ESE's works engine tuner

[wobbly]

Transfer stagger " works " simply due to the fact that at TPO there is way more blowdown pressure pressure above the port timing edge than there is case pressure
in the ducts created by the dropping piston.
Thus there is reverse and then stalled initial flow down the duct that is opened first.
In the case of Honda using normal stagger with the A highest , this is created due to the fact that the T port outer extremities are much smaller in height than the Aux ports in a 3 port cylinder.
Thus Honda used as much A port height as they could to achieve the maximum Transfer STA within the vertical space available.

With a 3 port regime, to achieve the maximum Blowdown STA , the Aux have to be very deep , and this limits the timing height the A port can be lifted to.
Also limiting the A port height reduces the vertical short circuiting from the A into the Aux at low Transfer velocities, early in the cycle.

The added B and C chordal width total is much greater than the A alone, thus lifting that whole wider width, achieves a much higher total Transfer STA than can be achieved using normal stagger.
Lastly the natural scavenging regime of low A port reverse stagger, favors upper front side/peak and overev power.
Normal stagger scavenging that boosts the whole front side, is always used in wide band applications such as MX or more especially where there is no PV to help front side power.

I tested the two differing approaches in a KZ race engine, where I lowered a stock normal stagger engine , then ground up all the ports to replicate the Aprilia regime.
In EngMod and then on the dyno it showed a loss of around 3 Hp at 10,000 ( the usual lowest rpm on track ) and then gained around 2 Hp ( in 50 ) at the peak of 13800.
But it made an amazing 8 Hp more at 14600 - close to the max the rpm down the shute.
This setup went from 140 Km/Hr at our fastest track to an easy 145, but the serious lack of acceleration off the two slowest 2nd gear corners meant an average drop in lap time of 3/10 sec
even with shorter gearing ratios.
With a PV and a digital ignition if allowed , this reverse stagger setup would have been way faster.

[husaberg]

MX application, motor needed more bottom. It gained 2hp down low, lost 2hp on top.

Going to start modifying transfers now... but don't have anymore room for error to lower cylinder if they get too high.

Now tro

Hi Jonny with the CR250 being a mechanical PV, wouldn't you be able to fill the bottom with electronic control of the RC valve together with a Atac set up?
In some of Wobs early posts there is mention on how well it worked with the BSL.
There was also some work don't here with a different set up that allowed the valve to be closer to the pipe.
Cagiva also did combination ones on lil Jon's era bikes.
Farmaken I think?

here he used a spool valve to get it closer
https://www.kiwibiker.co.nz/forums/s...post1130327391

Cows are dry, that means more time in the shed

Here is the latest version ; using a jaycar frequency counter/switch to drive a R1 servo motor to operate the spool valve on the header pipe

Using a DPDT switch mounted on the servo to reverse the motor - unless someone can point me at an electronic limit/polarity switch to make use of the servo`s in built potentiometer ??

In the testing I have done, the volume of the resonator chamber isnt critical, once you have reached a certain size.The best place to start is equal to the cylinder displacement, and this will "work" every time.
Fitted to a world champ ski engine, these chambers, operated by a flat, throttle slide plate,added over 30% more power at 1/2 peak rpm.
They seem to work very similar to a PV, in that the pipe effects are dramatically reduced in the area where the wave action is way out of phase with the port.
This is seen in the sim, and on the dyno, in that you can change the pipe dramatically, and it has little effect when the PV is down, or the chamber is open.

Honda obviously found out how to make these things work just as I did.
As short a connecting tube as you can get, diameter about 1/2 the header,ATAC vol about the same as the cylinder swept vol.
We had about 1/3 of the throttle plate hanging down in the header when it was open, in line with the flow direction.
By experiment you find the point where the resonating volume starts to kill power, and then go back a couple of hundred rpm, and snap it shut with a rpm driven solenoid.
Easy with the Ignitech programmable output.
There is NO advantage to ramping the closing point ie interconnecting it with the PowerValve is nowhere near as effective as a single point solenoid action.
Spencers Honda 500 Tripple had two of them on the outer pipes, and it was completely unrideable without them.
You could get even better useable band width by having a double volume system, where another plate valve opened and shut the entrance to a second bottle vol.
The two being open initially, then the second vol being shut off, creating a much smaller vol that was then shut of at a higher rpm.
But hey the simple thing works a treat on engines with no option for a PV.
.

