I've got an 84 Z-28 with the 305 HO (L69). The stock camshaft has a lift .410 Int and .423 Ext and 320 duration. As I've said in my previuos post, we don't have camshafts in turboprop engines, so I'm gonna take the time to ask some really dumb questions. Is the lift the amount the lobes lift the lifter and pushrods and in turn the amount the valve is open at it's max?? Next what is duration??? Ok.. now for a more reasonable question. What kind of numbers would I be looking for to upgrade the motor?? My target HP is 275 to 300. Right now stock is 190. I want to eventaully put world torquer heads on, should that influence the cam i put in?? Who make the better more bullet proof cam??

 

OK the lift is the max amount the valve opens. The duration is the degrees of rotation the valve is open. As for what cam to use that depends on your exhaust, intake, heads, and carb.

By the why is your last name Heckert?


------------------
406SBC
-DART SPORTSMAN 2 HEADS
-RPM INTAKE
-750 SPEED DEMON MECH SEC. CARB
-HEDMAN HEADERS
-COMP CAM EX .507/.510
-1.6 roller rockers

 

Not to overwhelm you, but since you don't know a whole lot, I'll explain the best I can.

A cam's rated lift is at the valve. It's measured using a 1.5:1 rocker arm ratio. This is really the industry standard for SBC's anyway. If a different ratio rocker is used, the cam company will specify that. And as sb406 said, it's the max lift at the valve.

The duration to look for has been set by using the industry standard of .050". That measurement is much more important and usefull when comparing other cams. DO NOT buy a cam based on it's advertised duration. Different companies use different methods of measuring. Find and use the .050" specs for a cam comparison. That way you get an apples to apples comparison.

The length of duration is measured in degrees of crankshaft rotation. Ex. Lift .442"int/.465"exh, Duration 214 int/224 ex @ .050", LSA 112. Even the LSA is measured using crankshaft rotation. This is important to remember because the crank rotates twice as fast as the cam.

Look into Crane of Comp Cams. They both have specific cams designed for our engines based on the ECM's needs.

The cam is the "brain" of the engine. It determines what happens, and when it happens. Just remember this rule of thumb.
Low lift, short duration = More low rpm torque, less upper rpm HP.
High lift, long duration, = Less low rpm torque, more upper rpm HP.
Again, this a rule of thumb. The cams purpose can change a lot just by slightly changing any one of these measurements. Then there's the LSA & Intake centerline. More on that at a later date.

And like sb406 said, the heads, intake, and exhaust all have to work with the cam to make good power. Then you gotta get it to the ground. But that's another subject.

AJ

[This message has been edited by AJ_92RS (edited August 12, 2001).]