Turbo selection

[notjet]

Hi,
I have been looking for a turbo for some time now and have found this 36mm inducer 40mm exducer turbo. Now the turb A/R is 0.74, which i heard was tight but on some other threads it says it fine. Can this turbo be used as a gas producer or is it unsuitable?

Cheers, Neo

[racket]

More info please , a 0.74 A/R on such a tiny turbo is realively large , maybe a Link to the actual turbo ,

[notjet]

Hi Racket,
Its in german and the inducer/exducer sizes arent specified but i asked the seller so ill put the images in too

m.ebay-kleinanzeigen.de/s-anzeige/turbolader-2-0tdi-audi-a4-a5-q5-caga-105kw/2265909274-223-6273?utm_source=sharesheet&utm_medium=social&utm_campaign=socialbuttons&utm_content=app_android

[finiteparts]

That looks just like the little VNT turbos that come off the Volkswagon's. I have one and always wanted to make a tiny engine and play with the variable nozzle, which is super easy to control on that little guy since it is on a lever that is outside the turbine housing. A/R won't matter on that one, since it is a VNT.

With the VNT, I am sure you will be able to find a combination that works, as long as you have a very well behaved combustor and don't let hot streaks damage the VNT vanes, which are super thin and likely pretty susceptible to thermally induced damage.

Good luck,

Chris

[racket]

Hi Chris

That would certainly explain the large A/R , thanks for that :-)

Cheers
John

[notjet]

Hi guys,
Thanks for the replies, is it possible to take that out and run it like that? Its gonna ve my first build and there is a chance that i mess up but then ill have pieces of metal in my turbine...

Cheers, Neo

[notjet]

Nov 12, 2022 4:57:38 GMT -5 notjet said:

Hi guys,
Thanks for the replies, is it possible to take that out and run it like that? Its gonna ve my first build and there is a chance that i mess up but then ill have pieces of metal in my turbine...

Cheers, Neo

Oh i forgot to add that after doing sone research i found out that these dont like to boost up to 40-50 psi boost because then they will throw their wheels out is that an issue?

[finiteparts]

I don't think taking out the NGVs would be a very good idea. It may still run, but they are pretty integral in forming the turbine housing flowpath. If you take out the VNT vanes and mechanism, you would be left with a shitty looking flowpath. I would suggest just getting something else if you wanted to go that route. But, I think if you started off with propane and a well made combustor, have the NGVs wide open to start then move them around you will probably be ok.

The boost question depends on your use for it. Since you are calling it a gas producer, I am to assume that you intend to put some form of free turbine stage downstream of it? If that is the case, then the answer only depends on how much power you are trying to squeeze out of it.

- Chris

[notjet]

Hi,

Jetspecs said it could produce about 12 lbs of thrust, and since i have no idea of freepower efficiency i decided to just aim for 7/8 shaft hp,

i want it to be able to power a very light vehice at some point but my first goal is just having a working turboshaft that ill put a propelleror something on for load

[racket]

Very small turbos like these generally aren't designed for high boost levels, they prefer a broad flow range , so look at ~1.5 Bar max pressure from the comp .

Take Chris' advice and leave the NGV in place , set it to a mid range position , then fine tune position as development continues.

As for power output , these small turbos tend to struggle as component efficiencies aren't that great , forget what Jetspecs says , you're flows are outside what it was designed for , LOL............I don't think they even had turbos this small when we created Jetspecs :-(

Cheers
John

[notjet]

So i cant get 7 hp? :/
Well i guess ill have to look for something a little bigger then because i wont be able to afford building a second engine for now...
Anyways ill find something that works

Cheers, Neo

[racket]

Hi Neo

www.garrettmotion.com/racing-and-performance/performance-catalog/turbo/gt2052/ if you checkout the turb map for this slightly larger one it has max turb effic of 70% , some of the smaller ones have it down to ~66% effic , at that level it gets hard to have "left over" power for thrust or horsepower , its not a problem as a turbo , the pistons can be used to "supplement" turbine power by running higher exhaust manifold pressures than inlet manifold ones , something we cannot do .

You may be able to get your 7HP from this turbo as I don't have any idea of its actual specs , I can only make "guesstimations"

Cheers
John

[notjet]

Hi everyone,

I realise now that this whole turbo dilemma of mine is pointless since i set an unrealistic goal: i wanted a micro freepower unit i could mount on a moped that had maybe 7hp, but just didnt think of the poor efficiencies at those turbo sizes...

I will still be using a small turbo but no longer build it to power something. ill just use it as a demo that i can build a prop swinging noise generator which will still be a ton of fun and with such a small turbo i can make it super compact

[racket]

Hi Neo

With small units the freepower wheels RPM are extremely high , this complicates the gearing/bearings etc .

Your gas producer will be spinning at 150-170,000 rpm , so freepower will be at >50,000 as a minimum , I suppose the gearbox off a 1/4 scale buggy might do the job for a while .

Even our rather large engines have freepowers turning 30,000 rpm

Cheers
John

[notjet]

I found a good hx35 turbo for 200 bucks, shall i buy?
I guess if im gonna make a ridiculous moped ill have to give it ridiculous power... reason im still opting for moped is because now i have a free frame with all parts in my basement so it could be done for not alot of money...

Cheers, Neo