Why would you think that? Opening the blade across the flow would have three big disadvantages. It would be much more of a disturbance to the flow, it would heat up the blade much more, and the flow colliding against the protruding half of the blade would constantly try to rotate it. As the flow direction is alternating so close to the cylinder, that would mean a constant hammering on the governing mechanism.

The spool valve allows it to get far closer

[SwePatrick]

DYNO? = !
As a dynoowner i have noticed there are a lot of misconceptions about things regarding the function and what´s what.
And also i try to give some tips and tricks, not only for the dyno owner(you should already know), the guy about to dyno his 'machine' might find it useful also.

In this episode i try to straighten out question marks to become exclamation marks instead

Enjoy!

[jonny quest]

Husaberg, thank you for the information.

The engine I have is a 1992 - 01 CR250. They actually incorporate a resonant chamber right in cylinder... and opened and closed by the powervalve.

Wobbly great explanation. Thank you. There has to be something a little more. Do you think high A is actually cooling exhaust gas slightly? This is reason for results of high A vs high B?

It's funny this motor was touted as being amazing back in the day. It's not. It doesn't have much bottom, a huge dip around PV opening... and just hits really hard.

I tried stiffer PV governor spring... it takes hit... but makes quite a bit less HP mid on up.

Fixing higher auxiliary exhaust ports, they were .8mm higher than main did help bottom... but still a pretty big dip in curve by PV opening.

The main PV opens first, the auxiliary ports progressively open from bottom first, which I am starting to guess might not be the best.

[wobbly]

The higher A port scenario helps front side power because its flow regime is retarded by the Blowdown backflow - thus reducing its short circuiting
tendency being the closest to the Exhaust ports depression.
The problem with a stiffer governor spring is that it absolutely helps where the PV is opening too soon , but its higher spring constant also then slows the PV opening
rate - the only solution is a servo drive from the ECU.
These were tried in the early 2000 ( along with solenoid PJ ) but the manufacturers didnt like the cable servo drives complexity and cost, even though it worked perfectly.

Having the Aux higher is a weird anomaly, with no discernable advantages. Kawasaki still do it in the KR150 for a road bike , with the later version having the PV servo controlled
on the very high Aux only - and this gives good low end , but due mainly to the fact the small side rotary drum valves also open and close ATAC ( KIPS ) chambers as well.

Having the Aux PV opening the same as the main blade ie from the bottom - up, works way better than the complete disaster that is the simplistic KTM setup that does the reverse.
It is impossible to get this to work seamlessly even with a servo drive.

[husaberg]

Husaberg, thank you for the information.

The engine I have is a 1992 - 01 CR250. They actually incorporate a resonant chamber right in cylinder... and opened and closed by the powervalve.

Wobbly great explanation. Thank you. There has to be something a little more. Do you think high A is actually cooling exhaust gas slightly? This is reason for results of high A vs high B?

It's funny this motor was touted as being amazing back in the day. It's not. It doesn't have much bottom, a huge dip around PV opening... and just hits really hard.

I tried stiffer PV governor spring... it takes hit... but makes quite a bit less HP mid on up.

Fixing higher auxiliary exhaust ports, they were .8mm higher than main did help bottom... but still a pretty big dip in curve by PV opening.

The main PV opens first, the auxiliary ports progressively open from bottom first, which I am starting to guess might not be the best.

funny, i thought they gave up on that inc chamber far earlier.
What are your class limits? cc

[ApolloMotoMoto]

(...)

Normal stagger scavenging that boosts the whole front side, is always used in wide band applications such as MX or more especially where there is no PV to help front side power.

(...)

How much stagger between the ports in order to achieve this effect?

What differences are seen with different "amounts" of stagger? (in terms of degrees between openings)

I currently have 1.4 degrees between opening's with a "Normal" stagger (A First), used in a VERY wide band application (single-speed, direct-drive road racing on kart tracks).

Wondering if more stagger might be a good idea?

