460 Ford Crate Motor 1970 BOSS Mustang

They say that hindsight is 20/20. I believe they are correct!

In 1993, I converted my BOSS 302 from a street cruiser to a drag race vehicle. Then a lot of changes went into this package. I installed an electric water pump, electric engine cooling fan, electric fuel pump and many other items to get the car to run 10.90s. I retained the production charging system because of its light weight.

In 2001, I decided to bring the BOSS back to the street as a Pro-Streeter. This meant reinstalling most of the “street” trim that was removed earlier. Driving on the street showed that I had some short comings. The engine did not want to restart when hot. I then totaled up the amperages when running: electric fuel pump = 20 amps, ignition system = 10 amps, water pump = 20 amps, engine cooling fan = 20 amps etc. Oh boy, that’s over 70 amps on a 55 amp alternator! My electrical system is over-taxed. My next move was to install a 140 amp “one-wire” alternator. This move required that I disconnect the dash mounted ammeter because the new system has the potential to peg the unit and subsequently “smoke” the gauge. As for the water pump, I figured, if it would work on the strip, why not on the street?

With all of this in mind, let’s get to my interpretation of the Hot Rod Magazine article.

HRM Fix the 460 in this Mustang

By Marlan Davis, Photography by Cole Quinnell
Hot Rod Magazine, December, 2012

460 Ford Crate Motor 1970 Boss Mustang

The Combo

Engineer Marcus Simmons has been involved with hot rods, the Detroit automotive industry, and racing his entire adult life. He’s owned his ’70 Mustang Boss 302 almost as long, ordering it brand-new from the dealer back in late 1969. Since then, the car has gone from a street cruiser (having done a cross-country jaunt to California back in 1972 and a 140-mph-plus Banzai run down the freeway), to a full-on, pure drag racer, to its present incarnation as a Pro Street car. Currently, the car runs a 560hp 460 Ford big-block crate motor, C6 automatic Trans, and 4.57:1-geared 9-inch Ford rearend with a Detroit Locker diff and 31-spline axles.

Southfield, Michigan's Marcus Simmons has owned his '70 Boss 302 Mustang since he bought it new. Although now blind, he still rides shotgun in the car on cruise nights.

In its long career, the car has been a street- driven muscle car, a pure race car, and has now been returned to the street in Pro Street guise.

Mr. Simmons complained the car's current 460 big-block wouldn't crank when hot. Was it the starter, the electrical supply system, the cooling system, or some combination of those factors?

The Problem

Even under the best of conditions, transforming a gutted race car back into a streetable vehicle is a lot of work. In Marcus’ case, it was made even tougher, as he is now blind. The diagnostics and troubleshooting Marcus was once able to perform himself at his fabrication shop, Simmons BOSS CREATIONS, must now occasionally be farmed out to third parties. When he contacted HOT ROD, Marcus’ main complaint was "the vehicle will not turn over when hot. I am using 00-gauge battery cables from the 850-CCA Motorcraft battery and a dedicated 0-gauge negative return cable back to the battery. When that didn’t help, I added a layer of starter wrap to the starter. No change, even after adding a second layer."

Further conversation revealed that "running hot" meant as high as 240 degrees F in traffic--this despite a big Summit Racing aluminum crossflow radiator; a shroud-mounted 3,300-cfm Flex-a-lite electric fan; a Meziere electric water pump; and Evans waterless coolant. When a vehicle gets that hot, all sorts of things can go wrong, and not just with the starter. If the coolant temperature was 240 degrees F, the oil temperature could be approaching 300 degrees F, putting the engine in serious danger of meltdown.

On the electrical side, Marcus seemingly should have had it covered with the big battery, the fat cables, and a typically highly efficient, 140-amp GM 12SI alternator. Still, when things get that hot, you could be looking at a case of excessive voltage drop compounded by heat soak.

