Ford Small-Block V8 Engine Swap - Swapping From Six To Eight

The most efficient cooling package is an aluminum radiator with twin electric cooling fans. You want at least 2,500-3,000cfm fan capacity for optimum cooling. Figure in a thermostatic switch, a manual bypass switch, and a fan relay for best results.

Header size and type is very important. Long-tube headers yield the best performance. However, they also give off a lot of heat. Shorty headers offer less performance, but give you a break in the heat department. Cast-iron exhaust manifolds offer the lowest performance of all, yet they yield less maintenance and noise.

Exhaust system selection is more crucial than header choice because performance and noise levels are of utmost consideration. Cabin noise levels are more important than performance because excessive cabin noise will damage your hearing. Exhaust pipes must be the right size. Mild street Mustangs need 2 to 2 ¼-inch pipes. They do not need 2 ½- or 3-inch sewer pipes. When you start courting 2 ½- and 3-inch pipes, fit becomes a huge challenge. Keep it simple and modestly sized.

We chose to go with a Tremec T5 five-speed transmission for efficiency and enjoyable driving. You will need the entire package -- transmission, bellhousing, clutch, flywheel (must be match balanced to the engine), crossmember and transmission mount, shifter, driveshaft, and clutch disengagement mechanism.

The T5 transmission is a good fit, but not everywhere. It gets tight at the shifter passage in the transmission tunnel. Some trimming is required.

Axle ratio is important to drivability and efficiency. When we say "3.00:1" ratio, that means three driveshaft revolutions for every one axle revolution. This determines where your engine is rpm-wise when you're in straight drive and overdrive. When you have overdrive, you need a higher axle ratio to keep your engine in its power band during cruise. So 3.55:1 and 3.70:1 make more sense with overdrive. In straight drive, you need a lower ratio around 2.80:1 to 3.00:1 to keep cruise rpm conservative.

For the kind of power our 289 makes, we're able to get by with an 8-inch Ford rear end. Because we've gone with overdrive, we contacted Randy's Ring & Pinion for a Limited-Slip differential with 3.55:1 cogs, which puts the 289 at around 2,000 rpm at 70 mph in overdrive. If you go with 3.00:1 or 3.25:1 gears, this drops the 289 below its power band. If you're going with straight drive - a C4 or Top-Loader three- or four-speed transmission - axle ratio needs to be 2.79:1, 2.80:1, or 3.00:1 for optimum street performance and efficiency. If you want more pep, go with 3.00:1 or 3.25:1.

Inland Empire Driveline and Mustangs Plus set us up with an aluminum driveshaft package that included slip yoke and both universal joints already assembled and ready for installation. Remember, you need to provide Mustangs Plus with proper information. If you have a 9-inch rear end and you receive a driveshaft for 8-inch, the shaft will be too long. By the same token, if you have an 8-inch rear end and receive a shaft for 9-inch, you will come up short.

When you swap from a six to a V-8, you have to install a V-8 accelerator linkage. And remember - does it have an automatic or a stick? The transmission kick-down lever applies only if you have a vintage C4 or C6 transmission. If you have an AOD, it's a different ballgame because you're using a throttle valve cable set-up.

We suggest getting away from a classic Mustang's original externally regulated charging system and going with an internally regulated, high-amp, single-wire alternator. We've found the best single-wire alternator out there is the Powermaster 3G alternator. This is the Tough Stuff single-wire, high-amp alternator from Mustangs Plus.

While you're busy gutting your classic six-cylinder Mustang in preparation for V-8 power, we encourage you to replace brake and fuel lines. And if you're doing a '65-'66 or early '67 Mustang, opt for a late '67 through '69 fuel line package, which is safer and less vulnerable to damage.

Although four-wheel disc brakes are nice to have, they're not always practical for tight budgets. At the least, you want power front disc brakes and a dual braking system for optimum safety. Opt for the heavier '70-up spindle, which is more durable than we normally see for '65-'69. If you go with the heavier spindle, you will need the appropriate outer tie-rod ends from Mustangs Plus. Street slang for this piece is the "Granada spindle."

Choose the best suspension components available for the money. Scott Drake Reproductions makes really nice upper and lower control arms that are authentic in appearance. These are Grab-A-Trak components from Mustangs Plus we chose to assemble ourselves. Lower control arms needed to be painted.

We chose 620 lb. coil springs for exceptional handling. They also lower ride height by 1-inch.

These are four-leaf, mid-eye Grab-A-Trak springs from Mustangs Plus. The mid-eye configuration lowers ride height by 1-2-inches. We suggest the use of urethane bushings for improved stability.

Grab-A-Trak gas shocks offer a smoother ride than KYB gas adjustables. However, you can adjust the KYB units for smooth or harsh ride depending on what you desire for handling.

We tossed the factory sway bar and went with this 1-inch sway bar from Mustangs Plus with urethane links and bushings for better handling -- a reduced roll rate and improved stability.

We called Jerry Choate at Scott Drake Reproductions and asked for a set of '67 14 x 5 ½-inch styled steel wheels with all the trimmings. Then, we transferred the tires from the six-cylinder four-hole rims to our styled steel units.