez être inscrit et connecté pour voir ce lien]
In the following link,   there are some details of the way they Puch made the two system intake.
[Vous devez être inscrit et connecté pour voir ce lien]

peter1962 a écrit:

Paul Olesen a écrit:

Does anyone recall an engine which utilized both a cylinder reed and case reed intake system? I have heard rumors such engines have been made before however they were probably made before my time. If anyone can provide a specific example or recall how well they worked I would be very interested in learning more.

I'm pondering a big bore two-stroke design and don't think I can get enough intake area into the crankcase itself.

Case reed + cylinder reed ?   Don't think so.    But a combination of a classic cylinder intake without reed and a rotary valve has been made.  
Puch made such an engine,   and became world champion with it in 1975 with Harry Everts,   the father of Stefan Everts.  
[Vous devez être inscrit et connecté pour voir ce lien]
In the following link,   there are some details of the way they Puch made the two system intake.
[Vous devez être inscrit et connecté pour voir ce lien]

Very cool, thank you for the info!

Some outboard racers in the USA years ago, having found that their (alcohol-burning) engines had insufficient carburetion, added extra carbs feeding through small reedblocks into the case.

Paul Olesen a écrit:

Does anyone recall an engine which utilized both a cylinder reed and case reed intake system?

An other "dual inlet" engine: Suzuki TS50 and ts80. reedvalve to the crankhousing and pistonported to the cylinder.
But I think a "dual inlet" would cause more problems that it may solve: Long distance from reed to carb for example.
Why don´t you use a snowmobile v-force reed? Those are available to 80mm width :-)
The problem will be to find such a huge carb...

Tim Ey a écrit:

Paul Olesen a écrit:

Does anyone recall an engine which utilized both a cylinder reed and case reed intake system?  

An other "dual inlet" engine: Suzuki TS50 and ts80. reedvalve to the crankhousing and pistonported to the cylinder.
But I think a "dual inlet" would cause more problems that it may solve: Long distance from reed to carb for example.
Why don´t you use a snowmobile v-force reed? Those are available to 80mm width :-)
The problem will be to find such a huge carb...

Thanks for sharing the dual engines.

I have looked, considered such options, and am still thinking things over. The engine I'm thinking about making is a 500cc single cylinder. I started on a 400cc design using snowmobile intake parts and have recently decided to reconsider the 500cc engine.

The dual intake scenario makes me wonder if there are additional advantages other than gaining enough intake area. The engine will be fuel injected and I was hoping to make a couple barrel throttle bodies. With dual throttle bodies I could control how they open and perhaps could get better low end response than what I could with one big throttle body.

I have some spare barrel throttle bodies, spare from the YZ250EFI project, Only 39mm though.

Hm. Drive by wire and a "Small" Reed like CR125 or Rotax 123 on the cylinder and a full closed XXL  throttle body attached right at the crankcase (ducati panigale for example)?
For lower revs and lower load the Reed on the cylinder, at higher revs 24/7 to the crankhousing?!

But by the way: a 500ccm single may be really hard to ride when it is optimized to full power. Perhaps you will not need the big reed

Tim Ey a écrit:

Hm. Drive by wire and a "Small" Reed like CR125 or Rotax 123 on the cylinder and a full closed XXL  throttle body attached right at the crankcase (ducati panigale for example)?
For lower revs and lower load the Reed on the cylinder, at higher revs 24/7 to the crankhousing?!

But by the way: a 500ccm single may be really hard to ride when it is optimized to full power. Perhaps you will not need the big reed

Yes, perhaps something like that. I've been leaning towards sizing them the same to start with. Once the hole for the block is there fitting a smaller one wouldn't be too hard. I suspect it may take a few iterations to get the setup right.

It may end up hard to ride. I'm not sure, I would think between ignition timing, pipe, and power valve setup I could get the curve looking decent. If it is too powerful I can always four stroke it.

peter1962 a écrit:

Case reed + cylinder reed ?   Don't think so.    But a combination of a classic cylinder intake without reed and a rotary valve has been made.  
Puch made such an engine,   and became world champion with it in 1975 with Harry Everts,   the father of Stefan Everts.  
[Vous devez être inscrit et connecté pour voir ce lien]
In the following link,   there are some details of the way they Puch made the two system intake.
[Vous devez être inscrit et connecté pour voir ce lien]

the old suzukis had a strange cylinder. looks to be a reed petal on the bottom of the cylinder. ive never seen one first hand but it almost seems like half piston port and half of a half of a reed valve   [Vous devez être inscrit et connecté pour voir ce lien]

brokedown a écrit:

peter1962 a écrit:

Case reed + cylinder reed ?   Don't think so.    But a combination of a classic cylinder intake without reed and a rotary valve has been made.  
Puch made such an engine,   and became world champion with it in 1975 with Harry Everts,   the father of Stefan Everts.  
[Vous devez être inscrit et connecté pour voir ce lien]
In the following link,   there are some details of the way they Puch made the two system intake.
[Vous devez être inscrit et connecté pour voir ce lien]

the old suzukis had a strange cylinder. looks to be a reed petal on the bottom of the cylinder. ive never seen one first hand but it almost seems like half piston port and half of a half of a reed valve   [Vous devez être inscrit et connecté pour voir ce lien]

Thanks for sharing that brokedown, that's really interesting.

Hiya Paul,

Long time no see.

I think the piston port/ 1/2 reed block design is a non go-er for what you want.
Suzuki used this set-up for a good while on their strokers (google Suzuki X7, and RG250 MK1/MK2/MK3 for pics). However they slowly redesigned that out over the years and their final iteration, the RG250MK3, could never be made to produce any decent power with that arrangement. When the late 80's 250cc UJM market hotted up Suzuki's replacement for the RG, the RGV, came out with full crankcase reed induction it gained 20bhp (33 -> 53) in full power street spec.

I think i remember your target bhp figure for the 500 was 100bhp @ 9000rpm. As your in the USA, an available 50mm Lectron would be the carb of choice that on paper could deliver that level of power. However I have a feeling, fuel inj or carbs, that the limiting factor may be the reed block size and/or the life of the reed petals, if using a single inlet.
One possible solution is to use two reed blocks from say a CR250 and mount them vertically side by side into the crankcase above the gearbox. In that way you have off the shelf blocks and manifolds and can use of the shelf carbs of say 36-38mm. Do a google for "Honda RS250 NXA crankcase" and you see what i mean (if no luck with google PM me and i'll send you some pics off my other PC). Instead of the Honda arrangement of supplying the 2 crankcase spaces your 2 inlets would just supply the one. I reckon with a bit of a juggle on Solidworks, it would fit into a single cyl design.

Dutch

dutch fisher a écrit:

Hiya Paul,

Long time no see.

I think the piston port/ 1/2 reed block design is a non go-er for what you want.

Dutch, how have you been?! Life got busy and I needed to take a little break from my designs and the forum however I realized two-stroke engines are what make me really happy so I needed to get back into them!

I definitely agree there needs to be two reed blocks and never intended on one reed and one piston port.

dutch fisher a écrit:

I think i remember your target bhp figure for the 500 was 100bhp @ 9000rpm. As your in the USA, an available 50mm Lectron would be the carb of choice that on paper could deliver that level of power. However I have a feeling, fuel inj or carbs, that the limiting factor may be the reed block size and/or the life of the reed petals, if using a single inlet.  

You have a good memory sir! My initial reason for abandoning the 500 design was due to insufficient intake area of a single block thus my change to a 400cc. I haven't been able to shake the 500 idea and have thought that a pair of valves may do the trick each utilizing their own throttle body.

dutch fisher a écrit:

One possible solution is to use two reed blocks from say a CR250  and mount them vertically side by side into the crankcase above the gearbox. In that way you have off the shelf blocks and manifolds and can use of the shelf carbs of say 36-38mm. Do a google for "Honda RS250 NXA crankcase" and you see what i mean (if no luck with google PM me and i'll send you some pics off my other PC). Instead of the Honda arrangement of supplying the 2 crankcase spaces your 2 inlets would just supply the one. I reckon with a bit of a juggle on Solidworks, it would fit into a single cyl design.  

Thanks for the NXA tip, I've been playing with both vertical and horizontal stacking of two valves. I think between the two I can make something work.

Have you had any more successes with EngMod? I've been reading the Kiwi forums a bit and a lot of good info has been presented there which has helped me along.

Paul Olesen a écrit:

Have you had any more successes with EngMod? I've been reading the Kiwi forums a bit and a lot of good info has been presented there which has helped me along.

To be honest I'd be inclined to spend the money on the best and proven designs of air flow bench and inertia dyno available on the internet, than sim software. Even the best software in the world is still only a predictor expert system that needs either calibrating or proving by dyno or other measuring equipment.

To intents and proposes, the info contained in these series of topics and on Kiwibiker, is of such depth of value to be enough for anyone with a mechanical vent and common sense attitude towards 2 strokes, to be able to build/tune quite an impressive motor.
The effort is in reading, digesting and comprehending the sheer volume of info.

