ESE's works engine tuner

[lodgernz]

Thank all peoples for decompresion valve ideas!!!
I own 8 CNC machines and will try make automatic decompression valve.
For me easier make than buy.

One can never have too many CNC machines

[aljaxon]

Attachment 354493

Not an attempt to cut off Frits, as his 7 degree rule is most likely tested and accurate, but I like to use 7.5 degrees as max, simply because thinking about fives and zeros when it comes to angles is easier than fours and eights.

Here is one I recently did that uses 2.5 degree cone ends for a total of 5 degree junctions for the first few sections, then it goes to 5 degree cone ends, and finally 7.5 degree cone ends for the diffuser hook. This keeps the head pipe more straight, and using multiples of 5 keeps things quick and easy for the layout method that I use.

The cheap Cone layout software eliminates the need for cutting and turning, which shortens your pipe and has to be accounted for in the design process. You do need to add the material thickness to your diameters in cone layout as we have found them to be that much smaller after final measurements.

that cone program is excellent but as you say gives you dimensions for the centre of the material used. so the thickness needs adding on to the diameters. using that software and autocad to draw the centre line of the header to work out the angles to fit the bike i dont have to adjust or pie cut any of the metal cones. i used to make card templates and adjust the angles . much easier to print out a modded dxf file and cut the card. and then adjust to get the right fit. then once worked out its a simple case of sending the dxf files to the laser cutter all dims to 1/10th of a mm. works for me. now i dont even need to make the card cones. i just put an exit angle of 5 degrees on each cone and that gives you a bit of leeway. i even fiddle the phi figure to get the seams out of view and it looks like you have done that too condyn. if you arent bothered about visible seams then a 5 degree exit and entry to each section on that cone program virtually eliminates the need for any pie cuts. its all in the planning.



just made some 19mm rollers so as to be able to roll my 25-30mm diam header sections. ive always had to bend them around tubing and it took a while matching up the seams of each section.
i was looking forward to making one of those pipes with zillion blue-colored 'titanium' welds, going for the smallest angle and the most segments and the most labour. as per frits comment.
(although mine are in mild steel.)
wont go that far but i want to have less of the spiders legs look to the headers.

a pal has just ordered the mota8 upgrade and well have a bash using that. does it allow for incorporating a wobbly duct?

we've made good cruising pipes using wobblys suggested percentages. including a flukey fat pipe that does everything. now to make widish powerband pipes suitable for 4 wide spaced gears. 7-11k and 9-13k,

[wobbly]

Here is the latest 4DP racebike pipes cut up in SolidWorks such that the 3D bends all have the cut seams in line - means the pipe can be assembled without the bike or a jig except for the rear mounting.

[wobbly]

Mota doesnt know who Wobbly is , but you can enter the " correct" duct exit into the input and it wont have any idea what you have done.

[Javier Ruda]

I’m using Janbros spreadsheet for calculating STAs and having a good match between transfer and blowdown.

For the auxiliary exhausts, which horizontal angle should I use?

It’s like a 90° turn from cylinder wall to auxiliary duct. Should 45° be ok for the calculation?

[wobbly]

The axial down angle of the Main and Aux affects the effective area value due to the Cosine.
But horizontally you simply enter the actual flow width , not the Chordal at the bore face.
I dont use JanBro's spreadsheet , but that is how its normally done.

[Javier Ruda]

Thank you wobbly, I will use the section of the duct, and forget about the port area.

[wobbly]

You have to be careful though with the Aux flow. Much of the bulk flow occurs close to the port opening width , due to the high pressure ratio across the port at that timing.
With very well designed triangular shaped Auxiliary ports the actual effective area is a combination of the chordal area at port opening , and the duct area behind the port.
So to represent reality both must be taken into account - as does EngMod , but I don't know about a spreadsheet based calculator.

[Javier Ruda]

I understand, it is too complex for a spreadsheet.

I will do an assumption considering that the original Rotax 122 had matching numbers for blowdown and transfer. So I could use the auxiliary duct angles used in the spreadsheet that fulfil that assumption. The shape of the new duct is very similar, just only a bit wider and taller to be 5° below exhaust opening. For the port window, I didn’t dare to do it very triangular, just only flat and slightly wider at the top.

[skako]

Hi,
which is the optimal duration of measurement on the dyno desk (it is related to the inertia of the dyno), for the engine to reach from 2/3 RPM to max. power RPM.

[wobbly]

The inertia and the gearing should be such that you can do three back to back WOT runs and the egt does not change at the end of each pull.
Not enough inertia , or too short gearing , and the pipe heat will increase more , as you repeat the runs.
Of course you need sufficient airflow to get repeatability as well.

[skako]

The inertia and the gearing should be such that you can do three back to back WOT runs and the egt does not change at the end of each pull.
Not enough inertia , or too short gearing , and the pipe heat will increase more , as you repeat the runs.
Of course you need sufficient airflow to get repeatability as well.

I'm interested in what time interval it is most often, 5, 10, 20 seconds, so that I don't take too much inertia of the flywheel for my needs.
I also have to pay attention to the max. allowed RPM for the flywheel so that a possible accident does not occur.

[wobbly]

My engine dyno for 50Hp KZ engines takes 12 seconds from 9000 to 15000 WOT.

[skako]

Thanks wobbly for the info.

[F5 Dave]

12 seconds in one gear? They will never do that in real life except at Bonneville surely? Assuming they have a go-kart class.