So was the problem caused by the cooling system, the electrical system, or both of them? To find out, we sent the car to Diversified Creations, a high-end Detroit-area shop that does everything from dyno-tuning to complete, ground-up car fabrication. Regular readers may recall Diversified as the builders of the HOT ROD E-Rod Z28 Camaro.

The Fix: Cooling

Reasoning that it was impossible to diagnose the starting problem until the overheating issues were addressed, Diversified first checked each cooling-system component. The big 460 had been dropped in the former drag-race car using a front engine plate in lieu of normal side mounts. This led to clearance issues with stock-style accessory drives. Mr. Simmons had to mount the large aluminum radiator at about a 15-degree back rake for engine-plate, water-pump, electric-fan, and alternator clearance (the radiator bottom bolts in front of the core support and the top is behind the core support). The odd radiator installation; the engine bay–spanning, bulky engine plate; the old Mustang chassis’ intrusive high-mount shock towers; and tight-fitting, heat-radiating, big-tube exhaust headers collectively made for poor engine-compartment air circulation. As Diversified’s head honcho, Mike Copeland, put it, "There’s just no place for heat to go, so it heat-soaks everything." Diversified found that at least the thermostat was opening, the electric fan was getting juice and moving air, and significant radiator inlet and outlet temperature differentials indicated the radiator was in fact cooling.

On the downside, the radiator cap wouldn't maintain system pressure. Diversified replaced the modified cap with a new 16-psi one, which should have improved the cooling system's efficiency. But at this point, the now-higher system pressure resulted in leakage out of the thermostat-housing gasket as well as from the silicone beads sealing the water pump to the front-engine mounting plate and the mounting plate to the engine. Replacing the leaking thermo-housing gasket was a cinch; fixing the leaks in the engine plate took some effort. Diversified TIG-welded shut the plate's ragged and misaligned coolant-transfer holes, then carefully drilled new, properly aligned holes. Stock 460 Ford water-pump gaskets were then installed on the plates' water-pump side, and custom gaskets fabricated from universal sheet-gasket material were made for the engine side.

460 Ford Crate Motor 1970 Boss Mustang01 The radiator cap had been modified, so it couldn't hold pressure. Apparently,this was another shop's "fix" for persistent coolant leaks. Always run the highest pressure the cooling system can tolerate; the higher the pressure, the more effective its cooling ability, as higher pressures raise the coolant medium's boiling point. The modified cap was replaced by this new, 16-psi cap.
460 Ford Crate Motor 1970 Boss Mustang02 The cooling system runs just water because the car may still sees some track time (leakage of ethylene glycol–based coolants makes the track surface slippery). Pure water is also a superior coolant in its own right. However, to prevent corrosion and enhance cooling efficiency even more, Diversified poured in two bottles of Flex-a-lite's Flex-a-Chill additive, a track-safe solution that's said to reduce engine temps by 20 degrees F.
460 Ford Crate Motor 1970 Boss Mustang03 While OK for drag racing, the 35-gpm Meziere electric pump (right) didn't flow enough volume to meet a street-driven vehicle's cooling needs. It was replaced with Meziere's blue 55-gpm Hi-Flow big-block pump (PN WP308B, left). Although the pump's larger motor extends the pump envelope, it still cleared the radiator by about 4 inches, providing room for the fan.

As received, the vehicle had a drag racing--style Meziere electric pump that flowed just 35 gpm (gallons/minute)--not enough for street use. This was replaced by a gonzo 55-gpm Meziere electric pump. It has no internal bypass, so to prevent cavitation, Diversified replaced the stock thermostat with a Moroso restrictor plate. The water pump needed larger inlet fittings, plus a new, larger, 1-3/4-inch-Id radiator hose. Lead Tech Scott Rouston isn't exactly sure what stock application the new molded hose he used is from, other than it's a Gates product; he went down to the local auto parts store and pulled one that "looked right" off its ceiling hanger. It required only slight trimming for proper fitment.

