ESE's works engine tuner

[SS90]

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Water testing the scavinging flow patterns.

Pic-1 the motor setup for test

Pic-2 the acrilic head

Pic-3 setting it up

Pic-4 testing



Pic-6 the flow formed rolling pattern twisting around like a tornado with it tail in the exhaust port.


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This is actually a little brave of me, but from my screen it looks like you have a large degree of shortcircuiting particularly from the rear transfer port (boost port), but also from the righthand set of transfers (looking from the top)

I recommend dividing the picture you posted into 4 sections, and enlarge it as much as you can, this is what I have done and I am getting a good picture.

Basically, it isn't the worst one in the world, all things considered it's "OK", but (in my opinion) you are getting short circuiting in two places, and I believe the cause is the same.

I believe the rear transfer (boost) port is causing problems due to it's proximity to the secondary transfers.

Here is what I would do.

Just for a test (easy one) using RTV (or hot melt glue), or what ever really, plug the rear transfer/boost port completely, and essentially remove it from the equation (just for the purpose of seeing if it is indeed causing the problem)

If the remaining transfer ports "even up" their patterns, then it is logical to say that the rear port is the problem, and as such, either a new angle will need to be found, OR, (maybe) remove the walls between the rear port and the secondaries, and angle the new "single" port about, 70 deg up into the head.

Sort if a "collide stream port effect" (this is only a theory, but I have been thinking about it for a few months now, and the idea keeps coming back)

Unfortunately, I know of no other cylinder with a set up such as that (with the secondary transfers so close to the rear port), so I can't compare it to something "proven"

With a little logic though, as we have talked before, perhaps (like you mentioned again in a recent post) a divider in the transfers MAY help a bit as well, but like I say, these cylinders are a bit of an "orphan", so to a certain degree, you may well be heading into uncharted territory as far as improving this area.

Also, an important thing to watch is try to get the air pressure VERY VERY low, and watch as the smallest bubbles start coming through the system..............

Obviously you need to watch with a variety of pressures, but the low pressure gives you a real insight to aspects a book can never do!

Basically in my opinion Teezee, from your pictures, the left set of transfers looks alright, the rest looks like it is short circuiting (to me anyway)

[TZ350]

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Thank you for your insights, I will try them. We will get better with practice at making bubbles and post better pictures.

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[bucketracer]

Great looking bubbles your making there TZ

[TZ350]

Do you have an exhaust time area for the setup that you have been using.

Jennings page 81-82 http://www.vintagesleds.com/library/...20Handbook.pdf

Port/Time/Area for the Exhaust Port 0.00018 – 0.00019 Cm2 x Sec / Cm3

Port/Time/Area is found by dividing Cylinder Volume into the Mean Port Area and multiplied by Time.

Mean Port Area is the area of the port uncovered by the piston when the crank is moved half way between port opening and BDC.

For my Suzuki GP125 exhaust port at 10,500Rpm Ex opens 83deg ATDC 71% bore dia 194deg duration, with a mean exhaust port area of 7.0cm2.

Step-1 Divide Cylinder Volume into the Mean Port Area.

Mean Port Area / Cylinder Volume

7.0cm2 / 125cc

7/125 = 0.056

0.056 cm2/cm3

Step-2 Time

Time = Duration / Rpm x 6

Time = 194 / 10,500 x 6

Time = 194 / 63,000

Time = 0.0031 sec

Step-3 find Port/Time/Area

cm2/cm3 x Time

0.056 x 0.0031 = 0.00017

0.00017 sec cm2/cm3

0.00017 is a little less than the 0.00018 – 0.00019 listed in Jennings so more exhaust port area or duration is required.

Tuned length for the pipe is 970mm measured from the GP125's piston to the end of the convergent cone.

Pipe dimensions Suzuki RM125 B/C page 82 Bell. http://www.kreidler.nl/artikelen/per...raham-bell.pdf

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[sonic_v]

0.00017 is spot on for an engine were you require a good spread of power. Basically, you have a 25hp exhaust port there. (for an air cooled engine) The fact that you are five short indicates that your problems are elsewere. Pulling the engine speed down via a longer exhaust system is likely to find some of this power plus your intake work should find most of the rest. I have found it possible to make excellent power with exh time/area as low as 0.00016 plus a nice spread of power.

Working at 10,500rpm will result in a considerable increase in bmep with the result that your engine should respond better to your retarding ignition.

