A 500hp 1973 Mercury Comet Quest For 10s

After chunking a few bearings, Tom solved his oiling problems with a high-volume pump, this Milodon windage tray, an 8-quart oil pan, and a Ford Racing restrictor kit.

Dyno Days

With the final assembly completed, Tom entered what the boys at Westech call "The Polygraph Room" where he bolted the 306 to Westech's SF-901 dyno. The power quest began with a Victor Jr. intake and a 750-cfm Demon carburetor, but that was just to ensure the engine made acceptable power. Next, Tom bolted on his fabricated intake and eight-coil ignition with the FAST controller and set to tuning fuel and spark.

The Comp Cams beehive springs were originally designed to control hydraulic-roller-cammed big-block Chevys. Tom further reduced the chance of valve float with Comp titanium retainers. The 1.6:1 rockers are Comp Pro Magnums.

Once Tom had the engine fine-tuned, he uncovered some interesting personality traits. To no one's surprise, the engine was very peaky: utmost horsepower occurs at a stratospheric 7,100 while max torque hovers around 6,200. Not only that, but the engine clearly prefered larger 134-inch headers over the smaller, chassis-friendly 158-inch versions. The bigger headers made 10 more numbers everywhere in the curve, so it's a shame they won't fit in the car.

Oil's Not Well

One reason for choosing a '93 Explorer engine was to employ the factory 36-1 tooth wheel as a budget crank trigger. The factory Ford pickup and wiring harness make life even easier.

After his first set of dyno flogs, Tom discovered several distressed rod and main bearings. This predicated the addition of a Manley high-volume oil pump and an ARP pump shaft to improve oil flow to the rotating assembly. A stronger oil-pump shaft is critical since small-block Fords are famous for twisting them in two, even on mild small-blocks. A subsequent teardown indicated that even this didn't solve the problem. Tom next added an SVO engine oil restrictor kit and tossed the factory Ford hydraulic rollers in favor of a set of Comp mechanical rollers: "I didn't even want to play the game of seeing how much oil I could restrict with hydraulic lifters." It seems the hydraulic rollers pump much more oil to the top end, starving the rest of the engine. This is mainly due to the fact that the little Windsors are designed to direct oil through the lifters first, then down to the mains and rods. "I wore it out twice before we got that figured out," Tom said.

The intake manifold is a Weiand tunnel-ram base with a lid fabricated by Tom. He also used generic FAST fuel rails and bungs to complete the conversion to EFI. The throttle-body is an Accufab oval piece for a 4.6L Cobra.

Rule Number 7 in The Great Book of Camshafts will tell you not to run solid-roller lifters on a hydraulic-roller cam. The fundamental difference comes down to a lack of clearance ramps on the hydraulic-roller cam. Clearance ramps are a gentler lifter rise built into a mechanical-lifter lobe that closes up the 0.018 to 0.020 inch of lash built into all solid lifter camshafts. Tom meditated with his cam guru and dialed in 0.004 inch of hot lash into his valvetrain and has yet to have a problem. But maybe that's because Tom likes living on the edge. "It's definitely noisy. But the purpose of this car is to be noisy and pissed off."

Let the Beatings Continue

Tom employed 36 lb/hr FAST high-impedance injectors capable of flowing well in excess of 250 lb/hr of fuel, sufficient for over 500 hp and controlled by the FAST EFI computer.

So far we've covered the buildup and dyno sessions. By the time Tom bolted the motor in the car and got as close as low 10s with an automatic, he realized it was time for a manual gearbox. At that point, Tom says, "I had over 80 recorded engine dyno pulls and well over 180 runs altogether on both the engine and chassis dyno, not counting the runs down the dragstrip. That's pretty sick when you think about it!"

There's as much of a story on Tom's trials with traction and pulling off his 10-second dream as the engine buildup, so we'll save all the good drivetrain stuff for next month. Until then, mull over how much those stock cast main caps are moving around at 500 hp at 7,100 rpm!

Dyno Time

Test 1: The 306ci small-block with 158-inch chassis headers and 91-octane pump gas.

Since he used a distributorless ignition system, Tom plugged the original distributor hole with the factory stub drive. The cam sensor is not used with the speed-density system but could easily be connected if Tom wanted to convert this package over to sequential fuel injection.

Test 2: Same configuration with 134-inch headers and VP Ultimate 4 motorcycle race gas that is highly oxygenated. The headers alone made about a 32hp peak increase, while rest of the gains are from the fuel. This is one of Tom's power secrets, and we plan to investigate more on that later.

	TEST 1			TEST 2			DIFFERENCE
RPM	TQ	HP		TQ	HP		TQ	HP
4,600	352	308		382	335		+30	+27
4,800	365	334		389	356		+24	+22
5,000	375	357		391	373		+16	+16
5,200	375	371		393	389		+18	+18
5,400	376	387		394	406		+18	+19
5,600	380	405		398	424		+18	+19
5,800	376	416		396	438		+20	+22
6,000	375	428		399	456		+24	+28
6,200	375	442		401	473		+26	+31
6,400	371	452		401	489		+30	+37
6,600	364	458		396	498		+32	+40
6,800	358	464		391	507		+33	+43
7,000	353	470		382	510		+29	+40
7,200	342	469		372	510		+30	+41
7,400	332	469		353	498		+21	+29
Peak	378	472		403	512
Power/ci	1.23	1.54		1.31	1.67

This is what happens when valvesprings break. Luckily, Tom avoided complete engine destruction, replacing one valve and stepping up to the beehive springs that are on the engine now.

AFR 185 CNC Windsor Ford Flow Test

These are the flow numbers on the Westech bench using Tom's heads that are angle milled to 51cc chambers. This is with his 2.20/1.60-inch valves and valve job on a 4.030-inch bore with a radiused entry on the intake side and no flow tube on the exhaust side.

E/I represents the flow relationship in percentage of the exhaust port to the intake port. Generally, percentages over 70 to 75 percent are considered good.