Test drive new turbo

[lostagain]

This winter, I installed a turbo charger on the 4-71 DD in my '57 Courier 96. I finally got done, and had it out this afternoon up a long grade, 6 and 8% in 3rd gear vs 2nd gear last year. I like that! That's what I was hoping for and I got it. It accelerates noticably stronger from a stop up all the gears (5 speed Spicer). Now I'm looking for head rests LOL. It doesn't slow down nearly as much up the little rises on the flats either. I don't hold back traffic as much anymore, that's great... That's a good feeling...
I first took the blower to DD dealer for a rebuid, with the better oil seals. The turbo is a Airesearch TV71 that is the standard for the 4-71T in the DD service manual. It is supposed to give me 12 to 14 psi of boost. I had to build a custom adapter to mount it on the exhaust manifold. I rebuilt the intire exhaust in 5" . I used the old oil bath air cleaner (also 5" in and out). I was wonderring if oil would be pulled into the turbo compressor (800 to 1000 cfm from 400 before), but it does not. I was also concerned about flow restriction through it. I put a filter minder on the housing and it only shows about 16 inches water column (max allowed by the book is 25). So I'll stick with the oil bath, they clean better than paper element anyway. I kept the same N65 injectors, and the same trunk type pistons. It did not run any hotter than last year, and no smoke. That was expected because I'm not giving it any more fuel, just more air. So I'm thinking about N75 injectors maybe.
Anyway, what a great thing to do! It was worth while...
The only thing left to resolve is that the turbo is robbing too much oil from the engine. Once the oil has warmed up , I get no pressure at iddle and about 35 psi while running. The smallest part of the turbo oil supply line is 1/8th NPT (that's the fitting that came with the turbo). It looks like it is getting lots of flow when I disconnect the return line while running. So would someone be able to tell me how much I can safelly reduce the size of the oil supply to restore oil pressure, without starving the turbo. Any suggestions appreciated.

[RJ]

JC -

Don't restrict the lines going to or from the turbo.  It's very important that it receive the oil supply it needs, as the oil not only lubricates the bearing, it also helps cool it.  And since the turbo spins upwards of 100,000 rpm, there's a LOT of oil foaming that takes place, which is the reason for the large return line.

Back in my younger days, I spent a lot of time working on Corvair Turbos, and got to know them pretty well.  The ones with the most problems were those who's owners neglected their oil levels and oil & filter changes.

Two-stroke Detroits are notorious for "no oil pressure at idle", so you may be worried about something unnecessarily.  However, you need to compare the dash gauge to the one in the engine compartment, and see how close the two are reading.  It's quite possible that the electrical dash gauge is reading lower than the engine compartment's mechanical gauge.

The other, less likely possibility, is that your engine's oil pump is worn to the point it's not putting out the volume it did when new.  IIRC, there are instructions in the shop manual for checking the operating clearances, which affect output.

Dunno if N75s would do you any good, other than empty your wallet a little faster at the fuel island.  A pyrometer might be a better investment, to keep an eye on exhaust temps.  Install downstream from the turbo.

Glad you're project's come to fruition, and that you're please with the results!

FWIW & HTH. . .

[lostagain]

Thanks Russ, I checked both the electric gauge on the dash and the mechanical on the engine. I think the turbo is getting lots of oil. I ran it with the return line disconnected and a ice cream pail hanging underneath to catch oil, and there was quite a good steady flow. I built the supply line out of 3/8th hydraulic line, although it connects to the flange at the top of the turbo with a 1/8th fitting. The return line is 1/2 inch, and pretty well vertical down to the sump. I know the oil pump was good last year, and it still gives me 35psi just off iddle.

[Utahclaimjumper]

In the aircraft world we restrict the line FROM the turbo.>>>Dan

[RJ]

I built the supply line out of 3/8th hydraulic line, although it connects to the flange at the top of the turbo with a 1/8th fitting.

Hmmmmm. . .  Since the turbo itself restricts the amount of oil being fed with the 1/8th intake, you might experiment with just using a 1/8th supply line, rather than 3/8ths, and see if that has any effect on your oil pressure.  Your return line is fine (recommended minimum is 2.5x the feed, btw).


Dan - 

Curious - could restricting the return on an aircraft turbo be related to the altitudes normally operated at?  Hadn't heard this before, so it's piqued my interest.

FWIW & HTH. . .