My turbo efi slant is almost ready to fire up. I am getting ready to install the oil feed line to the turbo, and want some opinions here. This is a stock unit, from an 85 Grand National. One of the local speed shops here has a mechanic who I resonate with, and he has built many turbo motors. He claims the oil feed line on turbos is typically too big. He claims the line feeds more oil into the turbo than it can handle, that the oil backs up into the intake air stream, and the engine susequently smokes from the excess oil. He installs a 1/8" jet into the oil fitting at the turbo oil inlet to control the oil better. Can anyone here see any problem with simply reducing the size of the oil line from 1/4" to 3/16"? It seems like this 3/16" line would still provide more oil then could pass through Jeff's 1/8" jet. Is this guy crazy, or does he have a point? He is currently dialing in a fibeglass Willys with a twin turbo Chevy big block that dynos at 2000 horses. It;s a pretty awesome machine that runs mid sixes. One of the reasons I say he resonates with me, he still respects my slant project, and hasn;t even hinted at looking down on it. That is a little unusual. Several speed shops around here kind of look over your head to see who is next in line if you mention you are building a slant six engine.

Vader,
I've read that coking is a potential problem in turbo oil feed lines, and that it is recommended that they be replaced periodically or at least whenever the turbo is re-built. If that's the case then reducing the line size, or especially using an 1/8" jet, doesn't seen like a good idea. Perhaps with a race car that is regularly "torn down" this is not an issue. But, with a daily driver I would stick with the design engineers original specifications.
Bob D

That makes alot of sense. When the oil sits in the line after you shut off the engine, and it is still hot, the static oil then burns and leaves a hard film, which in time gets thicker and thicker. They recommend that you let your engine idle for a few minutes when stopping, to minimize this effect. Any other thoughts on the oil feed line size? What size line did you use, Bob, and others out there with turbos? Perhaps the coking effect would be less dramatic with stainless steel covered rubber lines with AN fittings.

I would use the 1/4 inch oil feed line. If you make sure the oil return line is large enough ( absolute minimun inside dia 5/8 or #10) continous downward slope, and drain into the engine above the oil level, you should not have any problem.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I used a 1/4" line. This is what was used on the '84-'85 Buick turbos. Of course Charlie is correct about using a return line that is large enough. Mine is AN-10. Vader, where did you end up feeding your return line?
Bob D

My turbo setup uses 1/4 inch copper line, "T"ed off at the oil pressure switch. Return line #10 installed in the oil pan about 2 1/2 inches below the flange, on the driver side.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

I drilled a hole dead center in the block, just above the oil pan, and tapped the hole for a 3/8" NPT thread. I then installed a 5/8" heater hose barb in the hole. I checked on of my spare slant blocks, and saw that the only thing behind that surface is the main counterweight, with about 1/2" to 3/4" space between the counterweight and the block surface. I figured this is enough. The hose barb is flush with the inside of the block when it is tight. I will go ahead with the 1/4" feed line. Thanks for the advice.

That 3/8 npt fiting might be too small. That is 1/2 inch smaller dia than the ID of the hose. Also, do not use heater hose. Use a hose that is oil resistant.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Thanks for the advice on the hose Charlie. A 3/8" NPT thread is considerably bigger than 3/8". I think it is the outside diameter of a cast iron pipe that is 3/8" inside. Anyway, a 5/8" hose barb threads right into a 3/8" NPT pipe thread with no restriction on the inside of the hose barb, since the hose barb is much thinner walled than a cast iron pipe. Granted, a 5/8" hose barb is smaller than 5/8" inside. If the inside diameter of the hose barb must be 5/8" then we are looking at a 3/4" hose and barb. What size hose did you run, and how do you have it plumbed? Do you have it clamped to a hose barb?

I do appreciate your advice. Of course much of what I have done is slated for change once the car is running. Some of what I have done so far will get upgraded with tuning and testing. Most particularly the inner cooler tubing, which will get smoothed out, and re-routed. I am to the point now where I am really getting eager to just start it up again, and start working the bugs out of it.

I used AN # 10 braided hose. I would have to go measure it, but if I remember right, the fitting in the pan was a 3/4 inch pipe thread.

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Charrlie_S
65 Valiant 100 2dr post 170 turbo
66 Valiant Signet 170 nitrous
64 Valiant Signet
64 Valiant 4dr 170
64 Valiant 4dr 225

Hey.. One other thing to consider. Is the turbo a sleeve design which uses the oil to suspend the bearing surfaces, just like in your engine? or is it a ball bearing design where the oil is really just for cooling the bearings, and extra lubrication for the bearings? It might make a difference.
My friends T28 is the latter, and it was free enough when new that you could blow on the compressor vanes and make it spin... Has about 50 K on it now, it does not do that anymore. It is water, and oil cooled, that helps with the coking too.

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Stock 75 Duster 109K. Working on Turbo setup.

I must condess I am rather ignorant of the specifics of this turbo design. It is whatever was standard on the Buick Grand National in '85. It is new, and very free wheeling. It has only oil and not water to cool it. My brother's 2'2 Dodge turbo has both oil and water. I was a little surprised that the Buick had only oil, especially since they are so similar otherwise. Does anyone out there know more about this? BobD, what can you tell us about the GN turbo design?

Back to the oil drain: If the oil back up the drain, the engine will burn the excess oil through the intake. If this settup produces oil consuption, then I can always increase the drain line size later. Charlie, I will see what a 10 line translates to in inches.

The stock Buick turbo doesn't use ball bearings. Vader, if you start burning oil through the turbo you may already have damaged the seal.
Bob D

This turbo hasn't turned over once yet. It is new old stock, and I haven't started the engine with the turbo as of this date. Right now I am waiting for my header and down pipe to get back from the Jet Coat people. I realize the seals could be bad on a 20 year old piece though. I hope that is not the case.

Bob, what size oil drain do you have? Is it 5/8" or 3/4"?

Vader,
I'm using 5/8" (AN-10) stainless steel reinforced oil resistant hose. The 5/8" hose barb at the engine has a 1/2" NPT as opposed to your 3/8" NPT. My concern (and I think Charlies as well) is that the 3/8" NPT to 5/8" barb that you are using might be too restrictive.
I realize that your turbo hasn't been used. What I was saying was that if you wait to see if there is any smoke because of the return line being too restrictive it will likely be too late to save your seal.
By the way, to attach the AN-10 return line to the turbo end I got an adapter from Road Race Engineering ( www.roadraceengineering.com , Garret oil drain flange with 5/8" hose barb fitting, $13) that attached to the oil return at the turbo. This allows the use of a 5/8" hose in place of the stock metal return line used on the Buicks.
Bob D