Muscle Car Time Machine
Our Tech Insider takes a step back in time to create the ideal muscle car. Come along for the ride.
Words: Larry Shepard
The topic of automobiles and engines can be very complicated, indeed. Over the course of history, there have been many automotive eras, but perhaps the best known and most popular auto-related era is the muscle car era. At the end of the 1971 model year, production on the 426 HEMI® and the 440-6-bbl ceased. At the end of the 1978–1979 model years, all big block production was discontinued.
You can argue the merits of the various nominations for the best muscle car from this era. So the question becomes: What would you do if you could go back in time and build a better muscle car? To help us focus on a specific vehicle, let’s put some limits on the field. Our muscle car will be driven daily rather than raced. The 1968 426 HEMI A-Body cars are the most popular race cars today.
To make it somewhat more fun, let’s rule out the new 5.7L, 6.1L or 6.4L (392 cid) HEMI engines from the vehicle, along with multi-point injection. That would mean that the induction system is carburetor-based. We are still left with lots of options, so which approach should we choose? NHRA drag racing has classes for new cars that use older engines that are called GT classes. We’ll do our improved muscle car somewhat in reverse as we install new technology and parts into older engine/car packages.
In no particular order, let’s begin our improved time-machine car with a 318 4-bbl. You need an aluminum dual-plane intake like P4876335. The 318 engine was used in almost all body styles from 1967 thru the 1980s, but it was only an actual production engine in the late 1980s. To this basic package, you can add a good set of heads like the LA aluminum cylinder head P5153849. The stock 318 heads use small valves so you’ll want to upgrade. While the production 318 4-bbl used a Thermo-Quad carburetor, they are hard to find today so I would recommend an Edelbrock AVS 500 or 600 cfm carb. Now you would have 340 performance with 318 fuel economy—the best of both worlds.
The next candidate is the 360 6-bbl in the A-Body—bigger engine, light car. The 340 6-bbl was only installed in the E-Body cars, which are heavier than the A-Bodies and the 6-barrel induction system was only installed on the 340. To create a 360 version, you will need the aluminum 6-barrel intake manifold P4529054. While you could use the good 360 high-performance heads, the 308 or 576 castings didn’t appear on 360 production engines until the late 1980s and mostly on trucks, so you could use the same aluminum heads as the 318 or you could upgrade to the bigger port version—P4876310AB. This big-port head also requires the offset W2-style rocker arms like P5153586.
The low-deck, big blocks commonly called 383s and 400s can also be upgraded by using a 6-barrel intake system, which requires the aluminum intake manifold P4529055. The 6-bbl was not a production option on these engines. Most of the 426 HEMI engines built in this era used dual-4-barrel induction systems. The most common was the Street HEMI engine (1966–1967), which used two AFBs in-line. Switching to a single-4bbl requires a new intake manifold (P4876188). To maintain performance, use an 850-cfm Holley carb with vacuum secondaries. You can use a 750-cfm version to gain fuel economy and throttle response but you trade it for a few horsepower. You could also consider an Edelbrock AVS carb rated similarly—750 or 800 sizes.
Perhaps the 440 engine has the most options. One of the easiest is to make a 440 6-bbl, which requires the aluminum intake manifold P4529056. I would recommend upgrading the cylinder heads at the same time. There are many choices for big block heads and I selected the aluminum 440 head (P5153524). The Max Wedge heads were discontinued in 1964 and for the next 35 years were the desired swaps for all big blocks but were hard to find. Today new Max Wedge cast iron heads like P5249824 are available. You also will need a single 4-barrel intake manifold (P4876128) to complete the package. Carb choices are similar to the one 4-bbl HEMI mentioned earlier.
All of these engine packages share some common considerations that I’ll cover quickly. Since we limited our discussion to carbureted induction systems, the first thought is to be sure that parts are readily available. Holley carbs should be vacuum-secondary models. Edelbrock makes new AFB carbs along with the newer AVS carbs in several sizes. The 1972 and newer ThermoQuad carbs are good carbs, but parts are hard to find so they were not discussed. Where available, use the AVS version for street applications. The three 2-barrel Holley system was last used in production in 1971 but the three carbs (several versions) are still available new from Mopar Performance. The 318-340-360 small block carbs, like P4349239 ends and P4349241 center, can be used on the similar-sized 383s and 400s. As a general consideration, the 6-barrel style of induction system is the best overall choice for the street because you use the end carbs for power and the center carb for driveability and fuel economy.
A typical set of aluminum heads for these V-8 engines saves about 50 pounds. Lighter weight is better for both performance and fuel economy. Most of the muscle car era engines used cast iron heads and cast iron intakes, so aluminum upgrade parts help both aspects. For general street use, you would prefer a dual-plane intake design over a single-plane design. The 6-barrel intakes listed are also considered dual-planes. Selecting parts for dual-purpose use can be a trade-off, and cams offer many possibilities. You would like more lift than the stock or production cams to match the high-flow heads and induction system. More cam lift tends to come with more duration. The way to solve these concerns for street/dual purpose engines is to use cams that are ground on wide centerlines like P5007696 (A-engine) or P5007697 (B-RB engine). Both are ground on 114 centers along with .484" lift and 284° duration. Note: .430" to .450" lift with 268° to 276°duration are common high-performance cam numbers. The wide centers keep the overlap down or low, and this feature helps low speed engine performance characteristics like torque, driveability and fuel economy.
Another aspect of engines built in this era is that long stroke cranks have become readily available in the last few years. The 4.15" crank like P5007250 for the big blocks is very popular but less well known are the 4.00" cranks for the A-engine small blocks like P5007256 (cast) and the 3.58" stroke cranks like P5007257 for the small-main 318 and 340 blocks. As an example, this allows the economy 318 to become 343 inches or bigger.
Our time machine engine obviously has to be installed in a body. Availability and popularity has made the E-Body versions expensive. The B-Body and A-Body cars are also becoming popular. The somewhat newer F-Body (1978 and up) offers some options that are less expensive and more readily available. The problem is that none of these cars came with any of the big-block engines. This is solved by Schumacher Creative Services (206-364-7151 or www.engine-swaps.com) who makes bolt-in motor mounts to allow this swap.
With any muscle car project, you should not ignore the chassis. Smaller engines tend to get better fuel economy, but larger engines—along with additional displacement—can be more fun. If you build a larger engine, either by engine swap or longer stroke crank installation, the first thought might be less economy. However, one of your options would be to turn the engines slower. To do this, you might consider installing a taller rear axle ratio (use a 2.76 in place of a 3.91, for example). Today you have other options. The most popular transmission for our cars is the Torqueflite automatic (3-speed). The manual transmission tends to get better fuel mileage. Parts for the A833 (4-speed) are now available from Passon Performance (www.passonperformance.com). Using an overdrive transmission allows you to have the low-numerical axle ratio (3.91 or 4.10) and still have low cruising rpms. The 5-speed HD Tremec manual transmission from Keisler Overdrive (www.keislerauto.com) is one approach. Using the 4-speed overdrive automatics, called A500s or A518s depending on the engine, offers similar gains for automatic transmission-equipped cars. This is done by using an adapter from SMR Transmissions (www.smrtrans.com).
