We Kicked A**...
...and Phil took names!

Part 1 of 3 Part 2 of 3 Part 3 of 3

This February Grassroots Motorsports Magazine (GRM) is holding their third annual racing challenge in Orlando Florida. Cars entered in the challenge compete in a ¼ mile drag race, an autocross (slalom) course, and a concours event. Each car is scored 40 points for speed, 40 points for handling, and 20 points for appearance. The challenging part of this year’s contest is that each team is allowed to spend a maximum of $2002.00 on the car. This figure includes the car itself, tires, replacement parts, and consumables.

Phil Fox and I are entering a 1968 GT6+ that he bought a few months ago for the princely sum of $200. For $200 he got a car with a dented body, lots of surface rust, an engine that ran poorly, a gasoline leak, and a worn out interior. If it weren’t for the contest it would probably have become another parts car.

In order to compete against cars built within the last 10-15 years we realized we’d have to do something radical to make the GT6 competitive. An article I read about the first Porsche 911 Turbo mentioned that Porsche had deliberately used a low 6:1 compression ratio. The low compression ratio allowed them to safely use more turbo boost pressure without requiring high octane racing fuel. Porsche deliberately sacrificed low-end efficiency in order to get away with high boost pressure. This sounded like a perfect solution to our problem.

I recently bought a used engine (for $50!) from a 1975 TR6 to use for spare parts. A quick calculation told me that if I put the cylinder head from the 2.5 liter TR6 engine (which had a 7.75:1 compression ratio) onto the 2.0 liter GT6 engine block I would end up with a low 6.4:1 compression ratio. Perfect! The very next day I stumbled across a rebuilt Eaton M90 supercharger on eBay and I was hooked. After placing the winning $399 bid for the supercharger we had to figure out how to get the car into shape and make it work without exceeding the budget cap.

A few years ago there was an article in British Car Magazine about a TR6 supercharger kit which was produced in low volume until it was discontinued last year. This kit used a 2" SU carburetor (usually found on Jaguars and big Healeys) so I originally planned to use the same thing until I raised the subject with ISOA’s racing and fuel injection expert Mark Fisher. Mark recommended using the throttle body fuel injection setup from a mid-eighties Chevrolet and offered to help me find a reasonably priced junkyard solution. Throttle body injection sounded great so a couple of weeks later I stopped by Mark’s office over my lunch break.

Mark showed me the engine management computers that his company (Fuel Management Systems) makes and explained how he thought I could adapt one to our throttle body injection project, but then he asked me the $2002 question: have you considered running the car on propane? I knew Morgans imported into the USA in the 1980s all ran on propane in order to meet EPA regulations and I knew that propane produced less power than an equivalent amount of gasoline so I was skeptical.

Mark got me interested in a hurry when he said "Did you know propane has an octane rating of [up to] 120?" Mark loaned me a propane carburetor to play with and as I drove back to my office I could almost hear my own gears turning.

Even with an 8% power penalty for using propane we could generate more net power because we could increase the boost level to an absurdly high 20 PSI. For comparison, normal engines rely on atmospheric pressure (14.7 PSI) to fill their cylinders with the air/fuel mixture. A supercharger that pressurizes the intake to 8 PSI above atmospheric pressure (8 pounds of boost) will have an absolute intake manifold pressure of 22.7 PSI and will be forcing roughly 50% more air/fuel mixture into the engine for a proportionate power gain. With 20 PSI of boost we could double our original power output. Most engines will succumb to detonation when subjected to high boost pressures, but our low compression ratio combined with high octane propane fuel will give us tremendous resistance to detonation.

At this point we’ve fabricated a custom intake air box and carburetor adapter for the supercharger (see photo). An adjustable diameter pulley on the supercharger will let us experiment with different boost pressures, and a vacuum operated bypass valve from a Saab turbo (not pictured) will open when the engine is idling or cruising to preserve fuel economy. Once the engine work is complete we will rebuild the suspension and give the car a quick paint job before heading to Florida for the big event.

By Erik "Iceman" Quackenbush

Part 1 of 3 Part 2 of 3 Part 3 of 3

We Kicked A**... ...and Phil took names!

We Kicked A**...
...and Phil took names!