Sheetmetal closeout plates were also fabbed up to direct grille airflow through the radiator core (rather than letting it escape around its periphery). The cooling fixes brought overall engine gauge temps down to a satisfactory 190 degrees F, solving the engine overheating problem. Still, even with the hood off, engine-bay temps remained higher than optimal: 105 degrees F in front of the core support, 130 degrees at the front of the motor plate--but 210 degrees at the firewall. Short of re-engineering the entire engine installation, this was as good as it was gonna get.

460 Ford Crate Motor 1970 Boss Mustang

  1. 16-PSI Radiator Cap
  2. Flex-a-Chill Additive
  3. Meziere 55-GPM Electric Water Pump
  4. A Fix Coolant Leaks
  5. Moroso Restrictor Plate
  6. Closeout Plates
  7. Diagnose Electric Charging problem
  8. Rewire Alternator
  9. Trunk-Mounted Optima Battery

The Fix: Electrical

With engine temps now stable, Diversified turned to the electrical system. Voltage checks revealed both battery and alternator issuess. Proper charging wasn't an issue when the vehicle was still a full-on race car; it was normal for the team to put the vehicle on a charger at the shop and then spend the day at the racetrack. But now, cruising on the street, the vehicle had cranking problems after it got hot under sustained operation, and there was no handy access to the external charger.

At first, it seemed the battery was just ancient and worn out, but the warranty tag showed it to be relatively new. It had prematurely aged both functionally because the charging system wasn't up to snuff. Under operating conditions, the battery was constantly discharging. As a first step, Diversified replaced the Motorcraft battery with an Optima RedTop Absorbed Glass-Mat dry-cell battery, then ran more voltage tests.

It turned out the exciter wire that normally runs from an ignition terminal to the GM 12SI alternator's No. 1 terminal wasn't installed. Without a functional exciter wire, the alternator wouldn't charge until engine speed climbed past 2,000 rpm. At that point the alternator finally self-excited, yet when rpm dropped back to idle it still put out just 12.6 volts. This was inadiquate with all the car's electrical accessories, which was why the battery was losing charge under normal low-speed street-driving conditions. Diversified correctly added a exciter wire and added an inline resistor to mimic a stock GM dash-mounted idiot light bulb. The alternator needs resistance in the exciter-wire circuit to ensure proper turn-on and turn-off functionality.

There was also some concern about the alternator's underdrive pulley (another race-car trick that really has no place on a street-driven car). Diversified looked at adding a larger pulley, but clearance issues would require re-engineering the entire front drive and mounting system. In any case, in this instance, the exciter-wire fix proved sufficient to allow the 140-amp alternator to maintain proper low-speed charging capability.

460 Ford Crate Motor 1970 Boss Mustang04 The new pump has no coolant bypass; when the thermostat is closed on a cold engine, the resulting cavitation can shorten pump life. The workaround: Replace the thermostat with a restrictor plate. Moroso's kit (PN 63440) fits most Chevy and Ford V8s. Three different-hole-size restrictors are supplied: a yellow 5/8 -inch, a blue 3/4-inch, and a red 1 -inch. The 460 preferred the 1-incher.
460 Ford Crate Motor 1970 Boss Mustang05 At speed, much of the air sucked in through the grille took the path of least resistance, bypassing around the radiator sides and top instead of going through the core.
460 Ford Crate Motor 1970 Boss Mustang06 Blocking off these open areas by creating closeout panels from 18-gauge mild-steel sheetmetal and 1/8-inch pop rivets greatly improved cooling efficiency.


After resolving the overheating and charging issues, the starter now cranks fine under all conditions. The engine temp stays at 190 degrees F, the alternator maintains 14.7 volts, and the starter receives no less than 12.8 volts. Now Mr. Simmons, riding shotgun, can once again partake in Detroit's hot summer cruise nights with no problems.

Lessons Learned

Any doctor will tell you: Don't treat the symptoms--diagnose the cause to find the cure. Cough medicine may suppress the cough, but why are you coughing? Likewise, the cranking problem was only a manifestation of excessive engine temps, plus a charging problem. Voltage and temperature tests will show where the real problems lie.