As for venturi in your intake, I would suggest a taper from the choke of the carb out to 30mm should be adequate, keeping included angle below 14degrees as has been mentioned elsewere. I suspect that once the intake is flowing better, that you will be able to close the disc valve earlier. This is the area that needs looked at before thinking of a new pipe.

Just out of interest, what diameter is your exhaust port?

PS the work you have done on your carb might well make a big improvement!

[bucketracer]

Port/Time/Area for the Exhaust Port 0.00018 – 0.00019 Cm2 x Sec / Cm3

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TZ you have made a mistake the time you quote is for a rotary valve inlet not exhaust.

The correct time areas are.

Port/Time/Area for the Piston inlet Port 0.00014 – 0.00016 Cm2 x Sec / Cm3

Port/Time/Area for the Transfer Port 0.00008 – 0.00010 Cm2 x Sec / Cm3

Port/Time/Area for the Exhaust Port 0.00014 – 0.00015 Cm2 x Sec / Cm3

Port/Time/Area for the Rotary Valve Inlet 0.00018 – 0.00019 Cm2 x Sec / Cm3

So your time of 0.00017 is possibly better suited to 11,000 than 10,500.

[sonic_v]

Well spotted there BucketRacer. Fortunately I am working from what modern production two-stroke racing bikes (honda rs125, tz250, aprilia rs125) actually measure, which in standard trim is often or not 18-19.

Hence this is the reason I like to work in the 16-17 range for tuned motocrosser/road engines for track racing.

[SS90]

Well spotted there BucketRacer. Fortunately I am working from what modern production two-stroke racing bikes (honda rs125, tz250, aprilia rs125) actually measure, which in standard trim is often or not 18-19.

Hence this is the reason I like to work in the 16-17 range for tuned motocrosser/road engines for track racing.

Realising that F5Dave was quite right with his warnings regarding port timings etc (i.e "throwing them around), time area's for an Rs125,Tz250 etc are quite different in requirements.

By that I mean, 18-19 is quite high for an air cooled disc valve 125cc two stroke, (running a 24mm carb)

Where as the examples you mention are all Crankcase induction water cooled two strokes (the Yamaha and Aprilia have power valves as well) with carbs a up around 40mm.

And as you well know, 125GP bikes (the "production" ones anyway) only get ridden from around 9,000 to 13,000 RPM (roughly, let's not split hairs!)

And with a wee carb like Teezee has by 9,000RPM it's pretty much all over.

I think Teezee is trying to find a figure suitable for his piddly little carb.

That's how I see it, I may be wrong!

I am interested in the results with the carb bell mouth changes, I have tested dozens of Bell mouth types/designs, but never found anything that made a real difference (on low BMP stuff like this anyway)

With higher power stuff (Rs125's TZ250's) I have noticed gains/losses as far as that is concerned.

[sonic_v]

Realising that F5Dave was quite right with his warnings regarding port timings etc (i.e "throwing them around), time area's for an Rs125,Tz250 etc are quite different in requirements.

By that I mean, 18-19 is quite high for an air cooled disc valve 125cc two stroke, (running a 24mm carb)

Where as the examples you mention are all Crankcase induction water cooled two strokes (the Yamaha and Aprilia have power valves as well) with carbs a up around 40mm.

And as you well know, 125GP bikes (the "production" ones anyway) only get ridden from around 9,000 to 13,000 RPM (roughly, let's not split hairs!)

And with a wee carb like Teezee has by 9,000RPM it's pretty much all over.

I think Teezee is trying to find a figure suitable for his piddly little carb.

That's how I see it, I may be wrong!

I am interested in the results with the carb bell mouth changes, I have tested dozens of Bell mouth types/designs, but never found anything that made a real difference (on low BMP stuff like this anyway)

With higher power stuff (Rs125's TZ250's) I have noticed gains/losses as far as that is concerned.

Indeed 18-19 for exhaust time/area is too high for an aircooled engine and hence the reason that I have suggested a value of 16-17, which taking the mean values results in 11% less time area.

((18.5 - 16.5) / 18.5) * 100% = 11%

Also, to take into account that this is a tuned air cooled production road engine with a 24mm carb, I have suggested that peak power speed of 10,500 rpm would be about right.

If we take a production rs125 aprilia (disc valved intake ) as an example with a peak power speed of 12,500 rpm this represents a reduction in engine speed by 16%.

((12500 - 10500) / 12500) * 100% = 16%

In total these two measures represent a potential mass air flow reduction in the region of 25%.

On the subject of the 24mm carb, a correctly designed diffuser could easily make the intake flow at least as well as a 26mm straight through carb. This is easily sufficient for 25hp.

