ESE's works engine tuner

[peewee]

wobbly since we're on the subject, whats the formula for case comp ratio ? i figured about 680cc volume in the banshee with the piston at tdc, pouring oil through a hole in the dome. thats with oem rod, oem reed block, 64mm piston, 54mm stroke. basically a bone stock engine. when i enter 680cc into engmod it says 1.43:1. not quit sure how it arrives at 1.43

[Frits Overmars]

crankcase compression ratio = TDC-volume / BDC-volume

TDC-volume = 680 cc (I'll take your word for it)

BDC-volume = TDC-volume - cylinder volume

cylinder volume = 173,7 cc

BDC-volume = 680 - 173,7 = 506,3 cc

crankcase compression ratio = 680 / 506,3 = 1,343

And now for some reverse engineering:
what TDC-volume will give a crankcase compression ratio of 1,43?

TDC-volume = comp.ratio / (comp.ratio - 1) * cylinder volume

TDC-volume = 1,43 / 0,43 * 173,7 = 577,7 cc.

[peewee]

thnx frits i think i figured it out from one of your earlier posts. 680/ (680 - 175)= 1.346

i have made the bridge between the main exh and aux, 3mm wide. does that sound about right to you guys for a 64mm bore or could it be a bit narrower and still work fine ? unfortunatly these are iron lined cylinders.

one other question. seems a bit strange but engmod says my STA will be good at 10.5k rpm and 80hp on these yamaha cylinders. 188* main 70% bore, aux fairly large width and opening 3* after the main window. A trans 126* and stock width, B 128* and widened as much as i could. C 128* stock width. i know the blowdown is based on crank degrees and area but does 30* blowdown seem in the ballpark ?

[wobbly]

Post the STA summary page for the Banshee on here, then we can say for sure what is right and what isnt.
30* of blowdown is a meaningless number, everything depends upon the interaction of all the Specific Time Areas.
Quoting one tiny part of the overall relationships in any engine is an exercise in futility.

[peewee]

not sure if you can read it. is there a way to make the photo bigger ? i guess if you double click then it gets bigger. learn something new everyday

before you ask why the reed block is much higher its because its using the vf4 which shows alot of improvement over the stocker

wobbly about the 3mm wide divider between the main and aux. does that sound right or can i narrow it a bit without mechanical problems ?

[wobbly]

3mm is fine with a nicasil cylinder, seen plenty of bridges that narrow with no issues at all.
But the narrow width will wear quickly in an iron bore.
Making the bridge thinner isnt the way to go, getting the Aux shape and especially grinding a pocket into the rear wall to get radial
flow exiting down the duct is way more productive.
The STA numbers are fine.
The VF reeds nearly always have alot more tip curtain area than the area of the ports in the block, simply as the V angles are narrow.
But this will not be an issue for power production at all with the numbers shown.

[husaberg]

I have never noticed this cylinder Nor do I know what variant it is, Anyone?
Attachment 306581

Right. In fact it's two DEA cylinders; the left and center pictures show a 2013 cylinder; the right pic shows a 2014 cylinder from the DEA superkart tandemtwin with RSA-based cylinders. The notches in the bore surface are supposed to retain some oil for the benefit of the exhaust bridges.

They look a bit more than just notches...Do they go through to the transfer ducts ? When i saw them in the pic I wondered if they matched holes in the piston skirt at BDC for a little under piston cooling/mixture moving through but assumed not for reasons you'd already mentioned.

I won't comment, Smitty. There are several promising people around but I can't claim to know all of them. Naming names means excluding names and that may well do unjustice to some. Who am I to know who will rise and shine in the future?
Both Jan Thiel and yours truly are trying to spread our two-stroke knowledge with the intent that you guys take over where we sign off (although I have no intention of signing off just yet).

No Grumph, notches don't. This picture shows under what angle and how deep the cutter went in.
Attachment 306604

Here are two combustion chambers with identical compression ratios, squish areas and squish clearances. Which one do you think has the smallest surface area?
Attachment 306605 And where do you see a performance step-up?

So over 360° a shorter rod will shorten the piston stroke?

Sigh.... a longer rod dwells longer at TDC and shorter at BDC; it accelerates the piston less at TDC and more at BDC.

Thank god someone is awake.

Yeah, I know, I sound like a grumpy old man. It's the weather, you know. Cold wind, rain... Wish I were in NZ right now.

Thank you Frits - much better angle to see how deep the notches are. I suppose the question is - did they work ? If they weren't used on the later engines, the assumption is, it wasn't worth doing.

Ha, weather...two big race meetings here on successive weekends. One VERY wet, one quite warm. Not our usual early summer at all.
Big job in the workshop today - and i'm going to have to light my fire to get warm enough. Enough to make me a grumpy old man...

