ESE's works engine tuner

[lodgernz]

Easy - double the A and B port axial angles.
Move the B port front edge as far forward as you can to make a narrow bridge - and grind it perpendicular to the front/rear axis.
Move the B port rear wall around as far as you can ( limited by the ring pins generally ) and get a hook in there pointing 1/2 way to bore centre.

Wow! Thanks Wobbly.
So you think the A port directions are OK? I thought they were supposed to converge somewhere, but not as far back as these would, if they actually did. If you know what I mean.
I don't want to raise the ports since the A duration is already 132*, so I'm going to have to widen them anyway.
Thanks again for the guidance on doing that.

The piston dome height is 2mm, so the edge angle is about 11*. Should either transfer try and match that angle upwards?

[wobbly]

The A port radials as they are, are good for mid power - but having the A port up at 132 is super high so epoxy filling the roof to get mid 20* axial on them
may let you drop down some timing as well.
Having the A port higher with the rest staggered down is good for a non powervalve engine - as is the steep backward A port radial - sacrificing peak for band width.
But with a T port as drawn you would need to be up close to 200* with over 90% width to justify that big number on an A transfer.
Getting the A port axial up at 25* puts that flow column up over the B ports, that if aimed directly at each other collide, slow down and attach to the boosts flow up the rear wall.
This all fits in with Frits leaning tower principal of a correctly directed efficient loop scavenging column.
As usual the ports need to be analysed properly to get them synergistically STA matched to the end use.

[peewee]

Wow! Thanks Wobbly.
So you think the A port directions are OK? I thought they were supposed to converge somewhere, but not as far back as these would, if they actually did. If you know what I mean.
I don't want to raise the ports since the A duration is already 132*, so I'm going to have to widen them anyway.
Thanks again for the guidance on doing that.

The piston dome height is 2mm, so the edge angle is about 11*. Should either transfer try and match that angle upwards?

if you look at the cardboard disk on the previous page, it sounds real similar to what wobbly is describing, unless im misunderstanding him. it might give you a general idea what to do. anyways ive learned a couple things the hard way. if you bring the B ports farther around back, be sure to pay attention to the ring pin locations like wobbly said. you can grind the port very close to the ring end but atleast let the ring end have alittle wall surface to ride on. ive let the ring end ride on alittle over 1mm of wall surface and never had a problem but it might not be a bad idea to use alittle more than 1mm though. better safe than sorry i guess but its your call

also if you bring the B port around back a significant amount, be sure the duct can be made of appropriate size also. seems like frits once said the rsa B window area was slightly larger than the duct opening but im not sure if its a good idea to have the window extremely larger than the duct opening. perhaps the shape up through the duct may be a factor in the size relationship between the window and duct entrance but i dont know

[peewee]

this might help you also. what i did is marked my ring pin locations with red marker. then use blue to mark where i wanted to grind the window. theres not much room between the ring end and window but it worked fine and i never had a problem with it

[Frits Overmars]

If anyone has the time to comment, I'd appreciate any opinions on the transfer port angles shown in the attached images.
Attachment 300252Attachment 300253

Here are some suggestions:

Getting the A port axial up at 25* puts that flow column up over the B ports, that if aimed directly at each other collide, slow down and attach to the boosts flow up the rear wall.This all fits in with Frits leaning tower principal of a correctly directed efficient loop scavenging column.

You'll find it here: http://www.kiwibiker.co.nz/forums/sh...post1130452977

[lodgernz]

Here are some suggestions:

You'll find it here: http://www.kiwibiker.co.nz/forums/sh...post1130452977

Thank you Frits. I'm ashamed to say that I'm familiar with both of those posts, and I've pored over them for hours, but I'm still struggling to fully understand the details. I'll try again (blush)

Thanks also Wobbly and Peewee for your good advice.

[lodgernz]

Frits, I also have a question for you.
Attached is an image of another of your wonderful posts from the pit-lane.biz GP125 thread.
In this post you give working target values for the blowdown and transfer STAs of the RS125A, but you don't offer a value for the exhaust.
I infer that the STA for the exhaust itself is less important than that for the blowdown.
Is this correct?

[senso]

If the crm80 is 75cc honda engine that I know, be very carefull with the exhaust port, the casting is thin, with some radiusing only in the liner you can probably get to 190º(around 22 mm), then the exhaust duct will be narrower and if you try your luck you will rupture it, measure everything first.

And thanks for showing those measures, might come in andy when I get to re-assemble my ns-1 might as well re visit the cylinder, but I'm also striked how far back the A/primary transfers shoot.

About the ducts, the nsr/crm 75 engines have plenty of room in both the crankcase and in the cylinder to carve so nice big ducts.

[Frits Overmars]

Frits, I also have a question for you. Attached is an image of another of your wonderful posts from the pit-lane.biz GP125 thread. In this post you give working target values for the blowdown and transfer STAs of the RS125A, but you don't offer a value for the exhaust. I infer that the STA for the exhaust itself is less important than that for the blowdown. Is this correct?

