ScottsCrazyBuilds Jet Kart

[slittlewing]

If boost pressure is above oil pressure it pushes past the ring seals and aerates the oil, also as the air can pass through the ring gap easily. The other way around this doesn’t happen due to viscosity and the “easier” path for the oil to return to tank at ambient than against the boost pressure into the engine. If you have a sensible delta pressure or course… (hence you can apply oil pressure with the engine stationary i.e. no boost and not see leaks past the turbine for example). In my early days with the “jet sled”, I had a clear plastic oil tank and you could see it bubbling loads with lower oil pressure than boost !
That’s my experience anyway 😂

In automotive engines, oil pressure is between 2 and 6 bar and boost is always below or at max one bar for normal cars. Granted they therefore use restrictors on the turbo oil feed line to reduce the flow and delta pressure. 

Cheers
Scott

[racket]

Hi Scott

Yep , we should never actually see pressurised oil at the seal , the turbo shaft oil slinger bits should throw off any lube exiting the bearings into the drainage passageways , its only when oil backs up because of poor drainage that theres problems .................we probably have pretty poor drainage compared to turbos simply because of our designs but our saving grace is positive air/gas pressures during running .

I've found theres always a bit of leakage at the turb end if I've been doing some static testing , but its not a problem , the main thing is to de-aerate the oil on its return to tank , so a nice distance drop onto the de-aerator plate .

Cheers
John

[slittlewing]

Hi All

A video of my new engine design and first fire up in old chassis, and on old ecu etc! 

Cheers

Scott 

[racket]

Hi Scott

Congratulations :-)

A challenging time ahead for you , embarking on new frontiers with those higher PRs .

I'll be interested in your new "numbers" as that comp is now working a lot harder and won't be as well matched to the diffuser , same with the turb stage NGV throats .

But its a good combo of wheels and should cope OK .

Yep , they keep getting noisier the more we crank them up, theres a lotta horsepower being generated and consumed in that "tin can" :-)

Your mate has made some nice bits, he deserves some congratulations as well .

Cheers
John

[slittlewing]

Many thanks John, it was certainly a relief when it worked correctly as there was no way back to the old setup! It needed a different start procedure and took a while to figure out how to light it, I thought we might be going home empty handed for the first hour or so!

You did a really great job on matching the wheels and choosing them along with the NGV angles and sizes etc. They seem to have no issue upto the 3.8bar 4.8:1 PR tested so far 👍

And Carl is awesome. He did a great job of getting the awkward pressed stainless parts to perfect clearances, same with the old turb snout that now becomes the inner of my slipjoint!
Cheers

Scott

[racket]

Hi Scott

Yep , the comp/turbo wheels are a good match , probably about as good as us DIYérs can get for a build , the turb wheel is a common unit, so readily available at a reasonable cost, and the comp is a rather forgiving design with its large backsweep , the in/out area ratio of the comp is weighted towards more modest pressure ratios , thats why I'll be interested in your high PR numbers to see if comp efficiency suffers .

LOL...........I felt for Carl watching him cope with that large stainless dome squealing its head off as he was turning it :-)

Cheers
John

[slittlewing]

Hi All,

Did a little video below on new tool, 3D scanning to produce the floor. Really fascinating bit of technology, and pleased with the end result!! 😍

cheers

Scott

[racket]

Hi Scott

Nice bit of kit :-)

LOL..........cleaning up the baby powder would have been fun , the workshop will smell sweet for a while ;-)

It'd be interested to see how the scanner would work on a comp or turb wheel for getting angles etc .............. some great tech available these days.

Cheers
John

[enginewhisperer]

I have scanned a comp wheel before on a basic desktop 3D scanner and it worked ok for something like getting dimensions and angles.

The tricky part is that the scan is essentially a 3D image, not a CAD file with solid dimensions, so for complex parts most of the work is in reverse engineering the real dimensions from the scan data.


I'd say it's a bit overkill for something like making a gokart flat floor - but it does save a lot of tape measure work

3D scanning / reverse engineering is actually one area I think AI will make a big difference.
If it could look at the scan data and turn it into sensible CAD models based on real material specs and logical design aspects like things being parallel and located at round number measurements it would save a massive amount of time.


Oh and cleaning up the powder and reflective dots is a huge horrible job!
I am still finding dots all over the place after my race car was scanned for aero CFD work.

[slittlewing]

Engine whisperer is right, you do have to reverse engineer a 3D image! However you could certainly take accurate measurements from a scan.

The baby powder is a bit messy but made it a little more fragrant in the garage compared to grinding dust hahahah. You can buy sprays that self evaporate but they are expensive so baby powder it is.

Making the Floor would have obviously been possible without, but a lot harder. I was able to get all clearances to wheels perfect including lock to lock on front, splitter that matches nose profile, diffuser to sneak under rear axle, cutouts for brake disc and all the bolt holes laser cut in one! I think I’ll certainly be using it a lot more on this project and others 👍

Cheers

Scott

[richardm]

Jul 6, 2024 20:26:56 GMT -5 racket said:

Hi Scott

Nice bit of kit :-)

LOL..........cleaning up the baby powder would have been fun , the workshop will smell sweet for a while ;-)

It'd be interested to see how the scanner would work on a comp or turb wheel for getting angles etc .............. some great tech available these days.

Cheers
John

Hi John! Remember I sent you some pictures of daughter's friend scanning that compressor wheel. He has done it again but on a special rotating table this time. Still waiting for him to translate the whole thing in usable data to machine the housing..Ill keep you posted 

[slittlewing]

Hi All,

Here was the first test of the new Afterburner and engine together. Highest thrust so far, a little “warm” of course! 

Cheers

Scott 

[racket]

Hi Scott

Nice A/B temperature :-)

Getting a suntan off that , can't ask for any more , gotta be happy with that .

Interesting where your initial A/B combustion was occurring , the skin glow slowly moving back towards the inlet end .

Are you modulating the A/B fuel supply with the P2 changes ??

Cheers
John

[slittlewing]

Cheers John! A next test with higher P2 would be nice, a little bit tricky to manage in the time available before the thing is glowing white, whilst stationary. But also the only way to get a full set of readings!

Yes, AB Fuelling is automatically ratio'd to P2.

Cheers

Scott

[racket]

Hi Scott

Yep , were getting close to the edge with our engines ..............LOL , but thats where the challenges lie, and the satisfaction when they're overcome :-)

The A/B fueling will explain the temp profile, nice .

Cheers
John