ESE's works engine tuner

**peewee** · 28th August 2014, 14:06

Originally Posted by wobbly

What you need to remember is a proven fact at the end of the day is that an Aprilia B port total effective area is greater than the duct
smallest CSA that is feeding it.
What is important is the radial and axial geometry of that port entering the cylinder, and the effect this flow regime has on the scavenging efficiency.
Jan the maestro himself wondered on a forum somewhere ,about something I realised ages ago,the volume that is held sitting in the transfer ducts is that - that ends up in the cylinder.
The case simply refills that volume - there is no " flow " as such from the case into the cylinder even when the pipes big diffuser negative pressure ratio, is creating the max bulk flow around BDC.

this reminds me. hey frits was the duct volume ever measured on the rsa ? not just the tunells of the cylinder but all the way to the top of the crankshaft wheels paralell with the cylinder wall, which would be considered the full duct i believe ?

**Frits Overmars** · 28th August 2014, 21:36

Originally Posted by peewee

was the duct volume ever measured on the rsa ? not just the tunells of the cylinder but all the way to the top of the crankshaft wheels paralell with the cylinder wall, which would be considered the full duct i believe ?

Not to my knowledge. Measuring the part above the cylinder base would be simple but as you say that is only half the story. Measuring the part below the base gasket would be much more complicated (and messy). But measuring isn't even necessary; if you have the drawings, the 3D drawing program can give you all the values you wish to know.
I was mainly interested in the total crankcase volume, including the transfer ducts and the inside of the piston (675 cc at TDC for the RSA); find my 'Helmholtz-Blues' and you'll see why.

**Frits Overmars** · 28th August 2014, 21:47

Originally Posted by wobbly

What you need to remember is a proven fact at the end of the day is that an Aprilia B port total effective area is greater than the duct smallest CSA that is feeding it.

CSA?? Enlighten me Wob; I do not have that much Kiwi.
Anyway, I can guess that you mean the duct entrance at the cylinder base and yes, it is a bit smaller than the duct exit. But the entrance is open all the time and the exit isn't.

Jan the maestro himself wondered on a forum somewhere ,about something I realised ages ago,the volume that is held sitting in the transfer ducts is that - that ends up in the cylinder. The case simply refills that volume - there is no " flow " as such from the case into the cylinder even when the pipes big diffuser negative pressure ratio, is creating the max bulk flow around BDC.

This is going to be semantics: of course there is flow from the case into the cylinder, but not in one go. A particle, registered at the crankcase entrance, will show up in the cylinder after four to five crankshaft revolutions, as Wobbly implied.
How do you find out? Label that particle with radioactivity.
On second thought: don't try this at home.

**husaberg** · 28th August 2014, 21:54

Originally Posted by Frits Overmars

CSA?? Enlighten me Wob; I do not have that much Kiwi.
Anyway, I can guess that you mean the duct entrance at the cylinder base and yes, it is a bit smaller than the duct exit. But the entrance is open all the time and the exit isn't.This is going to be semantics: of course there is flow from the case into the cylinder, but not in one go. A particle, registered at the crankcase entrance, will show up in the cylinder after four to five crankshaft revolutions, as Wobbly implied.
How do you find out? Label that particle with radioactivity.
On second thought: don't try this at home.

Buggar I have a readily available source of high quality Yellow Cake.

**wobbly** · 29th August 2014, 08:13

CSA is a term used in 4T port nomenclature to describe the smallest Cross Sectional Area, usually the venturi under the seat.
But in the Aprilia the CSA at the gasket line is well bigger than the actual CSA down further into the duct, that - is smaller than the chordal flow
area of the port.
Yes, the port is always gradually opening, gradually closing, or blocked, never really thought about that in relation to the duct feeding it.
But I have recognised in the past that really well designed cylinders ( like Calvins Cheetah for the RZ/Banshee ) seem to perform much better than
you would expect from the severely crap duct geometry ( small and very little inner wall ) due to the narrow bore centres.
They have a ton of port area, but the duct volume is very small, simply as there is no room and I believe the the small duct entry/exit ratio plays a large part in
allowing the system to work so well.
Same design route taken by Team Roberts in the Rainey era,they dynoed the factory cylinders to death ( and had a Czech CNC flow visualiser ) and the ducts on those
500s had a huge amount of epoxy added.
Their technology showed up later on the 250s that finally gave Yamaha a title with Jaques on board - that TZ was seriously fast at the time.

