i need to pick out a cam to put into my L98, but b4 i do, i need to be edumicated on all the details. i read the tech article and learned about lobe seperattion but i need to learn about duration and lift. i know what they are, i just need to know how they affect the performance of the motor. any help would be appreciated. reccomendations would be cool, too.

 

This isnt really going to help, but I would go with the lt4 hot cam it would work best in your situation. You will need a custom chip, but thats no biggie.

 

www.compcams.com

 

Duration:

Duration is the amount of time that a given valve is open measured in degrees, The more duration there is the wider the lobe has to be, obviously if you have two lobes for one cylinder and they're both big and fat (excessive duration) your overlap will also be large. Measured in "Advertised" and ".@ 050 lift" make your comparison on the "@ .050 lift" because that way two different manufactures are going to give you the same specs instead of where THEY feel the cam begins to flow. A good duration number for a SBC 350 thats Fuel Injected is around 218-225° range. Once you change cam shaft specs you must consider prom tuning.

LSA:

LSA or Lobe Sepration Angle Is the amount of degrees between the Intake and Exhaust valve on a cylinder. Think of the two lobes as a \ / If you move it together \| there's going to be more overlap or time that the two valves are open and you lose volocity at low rpms, if you seperate them \__ then you have a wider LSA, or less overlap, and more low RPM vacuum, Overlap becomes usefull at high rpms because of the flow volocity and scavaging effects, however at low rpms it causes your idle to be poor and choppy (however nice sounding ) A common LSA for a SBC carberuated engine is 110°, and for a Fuel injected engine is 114° The reason that fuel injected engines need a wider LSA, Lower overlap, and better vacuum is because to much of a choppy idle will send reverberation through your MAF/MAP sensor and the ECM doesn't know what to do with Positive pressure (unless its a 2/3 bar map)

Lift

Lift tends to be like "Free money" in the cam world, for the most part you can get crazy with lift numbers and it only gives you more power, however you need to take into account the wear on the springs/valve guides, as well as valve to piston clearances when you get funky with lift. A reasonable SBC lift number for the street is .500



Then there are the type of cams, There are the following:

Hydraulic:

Hydraulic cams are cams that use a hydraulic lifter, these lifters have a spring/plunger that fills up with oil and this stiffens them up, these are most commonly used on the street because to a point they are self adjusting due to the hydraulics/spring, they are also alot quieter than the solid type (see below) because they run at "zero lash". Lash is the gap you can find between your rocker and valve stem.

Solid:

Solid lifters would be lifters that do not have a spring and do not operate by hydraulics, they're noisier due to the fact that you need to maintain some lash, or gap in the valve train to accomidate heat expansion and centerfugal force from high RPMS. These lifters are lighter and stiffer thus they are ideal for high rpm race engines, they need constant adjustment and are noisy which makes them not ideal for the street.

Roller:

Roller lifters have a roller tip that glides smoothly over the cam, this wheel allows for more aggresive lobe ramps which gets the valve to full lift sooner, and holds it there longer giving you that extra flow, not to mention dramatically decreases wear, less friction = more power. These come both solid and hydraulic.

Flat tappet:

Flat tappet have been around since the begining of the engine, these lifters do not have a roller wheel, and again come in solid and hydraulic.


Any questions?

 

No one even replied to say "thanks for the effort"
Well here you are... :rockon:

 

:hail: :hail: :hail: :hail: Nice info! That will help me pick my cam, thanx.