ESE's works engine tuner

[Ns1Montesa]

Hi everybody,

this is my first post in this forum. I want to say thank you to all you people sharing their knowledge, ideas, experiences and pictures about two strokes in this thread. I would say this is the best place to expand your knowledge about two stroke engines in the WWW.

I am from Germany, so please excuse my bad english. I hope it is good enough to ask some questions and participating in this great thread.

At the moment I am working on a Honda NS1 Engine. It is a 75cc single engine, reedvalve in cast iron water cooled cylinder. Should be the same as mbx80 and close to the air cooled honda engines like mtx80, mb8, mb100 and so on.

I do not race this bike/engine. I just want to know how much reliable HP I can get out of it. It is just for fun.

At the moment I am a little bit stuck at around 16hp at the wheel. My thinking was that the inlet is the most restricting part in the engine. So I decided to drill some Boyesen ports from reed case to B transfers to get more port area linked directly to the crank case.
Today I tested it on the Dyno and I was very disappointed. I did not change anything, just added the Boyesens and the power dropped about 0.5HP. After setting the carb leaner, from 135 to 125 mainjet the peak power was close to the old power, but the low end power is still worse than before.
Is it normal that I need to rejet the carb after adding Boyesen ports? And what is the reason for the power loss in low and mid range? Is it because I increased the volume of the crank case or are the ports disturbing the flow of the B transfers?

The engine is running with Ignitec, PWK28, homebuild expansion chamber, CR around 12,5 to 1, EX duration 192° Transfers 128°


Would be awesome if somebody knows how to solve this issue or can explaine why boyesens are not working for me. And If someone knows more about getting power out of these honda engines, please let me know

cheers

josh

[husaberg]

Hi everybody,

this is my first post in this forum. I want to say thank you to all you people sharing their knowledge, ideas, experiences and pictures about two strokes in this thread. I would say this is the best place to expand your knowledge about two stroke engines in the WWW.

I am from Germany, so please excuse my bad english. I hope it is good enough to ask some questions and participating in this great thread.

At the moment I am working on a Honda NS1 Engine. It is a 75cc single engine, reedvalve in cast iron water cooled cylinder. Should be the same as mbx80 and close to the air cooled honda engines like mtx80, mb8, mb100 and so on.

I do not race this bike/engine. I just want to know how much reliable HP I can get out of it. It is just for fun.

At the moment I am a little bit stuck at around 16hp at the wheel. My thinking was that the inlet is the most restricting part in the engine. So I decided to drill some Boyesen ports from reed case to B transfers to get more port area linked directly to the crank case.
Today I tested it on the Dyno and I was very disappointed. I did not change anything, just added the Boyesens and the power dropped about 0.5HP. After setting the carb leaner, from 135 to 125 mainjet the peak power was close to the old power, but the low end power is still worse than before.
Is it normal that I need to rejet the carb after adding Boyesen ports? And what is the reason for the power loss in low and mid range? Is it because I increased the volume of the crank case or are the ports disturbing the flow of the B transfers?

The engine is running with Ignitec, PWK28, homebuild expansion chamber, CR around 12,5 to 1, EX duration 192° Transfers 128°


Would be awesome if somebody knows how to solve this issue or can explaine why boyesens are not working for me. And If someone knows more about getting power out of these honda engines, please let me know

cheers

josh

Hi Josh send a picture of the reed valve and intake port

[wobbly]

Two conflicting issues going on there.
First is that ,yes , the hole thru from the inlet into the B port entry is affecting the flow regime into the duct.
Second , Boyesen ports were developed as a "quick fix " when cylinder mounted intake flow became the restricting bottleneck in an engines tune.
When this happens the increase in bulk flow , due to more unrestricted intake area , has a much greater positive effect on the Delivery Ratio than it has a negative effect on the B port duct entry.
It would seem in your case that the intake bulk flow capability isnt the bottleneck you thought it was.
You may find that the intake capability doesnt become the weak link until you approach , im guessing ,say 20 Hp.
It has been seen many times with lower Hp engine setups that the so called " Power Porting " approach ie no holes in the piston that then forces higher reed box pressure /flow to enter the cylinder via the boost port
makes more power.
But this quickly has reduced positive effect as the need for outright bulk flow , to support much higher power , takes precedence.

