Just found out I'm cam illiterate!

[mysweetlx]

I'm contemplating stepping up to a "big boy" cam soon, and I realized I need little education in cams. I know that depending on the lift/duration of a cam it opens up and closes the valves at a specific rate, but what exactly is lift and what is duration (what does each really do)? Also, I know Ford's letter cams have the same #'s for both the intake and exhaust on lift and duration....why is this and does it help/hurt? Is it better to have higher or lower #'s, and how much difference in the 2 lift and 2 duration #'s should there be? Sorry for all the questions, I'm trying to get edumacated!

[Unit 5302]

Your combo isn't setup for a "big boy" cam. You have a modified 302 that will make max power around 5500-6000rpm with those heads at best. Adding a monster cam is for strokers, or higher rpm engines.

Lift is how high the valve lifts off the seat in the head. Take a look at say, an E303.

.498/.498 220*/220*@.050 282*/282* LSA 110* LCA 107*/117*

.498/.498 lift. That means the maximum valve lift is .498" including the rockers multiplication effect. Standard rockers have a 1.6:1 ratio, meaning it multiplies the true cam lobe lift by 1.6. That means the camshaft's actual profile is smaller than the advertised lift. An E303 cam itself has a lobe lift of .31125"

220*/220*@.050 That means the duration at .050" lift (which is the industry standard measurement) is 220* So for 220* of the crankshaft the intake valve is at better or equal to .050." Same for the exhaust. Having the same duration for intake and exhaust just means the cam isn't favoring either the exhaust flow, or the intake flow. It's important to note duration is based on crankshaft rotation, not camshaft rotation. A crankshaft will rotate 720* per each camshaft rotation.

282*/282* is advertised duration. From the time the cam begins to lift at all, it's lifting 282.* Different manufacturers measure this at different lifts. .004-.006 or so.

LSA is Lobe Seperation angle. It's how far apart the lobes between the center of the intake and exhaust lobe are spread. The wider the spread, the higher your engine vacuum will be, and it's also important for low end power. The closer they are, the less vacuum you'll have, and you'll be trading lower rpm drivability for higher rpm power. Anything with less than a 110* LSA isn't going to be a good low rpm cam. Most street 5.0 cams are somewhere between 110*-114*.

LCA is Lobe Centerline angle. LCA is measured at TDC and by the peak of the lobe lift in relation to TDC. Since lobe lift is usually at the center of the lobe, LSA and LCA are normally the same. You can change cam timing to be more aggressive or less aggressive by installing the cam retarded or advanced. If you change the cam timing, you'll change the charachteristics of the cam somwhat. Lobe Centerline angle affects the camshafts performance profile much the same as LSA does.

[mysweetlx]

Thanks Unit....you can always be counted on for breaking things down so it can be understood easier. I used the wrong choice of words, "big boy" cam. What I meant was getting away from the Ford letter off-the-shelf cam, and getting something like a AFM custom ground cam or something like it.....how are the Crane xtreme cams? Why does Ford have the same #'s for intake and exhaust anyway....and why don't others make cams that way? Thanks again.

[Unit 5302]

The Comp Cam's XE series isn't a cam line that I like. Lot's of people seem to really like them, though. the Xtreme Energy series attempts to compensate for poor duration with valve lift. The LSA on the cams is high which allows for good low end power, but the short duration and wide LSA isn't going to be as good for higher rpms as a similar lift cam, or somewhat reduced lift cam. Due to their high lift height I don't see how the cam could be all that efficient.

The Ford alphabet cams do not attempt to favor the exhaust side of the head. 75-80% of intake flow is what you'll want the exhaust to flow. The stock E7TE heads look terrible by just peeking at the flow number. 115cfm exhaust or so. 155cfm intake, but when you do the math, they are right about where they should be in relation. You don't need the exhaust to flow as good as the intake because you have a piston forcing the air out of the cylinder under pressure. The GT-40Y heads definately need some help. Their exhaust flow numbers are terrible. If your heads flow worse than 75% exhaust compared to intake N/A, a cam that favors the exhaust is a better investment. If you're forced induction, you want it about 80%.

