ESE's works engine tuner

[TZ350]

Completed my Suzuki RG50 with what was originally a piston port/case reed inlet with its now new rotary valve conversion.

Next move is to put it all together with the cylinder from my current RG50 engine so that I can compare before and after conversion dyno runs.

[F5 Dave]

That will be interesting Rob. I never thought to try that.

That said, throttle response will be interesting on a kart track. I had mildish piston port component to mine but the change to derbi full reed was noticeable in certain corners, particularly at Kaitoke with its downhill section that promoted load up.

[Vannik]

Fair enough. I have seen the duct work first hand so that's proof enough for me.

I try:



Probably needs updating. Any ideas?

[OopsClunkThud]

I did a series of 2D CFD runs looking at the port roof angle, piston angle, radius... as the piston moves from just opened to almost BDC. at low pressure ratios after blowdown was done large scale turbulent eddies would form. The image shows the piston at 130° ATDC, and the impact of the downward angle of the port from flat at the top and angled down in 5° increments. The eddies along the top of the port could be kept in check with a port angled down at 15° or more.



Adding a radius I ran into competing priorities. The lower the pressure ratio, the larger the radius needs to be to prevent separation, but a large radius blocks the flow when the pressure ratio is high (during blowdown). In my single port case I was already limited on blowdown, so any radius seemed to harm the blowdown more than it helped reduce eddies.

I have not simulated it but raising the floor would likely reduce the eddies at the bottom. Also a very large radius could be applied to a raised floor with zero effect on time area.

Note: these were steady state 2D simulations and I'm no expert.

[wobbly]

Neels , the only comment I have to add is that I have done some back to back tests determining the optimum geometry for the interface of the Aux ducts and the main.
Jans general comment was the shorter the divider the better.
This fits in with the idea that a short divider ( or septum technically ) which isnt cooled directly by water would transfer less heat into the stored plugging charge.
So I tested this on a KZ cylinder , putting a radius on the joining edge and effectively 1/2 the divider length.
Result , average 1/2 - 3/4 Hp from peak torque all the way up over the top of the pipe.

[andreas]

I forget now, what is considered the optimal mean downward angle of the duct - 25*? But how much testing has been done with a larger angle? seems there could be some gain to be had in minimizing eddying, despite the loss of cross area.

[Pagi]

Frits, with your top raduis exhaust duct drawing i have seen somewhere ( raduis = 5 % of stroke ), what height of duct should be taken for the calculation of the time-area, with or without the radius ?..........

[Frits Overmars]

Frits, with your top radius exhaust duct drawing i have seen somewhere ( radius = 5 % of stroke ), what height of duct should be taken for the calculation of the time-area, with or without the radius ?..........

The radius obviously has an influence so you cannot just neglect it.
Blowdown starts as soon as the first bit of light becomes visible between the piston and the top of the exhaust port. But calculating it is not going to be easy.
The elliptical shape of the port already makes it difficult to determine the open port area for each crank angle position and it certainly does not get any easier if the top edge of the port has a radius, and even more so if the piston timing edge also has a radius.

[Pagi]

The radius obviously has an influence so you cannot just neglect it.
Blowdown starts as soon as the first bit of light becomes visible between the piston and the top of the exhaust port. But calculating it is not going to be easy.
The elliptical shape of the port already makes it difficult to determine the open port area for each crank angle position and it certainly does not get any easier if the top edge of the port has a radius, and even more so if the piston timing edge also has a radius.

yes it seems logical ... hence my question !!!! so we can consider that taking your measuring system with a 45 ° rod as the correct basis .....

[wobbly]

Please be aware that Jan applied the radius to the EX port on the Aprilia due to his boss "the great leader " haha, having designed a new " better " pipe that lost all the top end.
As it now transpires having an accurate analysis of the Aprilia porting , many years later , it turns out the Transfer STA is about 8% ahead in power capability over that of the calculated Blowdown - simply from the numbers.
By increasing the Cd of the Exhaust port with a radius to assist Blowdown flow it would appear that this dramatically increased the power capability , mimicking that of a port with 8% more STA.
To now go blindly adding Ex radi - just because it seems like a good idea , when it may not be needed if the STA numbers match correctly , is a mistake.

