I'm sick of constantly rising gas prices, but I don't want to give up my '72 Chevy Stepside pickup. I spent the last five years restoring and modifying my truck. I replaced the original six-cylinder engine with a 350 crate motor. The engine is pretty basic: an RV cam, 8.5:1 cast pistons, a factory cast-iron intake with a 625-cfm carburetor, and small-diameter exhaust headers. It runs well and gets low- to mid-teens fuel economy. I know that's respectable for an old truck, but I'd like to do better.
My mom drives an '01 Pontiac Grand Prix with the supercharged 3.8L V-6. On long trips, she can get close to 30 mpg. She regularly gets mid-20s mpg, and she could easily spank me in a drag race. That got me to thinking about swapping in a smaller, more efficient engine. How much trouble would it be to install a supercharged (or nonsupercharged) 3.8 V-6 in my truck? I know there's enough room to put any size engine in it. Could I expect to get close to the mileage my mom gets?
I also thought about swapping in one of the GM four-cylinder engines. I remember a friend had a little Pontiac with a four-cylinder engine called the Iron Duke. Would something like that be viable?
I realize I'm stretching a little here, but I have no intention of giving up driving my truck. So, I'm trying to find a way to deal with these crazy gas prices. Would changing to a two-barrel carburetor make much of a difference? I'd appreciate any thoughts you have on my proposals. Thanks.
Every time gas prices spike, so do letters about engine swaps and ways to maximize fuel economy. Unfortunately, there's no easy answer. Older trucks are heavy and boxy-two things that aren't conducive to high fuel-economy numbers. Carbureted engines just don't have the fuel efficiency of modern, computerized fuel-injected engines.
As you mentioned, there's room for just about any engine in your engine compartment, but that doesn't mean hooking up any of the engines you're considering would be easy. We think the complexity and cost of adapting a 3.8L GM V-6 (an excellent engine series) to your '72 could be prohibitive. You'd spend more cash making the swap than you'd save with the few more mpg the engine might give your truck.
What it boils down to is maximizing your present combination and making a few lifestyle changes. Tried-and-true efficiency items include: monitoring tire pressure, keeping tire pressures at the upper end of recommendations, checking alignment, not carrying unnecessary weight, keeping the engine in top tune, and driving smoothly. Lifestyle changes can include: combining errands, shopping online, getting a subscription to Sport Truck so you don't have to drive to the store, carpooling, taking the bus, riding a bike, and taking vacations closer to home.
Swapping your present small-cfm four-barrel carb for a two-barrel probably isn't worth the cost and effort. In a heavy vehicle such as your truck, a four-barrel with relatively small primaries can be as efficient as a two-barrel carb.
In a similar vein, a four-cylinder engine would have to work very hard to keep you moving. Engines are the most fuel-efficient when they operate at low load levels. Therefore a small engine that's constantly downshifting and keeping revs up isn't very economical.
You might consider adding an aftermarket fuel-injection system, but if you do, you should weigh the cost versus how much gas you can buy for that sum. When making such a comparison, remember you're looking at the cost of the gas needed for the fuel economy difference between the two systems. That methodology means that some very worthwhile fuel-saving products actually have a long payback period, although the higher gas prices go, the shorter that time is.