The GTO's interior features...
The GTO's interior features many replacement components from Ames Performance. The Hurst Comp Plus shifter is connected to a rebuilt close-ratio Muncie four-speed transmission, which features an 11-inch street/strip clutch disc and pressure-plate assembly from South Bend Clutch on one end, and a new driveshaft on the other.
CTS had preset the center mixer, and Mark finely tuned it and the end units for maximum performance. "CNG molecules are much larger than those of typical gasoline, so it doesn't burn as efficiently and typically doesn't provide as much power. It also has an octane rating of 130, so it burns slower too. CNG requires a much hotter spark to initiate ignition, and it generally requires additional spark advance to completely burn." The GTO was already equipped with a complete MSD ignition system, so Mark simply had a CNG mechanic reset its distributor timing curve for optimal performance.
The GTO fired immediately upon initial startup and has run flawlessly on CNG since, states Mark. He admits, however, that he was concerned his Pontiac's wonderful exhaust note would go away, but much to his surprise, he says it sounds better on CNG than it did on gasoline. "The exhaust tone changed slightly, but it sounds like it's more finely tuned than ever before. It's simply music to my ears."
When asked if he's noticed a performance decrease after converting the GTO from gasoline to slightly less efficient CNG, Mark responds, "None that I could really tell. It feels great everywhere. I still love the power rush when the Tri-Power's end mixers open, and it accelerates just as well from a stop." One unexpected benefit he found was startup after it's sat for long periods. "On gasoline, the carburetors would go dry; it took a lot of cranking to fill the float bowls. It fires up immediately with CNG."
The entire CNG conversion cost Mark around $5,000, and measured economy on CNG is roughly 10 mpg-10 gas gallon equivalent (GGE) in alternative-fuel lingo. "Right now gasoline runs about $2.70 per gallon in Birmingham; CNG is $1.36 per gallon. You can see how much of a savings that is. That may not seem like much, but it adds up over time. I don't plan to drive the GTO too often though. I feel driving it sparingly will help me appreciate it more, and I know that it'll cost much less to drive when I do."
Mark says that the GTO has taken on a new life since its conversion to CNG operation.
"I enjoy taking it to conventions and shows, and sharing my experience with other hobbyists. I'm even planning to participate in A Drive To Inspire event this summer, where the GTO will travel 2,200 miles on Route 66, from Santa Monica to Chicago, operating solely on CNG. [The fuel range of the GTO is 140 miles; it will be tailed by a refueling truck housing twin 36-gallon CNG fill-tanks.] I hope to set a world record and show hobbyists around the world that vintage automobiles can operate reliably on CNG."
So what did Mark get for thinking outside the box? The world's first Tri-Power "CNGTO!"
The PEV-series regulator reduces...
The PEV-series regulator reduces incoming CNG from a pressure of 5 psi...
...to just 0.5 psi by the...
...to just 0.5 psi by the time it reaches these flexible hoses, which feed the mixers.
A conventional smog pump,...
A conventional smog pump, added by the previous owner, was plumbed to depressurize the 469's crankcase, improving performance. Though it now effectively evacuates excess CNG vapor from the crankcase, it isn't required when converting to CNG.