Budget Ford Mustang Build - Back-To-Basics Budget 5.0 Buildup Part 2 - Tech

Cheap Power Iron Cylinder Heads
If the existing heads on the engine are good, then they can be given a basic do-it-yourself porting job that will use up about a couple of weekends of time. But be aware that 5.0s tend to wear out valveguides, so if the odometer has more than 100,000 miles on it, you have only a one-in-four chance of owning heads with guides fit for further use. Our spare heads needed guides, but the original heads on this test engine did not. Because of this, we are not including the cost of the seat and guide job here, but chances are you will need to consider this option.

Getting fresh guides can be done one of two ways. The first option is to have K Line guide liners or regular brass/bronze guides installed and the seats recut. Expect this to run in the neighborhood of $180, and if the valve stems are good (as is often the case) they can be reused. Your second option is to use the oversized stem, stock replacement valves, sold to the trade by Engine Tech in Carrollton, Texas. These valves have a +0.015 stem and a +0.030 valve head on both intake and exhaust. To convert will cost about $220, but your heads will now have oversized valves, which is a plus. Also, note that these valves have the keeper grooves about 0.030 inch lower, so if you intend to use higher lift than a stock cam and stiffer springs, they will need to be used with +0.050-inch keepers to regain installed spring height.

Back to the porting. Nothing other than reducing the obstruction caused by the valveguide bosses and blending in port irregularities was done on these heads. The main body of either port was not enlarged other than what it took to clean up major bumps in the casting with a 60-grit emery roll (you will need about two dozen of them). Close attention was paid to blending in the port pocket with the valve seats. The valves had the sharp edge formed between the seat, and the back face of the valve was rounded off so the back transitioned into the seat progressively. Check out the graph (Fig. 1) and you will see that extra flow is achieved right off the seat. This is due to the smooth blend of the ports into the seats. Because extra air is now accessible by the engine throughout the lift range used by even the stock cam and valvetrain, we can expect a decent return in output for the time invested.

With 0.030-inch shims under the springs to increase the spring force, the spare ported heads were assembled and set to one side, ready to swap out with the stockers when we go to the dyno.

Meanwhile, the rest of the engine was rebuilt using the head gaskets in our Speed-O-Motive gasket kit. After they were cleaned, the cam, lifters, and pushrods all went back in the same position they came from. A note here concerning head bolts. We managed to get the threads smooth by using a wire brush in a drill press. The threads must be smooth so they do not have excessive friction, otherwise the clamping loads on the head gaskets will be below par. As such, the head gaskets will blow easier when nitrous is used. If there is any doubt about the usability of the bolts, replace them with new ones.

Engine Dyno Break-In
To break-in our engine and check that all was well before we installed it in a car, it was run on our DTS engine dyno. Since (at that time) the dyno was not equipped to run a fuel-injected 5.0, the long-block was fitted with an Edelbrock Performer intake manifold and a Barry Grant 650 Speed Demon carb along with a mechanical distributor supplied by Performance Distributors. After a two-hour break-in, the carb and timing were optimized and the figures in the chart (Fig. 2) were achieved. For an otherwise-stock engine, this unit was putting out some good numbers, but we knew some of that power would go away when the fuel-injection system was fitted after engine installation in the vehicle.

After break-in and servicing, the engine was installed into the car. Remember, the car has BBK long-tube headers. Just for the record, on the chassis dyno these have repeatedly shown a 17-20hp increase over the stock headers on near-stock engines. With the timing set to 14 degrees at idle, the Comp Cams Special's engine turned in rear-wheel output figures as shown by the blue curves in Fig 3. The increased output from the rebuild amounted to some 15 lb-ft and 10 hp in terms of peak numbers, but the low-speed torque was up as much as 20 lb-ft of torque. All this came with a glass-smooth idle, better throttle response, and an engine with zero blow-by.

Changing out the stock heads for our ported ones shows just how much these engines are starved of air. Compared to a set of aftermarket heads, our ported iron ones are still down on flow. Also, the stock fuel-injection intake can hardly be considered much better than mediocre, so getting the full benefit of the heads is not practical at this stage. Even so, the heads boosted torque by 10 lb-ft at peak and over 20 lb-ft at 5,800. Power increased by over 20 points, and the engine hung on longer at the top-end, thus allowing a shift point about 300-400 rpm higher.

On The Track
With winter fast approaching, the opportunity to run the car at this spec did not present itself. This was compounded by the fact that our second engine was about done and waiting in the wings. What we will need to do here is get some numbers from our computer simulation using the rear-wheel power curves generated from the chassis dyno test. With the original 225 rwhp we managed a best-on old and not very grippy drag radials-of 9.044 for the eighth-mile at 77.2 mph. Assuming no other changes except our fresh powerplant, the car's computed performance was 8.86 seconds at 79.45 mph. The sad part is that the extra power available would still not have returned a 60-foot time under 2 seconds. This is proof positive that tires have to be high on the priority list. Maybe that will happen next month, along with the upgrade to aluminum heads and such as seen in our lead engine shot.