ESE's works engine tuner

[Frits Overmars]

Would a custom combustion chamber need to be made to match the piston edge...

Obviously. But that is true for all piston shapes. And as the piston edge is radiused all-around, matching the combustion chamber to it is a piece of cake.

I'm sure we'll need to maintain a sharp edge on the piston dome at the transfer ducts to promote piston cooling also..

How do you figure that? A radiused piston timing edge at the transfer ports greatly promotes flow attachement to the piston dome, which does wonders for both the flow coefficient and the piston cooling.

and maybe sharp edge on the piston dome and on transfers windows help to resist little, when exhaust gas enter to transfers.

Flow from the cylinder into the transfers must of course be discouraged, so the top edges on the transfer windows must indeed be sharp. But a radiused piston top edge has very little influence on flow in that unwanted direction.
The nozzle effect that we hoped to achieve at exhaust opening, does not play a role at transfer opening because, even if the blowdown time.area has been insufficient and the cylinder pressure is still higher than the pressure in the transfer ducts, the pressure ratio will be subcritical, so the flow will be subsonic.
The benefits of a radiused piston top edge for better transfer flow into the cylinder and better piston cooling are far more important.

[Jannem]

It's my pleasure to get that # 1 question out of the way then: there is no mass flow limitation.

One down.

The picture with the nice colours below shows how at the beginning of exhaust port opening, the flow tries to cling to the exhaust duct ceiling, using it as a nozzle. The exhaust duct floor is too far away to help create a full nozzle, but that temporary half-nozzle at the ceiling is worth thinking about. How can we encourage that?
That's why I'm in favour of a radiused top edge on the exhaust port and a radiused piston top edge. It may not prevent a whole lot of energy loss, but every bit helps.
Attachment 334948

That makes me want to try another, perhaps a bit oddball porting idea in addition to the radius.

[Frits Overmars]

That makes me want to try another, perhaps a bit oddball porting idea in addition to the radius.

Keep 'm coming Jannem .

[lohring]

Loft i great for exhaust design! you may need to do some 3D sketching witch can be a bit tricky. For transfer ports i recommend using revolving! get a straight over and underside with the correct angles whit loft can be a nightmare.
expect a lot of error 40

That's a really great hint. Thanks, I'll try it on the Aprilia clone cylinder that's my next Fusion 360 project.

Lohring Miller

[Muhr]

I got mail from som members about if it passable to by a cylinder. The short answer is no, the long answer is that I make these cylinders to an engine I have drawn and will not fit any other engine. If it turns out that the cylinder works well and there will be a cylinder over, then we'll look at it. This is supposed to be a hobby project.

i got a question if te bolt pattern is the same as SX i attached a picture

When I was doing a lot of engine reconditioning work we used to get engines with wet liners that had pin holes right through them.

The culprit seemed to be localized cavitation, a bubble would form on the liner surface then collapse. This happened often enough in the same place that the resulting water hammer against the liner would eventually eroded a hole through it.

I thought it was localized boiling but it is apparently a result of cylinder wall flexing.

Interesting reading!

[Greg85]

Hey guys!

I found some nsr500 engine pics! http://www.geocities.jp/noda_keni/h/...0/00nsr500.htm

hello would anyone have any pictures or info on the reed valve honda nsr 500gp thanks

[Muciek]

On honda nsr forum there are threads with 500 v2 , guys were restoring them to track condition. There were pictures of reeds cylinders ect , but for the 4 cyl I don't think theres much more than You could find here in Husaberg galleries.

