Cam Profiles…what works for YOU?
These are very general guidelines for a modern, four-valve per cylinder DOHC, four-cylinder engine of between 1600 and 2400cc’s.
240 DEGREES OF DURATION, 0.390″ LIFT, 15 DEGREES OF OVERLAP
Typical stock cam works well from 700-6500 RPM, smooth as can be. Relatively low emissions.
265 DEGREES OF DURATION, 0.420″ LIFT, 30 DEGREES OF OVERLAP
Good street cam, pulls well from 4000-7000 RPM, slight lope to idle. Will idle at about 900 RPM. Might pass a smog test. Might work with ODBII. Works well with most bolt on power modifications like adjustable cam pulleys, header, exhaust, air intake. Cars feels fun to drive on the street and is most likely more responsive than stock almost everywhere in the power band.
Most people should stop here!
280 DEGREES OF DURATION, 0.440″ LIFT
Mild race cam, pulls well from 4500-8000. Idle at 950 RPM with a definite lope. Could pass a smog test with tricky fuel and ignition management, most likely OBDII will not like this. Car might not feel good from a seat-of-the-pants perspective. Higher compression (10:1), adjustable cam pulleys, headwork and headers become a big plus at this point. Special matched valve springs are most likely needed.
290 DEGREES OF DURATION, 0.460″ LIFT
High RPM lobe of a VTEC cam (duration only) really wild street cam or mild race cam, power band from 5500-8500. Idle lopy at about 1200 RPM. Most likely will fail HC and CO part of smog test. ODBII system may experience some serious emotional problems. Higher compression (11:1), adjustable cam pulleys, headwork, headers and other stuff become almost mandatory. Racing valve springs needed. Compression puts engine almost to the point of not working with pump gas.
305 DEGREES OF DURATION, 0.500″ LIFT
Full race cam, power band from 7000-9500 RPM. Idle lopy at about 1400 RPM. Smog? Hah! OBDII system giggles and spews failure codes before becoming catatonic. High compression (at least 12:1), headwork, short runner intake manifold, custom tuned header, bigger injectors, high-powered ignition and stiff valve springs become mandatory. Car won’t run on pump gas any more because of compression. Close ratio transmission necessary due to narrow power band. Car is just about undrivable on the street unless it’s certain streets of Long Beach in April.
Finding top dead center is done by using a dial indicator on top of the piston at its highest point. Turn the engine over slightly, mark this point on dial indicator. Turn engine other direction slightly. Mark this position and divide the two measurements to get the exact top dead center of engine. Rotate and tighten degree wheel to mark this point as true top dead center.
Duration of a cam is measured on the cam by dial indicator and degree wheel when the dial indicator reads 0.003″ lift. Why 0.003″? It is because it is really hard to see when a dial indicator first starts to move versus degrees on a degree wheel when measuring a cam. The opening point is spread out over quite a few degrees and it is pretty hard to nail the exact opening point–0.003″ is an easy spot to pick where you can get a definite reading.
Sometimes cam makers will state duration differently. Commonly, the makers of domestic cams will pick 0.050″ as the measuring point for the cams duration. This is because some engine builders feel that the sloppy pushrod and floating rocker arms that domestic engines sport pass a lot of slop into the equation, and 0.050″ is a more accurate point to take a cam duration.
Some Japanese import cam makers use 1mm or 0.040″ for the same reason. Duration taken from these points of higher lift will be quite a bit less than advertised duration. A cam with 260 degrees of duration will have a 0.050″ duration of around 215 degrees. Some cam grinders use .030″ or even something like 0.020″ because they feel that that is the best place to measure duration.
When purchasing a cam, find out how the duration is measured. For instance, a cam with 260 degrees of advertised duration is a good, mild street cam. A cam with 260 degrees of duration at 0.050″ lift is a full race monster.