ESE's works engine tuner

[Frits Overmars]

Was the 2009 RSA really slower than the 2006? Are you 100% sure? Dyno test? I tried to ask the dyno-man but he did not respond me.... He simply said that the crankcase volume was too big! ... Throttle response? What would be the upper limit of crankcase volume?

No dyno test results Jan. If they would not give those results to you, they certainly were not going to give them to me. But a dyno-man refusing to respond to a question from the engine creator, is already an answer in itself, wouldn't you say?
The difference between the 2009 and 2006 models stems from the riders' seat of the pants. And it should be possible to find conformation in top speed comparisons.
There may be an optimal crankcase volume regarding throttle response for reed valve engines, but I haven't seen it for disc-valve engines.

[Haufen]

Is there any other reason why a reduced crankcase volume could be better?
Throttle response?
What would be the upper limit of crankcase volume?

Happy belated birthday, Jan!

I found smaller crankcase volumes to be less sensitive in regards of jetting. With larger volumes, jetting may get very borderline at some point. A smaller volume gave me the same power and allowed for a much more robust and forgiving jetting and general setup. Both volumes had their individual inlet timings deduced on the dyno. So I'd say it's not only the smaller volume in my case, but the smaller volume which allowed for a better overall setup of that engine when also other parameters were tweaked.

I was planning to do further testing with that engine in order to find out the tipping points of case volume, i.e. when is it too small etc. but unfortunately did not get to it for some time now. Also, I want to do some tests with the same volume to find out WHERE to place the volume and if this is even important at all. I can imagine having a nice reservoir at the transfer entry might be better compared to an engine with cutouts in the crankwebs or extra volume in between the webs as in the latter case, the mixture might not be available in time.

[Vannik]

I found smaller crankcase volumes to be less sensitive in regards of jetting. With larger volumes, jetting may get very borderline at some point. A smaller volume gave me the same power and allowed for a much more robust and forgiving jetting and general setup. Both volumes had their individual inlet timings deduced on the dyno. So I'd say it's not only the smaller volume in my case, but the smaller volume which allowed for a better overall setup of that engine when also other parameters were tweaked.

I assume this is with a reedvalve engine?

In what range did you experiment?

I have always wondered about the influence of where the mixture is "stored" in the crankcase. Are you planning tests of this?

Cool info, thanks for sharing.

[jamathi]

No dyno test results Jan. If they would not give those results to you, they certainly were not going to give them to me. But a dyno-man refusing to respond to a question from the engine creator, is already an answer in itself, wouldn't you say?
The difference between the 2009 and 2006 models stems from the riders' seat of the pants. And it should be possible to find conformation in top speed comparisons.
There may be an optimal crankcase volume regarding throttle response for reed valve engines, but I haven't seen it for disc-valve engines.

Did'nt Hans Spaan test the difference?
The RSA won the world championships from 2008 until 2011.
So they were no so bad...

[Haufen]

I assume this is with a reedvalve engine?

In what range did you experiment?

That was with a rotary valve engine. I was able to reduce the volume by around 60cm³ in between these tests.

I have always wondered about the influence of where the mixture is "stored" in the crankcase. Are you planning tests of this?

Cool info, thanks for sharing.

Yes, I am planning to test this. Unfortunately, the crank with the smaller and already prepared webs is no longer with us, but I'll figure something out. Also, I want to reduce the volume even more using a 3d printed plastic insert to see if there is a tipping point somewhere on the way.

[wobbly]

What many dont seem to get is that there is no " flow " from the case , thru the transfer ducts and out the port into the cylinder - even around BDC where the most bulk flow occurs.
There is more volume in the ducts , than there is mixture transferred into the cylinder.
Having a greater volume directly below the transfer duct entries may have a beneficial effect on power , rather than volume that is effectively " trapped " inside the crank.
But I believe a change in total volume , that moves the case Helmholtz frequency , has more influence.
RV engines " like " big case volumes , no matter how its achieved.
Reeds I have found have a tipping point at exactly 1.3 ratio . Any bigger than this and the reed stiffness has to be changed to so soft , they loose control and flutter .

[F5 Dave]

So what if you are trying to compensate for an old engine with thin elevator transfers of limited volume? That collection area may be more critical so testing could be skewed if the design tended towards that unfavourable situation. Perhaps.

[SwePatrick]

What many dont seem to get is that there is no " flow " from the case , thru the transfer ducts and out the port into the cylinder - even around BDC where the most bulk flow occurs.
There is more volume in the ducts , than there is mixture transferred into the cylinder.
Having a greater volume directly below the transfer duct entries may have a beneficial effect on power , rather than volume that is effectively " trapped " inside the crank.
But I believe a change in total volume , that moves the case Helmholtz frequency , has more influence.
RV engines " like " big case volumes , no matter how its achieved.
Reeds I have found have a tipping point at exactly 1.3 ratio . Any bigger than this and the reed stiffness has to be changed to so soft , they loose control and flutter .