[F5 Dave]

Time to break out the devcon.

[Ns1Montesa]

Two conflicting issues going on there.
First is that ,yes , the hole thru from the inlet into the B port entry is affecting the flow regime into the duct.
Second , Boyesen ports were developed as a "quick fix " when cylinder mounted intake flow became the restricting bottleneck in an engines tune.
When this happens the increase in bulk flow , due to more unrestricted intake area , has a much greater positive effect on the Delivery Ratio than it has a negative effect on the B port duct entry.
It would seem in your case that the intake bulk flow capability isnt the bottleneck you thought it was.
You may find that the intake capability doesnt become the weak link until you approach , im guessing ,say 20 Hp.
It has been seen many times with lower Hp engine setups that the so called " Power Porting " approach ie no holes in the piston that then forces higher reed box pressure /flow to enter the cylinder via the boost port
makes more power.
But this quickly has reduced positive effect as the need for outright bulk flow , to support much higher power , takes precedence.

Thanks for your reply wobbly.

Bad news, but there is something positive about it. Now I know the stock intake port should be good enough for more power.

Is there any good method to determine where the bottleneck of an engine is? I tested various exhausts, but none of them gave more than around 10nm of torque. Changed the carb from 24mm to 28mm. That only made the powerband broader and gave very little increase in peak power. Tested a Vforce3 reed from a KTM sx50, made aboslultely no difference.
How much can I expect from pointing the transfers more upwards? Untouched they are close to 90 degree in relation to the bore axis.

Hi Josh send a picture of the reed valve and intake port

Here is the reed I am using and the Intake. The reeds are the size of the Minarelli AM6 ones.

Cheers

Josh

[husaberg]

Here is the reed I am using and the Intake. The reeds are the size of the Minarelli AM6 ones.

Cheers

Josh

Wow,Far better than a H100 or MB5.
The CR85 has a slightly bigger looking one with single reeds and a stuffer. its a bolt on with maybe only the cavity requiring work if the MB engiges are anything to go by.

[Frits Overmars]

Hi everybody, this is my first post in this forum. I want to say thank you to all you people sharing their knowledge, ideas, experiences and pictures about two strokes in this thread. I would say this is the best place to expand your knowledge about two stroke engines in the WWW. I am from Germany, so please excuse my bad english.

Hi Josh, herzlich willkommen. I wish my German was as good as your English. But as I keep saying, German is a much richer language than English: if offers far more opportunities to make mistakes

Is there any good method to determine where the bottleneck of an engine is? I tested various exhausts, but none of them gave more than around 10nm of torque. Changed the carb from 24mm to 28mm. That only made the powerband broader and gave very little increase in peak power. Tested a Vforce3 reed from a KTM sx50, made aboslultely no difference.

You can compare a two-stroke engine with a 10-digit combination lock. Even if you get nine out of those ten digits correct, you won't know because nothing happens. Only when you have all ten correct, you may sing and dance.
How do you determine the bottleneck? Work, lots of work. And experience, lots of experience.

How much can I expect from pointing the transfers more upwards? Untouched they are close to 90 degree in relation to the bore axis.

Raising the axial angle of the A-ports to about 25° can give a nice improvement. Better leave the axial angles of the B- and C-ports alone for the time being.
If you can find the time, visit one of the German SimsonGP races; free admittance if you give them my regards (and also if you don't ).
Several riders there use your type of engine, and a good one produces about 22 hp, even with the cast-iron cylinder.