As for "low bmep stuff like this" I would suggest that this engine has the potential to give a bmep of 9.5 bar at peak torque which is not exactly low bmep.

An engine set up as above will pull strongly from 7500 rpm through to 11000rpm.


Just out of interest TZ, do you have aspirations HP wise for this engine.

[TZ350]

SS90 is right my thinking and planning now centers around what is possible with a 24mm carb.

My exhaust port dia at the flange is 36mm and mid 20's for rwhp would be good, I feel I have the cooling to handle it.

I have been reading up about designing venture tubes as flow measuring instruments because there is quite a bit of information about diffuser angles.

So far I have read that given a convergent angle of 10.5deg into the front of the venture then a diffuser of 5-7deg has a lower net pressure loss than a 14-15deg diffuser.

And then there are the other things like:-

4-Strokes like a convergent inlet port. Other rotary valve arrangements I have seen are size for size and one or two convergent.

There is also the thought that pressure waves like convergent and sound waves like divergent diffusers.

When I set up MOTOR with a 24mm carb and 30mm port it predicted a power increase throughout the rev range.

I tried this once but was not very impressed.

So I am not sure what to make of any of this yet.

Its easy to imagine the carb as the throat of the venture.

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[SS90]

Also, to take into account that this is a tuned air cooled production road engine with a 24mm carb, I have suggested that peak power speed of 10,500 rpm would be about right.


((12500 - 10500) / 12500) * 100% = 16%

In total these two measures represent a potential mass air flow reduction in the region of 25%.

On the subject of the 24mm carb, a correctly designed diffuser could easily make the intake flow at least as well as a 26mm straight through carb. This is easily sufficient for 25hp.

As for "low bmep stuff like this" I would suggest that this engine has the potential to give a bmep of 9.5 bar at peak torque which is not exactly low bmep.

An engine set up as above will pull strongly from 7500 rpm through to 11000rpm.


Just out of interest TZ, do you have aspirations HP wise for this engine.

That's quite interesting sonic_v.

personally, I have never seen more that 21PS from an engine with a 24mm carb, regardless of bell mouth/venturi design.

Two years ago I was lucky enough to work with someone who uses MOTA for a living, and was quickly shown that it is a tool that requires years of experience.

With an experienced operator on a 125cc aircoled engine the result was always 21PS, and when we built that engine, it was pretty much 20PS.

Previously (when I had tried to use the program) I, like Teezee and Thomas has seen 28PS as a prediction.

I simply didn't have the experience.

I too had thought that 24PS or so was possible, but I don't know of anyone who has built a 125cc air cooled disc valve engine with a 24mm carb that has more than 20PS.

OK, I don't knnow everyone in the world, but the limitations of that carb size, particularly operating over 9,000 RPM is quite something to overcome.

I will see if I can find a copy of the dyno runs.

My experience with air cooled 125cc engines to get around the BMEP you are suggesting requires a carb size in the area of 28 to 30MM.

Have you found different?

[TZ350]

Yes you don't want to take MOTA's predictions of ultimate power to seriously but it is a good friend that's qualified to give me an informed opinion of what the likely outcome will be of any changes I make.

MOTOA's certainly been a whole lot better at it than my mates at the pub have been.

Now that I have a base line run I could adjust MOTO to reflect the torque curve and then it will more accurately show the power output and any changes I make.

The big overoptimistic HP numbers are great for psyching the opposition though.

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[sonic_v]

TZ I would agree with the shallower angles you are quoting for optimum pressure recovery. Really it is all a matter of what is an acceptable intake tract length as the shallower angles will increase it.

I do not know if you use a fairing and thus have a packaging problem. Personally, I have cut a hole in the fairing before now that the bell mouth just peeped out of. No problems at all.

Your carb looks a lot better than the original standard version, and thus I would concentrate on the downstream side. i.e diffuser.

As for Mota. Do you still have to estimate the exhaust gas temperature. It is a long time since I have used it. Can you model a diffuser in the intake or is it modelled as a step. i.e A jump from 24mm to 30mm?

[SS90]

As for Mota. Do you still have to estimate the exhaust gas temperature. It is a long time since I have used it. Can you model a diffuser in the intake or is it modelled as a step. i.e A jump from 24mm to 30mm?

That's interesting. I was quite amazed at the importance of how you represent the intake with Mota, it seems to be where many people fall flat.

[SS90]

I can't claim responsibility for this engine, but (so far) the highest power I have seen from this capacity with a 24mm Carb is this series of runs.

The red line was a different exhaust.