ESE's works engine tuner

[husaberg]

Nope. Single like the 125

I was mean three transfers rather than 5?


Back re the crankcase volume seeing as I have had no job offer (as yet) from Frits.

Something Wob I think and Grumph had said about the Reed valve Hondas having the shorter rods with the reed valve engines.

Long vs Short rods

I think (if I have got this right if I haven't the panel will fix it and burn me later at the stake)

Short rods have a higher acceleration rate away from and until about 90 degrees either side of TDC and BDC. This could be an advantage with a reed valve engine.
Conversely after 90 degrees either side of TDC or BDC the longer rod then actually accelerates more but then slows again nearing either side of TDC or BDC. Dwelling for longer.

Honda stuck with shorter rod despite huge amounts of R&D money with I guess was thrown about.
I don't know the rod length of of the Yamaha and Suzuki Cagiva GP500's but none of them seem that long either

Note I believe The longer rod should have less thrust friction as most of the this acceleration occurs with the piston and rod in a more parallel position though.

I note RAW on a Superkart has noticed the carburation is very different when he went to longer rods but I guess the burn will be different and so would be the optimum carb and especially the ignition timing.

[Frits Overmars]

Long vs Short rods: (if I have got this right if I haven't the panel will fix it and burn me later at the stake).
Short rods have a higher acceleration rate away from and until about 90 degrees either side of TDC and BDC.
Conversely after 90 degrees either side of TDC or BDC the longer rod then actually accelerates more but then slows again nearing either side of TDC or BDC. Dwelling for longer.

I'm sure you've grasped it Husa, but the way it comes out of your keyboard indeed deserves burning. And your and is simply wrong. You might damage the younger brains here!
Short rods have a higher acceleration rate approaching and leaving TDC but a lower rate approaching and leaving BDC. That is all there is to it.
I posted the graph hereunder before, but it may not have sunk in with everybody, so I made an additional sketch.


When the crankshaft rotates away from TDC, the big end pin pulls the con rod downward. But because the rod also has to sway sideways, the small end drops more than the big end. The sketch (made with MS-Paint, so everyone can understand) shows a crankshaft with a 100 mm stroke, rotated through an angle alpha of about 70°.

On the right there is a 220 mm rod. Because of the swaying the small end has dropped an additional 4,8 mm.
On the left there is a 110 mm rod. Because of the swaying the small end has dropped an additional 9,9 mm, although the angle alpha is the same on both sides of the sketch. It's as simple as that.

[Dutch Fisher]

Frits, I don't understand, is my brain damaged?

[Frits Overmars]

Frits, I don't understand, is my brain damaged?

Dunno, Dutch. I've got a hunch that your brain is not all that young. Anyway, if you keep reading what I write, you're exposing it to danger .

[Martin1981]

Frits, you said that the best rotary valve engine has 10% more power than the best reed valver.

can you also tell us how much better is a case reed engine than a cylinder reed engine (in%)?

[Frits Overmars]

Frits, you said that the best rotary valve engine has 10% more power than the best reed valver. can you also tell us how much better is a case reed engine than a cylinder reed engine (in%)?

Nope. The 10% was not a calculated but a measured value; it was based on Jan Thiel's work with the reed valve and rotary valve Derbis.
I doubt if we can persuade Jan to come out of retirement and start tuning a cylinder reed engine for us (he doesn't like reed engines anyway).

[wobbly]

Long rods that affect the case volume then influence the carb tuning dramatically as well.
I did a Rotax 257 single years ago for sprint kart racing, filling the crank webs with that UHWMP stuff.
This raised the case com form down near 1.3 up to about 1.35.
It needed complete rejetting and the main dropped from a 185 to a 165 due to the much stronger signal across the jets.
Going the other way on a 250 tandem twin by fitting long ( 120 ) rods and making full circle ( no pockets ) cranks, the jets then need to be huge
in size by comparison.
Honda used the short rod for years in the customer engines, but when push came to shove the final version used to win the last 250GP title used a long rod, for a reason obviously.
The big reed boxes that design had from day one, gave a relatively big case volume by default.