**peewee** · 29th August 2014, 15:14

Originally Posted by Frits Overmars

Not to my knowledge. Measuring the part above the cylinder base would be simple but as you say that is only half the story. Measuring the part below the base gasket would be much more complicated (and messy). But measuring isn't even necessary; if you have the drawings, the 3D drawing program can give you all the values you wish to know.
I was mainly interested in the total crankcase volume, including the transfer ducts and the inside of the piston (675 cc at TDC for the RSA); find my 'Helmholtz-Blues' and you'll see why.

i had to find out what the transfer volume was so i poured in oil, beyond just the cylinder ducts, mainly so i could get a approximation of the full duct volume down to the crankcase area. im not sure of the full crankcase volume however. anyways i got 150cc of oil in the 2 side transfers, x2 would be 300cc for all 4 side transfers. i didnt factor in the C port , but it doesnt even seem like a real duct on this engine. anyways the engine is 89x79 500cc with 144mm rod. i figured it would hold more volume in the transfers but i guess thats why its only a measly .13hp per cc

**peewee** · 29th August 2014, 15:48

Originally Posted by wobbly

But I have recognised in the past that really well designed cylinders ( like Calvins Cheetah for the RZ/Banshee ) seem to perform much better than
you would expect from the severely crap duct geometry ( small and very little inner wall ) due to the narrow bore centres.
They have a ton of port area, but the duct volume is very small, simply as there is no room and I believe the the small duct entry/exit ratio plays a large part in
allowing the system to work so well.
.

i think calvin did a good job considering what he had to work with (crowded inline twin). his cylinders seem to run well even with the shit transfer duct geometry like you mentioned. still they dont hold a candle to the rsa in terms of hp per cc though. seems like frits mentioned one time that the 6 smaller side transfer port design really helps when you have crap duct geometry, other wise the cheetah may not run as well had it used 4 side transfers

**F5 Dave** · 29th August 2014, 17:15

Well 72 odd mm compared to 54 it's a different kettle of fish.

**peewee** · 29th August 2014, 17:41

yes indeed a different kettle but theres a smaller cub cylinder at 64x54 and those arent near the rsa level either. dont get me wrong i think calvin did a fine job considering what he was up against. ill probly buy some of his smaller cylinders, simply because ive had singles all my life and want to tinker with something different

**F5 Dave** · 29th August 2014, 20:24

I've got a 496 but life has got in the way of riding it much.

**136kg136ps** · 30th August 2014, 01:52

Wob,as Calvin's cylinders were mentioned.What cylinders and configuration would be the maximum displacement you would use on a track bike?Given a competent chassis and a class to race it in and my local track being Daytona.

Thanks as always to TeeZee for the thread and to you and Frits et al for making it a class on winning twostrokes.

**peewee** · 30th August 2014, 05:34

Originally Posted by F5 Dave

I've got a 496 but life has got in the way of riding it much.

theres alot of various combinations of cylinders. what is the bore and stroke on the 496 ? i wanted to give the 68x68 cub a go but i dont think that 68mm stroke crankshaft will fit in stock banshee cases. from what i hear, 64mm stroke is about the largest you can use in banshee cases and even then requires quit a bit of trenching and such to make it work. the billet cases for longer strokes above 64 are very expensive and out of my price range. i may have to settle on a 68x64 which should be possible on stock cases from what i hear. unfortunatly i dont think calvin made a 64mm cylinder intended for a 64mm stroke, which seems strange as that seems like it would be a good combo.