Yes,, i agree.
I like to compare when opening the transfers with popping a balloon.
Engine has been filled in crankhouse(balloon), piston blows up pressure in the balloon and the transfers are popping the ballon.

[Condyn]

F5, wobbly found my piston port vintage air cooled engine liked a ccr of 1.28.

Quick question for anyone about connecting rods. Is there a proper way to machine or ream the small end eye open 2mm for a larger pin? There looks to be plenty of extra material so I am confident it would still retain its strength in that area. I am just unsure as it is a bearing surface. Thanks.

[husaberg]

F5, wobbly found my piston port vintage air cooled engine liked a ccr of 1.28.

Quick question for anyone about connecting rods. Is there a proper way to machine or ream the small end eye open 2mm for a larger pin? There looks to be plenty of extra material so I am confident it would still retain its strength in that area. I am just unsure as it is a bearing surface. Thanks.

Ask Ken he makes such objects.

Frits, just saw your post....your proposed specific power index looks more meaningful and relevant.

Still, I'll post what I was going to post

Below, as a refresher, is link to explain BMEP:

http://www.epi-eng.com/piston_engine..._yardstick.htm

Not sure if this below covers the full history:

https://en.wikipedia.org/wiki/Rolls-Royce_Crecy

However, if it was going to seize, I’d take it in a tractor rather than 25,000 feet in the air…just a simple pain avoidance preference though…

[Condyn]

Thanks Husa, are you linking me to Ken or is there something buried in there? I did not have a proper look, however did not find anything of relevance right away.

[Frits Overmars]

I want to reduce the volume even more using a 3d printed plastic insert

I tried something similar in a Rotax 124 kart engine which basically was a 125cc crankshaft in a 250cc MX engine. That was in 1978, so no 3D printing then, just me pouring epoxy.

The effect was positive, but one of the mechanics, wishing to make it nicer, substituted my epoxy casting with a neat aluminium filler ring. The result was disappointing.
As it turned out, the positive effect of the epoxy casting was not due to its volume reduction but to its thermal insulating effect within the crankcase, keeping the gearbox heat away from the inhaled mixture.

Having a greater volume directly below the transfer duct entries may have a beneficial effect on power, rather than volume that is effectively " trapped " inside the crank. But I believe a change in total volume, that moves the case Helmholtz frequency , has more influence.

The total case volume determines the frequency of the Helmholtz resonance, which has to fit the desired engine rpm.
But if not all parts of that total volume are in open communication with each other, those parts that have only a narrow connection act as pneumatic dampers,
which can considerably attenuate the amplitude of the Helmholtz resonance. So try to avoid nooks and crannies.

[wobbly]

Sadly the balloon analogy is fatally flawed by physics. At TPO the Blowdown pressure exceeds the case pressure created by the piston dropping.
This is how stagger works - the Blowdown pressure across the port that opens first , reverses the initial flow down the duct.
What pulls mixture into the cylinder , in a race engine is solely the increasing depression created by the diffuser action , maxing out around BDC if done correctly.
Only a weed eater uses piston compression of the case to push flow into the ducts.

Edit : The last 250GP season was won by Aoyama on a semi works Honda RS250 run by the Scot team in 2009.
He won the title pretty easily , with poles and lap records as well.
Sure , the Aprilia riders didnt do themselves any favours by stealing points off each other , but the HRC was faster , more often than not.
Would seem that the geniuses at the factory tuned Jans jewel to a standstill by 2009.

Edit - Spelt balloon wrong - in case ballon was fuckoff in Belgian or something.

Edit - I dont think you can enlargen a small end eye , as the case hardened surface must be a minimum of 0.5mm deep for rollers to run on - dont know if re case hardening can be done a second time.

[Grumph]

Sadly the ballon analogy is fatally flawed by physics. At TPO the Blowdown pressure exceeds the case pressure created by the piston dropping.
This is how stagger works - the Blowdown pressure across the port that opens first , reverses the initial flow down the duct.
What pulls mixture into the cylinder , in a race engine is solely the increasing depression created by the diffuser action , maxing out around BDC if done correctly.
Only a weed eater uses piston compression of the case to push flow into the ducts.

Okay, i have a question leading on from this. Lets say i have a piston port cylinder - basic 3 port layout -with very poor transfers. Small cross sectional area - and no room to enlarge them. What would happen if I cut finger transfers - like TD1C auxiliaries - with enough stagger to bleed off blowdown pressure at the crucial time.
Could this be used to encourage better flow volume from the main transfers ? Given of course a suitable pipe.

[wobbly]

Grumph , very hard to predict with so little info , sufice to say that in the 3 port ( transfers ) 100cc screamer kart engines the best layout was soon dicovered that opening the boost port
well before the mains gave the best power.
In your case maybe the effect of bleeding down the pressure differential at TPO ( added to the extra transfer STA ) would prove useful - who knows , its a fuking 2T so they love proving us wrong
even when the logic is perfectly valid.