Smiles Per Gallon
You had an article called “Formulas for Fast,” which helped me when I built my '66 GTO. I now have a '66 Tempest and wish to go in another direction. How about helping out with this project, too?
I want to build a daily driver that's great on gas. I already have a 326 and 400 motor; the former runs but the latter doesn't. I plan on buying a 200R4 transmission and a fuel-injection system.
What kind of cam profile do you recommend? I'm hoping for 285-300 hp, but I'm willing to scale back the power if it will help the mpg.
How about wheel size? I don't want to go larger than 17-inch, but if doesn't make much difference, I want to stick with 14-inch Rally Is.
Here's the last challenge. I want to build it on a budget.
Rocky Rotella responds: George, you might be asking for a fairly tall order on a tight budget. I've never built an engine strictly for economy, but we can take some cues from what Pontiac did in the mid-to-late '70s when the industry placed more emphasis on fuel economy than performance.
Pontiac knew its 350 was becoming uncompetitive in a highly mpg-conscious market. When compared to the 400, its internal components were essentially the same size/weight, the cylinder head design was identical, and the compression ratios were adjusted accordingly to be equal. The only real fuel-saving opportunity the 350 offered over the 400 was a slightly smaller bore, which decreased displacement. In reality, that did little to significantly increase fuel economy over the 400.
Once Pontiac recognized it needed a new engine to compete with the fuel-economy ratings other makes were claiming from their small-displacement mills, it worked diligently to shed weight and improve efficiency of its existing design. Thus, the 301 was born. It weighed about 150 pounds less than the 350, and its induction system was specifically designed to reduce area and maximize port velocity. The result was a very successful low-rpm engine that attained the fuel economy expectations Pontiac was after. It was hung with a negative reputation from hobbyists because it didn't perform as well as a 350 or 400, but most overlook the fact that it was never intended to.
Let's apply Pontiac's approach to the engines you have. You mention the 326 runs but not how well, so I can only presume that both will require complete rebuilds. With that said, I think the 326 is a great engine. It's moderately sized and should provide excellent fuel economy with your intended build. Considering the points I mentioned about the 350, you may be better off rebuilding the 400. Also, if you're operating on a budget, I think replacement parts for the popular 400 are a better value.
Federal Mogul offers high-quality units for the 400 that we've used in the past; I strongly suggest considering them for your build. You can have custom pistons made with a shorter skirt and thinner ring pack to reduce friction and possibly improve economy, but the cost of doing so may exceed your budget, and the effects on mileage could be negligible.
You didn't mention the cylinder heads on your 400, but I'm guessing you plan to stay with original iron castings as costlier aftermarket aluminum units are out of your budget. I don't know that you'd see any benefit selecting original castings with 2.11-inch intake valves over those with 1.96-inch units, so I recommend using whatever your 400 currently has, so long as the compression ratio isn't so low that it kills efficiency (less than 8:1) or so high that it doesn't operate on pump gas (more than 10:1).
I suggest a target compression ratio between 8.5 and 9:1, which will allow reliable operation on mid-grade pump fuel. You might be able to squeeze a bit more power and efficiency out of it with a 9.25 to 9.5:1 compression ratio, and possibly even as much as 10:1, but with the Tempest being your daily driver, you may want to avoid having to spend extra money at the pump for premium-grade fuel.
Camshaft selection will play a critical role in your effort. A hydraulic roller will provide you with the greatest amount of valve-seat time and the least amount of maintenance. The seat time directly relates to valve less overlap, which improves idle quality, low-speed street manners, and ultimately economy. The quick rate at which a hydraulic roller opens and closes the valves will allow for excellent full-throttle performance at the same time. A hydraulic roller setup is quite costly, however, and may not fit your budget. If there's any area where you might consider allocating additional funds, it's here.
I suggest a target compression ratio between 8.5 and 9:1, which will allow reliable operation on mid-grade pump fuel
To achieve your specific goal, I believe you'll need a short-duration camshaft, and I'm not aware of any off-the-shelf grinds in this class. You'll likely need a custom grind. Go with 0.050-inch intake duration in the 210 to 215-degree range with exhaust duration about 10 degrees greater than that. To maximize idle quality, I'd suggest a lobe separation angle (LSA) of 112 to 114 degrees and an intake centerline (ICL) that is 4 degrees advanced (108 to 110 degrees). If you go this route, you'll need specific valvesprings to control the quicker valve action and match the overall valve lift, which needs to be no more than 0.500-inch in your build. Your camshaft supplier can help you with that.
If a flat-tappet setup is your preference, I suggest 0.050-inch intake duration in the 200 to 210 degree range with exhaust duration about 10 degrees greater. The Summit 2800 quickly comes to mind and is an excellent value for the application. It should provide excellent economy and performance, but I suspect not quite as much as a hydraulic roller.
Pontiac's typical cast-iron four-barrel intake manifold is an excellent piece for overall performance and driveability. It is, however, compatible with only spread-bore carburetors such as the Quadrajet. Since your intent is to use fuel injection, an Edelbrock Performer may be a better choice since it performs much like the stocker, but is compatible with all carburetor types, including those with carburetor-like throttle bodies. Its cast-aluminum construction offers some weight saving benefit, too.
Concerning modern fuel-injection systems, I have direct experience with the FAST EZ-EFI system. It contains all the necessary components and sensors for quick and easy installation, including a throttle body with a square-bore bolt pattern. As with most any EFI system you might consider for your Tempest, it will require some modification and fabrication, particularly to the wiring and fuel systems.
While the EZ-EFI learns as you drive, it allows you to further tailor certain settings, such as part-throttle fueling, and can allow you to optimize the fuel curve in light throttle conditions to maximize economy. MSD's Atomic EFI is very similar, and others may be too. You can also consider multi-port systems in which each runner has an individual injector, but the cost and ease of install may dissuade you from those options.
No matter which EFI system you ultimately choose, the manufacturing company can provide you with its capability for spark timing and transmission controlling.
The 200R4 has a moderately deep First gear (2.74:1) and a 0.67:1 Overdrive gear. I don't believe you'll find it economically feasible to swap transmission gears around, but a tight (low-rpm stall-speed) torque converter with a lockup function will reduce slippage and increase economy a bit. Combining this with your existing 2.93:1 rear-axle ratio will provide a good compromise of acceleration away from a stop sign and moderate cruising rpm at highway speeds.
Whether you choose 14- or 17-inch rims, the tire height will generally range from 25 to 27 inches in diameter. While that does affect overall rpm in high gear, it equates to only a couple of hundred rpm, and that's not likely enough to grossly sway acceleration and overall economy one way or the other. Instead, I suggest using the wheel-and-tire combo that best fits your preference and budget. After all, of all the components considered so far, these are likely the easiest to change down the road.
It's worth noting that there are other Pure Pontiac solutions, should you consider them. In 1959, Pontiac's 215hp 389E Economy V-8 was rated at 20-plus mpg in highway driving, and with professional drivers it averaged 21.7 mpg over a 2,400-plus-mile test. Likewise, both the Pontiac 195ci Trophy 4 and 230c OHC-6 promised over 20 mpg on the highway.
Hopefully these suggestions help.
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