WEDGE WORLD NEWS
From Hughes Engines
Dedicated to bringing news
And truth to wonderful
World of Mopar wedge engines
Issue #3 CAM SIZE
What size is your cam?
Don’t tell me what the lift is. You will sound like someone who lives in Chat Rooms or leaves their phone number on the walls of public toilets (same guy). The size of your cam is a major player in deciding how you should build your engine and how much power it will provide.
Using the cam (valve) lift to express the cam size is a common way of describing a cam size for one reason. Because it is simple, and everyone understands that the high lift makes more power – but does it? – Not always! Using lift can be and is very mis-leading You can have 2 cams with the same lift where one produces more (A lot more) power than the other one.
Ok then, how should a cam size be determined? By how long the valve is open, duration. Duration is how long, measured in degrees of crankshaft rotation, the valve is open. Now this is a mess too. Not everyone checks duration at the same lift point. The factories generally start the duration measurement when the cam has lifted the lifter .006” and stops when the lifter is .006 before closing. This .006” figure was not developed to help determine the power performance. But this is the way Mopar cams were measured.
You must keep in mind that an Engine is an air pump (That is another WEDGE WORLD article), and being an air pump, we are interested in how much air the engine can pump, and obviously the longer the valve is open the more air it can pump
Now we are down to how to determine where to start and stop the duration figure. At what lift points do we start and stop at.
Most creditable engine builders and cam grinders will use the duration @.050”. This means the lifter must be lifted .050” to start the duration and .050” before closing to determine the duration @.050” lift.
Where did this .050” figure come from? I believe that figure was first used by Harvey Crane (Crane Cam’s Harvey Crane) in the early ‘60’s – 1960’s. He wanted a standard for the high-performance industry that more accurately predicted the cam’s power potential. And to their credit most performance cam manufacturers use that figure today, and it works well.
The duration @.050” figure helps a customer determine what size and RPM range the cam will produce its best power.
Now about Lift. Lift is like an income tax refund – you can’t get too much, and it does not determine the cam size. The more duration a cam has the higher the air flow through the engine must be for the cam to “work”. “Work” means do the job you want it to do. High Airflow needs Higher RPM or more cubic inches. Why doesn’t everyone use the .050” figure? I don’t know for sure, but I don’t think they understand themselves (where have all the racers gone?) and salespeople don’t want to try to explain it to customers. So, the lift makes it easy – it's not right but it is easier.
What You Will and Will Not Get Generally!
Group 1. Smooth idle, high vacuum. Improved mileage and improved low RPM torque. You won’t get tire shredding power. You will not get aggressive idle. The power will improve from idle to 3800 -4000, good for towing, good vacuum, good stock replacement.
Group 2. Smooth idle, improved power from idle to about 4200 / 4500RPM good for towing Nice Resto cam, not a street racer cam. Better power at all RPM than a stock cam. Good vacuum. You trade off some mileage.
Group 3. These would be the 1st step in higher performance. To get the higher performance you would trade-off some vacuum, smooth idle, mileage, noise.
Group 4. Hot Street. You trade-off most everything, vacuum, idle, low-end torque, mileage to get higher RPM 2500+ Power. Need lower gears370 or lower, higher-Octane gas. More noise.
Group 5. This is for true race engines. You probably will own a trailer for trips to the track – it ain’t street friendly and “The Man” won’t like open exhausts. Too many people think putting a big hot cam in their wienie engine will make it a hot engine. Nothing could be further from the truth – it is the proper combination of parts that make it a hot or not. That is why we ask all those dumb questions. We don’t want you to make our cams look bad in a poor combination wienies engine.
Actual engine displacement will affect how the cam works, too. What this means is that as the displacement increases, (more air flow thru the engine), the cam will melo out some.
Because people think putting a hot cam in their engine makes it a hot engine. Know this: Putting a hot race cam in a nearly stock engine DOES NOT make the engine a hot race engine – it makes it a sloppy running dog you are ashamed to drive. We don’t want that to happen. This is why we need answers to the 21 questions when choosing our cams.