Yep (that should have been my answer, but the forum software insists that I use at least ten characters. So here you are).

[wobbly]

Here is a typical STA analysis that in practice made exactly the power predicted - less around 12% losses as shown by RWHp on a DynoJet with
a heap of added load to simulate aero.
The blowdown and transfers are a match ( this engine has 8 transfers so doesnt need extra STA ) but the Ex STA is well low - makes no odds at all to the power made.
In fact as the duct is a stock TZ350 size its reduced area and volume would be helping the overall power ability.

[lodgernz]

If the crm80 is 75cc honda engine that I know, be very carefull with the exhaust port, the casting is thin, with some radiusing only in the liner you can probably get to 190º(around 22 mm), then the exhaust duct will be narrower and if you try your luck you will rupture it, measure everything first.
And thanks for showing those measures, might come in andy when I get to re-assemble my ns-1 might as well re visit the cylinder, but I'm also striked how far back the A/primary transfers shoot.
About the ducts, the nsr/crm 75 engines have plenty of room in both the crankcase and in the cylinder to carve so nice big ducts.

Thanks for that warning Senso. The CRM80 is the same cylinder as the NSR75/80.
If your NS-1 is a 50, those transfer angles of the 80 won't be correct as the cylinders are quite different. If you have a Euro NS-1 75 then they will be the same.

[lodgernz]

Yep (that should have been my answer, but the forum software insists that I use at least ten characters. So here you are).

Heh heh... Thanks Frits, good answer.

Here is a typical STA analysis that in practice made exactly the power predicted - less around 12% losses as shown by RWHp on a DynoJet with
a heap of added load to simulate aero.
The blowdown and transfers are a match ( this engine has 8 transfers so doesnt need extra STA ) but the Ex STA is well low - makes no odds at all to the power made.
In fact as the duct is a stock TZ350 size its reduced area and volume would be helping the overall power ability.

Thanks Wobbly, fascinating stuff. Can I take it from your comment that the engine made the power indicated for the transfers and blowdown, despite the exhaust indicating a lower possible HP?

[senso]

lodgernz its an euro ns-1(or as known in Spain NSR 75R).
The 50cc cylinder unfortunatelly has a simple oval exhaust port, but suffers from the same problem the outside of the exhaust duct sits at 21mm from the top of the cylinder, with some radius(maybe around 2mm curve radius) I was able to squeeze 21mm from top of cylinder to the start of the radiused exhaust port, but it them goes to a safer 19.5mm to keep some wall in the duct, I love my honda engines, currently I have two crm 50, and my ns-1, and I have four more crm and nsr engines for parts.

Funny thing regarding my tuned crm 50, it is just a turned head to bump the compression ratio to 12:1 with a 0.9 squish gap and around 50% squish band, I had a cr80 reed cage with brand new boyesen dual stage reeds that was going to the ns-1 but I tried it first in the crm, and low and behold after 6 months of use the reeds no longer close, and as expected, the top reed was covered in black carbon due to the lack of blowdown, has the engine will happily rev up to 14k rpm(short transmission ratio to ride in the woods around the house), the piston is covered in a uniform layer of carbon as well.

Is this normal to happen to reed cages that run without the metal stoppers?
The reeds that are worse are the bottom ones, it makes sense in my head, they are the ones that see first the intake pulse and there is also a huge port going straight down into the crankcase.


Wobbly, there is one thing that confuses me a lot about the STA values for the reed-cages in engMod.
It reports in your example the Reed Block Ports has having an area of 1160.66 and then it says that the Reed Petal Opening has an area of 2950.
Is the first value the area of only the reed block ports and then it accounts for the angle of the reed cage and how much the reeds limit that area?

[wobbly]

The Ex port being smaller than the "old " required STA numbers in fact contributes to making even better power, as the duct velocity is higher at small port openings.
My experience has found as well that in a single Ex engine having the duct exit @ 90% of the effective port area makes the best power.

Re the reed STAs in EngMod - its the reed block ports that matter the most.
If the actual port effective area is too small, that becomes the choke point for power.
The reed numbers are the curtain exit area, these only become an issue if the stops are preventing enough lift and the reed curtain area is smaller than the port effective area.
So as long as the ports are big enough and the reed area is equal or greater, then the reed will work fine if the STAs match what you require.
Reeds do self compensate somewhat in that a small reed will simply be forced to stay open longer by the flow into the engine - so in many cases very little power is lost.
In fact they can and do work better than a reed that is oversize for the required application.

[F5 Dave]

In My triple ex port MB100 I am finally recreating (version one was about 1992) I have made the aux ports an ok sort of size but the cross sectional area of the tunnels are the compromise due to 'through barrel' studs (although I have a plan to avoid that, but it a bit too much hassle). So I've ovalised the tunnels to compensate but I'm wondering if just the reservoir of reasonably large aux ports will still benefit the initial blow down or will the tunnel be the ultimate restriction as I've read before in Tom Turners notes.