Here's the NXA inlet port design:

[Vous devez être inscrit et connecté pour voir ce lien]

So we meet again, Dutch  .

dutch fisher a écrit:

I think i remember your target bhp figure for the 500 was 100bhp @ 9000rpm.

Those figures make me wonder. What will you be using this engine for, Paul? A 500 single would point towards agricultural racing (otherwise known as MX). But then 100 hp would be gross overkill; throttle response and linear torque delivery would be far more important than horsepower.
Leaving this aside, I think 100 hp is doable, but not at 9000 rpm. The specific time areas won't permit it; max. power at 8000 rpm seems a better bet.

dutch fisher a écrit:

I have a feeling that the limiting factor may be the reed block size and/or the life of the reed petals, if using a single inlet. One possible solution is to use two reed blocks.

Been there, seen that (Aermacchi did it and I took their engine apart when I was still earning a living as a technical editor). They had a 500 twin with two reed blocks and two 34 mm Dellortos per cylinder. No case reeds back then, as this was almost 40 years ago.
By the way,works rider Walter Villa told me that the bike became much more forgiving after the reeds were dropped in favour of old-fashioned piston porting.
[Vous devez être inscrit et connecté pour voir cette image]

Hello again..
I was sitting and wondering how Jan manage to take such a big power band on the RSW-9000,max power13000 and good power till 14000rpm-thats a 5000 power band
As I can see the exhaust was extremely tuned,and to my little knowledge the large volume(4000cc and 32 pipe to cylinder ratio) and the so big degrees and diameters shorten the power band a lot but make big power.
Mr Jan or Frits,how did you manage to have a so wide power band with this exhaust system?
Correct me if what I'm saying is wrong :)
Cheers![Vous devez être inscrit et connecté pour voir cette image]" />

Lef16 a écrit:

I was sitting and wondering how Jan manage to take such a big power band on the RSW -9000, max power13000 and good power till 14000rpm -thats a 5000 power band. As I can see the exhaust was extremely tuned and to my little knowledge the large volume(4000cc and 32 pipe to cylinder ratio) and the so big degrees and diameters shorten the power band a lot but make big power.
Mr Jan or Frits, how did you manage to have a so wide power band with this exhaust system?

The power at 9000 rpm is about 25 HP, usable but not advisable if you are in a hurry, so good riders keep the revs above 11000 rpm. Maximum power is 54 HP @ 13.000 rpm as you say. At 14.500 rpm there is still 47 HP available.

This wide power spread does not come from the pipe alone, although a large pipe volume helps. But in addition to that the RSW and RSA engines had a very variable exhaust gas temperature thanks to the variable ignition timing and the variable mixture strength because of the pulsed power jet, and also a variable exhaust timing and a variable exhaust port area thanks to two guillotine valves in the main exhaust port.
[Vous devez être inscrit et connecté pour voir cette image]

Frits Overmars a écrit:

So we meet again, Dutch  .

dutch fisher a écrit:

I think i remember your target bhp figure for the 500 was 100bhp @ 9000rpm.

Those figures make me wonder. What will you be using this engine for, Paul? A 500 single would point towards agricultural racing (otherwise known as MX). But then 100 hp would be gross overkill; throttle response and linear torque delivery would be far more important than horsepower.

I foresee a couple uses for the engine. One for ice racing and one for road racing. As you point out torque and power delivery are more important than horsepower. While I think 100hp would be great if it was usable my original claim came when I was less wise.  Starting with an engine which makes 75 or 80 horsepower and has nice power delivery is probably better than trying to achieve 100 right away.

Frits Overmars a écrit:

Leaving this aside, I think 100 hp is doable, but not at 9000 rpm. The specific time areas won't permit it; max. power at 8000 rpm seems a better bet.

Agreed, another of my youthful less wise thoughts.

Frits, do you have any experience working with the EngMod software Wobbly is using? I've done some simulation work in EngMod however I often rely on it for looking at STA values and power estimates. My understanding is that blowdown area is the biggest factor in how much power the engine will make and exhaust STA is less critical. When I'm trying to determine how much power I can reasonably expect from an engine I focus on optimizing blowdown, transfer, and intake STA. When I do this the exhaust is usually left "short" on STA and the numbers indicate the exhaust area would have to increase to achieve the desired power. Have you seen a trend in relation to blowdown and exhaust STA.  For example on some of the porting setups I've observed from Wobbly's engines I see the the exhaust is between 80 and 90 percent of the achievable blowdown power number. So if blowdown power was estimated at 100hp the exhaust estimate would be somewhere around 80 or 90hp. There must be a point at which the exhaust does become the limiting factor?