[JanBros]

Wobbly, some pipe questions if I may :

End of header is always 31 to 33% and end of diffuser is always 62 to 68%.
a 2 stage header with something like 3.5/5.5* for 2/3 - 1/3 lengths from the piston

your header angles seem more steep than any other, is this beacause your spigot/exhaust duct is longer than simply bolting the exhaust directly to the cylinder and that it takes away length from the 31 to 33% header length, so the angles need to be steeper to arrive at the correct diameter and the end of the header ?

and do you have any suggestions about percentages for diffuser lengths when using a 3-stage diffuser with the steepest stage in the middle ? for the Aprilia tubo 102 it seems to be +/- 25/58/17%

Three angle rear cones were a legacy design that Jan was forced to use, as Frits explained.
But it is a long time issue for me that so often a sim will be strongly telling me that the system works well ( and it annoys Neels as well I know ) but in reality I have never been able to get more power on the dyno
than a 14* straight tailcone - believe me I have waisted so much time on this, and have given up.

when "always" using a 14° rear cone, do you adjust the total length of the pipe somewhere to get it back in line with the needed length, or do you simply "calculate" the total length, and then just stick a 14° cone at the back for all the reasons you mentionned before ?

[lodgernz]

How do you figure that? A radiused piston timing edge at the transfer ports greatly promotes flow attachement to the piston dome, which does wonders for both the flow coefficient and the piston cooling.

A radiused piston edge makes port opening determination more difficult. The 45º wire trick won't work. I suppose it could be done with 80º wire if the radius was an accurate 20º to the piston face.
Any better ideas?

[wobbly]

The 3.5/5.5 header angles came into being simply because so many engines liked that combination.
But be wary of monkey see monkey do.
The end result is always project specific, as I have just completed my TM KZ10D pipe and that ended up with 25% header and 2.1/3.1*.
This was due to a large step up from the cylinder exit to the header entry, and it made more power with a steeper first diffuser section and the less steep headers..
Just to confuse the issue even more - this is the first application where the 3 angle rear cone has made a significant gain over the existing ( two angle ).
The C model had 29.73 and 31.64 ( about 50/50 length ) the 3 cone has 28.61- 30.95-33.29 and this made a heap of overev power, plus a little more going up
to the same peak number ( where the engine drops back to after a gearchange ).
But going back,the steeper header angles work well on " most " high performance engines, just not the kart engine that is really only used between 10500 and 14500 all day.

[JanBros]

tnx, allthough part of my question was 3-stage diffuser, not the baffle.

[wobbly]

The Aprilia pipes were not that clever, in that Jan had a devil of a time making them work.
This isnt the correct way to do things, ie make a compromised pipe, then be as clever as all hell with the porting to make that pipe work.
If you reverse the % you quoted, to something like 17/59/24% then the steepest diffuser section can become the last, and this is superior in every way for
a very high specific output engine at very high rpm.

[nitro2tfx]

When the ratio between upstream pressure and downstream pressure reaches a value of about 2, flow velocity will reach Mach 1. Lowering the downstream pressure any further will not raise the flow velocity any further.

There is one little extra tidbit that goes with this, that isn't well known. As mentioned when the pressure ratio between the upstream and downstream reaches about 2 the flow velocity reaches Mach 1 and as such the flow velocity can't go any greater by lowering the downstream pressure, and it is generally assumed from that, that the massflow can't go any higher by lowering the downstream pressure.

Seems logical of course, BUT it is only true for certain shapes such as a nice bell mouth entrance etc. When less favorable shapes are used, an orifice being one example (but certainly not the only example), the massflow can be increased by lowering the downstream pressure below the critical Mach 1 ratio. Mach 1 is never exceeded, but the unfavorable flowpath of the unfavorable shape, improves as the pressure is lowered further, causing the massflow to increase. Most flow paths in an engine are not as bad as an orifice, but not as good as a bell mouth either, so there is some wiggle room here and there regarding the massflow vs. upstream to downstream pressure ratio.

[philou]

A normal exhaust pipe to this form :



some exhaust pipe have this shape :



Does the shape affect the operation of the exhaust pipe ?

[Jannem]

A normal exhaust pipe to this form :



some exhaust pipe have this shape :



Does the shape affect the operation of the exhaust pipe ?

The lower one certainly is worse from the pressure recovery viewpoint. Flow is going to hug the header short side and head towards stinger, leading to more separation in the one-sided more abrupt diffuser part.
From the wave tuning perspective, I doubt there's much difference. If you consider the actual through flow can be squeezed out from the stinger, the difference in flow efficiency may be mainly theoretical.

So, whether it makes a difference in the real world, I'll leave the experts with practical experience to comment