[Condyn]

First:
I am trying to source a longer connecting rod for an engine to get the r/s ratio to 2:1. The only rods I have access to that will meet this requirement are 3mm more narrow on the big end. I assume there is a slight strength compromise. Is it ok to source thicker thrust washers for this scenario? Having trouble finding them too, but might be easier than the rods I am after.

Second:
The engine I am working on/designing is a piston port with only A and B transfers. I have been thinking about adding a boost port from the intake duct. Is there a proper way to do this on a piston port? Add to the main intake window like a boost port on an old cylinder reed engine, or tap back into the port to leave a horizontal bridge between the two? The ring end gap is offset to one side and will definitely catch the proposed window and horizontal bridge if I do that. I understand the pipe does the pulling, but would something like this even work?

[katinas]

Hi Josh, like Husa said, it would be interesting to see more photos of the cylinder with all ports and piston.

Looks like original cylinder designed to concentrate intake flow mass directly to crankcase, through main intake windows/piston skirt together with another port arranged downward to crankcase, so there is no high flow through this additional holes, from piston movement (just from on-pipe) and its even better for back flow to reed space.

Rising piston side cutouts as high as piston construction allows, helps to rise flow velocity through this boyesens, as A and B opens longer at TDC and send stronger pulse to reed space, directly through this holes. And together with some original intake flow restrictions (base gasket with smaller cuts for down side intake) or piston without holes, mix velocity through boyesens could rise even more.
We noticed, modifications that concentrated intake mass flow more to transfers, require leaner mix.
Add photo of kit version for NSR/NS/mbx, and pistons, that could sing in a duet with the big boyesens, but not with piston ported or rotary valve type engines.

[peewee]

First:
I am trying to source a longer connecting rod for an engine to get the r/s ratio to 2:1. The only rods I have access to that will meet this requirement are 3mm more narrow on the big end. I assume there is a slight strength compromise. Is it ok to source thicker thrust washers for this scenario? Having trouble finding them too, but might be easier than the rods I am after.

Second:
The engine I am working on/designing is a piston port with only A and B transfers. I have been thinking about adding a boost port from the intake duct. Is there a proper way to do this on a piston port? Add to the main intake window like a boost port on an old cylinder reed engine, or tap back into the port to leave a horizontal bridge between the two? The ring end gap is offset to one side and will definitely catch the proposed window and horizontal bridge if I do that. I understand the pipe does the pulling, but would something like this even work?

if something doesnt fit you have to make your own parts. many pages back i showed some small end thrust washers i made. seems like was 4130 1mm thick

[yatasaki]

First:
I am trying to source a longer connecting rod for an engine to get the r/s ratio to 2:1. The only rods I have access to that will meet this requirement are 3mm more narrow on the big end. I assume there is a slight strength compromise. Is it ok to source thicker thrust washers for this scenario? Having trouble finding them too, but might be easier than the rods I am after.

Second:
The engine I am working on/designing is a piston port with only A and B transfers. I have been thinking about adding a boost port from the intake duct. Is there a proper way to do this on a piston port? Add to the main intake window like a boost port on an old cylinder reed engine, or tap back into the port to leave a horizontal bridge between the two? The ring end gap is offset to one side and will definitely catch the proposed window and horizontal bridge if I do that. I understand the pipe does the pulling, but would something like this even work?

You mean from or through intake port? If through you can connect crankcase with pipe which will pass through the middle of the inlet or with two pipes which will pass through corners of the inlet port. It depends of the configuration of the cylinder, studs and crankcase base but usually single center pipe is better option cause of bigger pipe cross section and inlet side walls are formed to follow cross section of the inlet port with transfer pipe in center.
CZ bikes used to have this kind of arrangement.

[wobbly]

Simple answer to the bottleneck question , is you need to use a port calculator to ascertain the relationship between the intake/transfer/blowdown STA numbers.
The engine will always hit a wall as soon as one of these is out of sync with the other two.
You now know its not the intake that prevented better ( if they actually were better ) pipes from working as intended.