Paul Olesen a écrit:

Frits, do you have any experience working with the EngMod software Wobbly is using? I've done some simulation work in EngMod however I often rely on it for looking at STA values and power estimates. My understanding is that blowdown area is the biggest factor in how much power the engine will make and exhaust STA is less critical. When I'm trying to determine how much power I can reasonably expect from an engine I focus on optimizing blowdown, transfer, and intake STA. When I do this the exhaust is usually left "short" on STA and the numbers indicate the exhaust area would have to increase to achieve the desired power. Have you seen a trend in relation to blowdown and exhaust STA.  For example on some of the porting setups I've observed from Wobbly's engines I see the the exhaust is between 80 and 90 percent of the achievable blowdown power number. So if blowdown power was estimated at 100hp the exhaust estimate would be somewhere around 80 or 90hp. There must be a point at which the exhaust does become the limiting factor?

Paul, I am corresponding with Neels van Niekerk, the man behind EngMod. He is working at incorporating my Power Range-concept in the next version of EngMod. I do not use EngMod myself (yet); I still use my own two-stroke simulation program, but I think EngMod is the best product of its kind on the market (my sim is not on the market).
Blowdown time.area is paramount; total exhaust time.area is utterly unimportant by comparison.

Frits Overmars a écrit:

Paul Olesen a écrit:

Frits, do you have any experience working with the EngMod software Wobbly is using? I've done some simulation work in EngMod however I often rely on it for looking at STA values and power estimates. My understanding is that blowdown area is the biggest factor in how much power the engine will make and exhaust STA is less critical. When I'm trying to determine how much power I can reasonably expect from an engine I focus on optimizing blowdown, transfer, and intake STA. When I do this the exhaust is usually left "short" on STA and the numbers indicate the exhaust area would have to increase to achieve the desired power. Have you seen a trend in relation to blowdown and exhaust STA.  For example on some of the porting setups I've observed from Wobbly's engines I see the the exhaust is between 80 and 90 percent of the achievable blowdown power number. So if blowdown power was estimated at 100hp the exhaust estimate would be somewhere around 80 or 90hp. There must be a point at which the exhaust does become the limiting factor?

Paul, I am corresponding with Neels van Niekerk, the man behind EngMod. He is working at incorporating my Power Range-concept in the next version of EngMod. I do not use EngMod myself (yet); I still use my own two-stroke simulation program, but I think EngMod is the best product of its kind on the market (my sim is not on the market).
Blowdown time.area is paramount; total exhaust time.area is utterly unimportant by comparison.

Frits, if i am not mistaking, this is the first time we here about this new concept ? Is it in relation with the 24/7 system on which you are working ?

Frits Overmars a écrit:

Paul Olesen a écrit:

Frits, do you have any experience working with the EngMod software Wobbly is using? I've done some simulation work in EngMod however I often rely on it for looking at STA values and power estimates. My understanding is that blowdown area is the biggest factor in how much power the engine will make and exhaust STA is less critical. When I'm trying to determine how much power I can reasonably expect from an engine I focus on optimizing blowdown, transfer, and intake STA. When I do this the exhaust is usually left "short" on STA and the numbers indicate the exhaust area would have to increase to achieve the desired power. Have you seen a trend in relation to blowdown and exhaust STA.  For example on some of the porting setups I've observed from Wobbly's engines I see the the exhaust is between 80 and 90 percent of the achievable blowdown power number. So if blowdown power was estimated at 100hp the exhaust estimate would be somewhere around 80 or 90hp. There must be a point at which the exhaust does become the limiting factor?

Paul, I am corresponding with Neels van Niekerk, the man behind EngMod. He is working at incorporating my Power Range-concept in the next version of EngMod. I do not use EngMod myself (yet); I still use my own two-stroke simulation program, but I think EngMod is the best product of its kind on the market (my sim is not on the market).
Blowdown time.area is paramount; total exhaust time.area is utterly unimportant by comparison.

Very cool Frits, I'm looking forward to seeing the addition of your concept to EngMod. Have you by chance inquired with Neels if it would be possible to incorporate a vector summation of the port leading and trailing angles, positions, and axial angles? This is something I'm envious you have at your disposal in your sim and must be fairly useful for keeping track of what port geometries are working?

Without the vast amount of tuning experience like you, Jan, and Wobbly have and only having examples of smaller displacement configurations it is hard for me to determine if I have a realistic design for my larger engines. I will head your advice though and pay little attention to exhaust STA and focus on blowdown, transfer, and intake. Thanks for the info Frits.