The down side of a timing edge radi , is much the same as having the much longer path length Aux ports , too high , ie the high amplitude initial blowdown wave front entering the header is smeared out in time by the gradually opening area.
Thus reducing the rarefaction return wave efficiency , and subsequentially this pulls out less plugging mixture around BDC.
In the Aprilia case the flow and increase timing upside , more than offset this downside - only needed due to a faulty pipe design, and Jan not having access to calculated sim or proven STA numbers at the time.
He could have had that data , but his boss told me in a job interview sims were a complete waste of time - which ironically is the same impression I had of him.

[Pagi]

Please be aware that Jan applied the radius to the EX port on the Aprilia due to his boss "the great leader " haha, having designed a new " better " pipe that lost all the top end.
As it now transpires having an accurate analysis of the Aprilia porting , many years later , it turns out the Transfer STA is about 8% ahead in power capability over that of the calculated Blowdown - simply from the numbers.
By increasing the Cd of the Exhaust port with a radius to assist Blowdown flow it would appear that this dramatically increased the power capability , mimicking that of a port with 8% more STA.
To now go blindly adding Ex radi - just because it seems like a good idea , when it may not be needed if the STA numbers match correctly , is a mistake.

The down side of a timing edge radi , is much the same as having the much longer path length Aux ports , too high , ie the high amplitude initial blowdown wave front entering the header is smeared out in time by the gradually opening area.
Thus reducing the rarefaction return wave efficiency , and subsequentially this pulls out less plugging mixture around BDC.
In the Aprilia case the flow and increase timing upside , more than offset this downside - only needed due to a faulty pipe design, and Jan not having access to calculated sim or proven STA numbers at the time.
He could have had that data , but his boss told me in a job interview sims were a complete waste of time - which ironically is the same impression I had of him.

thanks Wobbly......you answered my next question

[TZ350]

.
Keeping up with Alex's 2Stroke Stuffing adventures. https://youtu.be/y66bD2r8Bp8 looks like 30hp last time may not have been real. Or at least not real for the base tune but 21-22 hp looks consistent. 30hp showed up when the rotary valve slipped its timing. Now that the engine is becoming more reliable Alex is starting to look at tuning adjustments like boost, ignition and rotary valve timing. But any way you slice it, 20hp from 50cc at 10,000 rpm is certainly something.

[wobbly]

There have been a couple of questions re the Ex down angle and how this relates to flow and the duct exit area.
25* seems to be the best compromise here , and yes its been tested to death in the 125 KZ Kart class engine , the last bastion of real ( although severely restricted technically ) 2T outer limit performance.
Thus the idea of a 75% duct exit area is based on this proven tuning element.

On one side of the coin you have less flow separation from the roof with a steeper angle , but the immediate downside of this is that the chordal area X the down angle cosine , directly affects the Blowdown STA.
Less STA = less horsepower capability , thus you then have to generate more time and or area by increasing one or both of these.
At the outer limits of bmep , we are already up against the wall of what can physically be done.

With a 70% chordal width main duct and optimal roof radi , along with sufficiently lower Aux ports cut around to bore centerline , there is simply no more width/area to be gained to increase our Blowdown STA.
Timing wise as we approach 200* duration the power band shape becomes steeper and steeper each side of peak power , the worst effect is the power dropping almost vertically in the overev area.
I have seen , in an engine that had the Aux butchered upwards to equal the main port timing , the peak was 48Hp at 13800 , but by 14200 it had dropped to 20 - less than 1/2 in only 400 rpm.
A PV can ameliorate the front side power loss with high durations , but the only way to then help the overev is a shorter pipe , and that approach fucks the front side power even more.

The good old Catch 22 , with sadly , no free lunches either.

[porttiming124]

Neels , the only comment I have to add is that I have done some back to back tests determining the optimum geometry for the interface of the Aux ducts and the main.
Jans general comment was the shorter the divider the better.
This fits in with the idea that a short divider ( or septum technically ) which isnt cooled directly by water would transfer less heat into the stored plugging charge.
So I tested this on a KZ cylinder , putting a radius on the joining edge and effectively 1/2 the divider length.
Result , average 1/2 - 3/4 Hp from peak torque all the way up over the top of the pipe.

After cutting the length of the divider in half, do you know how long of the divider now?
I'm curious.

[wobbly]

55 to the radius - 67 to the bore = 12mm septum length.
And the new radiused end of the divider was tapered and thinned to almost a point by making the Aux duct wider.