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September 5, 1996
A Non-Technical Discussion on 5.0 Camshaft Selection
One of the hottest topics of debate lately has been choosing the right camshaft for your 5.0. Camshafts are on the forefront of everyone's consciousness more than any other bolt-on or component, perhaps because people feel it is the heart of the engine. The fact many people fail to understand is that its not the "Heart" of the engine, but just another component that needs to be chosen wisely. Poor camshaft choices are the root cause of why many Mustangs run below their potential.
Most often, people are lead to believe that they need a cam to match their recently purchased cylinder head combo. This is the first mistake. Many people don't realize that the cylinder head alone, with its larger valves and intake ports, and reconfigured chamber design shift the power band upward for a typical '85 through '95 5.0 even with its factory roller cam. Often, all that is needed to take further advantage of the new head's flow potential is the extra lift offered by a 1.7 ratio roller rocker. Some shops offer custom ground cams that promise miracles. Be careful, many of these cams were developed with a sheet of paper instead of a baselined engine and dyno. Some work well with their intended combination and some were only ground to make money.
When cam manufactures list an operating range for their cams, the power band is usually shown within a 3000 to 3500 rpm range. The problem with a power band rating is that the cylinder heads and intake have a large bearing on where the engine will actually make its power with that particular cam. We've seen cams rated to pull to 5500 rpm, barely pull to 5000 because of stock or poor heads. However, the power band can extend far beyond its factory rating with a well done set of heads.
The most common problems with a cam change in a 302 is its incompatibility with EEC-IV and a loss of low end torque. We've solved many of the idle problems with custom EEC-IV recalibrations, but tuning alone can't bring back low end torque when the low speed velocity of the intake port is gone due to the big valves, big ports and too large a camshaft.
T-5 cars are more prone to performance losses from too big a cam than automatic cars are (providing the automatic's converter is properly chosen). Traditional thinking is that because sticks can launch (stall) anywhere in the rpm band they want to, they can sidestep the problem of lost low end. A T-5 car can in fact launch wherever it wants, but the problem lies in its wide ratio gear selection and its solid connection (no torque multiplication) to the engine. The 1-2 shift and especially the 2-3 shift drop the rpm of the engine too far below where the previous gear left off. This is why midrange power is essential during the "recovery" of the gear change. If the low end and midrange isn't optimized a T-5 car can suffer dramatic performance losses during the recovery period because it takes a second to again reach its productive range.
On the opposite side of the spectrum, an automatic with a properly chosen torque converter never sees rpm below its productive range, regardless of what gear you're in. If the cam is making good midrange by 3000 and the converter stalls to 3200, you'll always be taking advantage of its power band, not waiting a split second to come into it. We're not trying to say that automatic cars are the only ones that can have large cams, remember this is in reference to 5.0s that are mainly 9:1 compression with T-5s, a close ratio gear box can also make a big difference.
Many people choose, or have chosen for them, a cam too large for a low compression (9:1) engine. This can account for a great deal of the low end power loss when the cam's duration is over 225° to 230° @ .050 on the intake and the N/A engine is not being revved over 6200 rpm. Higher compression will make more torque and horsepower across the entire band, but more importantly it makes a substantial increase down low. The moral, if you have a low compression engine, stay with a very mild cam.
Mid to low 12 second ETs are what most 3200 to 3400 lb N/A Mustangs typically look for. We've found this level of performance easily attained with the stock roller cam or a very mild replacement (less than 215° to 218° @ .050 on the intake) and a properly done set of heads. All too often people pay for an aftermarket cam and run no faster than an equally prepared car with the stock roller cam. Not all combinations can take advantage of the increased valve events. For supercharged cars, the stock cam is good enough for very low 11s and even 10s with good heads. We did it all of the '94 season with a B-Trim Vortech, Edelbrock heads, Tremec, 3.55 gears, with 3350 lbs through catalytic converters.
We've made a lot of generalizations and omitted several factors that can alter these rules of thumb, so don't take them as absolutes, but . . . There is nothing wrong with the factory roller cam, in fact, it's a very good grind and capable of impressive performance levels with the right combination of parts. Try to run well with the stock cam before spending the money on an aftermarket cam and the installation. A good cylinder head/intake combo alone will raise the rpm band of the engine without touching the cam, so be careful not to place your shift point beyond the factory 6250 rev limiter. A good cylinder head/intake combo will run very well with the stock cam and have tons of low end, baseline it with the stocker first so you can see any tangible gains. T-5 cars need lots of low and midrange torque, so steer away from cams that have more than 220° @.050 intake duration if your engine is below 9.75:1. Don't be fooled by promises of dramatic horsepower gains with this or that custom cam, many of them are no better than the less expensive Motorsport or other manufacturer's "off the shelf" grinds.
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