questions on cams
Jul 2, 2004 | 01:39 AM
#1
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From: Brainerd, MN
questions on cams
I am pretty new to engine mods and stuff and I just had a few questions. I have a 2003 SS and I have headers, exhaust, and a cai and i was looking at possibly getting a cam for my next upgrade. I was just wondering what a guy should look for when buying a cam, as far as lift and stuff. I don't know what all of those numbers mean. Just looking for a little help.
Jul 2, 2004 | 08:25 AM
#2
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From: Central, MA
Welcome to the site!
If you check up in the "internal" section of this site, you'll find some REALLY in-depth stuff about cams.
I only really know the "front page" stuff. The basics. There is a lot that goes on behind the scenes - the actual valve events...
Duration: Generally, the more duration, the higher the power will be in your powerband. I hear that intake duration is the bigger factor in this, over exhaust duration. Single pattern cams like a 220/220 are suposed to idle better over a split duration, like a 218/228.
Most cams durations are measured at .050" lift. This is a industry standard type thing. You may also see "advertised duration", which is measured at either .004 or .006" lift. The two specs will give you an idea of how agressive the "ramp rates" are on that cam...
Lift: Lift will give more power throughout the entire RPM range. More lift usually means more agressive lobes or ramp rates on the lobes. The quicker the valves open and shut, the larger the range of power you'll make. Quick ramp rates normally help a lot down low. "Lazy" lobes give up power.
LSA: Lobe seperation angle... It's a common variable between two identical cams. It's what dictates overlap. The lower the LSA, the more overlap and the more scavenging. Scavenging is what will help pull a fresh charge of fuel into the combustion chamber. It can be good at a certain RPM, but will hurt at 'non ideal' rpm's.
Comparing a 112 to a 114 - Very generally, the 112 will be softer WAY down low, like off idle. When the cam starts to "come alive", it'll produce more torque sooner, with higher peak power, but it will fall off quicker than a 114 cam.
The 114 takes that higher peak power of the 112, and spreads it out. It'll be a little more tame, but the cam will come alive sooner, and rev out a bit more than the 112.
Overlap is what causes lope at idle, so a cam on a 112 will lope more than the same cam on a 114.
A lot of people say 112's are good for manuals, because you can keep the engine in the meat of the powerband. 114's are supposed to be good for autos, because you need the broad power.
Very popular truck cams:
Comp Cams 206/212 112 ~.515
Comp Cams 212/218 114 ~.520 "low lift"
Comp Cams 212/218 115 ~.550 "high lift"
Comp Cams 216/220 114 ~.530
TR220 - Thunder racing 220/220 .550 112 or 114
Crane 208/216 .530 113
Engine size also plays a factor in a cam choice. The larger the motor, the more duration it can use. The most common 212/218 low-lift may lope pretty good, and be doggy down low in a 4.8.... but it may sound very close to stock, and not loose any lowend in a 6.0.
If you check up in the "internal" section of this site, you'll find some REALLY in-depth stuff about cams.
I only really know the "front page" stuff. The basics. There is a lot that goes on behind the scenes - the actual valve events...
Duration: Generally, the more duration, the higher the power will be in your powerband. I hear that intake duration is the bigger factor in this, over exhaust duration. Single pattern cams like a 220/220 are suposed to idle better over a split duration, like a 218/228.
Most cams durations are measured at .050" lift. This is a industry standard type thing. You may also see "advertised duration", which is measured at either .004 or .006" lift. The two specs will give you an idea of how agressive the "ramp rates" are on that cam...
Lift: Lift will give more power throughout the entire RPM range. More lift usually means more agressive lobes or ramp rates on the lobes. The quicker the valves open and shut, the larger the range of power you'll make. Quick ramp rates normally help a lot down low. "Lazy" lobes give up power.
LSA: Lobe seperation angle... It's a common variable between two identical cams. It's what dictates overlap. The lower the LSA, the more overlap and the more scavenging. Scavenging is what will help pull a fresh charge of fuel into the combustion chamber. It can be good at a certain RPM, but will hurt at 'non ideal' rpm's.
Comparing a 112 to a 114 - Very generally, the 112 will be softer WAY down low, like off idle. When the cam starts to "come alive", it'll produce more torque sooner, with higher peak power, but it will fall off quicker than a 114 cam.
The 114 takes that higher peak power of the 112, and spreads it out. It'll be a little more tame, but the cam will come alive sooner, and rev out a bit more than the 112.
Overlap is what causes lope at idle, so a cam on a 112 will lope more than the same cam on a 114.
A lot of people say 112's are good for manuals, because you can keep the engine in the meat of the powerband. 114's are supposed to be good for autos, because you need the broad power.
Very popular truck cams:
Comp Cams 206/212 112 ~.515
Comp Cams 212/218 114 ~.520 "low lift"
Comp Cams 212/218 115 ~.550 "high lift"
Comp Cams 216/220 114 ~.530
TR220 - Thunder racing 220/220 .550 112 or 114
Crane 208/216 .530 113
Engine size also plays a factor in a cam choice. The larger the motor, the more duration it can use. The most common 212/218 low-lift may lope pretty good, and be doggy down low in a 4.8.... but it may sound very close to stock, and not loose any lowend in a 6.0.
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