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Turbocharged slant six: cheap power and gas mileage (Part II)

Go back to Part I

Turbochargers can be harmful to your engine (and to you) - use caution. Allpar does not claim to have expertise in turbochargers and has not tested Mr. Holler’s methods or results.

A bonnet will allow you to run the pressurized air from the turbo right down the throat of the carburetor. Some of the late 70s and early 80s carbureted front wheel drive cars used a bonnet to direct air from a remote mounted air cleaner housing into the carburetor. Measure the diameter of your carburetor inlet and start scrounging around the salvage yard. Some Carter and Rochester 2-bbl carburetor used a 2 5/8” opening. The bonnet off FWD Chryslers with the 2.6 Mitsubishi motor will fit. Turbo City also offers bonnets for popular sized carburetors.


slant six


slant six turbo

When using a bonnet you will need to seal the carburetor sufficiently so that you don’t blow everything out the sides. If your carburetor has a bowl vent tube, vent it to boost pressure. If you have a sloppy throttle shaft(s), it (they) will need either bushed (bore out larger then install a bushing for a tight fit) or externally pressurized. If they are sloppy you’d be better off using a carburetor box or replacing the carburetor. Use phenoelic floats instead of the hollow brass ones to avoid collapse. The bonnet is the easiest of the two methods and, for low boost levels of 6 PSI or less, is the recommended method.

Once the turbo is physically mounted in the engine compartment, you are going to need a source of pressurized engine oil. The best place is at the oil pressure sending unit. Whether you have a gauge or a low pressure warning light, you have an oil sender. Get a 1/8” NPT “T” that will allow you to tap into the oil supply there and direct it to your turbo. One part of the T goes in the block, one part gets your stock sender, and the third part gets a line that goes to the turbo. This is the easy part.

Next you need a place to drain the oil once it has cooled and lubricated your turbo. FIND A PLACE BELOW THE BOTTOM OF THE TURBO BUT ABOVE THE OIL LEVEL IN THE PAN TO DRAIN THE OIL BACK TO THE BLOCK! Do not use the oil filler cap as your oil return. The pressure side of the oil comes in the top of the turbo. If it doesn’t on your application, rotate the center section so that it does. The outlet is at the bottom of the turbo. You don’t want to pressurize the center cavity with oil. In all cases, you will use a relatively small (1/4” in the Duster’s case) inlet line, and a relatively large (1/2” on the Duster) outlet line. This keeps the oil from building up in the turbo and blowing seals.

The only place I could find to drill and mount an oil drain on the Duster was the oil pan. I had to drill holes in the side of the oil pan and mount a receiver unit. I used self tapping screws and J. B. Weld to attach it. Allow a day for JB Weld to dry.

The coolant is much easier. If your turbo uses coolant lines also, you can just tap into the heater hoses with “T”s. One will be at a higher pressure than the other, ensuring a constant flow of coolant. With the coolant, it doesn’t matter which way the coolant flows, or which line is hooked up to pressure. Coolant is used to aid in cooling to prevent oil from coking inside after hard use.

Carbureted applications will require higher fuel pressures.  The simplest method is to drill into your fuel pump’s vent hole, epoxy a tube into the hole, and run your boost to that port.  The vent is a reference and if you increase the pressure above the diaphragm, then the fuel pressure will increase by the same amount.  Do not connect this port to the bottom of the carburetor.  You don’t want vacuum, just boost.  Someplace between the turbo and carburetor is best.

The final part of the installation is to secure all of our hoses with clamps and install our boost gauge. Folks, this shouldn’t be optional. There is no way you can determine how much boost your turbo is generating without a gauge. Furthermore, you don’t want to find out too late that the bugger really could crank out 20 pounds of piston melting boost.

Recheck all of your connections, fluid levels, linkages, bolts, nuts, or anything else you can think of. Start the engine. This could possibly be done at night, since the glow you personally will give off at this point should be enough to light up the whole neighborhood. This is the moment of truth, and a proud one when nothing goes boom! As soon as the engine is running, check all of your oil line connections for leaks. If something doesn’t look right, shut the engine off at once and make repairs. If everything does look good, allow the engine to fully warm up; about 15 minutes or so, shut the engine off and recheck your fluid levels.

Next, take the car to a quality exhaust shop and have them connect the dots. They will need to bend a pipe to connect your exhaust manifold to the turbo, and weld the flanges on both ends. Then they will need to connect the turbo to the rest of your exhaust system. You should plan on dropping the car off and picking it up later, as this may get involved. This operation may cost you up to $300 in parts and labor, and while $100 for a turbo and another $300 to have it piped up may sound expensive, have you priced a supercharger lately? These start at over $2000!

When you get it back from the exhaust shop, take it out for a drive. Take it easy at first. Watch your oil pressure and boost. If at any time something doesn’t feel or sound right, pull over and check it out. If there is a problem baby it back to the shop/house if possible and investigate. If not possible to drive it, have it towed. Make any necessary repairs or adjustments and try again. Gradually drive harder as you build confidence. If everything still looks and sounds good, you have successfully installed your turbocharger.

Extensive discussion of this page is in the A-body forums!
Confused? Something missing? See Slant Six Turbochargers Revisited!

Mike Holler, known on Allpar forums as mpgmike, also contributes to He has contributed many columns to Allpar:
Interiors Budget interior restoration: making the inside of your car look like new again
Red carpet treatment: Installing new carpet in an old car
Headliner repair
Porting Porting heads for performance: step by step
Head porting example, part 1 | part 2
Intake manifold porting
Exhaust manifold porting (turbo)
Poly Quad heads: porting revisited

Turbochargers Turbochargers - all you need to know (interview)
Turbocharging the slant six for power and economy • Revisiting the turbocharged slant six
Budget turbocharger rebuilding (and Turbo Rebirth)
Installing a boost gauge

Other Powder-coating for a brilliant, durable finish
Custom pistons: roll your own!
Prepping valves for performance: grinding and polishing
Old cars: an opinion
Discuss Mike’s articles! (if you are not registered for the forums, register first )

Also see our 2.2 turbo page. • Confused? Something missing? See Slant Six Turbochargers Revisited!

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