460 Ford Crate Motor 1970 Boss Mustang07 Diversified performed electrical voltage checks on the vehicle (see table) and realized two things about the electrical system: The battery wasn't holding a charge and the alternator wasn't putting out enough juice under 2,000 rpm. You could tell this because the cold-engine voltage, after charging the battery all night, was normal, but after sustained running, the voltage dropped when checked hot.
460 Ford Crate Motor 1970 Boss Mustang08 The 140-amp GM 12SI alternator didn't charge properly at low rpm because its brown exciter wire wasn't hooked up. Diversified ran it to one of the Summit Racing CD ignition control box's ignition terminals, thenadded an inline 50-ohm/10-watt resistor. This let the car properly charge every time the engine was running.
460 Ford Crate Motor 1970 Boss Mustang09 Prematurely aged from too many charge/discharge cycles, the Motorcraft battery was replaced by an Optima Spiralcell RedTop Group 34/78 dual-terminal battery with a beefy 800-CCA (cold cranking amps) rating. Optima nonspillable, maintenance-free,vibration-resistant batteries carry a 36-month free-replacement warranty.

Voltage Test Results

  Before Fix After Fix
Check Point and Condition Cold Hot Cold Hot
Battery, engine off 12.9 12.6
Alternator, engine off 12.9 12.6
Starter primary cable, engine crank 10.5 9.9 12.8 12.8
Alternator, engine on, sustained idling 13.0 14.7
Alternator, engine on, over 2,000 rpm 14.4
Battery, engine on, sustained idling 12.6 14.2
Battery, engine on, over 2,000 rpm 13.9
Note: All values are in volts.        

Parts and Prices
460 Ford Crate Motor 1970 Boss Mustang
10 Way back in 1972, when it was still a street muscle car, Simmons drove the '70 Boss 302 Mustang all the way out from Detroit to California, where he visited HOT ROD's old Hollywood offices. Here is the photo as it appeared in our very first Readers' Rides section. "I was just breaking in a new engine," Mr. Simmons says.

Summit Racing Equipment
PO Box 909
OH  44398
Optima Batteries, Inc.
5757 N. Green Bay Ave.
WI  53209
Allstar Performance
8300 Lane Drive
Diversified Creations
Fel-Pro/Federal Mogul Southfield
Radio Shack
Flex-a-Lite Consolidated
Dept. 50
P.O. Box 580
WA  98354
Meziere Enterprises
220 S. Hale Ave.
CA  92029
Gates Corp
Moroso Performance Products
80 Carter Drive
CT  06437
Simmons Boss Creations
Marcus Simmons
Southfield, Michigan's Marcus Simmons has owned his '70 Boss 302 Mustang since he bought it new. Although now blind, he still rides shotgun in the car on cruise nights.
460 Ford Crate Motor 1970 Boss Mustang
In its long career, the car has been a street- driven muscle car, a pure race car, and has now been returned to the street in Pro Street guise.
460 Ford Crate Motor 1970 Boss Mustang
Mr. Simmons complained the car's current 460 big-block wouldn't crank when hot. Was it the starter, the electrical supply system, the cooling system, or some combination of those factors?
460 Ford Crate Motor 1970 Boss Mustang
Diversified Creations' lead tech Scott Rouston (shown) and assistant Justin Oleski diagnosed and fixed the car's problems. Here, a heat gun is used to map engine-bay temperatures.
460 Ford Crate Motor 1970 Boss Mustang
It turned out the starter cranked fine--once the weak electrical and cooling systems were dialed in. Bolting-in this higher-capacity Meziere electric water pump helped cure the car's cooling problem.
460 Ford Crate Motor 1970 Boss Mustang
Ready to rumble: The vehicle now runs all day at 190 degrees F, the alternator properly charges the new battery, and the starter is “cranky" no more.