Killer Cougar?My '91 Mercury Cougar has a factory-installed 5.0L and AOD, and it's done a fine job for 160,000 miles. I love this car, but now I want it to roar with today's performance cars. Lots of people tell me to get a 'Stang or a Camaro, but I like my ride, even if it's heavy. I've read many articles on engine swaps and many more on crate engines and strokers. In your opinion, would a swap to a stroked 351W with EFI be better (in terms of cost and labor) than boring, stroking, and adding Trick Flow or Edelbrock heads to the existing 302? Are the factory '91 heads performance units or just standard 5.0 heads? Does anyone offer headers for the 302 or 351 in this application? How about a cowl-induction hood? I also think I need to change the rear gears to something in the 3.50 to 3.70 range, and possibly add a 2,500 to 2,800-stall converter. I value your input and suggestions. K. ForwardFranklin, TN
First off, you should probably forget about the 351W in that Cougar. When that body style was first introduced, the V-8 was not even offered, so when Ford had to go back and fit it because consumers wanted the extra power, a new, lower-profile EFI intake manifold had to be designed to fit under the car's extra-low hood line. Since the 351W is a tall-deck version of the standard small-block Ford, the extra height will be a problem, as will the added width.
If you're bent on extra cubes, build a stroked 5.0 using a 347 kit, available from a number of sources. This will allow you to effectively gain a significantly larger displacement while maintaining the stock external dimensions. If you are going to build an engine, you might want to source a 5.0L H.O. block from a Mustang or Lincoln LSC. These blocks have the taller lifter bores and retainer provisions that will allow you to run a factory hydraulic-roller cam.
Even a basic rebuild of a 5.0 H.O. will provide a sound foundation for more power. Using aftermarket heads as you suggested will make a major improvement, as your stock heads are lame standard-output units. Combine the upgraded heads with a better intake-try the Cobra manifold for the '94-'95 SN95 Mustangs, which is also designed for low-profile applications. We were unable to find headers for your application, though it's possible that Mustang shorty headers will work. Check with some of the Fox Mustang header makers for possible insights.
The rear-gear swap is a good idea, though we'd probably go with either 3.73s or 4.10s and leave the torque converter alone for now, or at least until you have the trans rebuilt.
Balance JobI understand that most Chevy 383 stroker kits incorporate external balancing by using a Chevy 400-style damper and flexplate. Even kits that are sold as balanced rotating assemblies frequently use the 400 damper and flexplate. Some kits, however claim to be "neutrally balanced." I have been lead to believe the GM Performance Parts HT383 crate truck motor is internally balanced like a standard 350. If this is true, can you clarify the differences and advise which is better, assuming a new crank is required? Robert l. KeelingLouisville, KY
When balancing an engine, the mass of the components hung on the rod journals of the crankshaft must be brought into balance by offsetting weight on the counterweights of the crankshaft. The balance factor takes into account the motion of the components, factoring 100 percent of the reciprocating weight and typically 50 percent of the rotating mass. Unfortunately, the standard GM 400 crankshaft traditionally used in these engines does not have enough counterweight mass to bring the assembly in balance. While the crank's counterweights themselves lack the required mass, GM's clever powertrain engineers simply hung the required weight at each end of the crank with eccentrically balanced dampers and flywheels/flexplates, creating "externally" balanced engines.
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