Selecting a Hydraulic Cam for your Pontiac Engine

The table below will help you select the right camshaft for your Pontiac engine. The first column contains the intended use or application category. (Stock, daily driver, street-strip, etc) The other columns to the right, contain the intake duration of a cam at .050" lift. Where the application and camshaft intake duration intersect, I've offered my opinion on whether a cam with the specified intake duration will complement the intended application. Each application as you will note, has basic equipment or component requirements which need to be examined.

In the table, the Minimum Requirements column denotes the intake, exhaust, carb, ignition, tranny, rear gearing, and compression needed to complement the cam in the specific intake duration column. To reiterate, the minimum requirements are provided so it doesn't mean that a stock or daily driver, for example, won't benefit from using an HEI or special MSD type electronic ignition. I am merely stating minimum component requirements. Let's consider a hypothetical vehicle.

Example: 3800 pound 1970 GTO, 400 +.030 over, dished pistons, minor porting, 3 angle valve job, stock 1.5 rockers, stock Q-jet, 3.55 rear gears, 4 speed, dual exhausts; stock point distributor; used only on the weekends; seldom raced, mostly for show. Less than 2000 miles per year on the road. Goal: to improve stock performance but at lower 9.5 to 1 compression to run on pump gasoline. The engine came with the OEM "S" camshaft (068); 212/225 @.050" ;288/302 advertised duration.

Step 1.
What is the intended application? Take a look at the
application category as I've defined them. Does the GTO fit one of the examples better than the others? Yes. It looks like the GTO best fits the "Weekender" category. Okay then, lets go with that one.

Step 2.
How is this GTO equipped? Take a look at the
Minimum Requirements columns found in the table. It certainly looks like the column 3 requirements (under the 210-225 intake lobe) fit because of the weight of the car, and the minor head porting. Moreover, the intake spec on the OEM camshaft (212) already places it in the 3rd column.

Step 3.
Assessment: a cam in the 210-225 intake duration range is probably the correct camshaft range for this car given its intend use as a "Weekender." As to which manufacturer's specific grind? That's a matter of choice, but be mindful that a cam with a lobe separation angle of between 110-112 crankshaft degrees works best in street applications providing excellent low end torque and good mid range power. Also, remember that a manual transmissioned car can handle a few more degrees of intake duration than an automatic as well as a tighter lobe separation angle (e.g. 110).

The applicable range in the hypothetical is 210-225; gearing and 4 speed allows for a higher duration so a cam with 220 to 225 intake duration should work pretty well. Note: the bigger the displacement the smoother the idle. Therefore, a 326 with a 220 intake cam will have a very lopey idle in contrast to the same grind working in a 455.

Okay-- see how this works--give it a try.


 Application  Intake lobe duration @ .050" lift
   200-210  210-225   225-235  235 plus
 Stock  yes  yes  not likely  no
 Daily Driver  yes  yes  not likely  no
 Street Performer not likely  yes  on the edge  over the edge
 Weekender yes certainly  yes  over the edge
 Street- Strip sure, why not certainly  yes  not likely
 Ultra Street no  no  yes  yes
 Race only not likely  yes  yes  yes

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 Minimum requirements: [to complement cam duration]

stock intake and carb, stock exhaust, stock heads, stock ignition, stock trans, stock gearing

Minimum CR:
8 :1

stock or after market dual plane intake, rejetted carb, good dual exhaust- preferrably with headers, slightly modified heads with higher spring rates to permit lift up to .500", stock valves, stock or recurved ignition, near stock converter, rear gearing of 3.23 in all small journal engines in 3600 pound cars
Minimum CR:
dual plane intake with special attention to carb jetting and CFM, headers, improved head flow to .500", intake port matching, consider SS valves, recurved ignition, 500 over stock stall converter, gearing of 3.55 in all small journal engines in 3600 pound cars
Minimum CR:
single plane intake with 750 CFM carb, headers, D port heads ported to flow beyond .530", recurved ignition/ electronics, electric fuel pump delivery, 1000+over stock stall converter, gearing of 3.90 in all small journal engines in 3600 pound cars; note: 3.23 gearing is a good starting point with big journal 421, 428, and 455 + engines
Minimum CR:

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   Application Categories Defined
 Stock no significant changes to the engine or drive line--just a cam swap.
 Daily Driver a streetable car with good manners in stop and go traffic, gets acceptable gas mileage (that's subjective, huh), and can easly ply the highways. Rear gearing is in high 2s and low 3s.
 Street Performer a vehicle that is not exactly stock. Minor engine power modifications make it the car of choice when you you don't have to sit in traffic or when you just need to go somewhere that's not too far away. Use is limited.
 Weekender this car is by choice, left for weekend usage because you don't want to drive this car in traffic if you don't have to. It is a serious street machine; your fun car. You tweak it, you baby it, and keep it under wraps. It's stock, hopped up with some mods, or lots of high performance mods. In reality it could be a stock vehicle, a daily driver, a street performer--any of the categories listed except race only.
 Street- Strip a vehicle that may be a stock vehicle, daily driver, street performer or weekender that is occasionally put to the test at the strip. The operative word is "occasionally." It's normally driven to the strip.
 Ultra Street a pseudo race car with less than tolerable street manners.
 Race Only race cars come in all shapes, sizes, and with varying displacements and modifications. If the car is soley dedicated to racing-- it's a race car.

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