In my experience if a case reed is done as well as it can be ( look at a TM - KZ10 ) then there is very little difference in power if a cylinder reed
is also done properly with plenty of intake STA via piston cutouts and big Boyesens or floor ports.
The only real difference is that the boost port duct does not have a proper inner wall, and thus the flow regime is not as well controlled.

[Flettner]

Long rods that affect the case volume then influence the carb tuning dramatically as well.
I did a Rotax 257 single years ago for sprint kart racing, filling the crank webs with that UHWMP stuff.
This raised the case com form down near 1.3 up to about 1.35.
It needed complete rejetting and the main dropped from a 185 to a 165 due to the much stronger signal across the jets.
Going the other way on a 250 tandem twin by fitting long ( 120 ) rods and making full circle ( no pockets ) cranks, the jets then need to be huge
in size by comparison.
Honda used the short rod for years in the customer engines, but when push came to shove the final version used to win the last 250GP title used a long rod, for a reason obviously.
The big reed boxes that design had from day one, gave a relatively big case volume by default.

In my experience if a case reed is done as well as it can be ( look at a TM - KZ10 ) then there is very little difference in power if a cylinder reed
is also done properly with plenty of intake STA via piston cutouts and big Boyesens or floor ports.
The only real difference is that the boost port duct does not have a proper inner wall, and thus the flow regime is not as well controlled.

Have a look at a YZ250, the standard reed stops almost block the back port off completely! Bad Yamaha.
V force fix the situation nicely, no reed stops.

[speedpro]

Have a look at a YZ250, the standard reed stops almost block the back port off completely! Bad Yamaha.
V force fix the situation nicely, no reed stops.

Would the reeds mask the boost port in their lift position and are they lifted when flow through that port is happening?

[peewee]

hey guys ive sorted this out with fairly good accuracy, i believe. the voids are about 5cc each so each crankcase would lose 20cc since theres 4 voids per crankcase. by lifting the cylinder 5mm via longer rod you gain back 23.25cc, this is with 64mm bore. so there you have it. feel free to double check with 100% accuracy but i think my numbers are close enough. i used clay against the inside then used some plastic over the top that conformed to the cheek radius , then added oil. if for some reason my numbers are way off, i guess ill have to buy everyone a beer

[F5 Dave]

Where are you from? Hmm, no, sorry. We'd be ok if Martin or Frits were buying.


Sorry little harsh, just kidding.

[TZ350]

Turbocharged 2T



http://www.apriliaforum.com/forums/s...t=turbocharged

[husaberg]

I'm sure you've grasped it Husa, but the way it comes out of your keyboard indeed deserves burning. And your and is simply wrong. You might damage the younger brains here!
Short rods have a higher acceleration rate approaching and leaving TDC but a lower rate approaching and leaving BDC. That is all there is to it.
I posted the graph hereunder before, but it may not have sunk in with everybody, so I made an additional sketch.


When the crankshaft rotates away from TDC, the big end pin pulls the con rod downward. But because the rod also has to sway sideways, the small end drops more than the big end. The sketch (made with MS-Paint, so everyone can understand) shows a crankshaft with a 100 mm stroke, rotated through an angle alpha of about 70°.

On the right there is a 220 mm rod. Because of the swaying the small end has dropped an additional 4,8 mm.
On the left there is a 110 mm rod. Because of the swaying the small end has dropped an additional 9,9 mm, although the angle alpha is the same on both sides of the sketch. It's as simple as that.

No Frits you give me far too much credit, I didn't understand it at all properly.
I think I do now though.
I was trying to gain some insight as to why Honda stayed with the shorter rods and more acceleration
But looking at it again more acceleration at TDC might actually be helpful re the reeds.
but swings and roundabouts.
Maybe they just had a plenty of forging capacity in that size of rods.
Then again you could write many many books with what I can't figure out. Geel free to do that btw.


looking at how this drawing works for the reed does raise a few schemes re the 24/7 though.

[koba]

An interesting side read about an engine in development with a local engineering firm.

http://engrich.co.nz/?page_id=310

[mr bucketracer]

An interesting side read about an engine in development with a local engineering firm.

http://engrich.co.nz/?page_id=310

i'v seen the engine , very nicey made but only taken 15 years to build (-;