$400 Slant 6 Turbo Setup
by Wayne edited by Chuck Rivers & Doug Dutra
Your knowledge and skill will determine if this is a difficult or easy swap. This was my first attempt at installing a turbo as well as my first experience modifying a Slant Six. My total cost was under $400 including a new exhaust system, and I was able to get the car running in 2 days. However, it took me many hours of tuning to get the car to run properly.
Even now I still have a lot of work to do. The best source for information I know of was a publication called "Real Safaris" (formally 21st Century Turbo). (The currrent address is unknown -ed.)
This newsletter was full of Turbo information. The members wrote in with questions, tech tips and pictures. At one point you could get a book, which is basically all past issues, and a one year subscription. This is what I did to install a turbo onto my SL6.
This is a totally custom setup. It wasn't really that hard. The turbo came off an 88 Dodge Lancer. It is a Mitisubishi turbo, slightly smaller than a TO3 that came on earlier 2.2s. Since the engine is totally stock and I didn't intend to spin it past 4000 RPM, the air flow requirements are about the same as a 2.2 spinning faster. Basically I just used with what I had, but a 2.2 TO3 may have been better and let's face it, these are pretty common in the wrecking yards these days. The "next step" is a TO4 from a Buick 3.8 Turbo Grand National or larger CID V8 but these might be slow to spool up on a stock 225.
I started by cutting the mounting flange off the 2.2 exhaust manifold and had it welded to the SL6 manifold. I cut the SL6 manifold right before the heat riser and put the flange on perpendicular with the head. This took a good amount of cutting, grinding and fitting work and you need to be sure to check the clearance of the turbo "snail" to the intake manifold base.
It probably would have been easier to just buy a mounting flange from Turbo City instead of finding a 2.2 manifold just to get a flange. The welding needs to be done by a qualified welder using nickel or cast iron welding rod, along with preheating and slow cooling the manifold. I have run the car hard enough so that the complete manifold and turbo assembly glows a dull red and have not had any cracking problems. Anyway, this manifold puts the turbo under the intake manifold and right in front of the starter. One of the new style, light weight starters would provide more clearance, but a stock one fits with almost no clearance. I have about 15,000 miles on the installation including a 6,000 mile trip from NY though TN and NC. So far this has not caused a problem. Take your time when laying out the manifold and do some trial fittings onto the engine with the starter, intake, front left engine mount bracket and dip stick in place. If you angle the turbo down slightly, you will have more clearance to the intake but then it comes close to the block. Don't forget to keep in mind the air intake and output lines while mocking up the turbo assembly and manifold.
I ran a 1/4 steel (brake line) oil pressure line off the oil pump where the idiot light hooks up by installing a "T" fitting. So far no problems there, but make sure to use a high quality line with compression fittings (flair fittings) as this line is subjected to intense pressure, heat and vibration and could crack.
I used a punch to put a 5/8" hole in the pan. (Punch, don't drill this hole. Punching "rolls-in" some material to create threads and keeps chips out of the oil pan.) Position this hole under the turbo and back where the #3 main cap is located. (Helps keep the oil off the rods flying by.) Place the hole up close to where the pan rail bolts to the block. Tap it 1/2" NPT (pipe thread) with grease on the tap to hold any metal chips. Clean everything well and epoxy in a fitting for the oil return line. Remember the oil return must be much bigger than the feed line, as the turbo does a good job of frothing the oil, making it drain slower. The return must be above the oil level in the pan.
I "T"ed off both heater hoses to supply and return coolant to the Turbo. I used 3/8" lines for both. An option to this is to spend additional time to drill & tap the water jacket access boss on the driver's side of the block, then run your water input line from there. The return can be "T"ed into one of the the water pump connections.
I used about 6 inches of the original 2.2 exhaust pipe and adapters to hook up to the stock exhaust system. The 2.2 pipe was 2 1/4" and the stock 225 pipe is only 1 3/4". After I got the car running and had a complete 2 1/2" system made, this increased performance dramatically. Note that turbos need big exhaust systems & low back pressure to spool-up fast and develop lots of boost.
I used the stock 2.2 air box, air cleaner and hose for the inlet side of the turbo.
As for the turbo's pressure output delivery, I used fiberglass to seal up the stock air cleaner. I attached a 2 inch steel pipe and used radiator hose to connect it to the turbo. Try to keep the rubber hose length to a minimum.
It is not easy to modify the power circuit of this carb, so I just increased the jet 14 sizes. (You must increase the amount of fuel to compensate for the increased air flow. - ed.) You must also supply additional fuel pressure in a blow though turbo setup. Fuel pressure must remain 4 to 7 psi over boost pressure.
The best way to do this is to run a line from the output side of the turbine (boost pressure) to the back side of the fuel pump diaphragm. There is a vent located here on most stock pumps which can be tapped for 1/8" pipe thread. I have found a 5/16" line is sufficient to feed the pressure over to the fuel pump. This simple setup will keep the fuel pressure above boost pressure at all times and requires no regulator.
I set the total mechanical timing to 16 degrees and ran 8 pounds of boost. I used a vacuum pot from a 318 and modified it to provide 25 degrees of vacuum advance. (There are adjustable vacuum advance pots available for the Slant Six. -ed.) This helped fuel mileage when not under boost by providing a more normal advance setting. As of this date it provided the best performance without detonation on premium pump gas. This is a tiral & error process and will take some time to get it right for your engine combination.
The setup worked out pretty slick. Once I had the system installed, it was carb rejetting, timing curve adjustments and a lot of trial and error work. I feel the turbo I used is a little small for a 225 SL6 but it spools up quick and runs pretty strong.
I did this more or less as a test. The car runs low 16's in the 1/4 mile with no drive train modifications (stock trans, rear end gearing etc.). The engine is a bit tired. It has over 210,000 miles on it now. Makes me wonder what this setup would do on a fresh motor with a little cam and some head work. The end result was a great increase in performance at the expense of increased fuel consumption. I have recently installed a 4 bbl manifold and a 600 cfm Holley. I use only the primaries, but this still seems a little large. Also, since the secondary side is wired shut, it causes a little turbulence problem at full throttle. The advantage to the bigger carb is being able to provide the addition fuel though the power circuit, not the main jets. Mileage is now about the same as stock, almost 19 on the highway, that is, if I keep it under 75.
This is the basics of my installation. There is a LOT of performance in a SL6, just waiting to get out once you find a way to get the fuel mixture in. As you can see, a turbo does this well.
Thanks for your interest and good luck,
Here are some additional turbo photos to help you plan your setup. (ed.)