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Text and Photography by FM Staff


Overview
What does it take to make 400 horsepower out of a 302? Sure, a supercharger or nitrous will do it, but we're talking naturally aspirated. In this two-part series we will show you that a well built 302, for no more money than a standard performance rebuild, can make 400 or more horsepower at the crank.

In Part One we will detail the short block preparation and assembly, including our cam selection. In Part Two we'll install the heads and intake, and figure out some details for dropping the late model block into an early Mustang project car. Finally we'll get it on the dyno and to the track.

Our motor will be carburated and run a single plane intake, which is going to push the power band pretty high in order to make the ponies we are after.

Block and Crank
We started out with a high-mileage 1989 5.0L block out of a daily driver

Seasoned 1989 5.0L "roller" block.
Mustang. We paid $50 for the short block. You should have no problem getting your hands on a used block for a similar price. We used the late-model roller-block simply because they are abundant, and have more power potential due to the roller cam.

Having 80-90 thousand miles on the engine we know the iron is "seasoned" and ready to work hard. Most engine builders will tell you that used cast iron blocks and heads are much more reliable than brand new castings because they have "settled" by going through many heat cycles.

Our objective was to make this a "budget" rebuild. Although we didn't set out with a specific dollar limit, the goal was to limit as much machine work and new parts expenses as possible.

The cylinder walls still had a nice cross-hatch pattern and showed no signs of damage, indicating
we may be able to get by without boring the cylinders. We had the machine shop

New cam bearings and oil galley plugs.
measure the bores, and they came up with 4.0015", at maximum taper. The piston had another 0.001" of skirt wear. Assuming the honing process would take the bore to 4.002", the block was still within factory tolerances (4.000"- 4.002") They also hot tanked the block to clean it out, and installed fresh cam bearings, freeze and oil galley plugs. This cost us $100 even.

The crank was within factory tolerances for main and rod journal diameters and runout. These are measurements which you should let your machine shop check unless you have the proper micrometer and dial indicators. We got away with a simple crank polish and cleaning for $50.

Pistons and Rods
The initial plan was to use the stock pistons. In 1988 and 1989 Ford put forged TRW pistons in the 5.0L. However, when we mocked up the heads and cam in order to check piston to valve clearance we

Stock 1989 Ford (TRW) Forged piston.
realized the larger intake valve would interfere with stock piston. (See Measuring Piston to Valve Clearance in the Fundamentals section of the Tech Department.) This put a literal bind in our plans to build this motor dirt cheap. Our options were to have the pistons "flycut" (a machining process which grinds larger and deeper valve reliefs into the piston), or to buy new pistons. In terms of cost, it was a wash. Flycutting requires the pistons be removed from the rods, so the labor cost would be $100, plus another $80 for cutting larger reliefs.

Machining the piston makes it neccesary to rebalance the motor; another $200 expense. The final result would
be a piston that is weaker, and still has a limit as to how large a cam we can run. On the other hand, a new set of aftermarket pistons, already cut with large valve reliefs, cost about $200. We'd still have to spend for balancing and getting the pistons pressed on, but at least we'd have the peace of mind that the pistons are good and strong and can accept larger cams in the future.

We decided to go with the Keith Black 281 piston. It's a lightweight flat-top piston which weighs 505 grams, with a 102 gram pin, together this is over 100 grams lighter than a stock piston. A lighter rotating mass translates to less parasitic loss and thus more horsepower. Additionally

Jacks Engines in Oakland,CA handled the machine shop duties.
the KB pistons all come with valve reliefs large enough to accept oversize valves as large as 2.10" and 1.80" intake and exhaust respectively.

Expect to pay between $150 and $200 for a complete balance job. You
will need to bring to the shop your crank, rods, pistons, one set of rings and rod bearings, as well as your harmonic balancer and flywheel or flexplate. If your car is a manual transmission, bring in your clutch pressure plate. A good machine shop will balance the pressure plate separately and give you all the balance specifications so if you need to replace something down the line you can reproduce the balance of that component.
(Short Block Assembly)
 
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In This Article:
We go through the steps and details required to achieve greater than one horsepower per cubic inch from our 302 motor. Part 1 details the parts selection and short block assembly. Part 2 deals with the top end assembly and leads in to the dyno results.


Part I Short Block
Part II Induction
Part III Installation
Part IV Dyno Testing
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