Holset HX50 Supermoto Jetbike

[racket]

Hi Scott

Thanks for that .

A very good find indeed :-)

Cheers
John

[slittlewing]

No worries!
A little update.. today I cut the old combustor cap off, ahead of replacement with a new one in 12mm thickness.
At the same time, I inspected the flame tube. A new "funnel" will be made, welded to the new top cap, and I will get rid of the "fins" which have suffered some heat damage on the slip joint. Thus, the new slip joint will interface purely on full tubing and sit a little further back:







Thats the plan anyway!!

The turbo will sit 4mm further back on top of the combustor, meaning the hole in the top cap will now be "offset".
This is to give more room at the front of the frame, where the silicone expansion hose attaches to the compressor.



Cheers

Scott

[slittlewing]

A little video of the previous failed top speed run and turbo damage..!

New laser cut parts should be arriving this week to make the combustor changes and accommodate the 12mm thick top cap for the new turbo





One thing, my existing flame tube is designed for hole area based on 63mm inducer. The old turbo we think was close to choke region I guess due to oversize turbine to compressor ratio (it was presumably designed this way for the fact it had a wastegate also). I wonder for the new 69mm inducer whether to add further hole area to the flame tube, or leave it as it is?

Cheers

Scott

[racket]

Hi Scott

Normally I'd say open up your FT holes a tad to accomodate the potential for extra flow , but in your case I'd recommend leaving things as is because of your FT cross sectional area , which at 4.5" dia is below the 3 times inducer area ,....... 69 mm = 2.71" dia = 5.79 sq ins X 3 = 17.38 sq ins = 4.7" dia required .

The extra pressure drop resulting from the ~20% undersized hole area will hopefully provide extra turbulence/mixing of fuel/air and promote faster combustion .

Also with the turbo being new , you can push it a bit harder and producer a higher pressure ratio that will also compensate for the "undersized" holes and area .

Yep , leave as is at this stage :-)

Cheers
John

[slittlewing]

Thanks for the informative response as always John! I will go with your recommendation 🙂

I am indeed hoping that with the new turbo, maybe 4:1 PR maybe possible respecting temp limits (hx50/55 comp map googling says it should be) so that makes sense. I was thinking of changing my injector from the current 13.5GPH to a 17.5 or 15.5 to help with this cause.

With my old tertiary zone “cone” that went from the slip joint to the top cap, it deformed during the bending process somewhat, meaning I had to slit the FT and accept a leaky seal.
Old:


With the new 4.5 tube I have a perfect fit before forming the cone. I have made lots of tooling (3D printed) to try and keep the area at the slip joint circular and try and reduce this leak path

New (before forming cone)


Cheers

Scott

[racket]

Hi Scott

With slipjoints the "inner" tube always runs hotter than the outer so some "rattle" when cold is acceptable , a 4.5" stainless tube will expand ~0.045" with a 500 C temp rise , so a ~1mm diametric difference between inner OD and outer ID wouldn't be a problem...............LOL, they tend to "form" themselves when heated , so some out of roundness is also OK.

A slightly larger fuel nozzle wouldn't hurt

Cheers
John

[slittlewing]

Sounds good, my slip joint should be leak-free then!!

I had laser cut goodies arrive this week to suit the new turbo:




After cad-ing a flat pattern, I cut the 4.5" tube appropriately and used my "expanding cone" pieces inside it to keep it round, whilst forming (or at least trying to haha)










This new transition is made over a shorter distance (and therefore greater bend angle) than the old one. Coupled with the expanding pieces keeping the other end round, the transition was really hard to form. I couldn't use heat to help, as my PLA pieces would have melted.

I am therefore switching to "Plan B" which should be an easier solution - a folded transition:



Fingers crossed anyways

Cheers

Scott

[racket]

Hi Scott

Love those laser cut bits, they always look so "perfect" compared to my home made ones .

Yeh , the transition piece seems to take more work than the rest of the flametube combined , no easy solution

You made some nice printed parts there

Cheers
John

[Sweetenough]

Hi Scott,
Lots of nice new parts 
To bad that it did not work out, but I think your plan B will be an easier solution
I made a quite short transition with folded transition, worked out quite nice.
Good luck with the fabrication!
Kind Regard
Thomas

[slittlewing]

Cheers Chaps, John I have to admit I quite dislike grinding and am not very good with cutting complex metal shapes. The 12mm top cap came really nice and I probably couldn't have even bought a piece of 12mm steel plate off ebay for the same money, so it was a no brainer to get it laser cut!! The 3d printer is turning out to be quite a good "jig making" machine haha.
You made a lovely job of that transition Thomas, it gave me motivation for the plan B!!

So I managed to make a "flat pattern" on CAD and transferred it to some 1.5mm stainless. I was then able to fold up a 2 piece transition, earlier this week:








Because I have offset the turbo flange 4mm from the FT circular centreline, I used my printed jig to align everything whilst tacking together:




Finally, I managed to get some reasonable tig welding done (I am very much a beginner) using a gas lens, 10LPM flow (much better than 7LPM last time I tried)






Very pleased with the end result. I would recommend this method for anyone trying to create a transition, if you have access to a metal folder. It did take me a couple of attempts - being just 1.5 degrees out on 10x bends = 15 degrees off!

A friend also turned a new spark plug boss for the engine on a lathe, which I hope to weld in this week once I get delivery of a step drill.

The next job is drilling the new compressor housing for an impingement tube. Last time I did this "by eye" and it didn't end up exactly where I wanted it on the compressor wheel. This time I am (predictably) making a drilling jig:




Fingers crossed it works out...

Cheers

Scott

[racket]

Hi Scott

Very "acceptable" transition piece ;-)

Now that drilling jig you're designing up would turn a crappy job into a precision one .......nice touch.

Development progressing steadily .

Cheers
John

[slittlewing]

Cheers John!! The drilling jig is now printed, but I stumbled upon a slight issue..

The new turbo compressor housing has a very deep "anti surge" section. I have modelled the impingement to act at a 45 degree angle, tangential to the rotor centreline, a few millimetres in from the exducer.

The impingement tube then comes through the deep anti surge pocket, and I want to avoid making a boost leak path so I guess it will need welding at the compressor wheel side, and dressing back.

The other end of the tube needs to avoid piercing the "scroll", otherwise that would also leak back into the surge port (which is too deep to lay weld inside).

I think how it is now should probably work, I just don't want to make the compressor housing into leaky scrap!!








Fingers crossed....

Cheers

Scott

[racket]

Hi Scott

If your tube is a reasonable fit in the machined hole you drill , I wouldn't be too concerned about leakage , you might end up doing more damage by welding at the shroud and creating a less efficient compression if the housing warps and a large area of the comps shroud has increased clearances , or even worse if it warps towards the wheel and reduces clearances to the point of contact .

If you calculate any leakage path around the tube it will only end up as a fraction of 1% of total flow areas at that point, a dob of silicone squeezed into any gap will surfice , keep any welding to the outer parts of the housing , and if you could tap the hole and thread the tube in it would be even better , welding always warps things .

Cheers
John

[slittlewing]

Thanks for the sensible advice John - good points well made!
I finished printing a “starter drill bit” jig (4mm) and then the 8mm to follow.
Have drilled through this evening and all went well aside from a small chip when trying to start with the 8mm on the curved shroud surface. I’ll see if my fabricator friend thinks he can put a tiny dab of weld on that without putting any real heat in and dress it back, if not I’ll leave it.

The good news is that the drill came through to the exact point predicted and without piercing the inner wall of the “snail”!







Cheers
Scott

[racket]

Hi Scott

Well done :-)

Cheers
John