A perfect example of this was an LC350 I analysed during lockdown.
It had been ported by a well known English "name " tuner , and he had actually done a very nice job of giving the staggered transfers the capability of 52 Hp/cylinder , but sadly the Blowdown STA was down at 34 Hp.
This was why several sets of pipes made no difference at all - and the worst/skinnyest most horribly made pipes worked OK.
Banshee VF4 didnt work, 34mm carbs didnt work , more com didnt work , long rods didnt work etc etc.

[F5 Dave]

First:
I am trying to source a longer connecting rod for an engine to get the r/s ratio to 2:1. The only rods I have access to that will meet this requirement are 3mm more narrow on the big end. I assume there is a slight strength compromise. Is it ok to source thicker thrust washers for this scenario? Having trouble finding them too, but might be easier than the rods I am after.

Second:
The engine I am working on/designing is a piston port with only A and B transfers. I have been thinking about adding a boost port from the intake duct. Is there a proper way to do this on a piston port? Add to the main intake window like a boost port on an old cylinder reed engine, or tap back into the port to leave a horizontal bridge between the two? The ring end gap is offset to one side and will definitely catch the proposed window and horizontal bridge if I do that. I understand the pipe does the pulling, but would something like this even work?

So first question, can you use the matching pistons to the new rods? I found out the hard way when my new piston was a few mm wider. The std piston was tapered at the top to retain the bearing and I never spotted it being too obsessed with moving ring peg, etc. OK i was a Klutz.
I used some hardened thrust washers which worked well but needed replacing every year racing.


2nd, and most obvious, can you fit a reed cage? Then you can fashion a straight std boost port in conventional style above reed cavity.

I used to cut the back 20mm off a scrap barrel and tack each corner so its strong without warping things, dig out the cavity and devcon the gaps. That gives you matching reed and manifold to use.

Or if your case, and desire to make things difficult for yourself, add the reed to the crankcases. Done that twice.

[husaberg]

First:
I am trying to source a longer connecting rod for an engine to get the r/s ratio to 2:1. The only rods I have access to that will meet this requirement are 3mm more narrow on the big end. I assume there is a slight strength compromise. Is it ok to source thicker thrust washers for this scenario? Having trouble finding them too, but might be easier than the rods I am after.

what size length and widths are you wanting?

[andreas]

Hi everybody,

this is my first post in this forum. I want to say thank you to all you people sharing their knowledge, ideas, experiences and pictures about two strokes in this thread. I would say this is the best place to expand your knowledge about two stroke engines in the WWW.

I am from Germany, so please excuse my bad english. I hope it is good enough to ask some questions and participating in this great thread.

At the moment I am working on a Honda NS1 Engine. It is a 75cc single engine, reedvalve in cast iron water cooled cylinder. Should be the same as mbx80 and close to the air cooled honda engines like mtx80, mb8, mb100 and so on.

I do not race this bike/engine. I just want to know how much reliable HP I can get out of it. It is just for fun.

At the moment I am a little bit stuck at around 16hp at the wheel. My thinking was that the inlet is the most restricting part in the engine. So I decided to drill some Boyesen ports from reed case to B transfers to get more port area linked directly to the crank case.
Today I tested it on the Dyno and I was very disappointed. I did not change anything, just added the Boyesens and the power dropped about 0.5HP. After setting the carb leaner, from 135 to 125 mainjet the peak power was close to the old power, but the low end power is still worse than before.
Is it normal that I need to rejet the carb after adding Boyesen ports? And what is the reason for the power loss in low and mid range? Is it because I increased the volume of the crank case or are the ports disturbing the flow of the B transfers?

The engine is running with Ignitec, PWK28, homebuild expansion chamber, CR around 12,5 to 1, EX duration 192° Transfers 128°


Would be awesome if somebody knows how to solve this issue or can explaine why boyesens are not working for me. And If someone knows more about getting power out of these honda engines, please let me know

cheers

josh

Although your engine has the long cylinder studs, it seems someone has managed to have aux ex-ports in it. Might be worth looking into.