Zoie_daGT

Here I guess is a semi-stupid question but, when looking at the specs of a cam, what do all the duration, valve lift, and lobe sep. angle all mean and affect??? Thanks for any help!!!

02StanGT

Duration is how long that particular valve will be open. Valve lift is exactly what it says: how far the cam will open the valve. I'm not sure but I think lobe separation angle is the angle from when the intake valve closes to when the exhaust valve opens. Hope that helps some.

JD1969

Here is a great write up, credit goes to LS1tech.com

Cam Overview:




A. Duration:


- The amount of time (in degrees) that lift is generated is called the duration of the lobe. Camshafts operate at half engine speed. This is easy to see because the gear that turns the camshaft is twice the diameter of the crank gear that drives it. That means that the cam spins at half engine speed. Because of this, camshaft duration is always expressed in crankshaft degrees. This makes it easy when it comes time to degree the cam to ensure it is positioned accurately in the engine.

- As you can see in the 2 cam cards there is duration @ .050 and duration @ .006. Duration @.050 is pretty much industry standard and that’s what you’ll see when looking at cam specs from the various sponsors and what most people are talking about when discussing duration

- Duration @.050 and Duration @.006 is a way you can determine the difference between two or more cams with the same given duration at .050. For example a TR224, TSP 224, and Comps 224. The lower the duration @.006 the more aggressive the ramp rate. The more aggressive the ramp rate the more overall and under the curve power.

- If you know the advertised duration (.006) of a cam you can calculate the ramp rate. To do this you take the duration @.006 and subtract it from the duration @ .050. A number of 53 or higher denotes an XE lobe or other mild lobe and a number of 49 or lower denotes an XE-R lobe or other aggressive lobe (Beast and 99 Black Bird T/A)

- Using the T1 and G5X2 as examples is as follows:

T1: 281 (.006) – 221 (.050) = 59

G5X2: Intake 281 (.006) – 232 (.050) = 49
Exhaust 289 (.006) – 240 (0.50) = 49

- Most cam companies use Comp lobes; either an XE or XE-R, the later being the more aggressive of the two. TR uses its own proprietary lobe and FMS uses Cam Motion lobes. Crane also grinds cams with VHP being one of there biggest supporters.

- Intake opening (IO) usually occurs before top dead center (BTDC), while intake closing (IC) happens after bottom dead center (ABDC). For the exhaust side, exhaust opening (EO) occurs before bottom dead center (BBDC) and exhaust closing (EC) after top dead center (ATDC). These data points are listed on the cam card that comes with each new cam.

- Traditional Splits refers to more exhaust duration and lift then intake (tsp231/237, g5x2 232/450, ect). Reverse split refers to more intake duration and lift then exhaust (TR 230/224, X1 230/227). Single patterns are defined as having both the same intake, exhaust duration, and lift. (TR224, TR220, FM4 226/226). Which cam is better depends on your application.

B. Lift:


- Lift is defined as the difference in height between the radius of the circle and the height of the eccentric. This is called lobe lift.

- When viewing cam specs the lift portion is the gross lift, meaning its calculated with the 1.7 stock rockers.

- To get the lobe lift you take the advertised (gross) lift and divide it by 1.7. If you follow the T1/X2 cam card you’ll see that they list both lobe lift and gross lift.

- If you want to add higher ratio rockers and want to know your new lift you do the following using the T1 as an example:

.559 / 1.7 = ~.329, you then take that lobe lift and multiply it by whatever rocker ratio you want. With SLP 1.85 rockers your new lift specs become .329 X 1.85 = ~ .609

JD1969

C. Lobe Separation Angle (LSA)


- LSA is defined as spread in camshaft degrees between the intake centerline and the exhaust centerline.

- Overlap is the number of crankshaft degrees that both the intake and exhaust valves are open as the cylinder transitions through the end of the exhaust stroke and into the intake stroke

- LSA is ground into the cam and cannot be changed without grinding a new cam

- Bigger duration cams will have more overlap then a smaller duration cam even if both are on the same LSA.

