First Choice

How to Choose the Right Cam

Bob Mehlhoff Feb 6, 2004 0 Comment(s)
148_0405_choose_01_z 1/9

One of the most defining aspects of a real performance car is a performance cam, a stick that raises lift, adds duration, and gives the engine a distinctive idle that sounds really cool. But sometimes choosing the right camshaft to deliver that extra power while maintaining good driveability can be challenging. Sure, it's easy to just pick the cam listed at the bottom of the cam manufacturer's page to ensure a radical idle, but you want more than just a signifying sound.

Like all other performance modifications, the best results are obtained when parts are matched to complement each other. Lower gears, freer-flowing exhaust, cylinder-head characteristics, and transmission type must all be considered before deciding which camshaft to choose. To make this decision properly, you must determine what you want from your car. Do you want it to be a double-duty street/strip car, a tow vehicle, or a very dedicated performance ride that sees limited street use? Compression ratio and engine size will also affect which camshaft is best. For example, the same performance camshaft installed in a 400ci small-block will sound significantly tamer and have a lower powerband than the same cam installed in a smaller 283. This is because (all else being equal) the smaller engine has less volume (less pumping capability) and less engine vacuum.

Before we travel too far ahead, let's lay down some guidelines first. For our camshaft discussion, we'll use five separate stages of engine and performance categories. Stage I is a daily driver--a 305 engine that we just intend to make perform better. Stage II uses a relatively stock 350 engine that has a performance exhaust system, aftermarket intake manifold, and a four-barrel carburetor. For Stage III, we'll use a 383 with Stage II components and add headers, 3.55 gears, and a 2,500-stall converter. Stage IV is a stout 406 small-block with better-flowing cylinder heads, 3.70-4.10 gears, aftermarket ignition, a 3,000-stall converter, and a shift kit. Finally, Stage V focuses on an all-out 502 Rat equipped with rectangular-port cylinder heads, lots of compression, and a single-plane intake with an 850-cfm carburetor.

Next, we'll consider camshaft duration, which is critical to the amount of power the engine will produce and at what rpm range it will do so. Since a camshaft with more duration bleeds off more cylinder pressure, it's important to consider displacement and compression ratio. As an industry standard, most camshaft companies measure duration at 0.050-inch valve lift. As a general guideline, we've provided the following chart to explain the range of camshaft durations and the anticipated powerbands.

148_0405_choose_02_z 2/9

This stout 406ci small-block uses a Comp Cams Extreme Energy (XE274) hydraulic flat-tappet camshaft. With 230/236 degrees of duration (at 0.050) and 0.490-inch lift, it produces gobs of power on the street and strip. Its latest outing produced a mid-12-second pass with 3.73:1 gears and a high-stall converter.

Hydraulic, Solid, or Roller Lifter

You'll have to choose between hydraulic, mechanical, or roller lifters. Hydraulic lifters are typical. They provide quiet operation and almost never need adjustment. However, for very-high-rpm operation, hydraulics will often bleed down and cause valve float. Mechanical lifters allow higher engine rpm (above 7,000) but require frequent valve adjustments and have a noisy clatter at idle. Today, most of the antipump-up hydraulic lifters work well to almost 7,000 rpm.

For the more serious street contender, enter the world of roller camshafts. The name roller describes the small wheels installed on the bottoms of the lifters that reduce friction and allow a very aggressive camshaft profile that can directly enhance power levels. Roller camshafts are available in both hydraulic and mechanical designs. Plan on spending considerably more for a roller camshaft, especially if your engine was originally designed for flat-tappet lifters.

148_0405_choose_09_z 3/9

It's a Spring Thing

The most frequently encountered problem when adding a new camshaft is using valvesprings that were not designed to work with it. Stock springs will often be too weak, bound-up, or just plain worn out. These conditions ensure limited rpm use or poor performance. Stock springs work fine for stock camshafts with low lift; with high-lift cams, always use the manufacturer's recommended valvesprings.