March 2008 Newsletter for Rear Wheel Drive Models

I Like Pressure Situations part II
-Adding a turbo to the non turbo 240-

If you’ve followed my story from the last issue of “The Brick” you’ll remember we left off with some needed fuel tweaking to get up to my goal horsepower of 200 bhp. In its’ stock form my 240 produced 104 hp at the engine and my dyno test reported 87hp at the wheels. Considering age and mileage this is about what I expected. Now I realize that trying to double the factory horsepower may be a lofty goal but I’ll be happy even if it only lasts a few miles that way, should be a great ride! For more pics and write up see https://www.ipdusa.com/tm-18

Onto the work
The first thing to consider when turbo charging a non turbo car is the pressure created in the manifold that was not there before. This pressure is feeding the cylinders with a greater volume of air but it is also pushing back on the fuel trying to exit the fuel injector. To combat this I removed the fuel pressure regulator valve from my K-jet fuel distributor and added .080 inch shims to up the pressure 16 psi. The reason for selecting 16 psi is that I’ll need a final boost target of 16psi to reach my 200 bhp goal. Moving on, the next step was to install an adjustable boost switch into the intake manifold that would turn on the cold start injector and spray more fuel into the intake when boost pressure reached 3 psi. This allows for some additional fuel as the K-jet fuel distributor reaches it maximum fuel flow at approx 4 psi. All this worked well but I was still running out of fuel around 7 psi and the engine would start to detonate badly. I needed another option. I decided to use the boost switch to turn on the frequency valve as well and add more fuel pressure thus richening the mixture. The frequency valve is part of the factory fuel system and is used in conjunction with the oxygen sensor to add or subtract fuel pressure (via a bleed line back to the fuel tank) and thereby control the mixture. By grounding the frequency valve signal wire at 3 psi with my boost switch, I was able to up the boost pressure to 10psi, but past 4500 RPM the engine was still a bit lean and I was starting to hear detonation.

1978 242 Turbo Conversion

Timing
With fuel somewhat under control I figured it was time to pay some attention to timing!ÊThe factory non turbo distributor allows for advanced ignition timing when the engine is in vacuum and retards the timing as the throttle increase and the vacuum decreases.ÊHowever, when the engine is in boost, the distributor is not able to retard the timing further to help reduce the risk of detonation.ÊSo a turbo distributor is necessary to keep timing in check. After installing the new distributor and setting the base timing back from factory spec by approx 3 degrees it was back to the dyno. After a bit of tuning I was able to reach 163 horsepower at the wheels. This means an estimated 180 horsepower at the engine.

Traction
After adding nearly 80 horsepower it was not surprising that traction issues began to arise. On any given corner, with just a little throttle, the inner tire would break loose and smoke like crazy. I had already ordered a limited slip differential, but it was on back order and I wasn’t sure when I would get it. I hadn’t welded a differential solid since high school and decided it was time for a trip down memory lane. Welding a differential so that both tires will spin together regardless of traction condition is not the best idea for a street driven car, but since this is my play car why not have some fun? I pulled the rear pan, cleaned all the oil and grease out and used my Miller to weld the spider gears to the side gears. I cleaned off any spatter and metal flecks, reinstalled the cover and filled the diff with fluid. Time for a test drive.

My traction issues are resolved nicely and the car launches hard and quick from a stop with little to no burnout. Turning, however is a bit of an adventure. Typical driving around town isn’t too bad until you enter a parking lot and try to park. The rear tires bark and groan in protest as they try to turn at different speeds while the front tires calmly turn about a dime. Another somewhat expected adrenaline injection occurs when it rains. The car doesn’t drive in a straight line so much as it motors down the highway in a fish like motion. I imagine this feeling is something akin to surfing but with less control and considerably more concrete dividers. All in all this project has been fun and I’ll keep pushing the limit to hit that elusive 200 bhp mark come bent rods or blown head gaskets! After that, I’m not sure what to do with this car but I’ve got a line on a local guy who just built a 383 cid stroker twin turbo for his 1980 242 and is getting ready to fire it up for the first time. Stay tuned...

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