- The key to making overlap work is maximizing the power in the rpm band where you want it.

- Long overlap periods work best for high-rpm power. For the street, a long overlap period combined with long-duration profiles combine to kill low-speed torque

- Reducing overlap on a long-duration cam will often increase midrange torque at the expense of peak power, but if the average torque improves, that’s probably a change worth making.

- Many enthusiasts purchase a camshaft strictly on the basis of how it sounds. A cam with generous overlap creates that distinctive choppy idle that just sounds cool.

- While doing my research on the T1 I cam across this dyno in which if I recall Tony (Nineball) stated that the blue graph was a T1 (112 lsa) and the other 2 where a B1 (114) lsa. 112 vs. 114

- What really affects where the cam makes the most power is the intake timing events. What affects drivability most is the exhaust-closing event.


D. Advance and Retard:

- When you see cams specs like 224/224 .563/.563 112+4; the +4 denotes that the cam has 4 degrees of advance ground in.

- Most off the shelf cams have 2 or 4 degrees of advance ground in. This lowers the power band slightly and offers more low end and midrange at the sacrifice of a bit more top end power

- For cams used primarily on the street the advance is best appreciated. For a strip or racing setup 2 or 0 degrees advance will net you more peak power in the upper ranges of the power band

- To find out if you cam has advance ground in you can check on the cam card. Besides the +2, +4, you can determine the number by looking at the intake center line (ICL). Referring back to the T1 cam card you’ll see that it states that those are the specs when installed on a 108 ICL.

- Subtracting the ICL from the LSA will give you the advance: 112 – 108 = 4 using the T1. Or 113 – 109 = 4 using the G5X2.

- Retarding the cam does the opposite of advancing it, it pushes the power band up slightly and gives more top end power.

- With an adjustable timing chain or degreeing the cam you can install the cam at different ICL’s.

- Keep in mind as stated; most cams already have advance ground into them so if you buy an adjustable timing chain and advance 2 degrees you’ll increase the overall advance to 6 degree’s if the cam has 4 degree’s ground in.

- Also with big cams and/or milled heads piston to valve clearances starts becoming an issue. If in doubt always clay the heads and find out your PtV clearance before installing/advancing especially if your cam has a big intake duration as advancing starts the intake valve events sooner.

- Degreeing or installing dot to dot at the said ICL is the best bet.

Zoie_daGT

I will have to read that again to fully understand everything but thanks for the explanation. It really helped a lot.

josh_0351

JD – This is very good scoop and IMO should be a sticky for future reference. THANKS A LOT!

DuckyGt

Ive been looking into buying some cams, but i have no idea about brands and how much it should cost me. What brand would be the best for my stang. anybody that could tune me in would be really helpful

JD1969

The thing with cams is that almost all companys that make a "custom" grind will use the same lobe profile, i.e. a Comp Cam lobe like the XE or XER, Comp will just grind the duration and lift to whatever specs the company wants. So the company that you buy from (as long as it is one of the major players) is less important than the actual specs and lobe profile of the cam, and those specs need to work well with the rest of your combo.

DuckyGt

Will putting in a aggresive cam make my idle really crazy or anything. How about reliablity will a cam affect my car to much im a senior in high school and need my car to last me through college. thx for any info

JD1969

It all depends on how agressive you go. There are cams out that will retain good street manners and give you an OK increase in HP. No matter what cam you put in, it will require a custom tune to get the most out of it, so figure that into the price when you buy the cams. You will also need to figure in the cost of new valve springs, and labor if cannot do the swap yourself. Cam swaps tend to be costly on the 4.6 because you have two cams, the tune will run around $400, and labor is about $60-90/ hour depending on where you live and who does the work. So figure out all the costs and see if the extra 30-40 hp is worth it for you.