ESE's works engine tuner

[Frits Overmars]

The trouble with these long posts is that I have to then edit and re-edit for ten minutes after I put them up here! Frits, as I recall, we are talking within the realm of your direct professional and educational specialty here. Is there any sort of "cookbook," meaning a technical explanation understandable by laymen, for low-drag cross-sections of gas-flowing ports that are making sweeping corners, and relating this to velocity and so forth???)

I know all about long posts (or posts that require a lot of time) and the need to re-edit even before I get to post them for the first time because other people were quicker than me. Sometimes those quicker reactions allow me to lay back and do nothing at all, for which I am grateful.
A cookbook that comes to mind is the classic 'Practical Gas Flow' but if I remember correctly it does not dive very deep into the details you are mentioning.

[senso]

Thanks for the response Frits, I have already seen your remarks about the clogged water passages in the rotax cylinders, and again thanks for the heads up.

Regarding the fact that buying a new cylinder, it would be more expensive, because the idea is to give a new life to an old stock cylinder that a friend of mine has, so buying cylinders is unfortunatelly out of question.
When I have the cylinder with me I will inspect both of them, because he has a good cylinder with just the oval port, and a seized cylinder with the oval plus the auxiliar exhaust port.

[Frits Overmars]

Regarding the fact that buying a new cylinder, it would be more expensive, because the idea is to give a new life to an old stock cylinder that a friend of mine has, so buying cylinders is unfortunatelly out of question. When I have the cylinder with me I will inspect both of them, because he has a good cylinder with just the oval port, and a seized cylinder with the oval plus the auxiliar exhaust port.

My thoughts about costs were based on Peewees proposal of cutting the waterjacket open and then welding (and re-nikasiling!).
Regarding your original question about the possibility of adding aux exhaust ducts in a cylinder that has none: I suppose that in the interest of economics Rotax uses the same coolant cores for all types, so there should be sufficient material in the right places. But I never checked....

[wobbly]

4T ports have been studied to death, and the best flowing examples have minimum turn to the valve axis and some have a flat floor giving a D shape to keep
velocity up on the short turn.
But as is described in the classical texts the CSA where the duct turns, is made bigger, and then necks back down to the venturi under the seat.
In a 2T we use the D concept on the short turn , but unlike a 4T where they are trying to get equal flow discharge radially thru the curtain area - and impart swirl, in a 2T we are
trying to achieve different things.
Firstly is to keep the flow accelerating uniformly down the duct length, and secondly direct the flow uniformly so the discharge exits into the cylinder with NO swirl ie a coherent column.
Thus we cant use the expansion theory around the turn, and IF the side walls were parallel at the exit then the best shape would be a rectangle to initiate and then preserve the columnar discharge shape.
But as is mostly the case, the front and rear walls converge radially, so the inner wall is best angled as an average of the two, and the square gets tipped over into a non parallel parallelogram ( whats that called ? ).
I have seen plenty of results from CNC anemometric flow visualising software, and have never seen any evidence that the flow in the corners of the ports is "lagging " behind due to
excessive wall friction.
So it would seem that the current techniques of linear area reduction increasing the velocity, and duct walls that initiate the radial flow directions early on - are the best compromise between raw
flow numbers ( cfm ) Vs a high discharge coefficient with a coherent exit stream.
As always no free lunch.

[peewee]

smitty i dont have a answer why them ktm ducts are shaped the way they are. but im sure ktm is more than capable of designing a better duct that would produce more power. we have to remember the intended purpose of the engine however. sometimes more is less. im not aware of many people that would be sucessful on a motox track with a 80hp bike. ktm could have borrowed a few ideas from the rsa and probly made the bike too powerful to ride on most any track but thats bad for business. without customers you may as well go sit in the welfare line and collect free soup.

so maybe that particular paralellogram type of duct shape doesnt give the most power but it may offer some other advantage and give a better power spread possibly ? just a guess . still its interesting that the latest generation of cr250 had a duct entry shape real similar as well. could ktm and honda be so stupid as to not put a single thought into duct shapes ? i kind of doubt it. but even with its paralellogram shape and sqaure corners, those engines manage nearly 50hp without much tinkering other than some carb adjustments.

if ktm continues their 2t development, which im sure they will, 10yrs from now im sure they will have something better, with less fuel consumption, while still maintaining the same amount of power. i wont mind as the race fuel around here is $10gal for the cheapest stuff

[peewee]

As long as the porting STA numbers are correct for the rpm and you have EVERY other aspect of the design spec'd to suit that rpm then
the higher the rpm the higher the power - as long as the torque holds up for long enough.
In the case of the Banshee style engine I have done designs with peak power at 11,000 and usable overev to 12,000.
With close to 100 RWHp on a Dynojet this is reliable and doable.

.

ive seen a pile of graphs using oem yami cylinders and dont recall any of them making it past 10.5k before the curve falls off. these engines were mostly done by big name shops. if i could do that good or even better i think it would be quit a accomplishment since my work shop is a measly one car garage

[F5 Dave]

You'd think from what some people say of me I'd be the Devcon king, but if anyone has some better solutions for smearing filler in small transfer ports I'd appreciate it. Actually I've swapped to JB Weld for the mean time as I can't afford more Devcon at this time of year & people use JB successfully in 4 stroke inlets so it can handle the heat.

But I usually use a screwdriver & in an inlet a wet finger will smooth it nicely. But in transfers of 100cc, or worse 50cc barrels getting it in nicely can work some days & be a major rework battle the next. I've even tried small brushes, but not with much success.

I should really heat it some to make it flow like I do in winter, but its warm here now so I haven't been doing so.

Techniques?

