Suitable Replacement Turbo

[sauerkraut]

I'm nearing the completion of my first turbojet. I built it around an old turbo that had been gifted to me. When I got it, I inspected the turbo and determined that it was in suitable condition to use.

Unfortunately, I just discovered a hairline crack near the tip of one of the compressor blades. I've decided that it is best to not use this turbo for fear of sending a metal shard out the end of it should the tip of this blade break off.

I can't find parts for this turbo, or even buy a new one. It is very old and lacks a nameplate.

Anyway, I've already built the combustion chamber. Now I need to find a suitable replacement.

Original turbo specs -
Compressor Inducer: 57 mm
Compressor Exducer: 78 mm
A/R: 0.7

Turbine Inducer: Unknown
Turbine Exducer: 78 mm
A/R: Unknown

T4 split turbine inlet flange

Flame Tube : 4.5" ID
Primary: 16 x 5/16"
Secondary: 8 x 3/8"
Tertiary: 6 x 11/16"

Housing : 6" ID

I found this, which seems to be a great deal.

www.ebay.com/p/15021691930

It is the most similar turbo I could find. I'm only concerned about the larger inducer size (69 mm).

Will my current flame tube work with this?

[racket]

Did you use Jetspecs for the combustor design/sizing ??

[sauerkraut]

Jul 25, 2020 18:11:08 GMT -5 racket said:

Did you use Jetspecs for the combustor design/sizing ??

I did not.

[racket]

The current cross sectional area of your flametube might be a tad small for the larger mass flow , it needs to be ~4.75" ID , but if you use your current wall hole areas with the undersized flametube dia , there will be greater pressure drop across the wall with greater turbulence within that could offset the slightly undersized area .

I think I'd try it, the 1.05 turb housing could restrict flow back a tad :-)

Cheers
John

[sauerkraut]

Thanks for the advice!

[sauerkraut]

One more thing -
My borked turbo has a 2" compressor housing outlet, and this new one has a 2.25" outlet. I've already got the combustion chamber welded up to a 2" pipe, placed between the primary and secondary holes. Will this cause too much of a loss in boost?

Also, the plan is to get this thing running on propane, and upgrade to a liquid fuel later on down the road. I see that others have had problems with fuel starvation due to OPD valves on propane tanks (I live in the US so there is no way around them, unless I want a tank I can't get refilled anywhere). Do you think that I will at least be able to get the engine to a self-sustaining RPM on propane with this larger inducer?

[racket]

If you can provide a tapered section of tube reducing from 2.25 to 2" so that there isn't a step , things should be OK

You will hopefully get to self sustain on your propane tank safety device , just be very gently with the valve opening

[turboron]

sauerkraut, the trick with the propane tanks with OPD is to connect the hose to the turbine and then crack the valve very slowly to fill the line. I have an 1/4 turn valve near the turbine which is kept closed during this process. Once the line is full and you have checked for leaks slowly open the tank valve all the way before opening the 1/4 turn valve and starting the turbine. I also have a eclectic shutoff valve and a needle valve between the 1/4 turn valve and the turbine. My starting procedure is to fill the propane hose, turn on the ignition with the needle valve at the minimum position, open the eclectic shutoff valve and then crack the 1/4 turn valve. Once the turbine starts I slowly open the 1/4 turn valve to full open and then slowly open the needle valve to reach idle. Once I am at idle I turn off the ignition and start blower.

Thanks, Ron

[sauerkraut]

I'm considering about where to place my temperature probe. Is there a practical difference between having a TIT probe or an EGT probe? If so, which would be better?

[racket]

Position it in the jetpipe downstream of the turbine wheel , it'll run cooler and won't go through the wheel as a T I T thermo could if it fails

[sauerkraut]

Update: The engine is assembled!

Unfortunately, I cant get it to light. In tests where I just blew air into the combustion chamber without the turbo, it lit just fine, so I'm a bit confused as to why I'm having issues now.

I'm using one of those chinese 12v ignition modules, outputting 500 kV.

[racket]

With a new engine build theres usually some fiddling required to get a reliable ignition sequence worked out .

Try spooling up on the starter , then remove starter and let the rpm decay whilst attempting ignition , this allows a range of air/fuel ratios to occur .

I start my engines without any airflow to begin with ,..... oil on , ignition on, start gas on , ignition of start gas , apply starter and add liquid fuel as the rpm rise

[sauerkraut]

I'm concerned about building up too much propane inside before it lights.

In the aforementioned testing, at times it took a good 5 or 10 seconds before ignition without any airflow present. That was a lot of propane suddenly lighting all at once, and ignition was followed by a noticable pressure wave. A hearty FWOOM that you could really feel around you.

Will this damage my turbo?

[racket]

It won't damage the turbo .

You might need to adjust your propane delivery position so that it discharges closer to the spark , it should only take a second or so .

With my engines I only feed propane into the lower half of the engine where the spark is , propane is heavier than air so the remaining air without propane in the top half softens the "explosion" ..............I've had some pretty load bangs with my turbo based engines where the full combustor has gone off at once

[slittlewing]

How is your spark plug mounted through the combustor casing and flame tube wall? It needs to be air tight (or at least very close to air tight) into the flame tube. I had problems previously where I drilled a hole a few millimetres oversize for the spark plug to go through, this meant a jet of fresh air shrouded/went over the spark plug and no combustible mix could get to it.

Some pictures of your setup and spark plug positioning would help also.

In terms of the sudden boom, I had this all the time with my downward pointing combustor and earlier “high” spark plug position but it didn’t damage anything, just added some more theatre to starting it up!! 😂

Cheers

Scott