That picture was from a 2013 DEA cylinder because it showed the notches best. But the 2014 cylinder has them too, so they can't be all bad.
Andrea degli Esposti (DEA) is a free thinker who does more than just copy Aprilia stuff. Here he is with his home-built pulsating flow bench.

So these notches are just like the round divots some piston to retain prevent seizures?

Ah, but do they keep the reeds open longer ? i remember Jennings writing up reeds in Cycle mag and quoting an SAE paper by the Yamaha guys who developed the DT/RD series. They found that yes, the opening period varied - as did the timing - but at peak RPM the reed timing was the same as the roadrace rotary valve timing they were familiar with. That was with the very basic steel reeds of the period, i have no idea if the modern composite reeds act differently.

https://books.google.co.nz/books?id=...ngines&f=false

pg 40 of the Robinson book it has the papers that Yam published referred to.

[wobbly]

Just a couple of minor points to add.
In the pic of the KZ10B intake the tuned length isnt quite as i drew the line from reed tip to bell end.
The length as should be used for sim accuracy is a point 2/3 of the distance down the block toward the tips ( the effective length of the reed port
opening varies as the petals are closed or fully open ) and the carb bell needs end correction for the actual reflection point off atmosphere.
In a PhD thesis paper i supervised we instrumented a YZ125 fully on a dyno at Uni for using fibre optics in the combustion chamber to control
fuel injection via the colour spectrum of the flame.
One thing discovered was the actual effective length of the intake, and it varied with reed tip opening, plus it showed that the end correction was
accurate when set at approx the intake curtain area length past the full bell diameter.
Without a bell, the end correction reflection point was the classically accepted 1/2 D of the intake pipe.

Re reeds staying open longer when the intake or the block ports are restricted in area.
Yes this is true, to some extent.
When I was testing a 485 Banshee based cylinder,the reed box was designed to have a CR250 sized block.
In the sim this showed that the 8 petals were only opening approx 4mm to make the required 60 crank Hp per cylinder.
Swapping the reed for a CR125 block that is 8mm narrower the power was identical, but the reeds were opening around 8mm ( actually impossible on the inners
of a VF3 )
The opening point of the reeds was pretty much identical,dictated by the case going negative plus the intake going positive from harmonic length tuning.
The big reeds closed a little earlier, but the intake flow was more dictated by the lift/tip area profile - with the small reeds petals jumping up to the stops
real quick, staying there then dropping real fast.
In reality the smaller reed made less power initially on the dyno, but I discovered that when the blocks were centred on the bore ( the large reed was offset outward to get it to fit )
the smaller reed made more power due to having symmetric flow into the case.

This leads onto understanding why having differing reed stiffness on the top and bottom of reed intakes works well where the manifold is on a vertical angle to get the fuel height correct in the carb bowl.
There is then also more power to be had when the petal stiffness is varied horizontally across a reed block, where the intake is bent to the side, as in a modern MX engine.

[peewee]

frits and wob. ill start cutting the aux ports in the next few days. might even get started today marking out the lines and what not. irrespective of how far around back of the cylinder i can take the window, should the rear wall be aiming nearly at the bore center like the drawing or is there more current knowledge that i should be following ?

[wobbly]

Thats exactly what i was saying about radial wall exit angle and a pocket to turn the flow.
Most ,even very current designs, have a very shallow rear wall exit angle that is real bad for blowdown flow efficiency.

[peewee]

ya i know what you meant about grinding in a pocket at the rear. still you didnt really say where the rear wall should be aimed. at the bore center or farther back toward the intake ?


what you think about this on the exh bridge if i keep it at 3mm ? ill be using different pistons with no cutout in front of the wristpin but you get the idea.

[F5 Dave]

So given a smallish tunnel after creating a pocket, I ovalised the tunnel to maximise area, the flow presumably will still be restricted by the tunnel but the pocket is still worthwhile? I've kinda done it anyway.

[peewee]

question for you guys using yamaha cylinders. is 11k rpm (4186 fpm meen piston speed) acceptable or do you try to keep it lower ? ill be using high qaulity long rods above 2:1 ratio with good bearings

[wobbly]

If you read my post I said that the radial exit angle and pocket in the Aprilia drawing are exactly what I was referring to, shallow rear wall angles dont work as well at all.
With good cranks and piston parts 11K is safe as houses.
I have many engines out there with 58 cranks and 115 rods that have been running for 2 seasons of road racing with the rev limit set at 12,000,no issues at all.
The piston oil holes are fine as long as they are sealed by the bridge as they run over it.

[2T Institute]

The HRC A kit 250 cranks have 109mm rods