With the help of all of this advise over the years, our little "motorized bicycles" are becomming quite the weapon on track. Taking our fastest lap times at a popular Kart track we run at, we are about 5 seconds behind the lap times of the 450cc Foul-Stroke Supermoto's, and about 10 seconds off the fastest mini-moto's that set the track record lap times. We run laps around the built Honda Grom's and its mildly hillarious to see "bicycles" out on track with leathered up racers getting the knee down.

The switch to 17" motorcycle rim's (17" moped spoked setups for most guys) and the use of the same 17" racing slicks those Supermoto's run is certainly part of this....

[wobbly]

In a fully optimized 5 port , no PV and with wide B and narrow C we have 2*/2.2* timing drop.
This seems to be alot more than in your application, and testing has shown that this setting gives the widest spread of power without hugely compromising
peak and overev too much due to lack of Transfer STA.
In this case the Blowdown and Transfer are exactly matching, and also exactly match the power capability.
One thing we have in our favor though is a carb of only 30mm bore in a 125 engine making 50 sprocket power - way smaller than would normally be the case.
Maybe this is a development path to look at in your project.
Every other aspect of the engines tune is basically unlimited , thus the very high bmep, despite the small venturi.

[ApolloMotoMoto]

In a fully optimized 5 port , no PV and with wide B and narrow C we have 2*/2.2* timing drop.
This seems to be alot more than in your application, and testing has shown that this setting gives the widest spread of power without hugely compromising
peak and overev too much due to lack of Transfer STA.
In this case the Blowdown and Transfer are exactly matching, and also exactly match the power capability.

In that case, I am bumping up my stagger from 1.4 degrees between opening's to 2.1 degree's between openings.

I, likewise, have the Blowdown STA exactly matching the Transfer STA for my entered power target in JanBros.

I will then recover the lost Transfer STA (from the additional stagger drop) by massaging them wider a few tenths of a mm here and there.

One thing we have in our favor though is a carb of only 30mm bore in a 125 engine making 50 sprocket power - way smaller than would normally be the case.
Maybe this is a development path to look at in your project.
Every other aspect of the engines tune is basically unlimited , thus the very high bmep, despite the small venturi.

I have been going back and forth on this recently, and I dont think I am going to be happy with the answer I come up with until we have these engines on a dyno.

90cc ~12+ BMEP/ 15-19 RWHP

Certainly not setting any records here.

We have run 21mm Keihin PWK clones since forever.

Recently we started playing with increasing the bore size of the carb again because we know we are making more power (2 years ago we were lucky if we were making more than 10hp out of a 70cc engine...).

24mm seems to be better everywhere. No loss in throttle response or low-end performance VS the 21mm, and it seems easier to jet with perhaps a better balanced velocity curve.

26mm is hard to tell the difference between a 24 and a 26 honestly, without a dyno I couldn't tell you which one was on the bike by feel once they are both jetted right.

28mm starts to suffer from the dreaded off-idle lean-bog if you whack the slide open too fast, but with the right jetting it all but completely goes away.

All of this is running open bore/ no filter (I know.... the shame of it...).

The last couple outings I fitted the karting airboxes I have run before to the 28mm and re-jetted it (went from a 114 main jet open bore to 90 main jet with the airbox -does this possibly suggest the air-box inlets are overly-restricting intake flow and possibly hurting powwe?)

WITH the airbox, the 28mm has better throttle response than a 21mm with an open bore, and a noticable boost in off-idle torque.

I just have not finished testing weather the airbox is restricting the top-end.

[wobbly]

It certainly sounds like the airbox Helmholtz resonant volume is wrong or the inlet tubes are too small if you have to lean down that much to get your egt back.
After reading all you have said my first reaction is to stick on a 19mm carb - again way small, but that im sure would be a jet off the bottom and you gain your peak and overev power with
inlet and pipe tuning.
That is one thing you have not mentioned - inlet tuned length from the bell mouth end to the reed tips.
You have changed carbs a few times, but what was the differences in length?

[ApolloMotoMoto]

It certainly sounds like the airbox Helmholtz resonant volume is wrong or the inlet tubes are too small if you have to lean down that much to get your egt back.

I'll measure the airbox inlets and compare the combined area to the area of the carb bores I have been running and see what I see...

After reading all you have said my first reaction is to stick on a 19mm carb - again way small, but that im sure would be a jet off the bottom and you gain your peak and overev power with
inlet and pipe tuning.
That is one thing you have not mentioned - inlet tuned length from the bell mouth end to the reed tips.
You have changed carbs a few times, but what was the differences in length?