[peewee]

if it were me i would probly use the stucco verde stuff. seems like it was $15 for 3' the last time i bought it. thats enough to do quit a few 100cc barells. plus its more like putty instead of a runny mess like jb weld. just dont use it with methanol. theres also some stuff called moroso a+b thats not very expensive and would surely do many 100cc barells. its a 2part putty also. i bought some but havent used it in a engine yet. im thinking it would work great like the stucco verde. probly shouldnt use it for methanol either

can usually find it on ebay for $28 with free shipping

http://www.moroso.com/eb/catalog/nav...nuId=main.menu

[peewee]

smitty i think youll agree this honda cylinder looks pretty similar to the previous ktm i posted. A entrance is darn near sqaure. B has the paralellogram type of shape. now if you look at the rear studs on both cylinders, there is more than enough material they could have made the B entrance most any shape they wanted but for some strange reason they chose the shape they did. im stumped as to why. so these shapes may not give the most power but there must be some advantage ? another thing i never found a answer to yet, not that i really care to find the answer either but its one of them things that keeps me scratching my head..... why are all the modern japanese and ktm 250cc engines using the same length rod with 72mm stroke ? hell heres another head scratcher, why do all modern 250cc engine use the 66.4mm x 72mm bore stroke combination ?

[speedpro]

Techniques?

I prep the surface, like you do. I cut a 3mm wide strip from say .8mm mild steel and very carefully bend it to the shape I want the devcon to be. I test this without Devcon by simply fitting it to the port and making adjustments to the shape so the curve matches what I want in the port.

I then jam some Devcon into the port more or less where I want it and then start carefully patting it into shape using my shaped tool. I keep it wet so the devcon doesn't stick and just keep patting away until the devcon is where I want it and the correct shape. Typically there is an amount displaced which can be removed before it dries or I find it easier to let it partially set then lever it out.

I could load a piccy of a couple of tools when I get home. It's too hard to pull up pictures while I'm riding my scooter home.

[Ocean1]

Techniques?

Can you make a devcon mould of the area you want to re-profile that you can subsequently remove from the port?

If so then cut some strips of sheetmetal that you can bend into shapes likely to enable you to deposit devcon over the required area. Use a release agent (glad wrap?) inside the port and then apply the devcon as thick as you can while still being able to extract it. Make some marks in the devcon so that you can re-position it accurately later.

Remove the devcon plug, (I suppose you could use polyester, (bog) and re-shape it as required, it obviously needs to be big enough to cover more than the area to be modified. If you can do it accurately weigh the plug before and after, if not try to get some idea of the volume/mass involved. Clean up inside the port to the usual standard and practice refitting the plug accurately.

The trick then is to apply a little more than the above resin over the port wall, apply release agent to the plug and carefully refit the plug over the fresh resin. When you're happy it's all in the right place slip a condom over the plug and inflate it. With air. 3-4psi should be heaps. You can use silicon lab tubing if you can get sizes that'll work, but you get the idea.

When it's hard pull the lot apart, (even with a good release agent it can take a bit to get the plug out). All going to plan there should be a perfectly shaped port inside there.

[F5 Dave]

I prep the surface, like you do. I cut a 3mm wide strip from say .8mm mild steel and very carefully bend it to the shape I want the devcon to be. I test this without Devcon by simply fitting it to the port and making adjustments to the shape so the curve matches what I want in the port.

I then jam some Devcon into the port more or less where I want it and then start carefully patting it into shape using my shaped tool. I keep it wet so the devcon doesn't stick and just keep patting away until the devcon is where I want it and the correct shape. Typically there is an amount displaced which can be removed before it dries or I find it easier to let it partially set then lever it out.

I could load a piccy of a couple of tools when I get home. It's too hard to pull up pictures while I'm riding my scooter home.

Thanks Mike I'll try that tonight.

[F5 Dave]

Can you make a devcon mould of the area you want to re-profile that you can subsequently remove from the port?

If so then cut some strips of sheetmetal that you can bend into shapes likely to enable you to deposit devcon over the required area. Use a release agent (glad wrap?) inside the port and then apply the devcon as thick as you can while still being able to extract it. Make some marks in the devcon so that you can re-position it accurately later.

Remove the devcon plug, (I suppose you could use polyester, (bog) and re-shape it as required, it obviously needs to be big enough to cover more than the area to be modified. If you can do it accurately weigh the plug before and after, if not try to get some idea of the volume/mass involved. Clean up inside the port to the usual standard and practice refitting the plug accurately.

The trick then is to apply a little more than the above resin over the port wall, apply release agent to the plug and carefully refit the plug over the fresh resin. When you're happy it's all in the right place slip a condom over the plug and inflate it. With air. 3-4psi should be heaps. You can use silicon lab tubing if you can get sizes that'll work, but you get the idea.

When it's hard pull the lot apart, (even with a good release agent it can take a bit to get the plug out). All going to plan there should be a perfectly shaped port inside there.

Thanks but I don't think you could remove the complex shape.

[Ocean1]

Thanks but I don't think you could remove the complex shape.

Murphy strikes again huh?

Not even in pieces?

[AndreasL]

When talking Devcon and the like...

I have this (s*%#)cylinder with way to high transfers (Approx 132-136° AFTER taking 2.3mm of the base surface!).

But I still need to lower the transfers by 1-2 mm roughly.
Gas torch and a skilled welder (not me) most probably will do the trick...but...

Any one have had succsess using any other method to change or reshape an area where we have constant abuse from one or two piston rings running back and forth? To comlicate things even further, as you all know, this part is "edge shaped".

Yes, I know "Get an other barrel!", but this is more or less what is avaible. Really bad manufactured items making performance parts for a SB Chevy look like race ready out of the box.

I'm naive enuff to hope for a simple sollution here. LOL