I do have 19mm bore PWK clones in my box of carbs....

All the carb changes have been with the exact same "body" Keihin PWK Clone, just different bore sizes machined into them. Mostly through scooter tuning channels, you can get Keihin PWK clone carbs in one common "small body" size from 19mm to 32mm;

19, 21, 24, 26, 28, 30, 32

Then the body size goes up, and you are into "real" Keihin PWK's.

So I can switch carbs to adjust the bore size within that range without changing the tuned inlet length one millimeter.

Although, this is not something I have never measured or calculated. I tend to favor putting the carb as close as physically possible to the reed to attempt to eliminate any resonance effects in the inlet duct, not because its a great idea, but mostly because I have not tackled "doing it right" yet. I use a short rubber boot, the distance from the bellmouth end of the carb to the tip of the reeds is still probably going to be a good 6-7 inches. I will have to go measure...

I have been using these PWK clones for YEARS, and I have boxes of them, and even larger boxes of all tunable parts, even the ones that aren't commonly found.

I have 5-6 different emulsion tubes, but I have not gotten to testing the different styles yet, I just make sure all the ones I used have the same "standard" emulsion tube I am used to using.

I have assortments of needle jets which most people will tell you are not a tunable part in a Keihin PWK.

I have multiple slides of all cutaway sizes, and a box with needles of 3 different "series" of needle styles, with the full range for each series.

And lots of different options for the "powerjet" with multiple probe lengths, dial adjutable or jetted with single jets. (but I wont be playing with these anymore until I have the new digital CDI to shut it off with a solenoid above a set RPM; I am getting better results right now with the powerjet closed off and "just" the main jet)


I have to admit, I had not considered trying the 19mm carb's again, but that is why we ran them to begin with; better low-end response, more snap comming up off the slow corners.

[JanBros]

In that case, I am bumping up my stagger from 1.4 degrees between opening's to 2.1 degree's between openings.

I, likewise, have the Blowdown STA exactly matching the Transfer STA for my entered power target in JanBros.

I will then recover the lost Transfer STA (from the additional stagger drop) by massaging them wider a few tenths of a mm here and there.

but by dropping the cylinder to create more stagger, the bottom of the transfers won't align anymore with the piston-top in TDC ? less piston cooling and less real transfer flow (control) because it will hit the piston and disturb the flow.

can't you raise the port itself and find some extra blowdown-sta ?

[ApolloMotoMoto]

but by dropping the cylinder to create more stagger, the bottom of the transfers won't align anymore with the piston-top in TDC ? less piston cooling and less real transfer flow (control) because it will hit the piston and disturb the flow.

can't you raise the port itself and find some extra blowdown-sta ?

The as cast stock cylinder's ports are so "low" to begin with that I wont need to drop the cylinder for the extra stagger.

Transfer timing with the crown edge of the piston lined up with the bottom edge of the transfer ports is around 110-116 depending on the casting.

I have 8x cylinders for the next batch of race engines that I havent started porting yet

I am finalizing the portmap template for these 8x based on the last 3x iterations of this portmap that I cut into previous cylinders, going back and forth between printed portmaps from the JanBros spreadsheet that I set inside my old cylinders to find where I can squeeze a few more tenths of a mm out of this casting. Over the iterations I have had ports a little too wide in the spreadsheet and then I find out that cutting them that wide in the cylinder breaks through into the stud bores. Each time I do it the spreadsheet portmap gets refined a little bit to more accurately represent what is actually getting cut into the cylinder.

This time I should be able to cut the portmap as entered into the JanBros spreadsheet -exactly-.

While I am spending the time doing this refining, I usually have some element of the portmap I want to try and "improve" from a scavenging/blowdown efficiency standpoint so I will post a theory question here to try and get some guidance from the "brain trust".

And you all never dissapoint!

Thanks again!

[ApolloMotoMoto]

can't you (...) find some extra blowdown-sta ?

Thats what SHE said...

Single exhaust port cylinder, 71% bore diameter width, using the FOS multi-radius shape.

Timing currently at 194 exhaust over 123 A Transfer

If you can find me some extra blowdown-sta without lifting the port any higher I am all ears