Cam manufacturers know what works, but they also have to cater to people who think they know what should work. I could say why doesn't anybody else make anything like the XE series? Camshafts have traditionally been more duration oriented than they are now. The B303 cam is an excellent example. It's poor in LSA, makes poor low end power, has little lift for an aftermarket cam, but it has a solid amount of duration, and quite a bit of overlap. Really the cam needs more lift to put down real power. People often go the route of 1.7's on the B303 to get some good lift numbers. The B303 was the first of the hydraulic roller SVO cams. So what is better? It soooo depends on exactly what you want to do with the car. That's where people like AFM can come into the picture. They know cams, and they should be able to pick out something that meets what you want the car to do.

The F303 cam you are running is respected in the world of forced induction because that's what it was built for. It's a good off the shelf supercharger cam. It looks somewhat similar to a B303 on 1.7's at first, until you look at the LSA. The F cam has a much wider LSA than the B cam. LSA is very important to a blower cam. Too much overlap and you allow the boost to go right out the exhaust. For a N/A car, the F303 has a spotty reputation. Again, here's where the LSA comes into play. With the right setup, some people like their F cam, but most do not.

Here's kind of a template.

High lift, long duration, narrow LSA. Race cam. It's gonna be peaky, lack low end power, make crappy vacuum, but when it's gets some rpms, you're gonna fly.

High lift, medium duration, medium LSA. High performance borderline streetable cam. The LSA will trade higher rpm race cam power for drivability and vacuum allowing you to keep power brakes and what not.

High lift, short duration, wide LSA. Street/strip cam. XE series cams fit in here for the most part. Good low end power, solid midrange, lacking a little higher up, but most cars don't run that high anyway.

Medium lift, long duration, narrow LSA. Best used at the track, definately not going to pass emissions. Low end power stinks, midrange is probably okay, higher rpms really wake up. Probably not the best EFI choice.

Medium lift, medium duration, medium LSA. Street/Strip cam. Pretty traditional in the setup. F cam probably fits in the weaker section here.

Medium lift, short duration, wide LSA. Entry level XE series? Good street cam. Better power than stock, good low end power, and the extra lift keeps the car more alive at higher stock EFI engine speeds.

Low lift, long duration, narrow LSA. Turd cam. Not enough lift to flow good, and it sacrifices sreetability too.

Low lift, medium duration, medium LSA. Emissions cam. The B303 falls inbetween the above category and this one. Low end not too great, but the cam makes up for it if you have gears and some aftermarket parts, maybe ported heads. Old school thinking.

Low lift, short duration, wide LSA. Stock cam type of performance.

To give a very rough estimate of what I'm talking about

High lift. .530+
Medium lift .500-.530
Low lift. .444-.500

Long duration. 228*+
Medium duration. 220*-228*
Short duration 216*-220*

Narrow LSA < 109*
Medium LSA 109*-112*
Wide LSA 112*-116*

Obviously there are tons of combos that don't exactly fit the parameters, but you can think of it as a little bit of a general picture.

[PKRWUD]

That was really excellent, Kell, I'm not surprised, but I am impressed! The only thing I would add is that as a general rule, roller cams keep the intake and exhaust numbers, for lift and duration, the same.

Take care,
-Chris

[Unit 5302]

Thanks Chris. I used to think I knew a little about cams, then after looking into it more, found out I knew just about nothing. LOL. There really is a ton of knowledge that needs to be learned to be comfortable understanding how different camshaft specs (some little known to most people) can make huge differences.

I think the B303 with 1.7's vs the F303 is one of the best examples that can be made. The specs people are familiar with lift, and duration are almost exactly the same, yet those cam combos are worlds apart because of differences in LSA and LCA.

I was just hoping I got the post in before you did. LOL, after a 10-15 min post or something like that, seeing somebody else posted exactly what you did 2min faster really makes you feel dumb. Hahahaha.

[mysweetlx]

DAMN Unit..........you're the *******' cam guru! How do you remember all that stuff?? I'm printing out your post so I can keep it as a reference guide. Awesome info. Thanks again for your help.

[Mach 1]

Originally posted by Unit 5302

High lift, short duration, wide LSA. Street/strip cam. XE series cams fit in here for the most part. Good low end power, solid midrange, lacking a little higher up, but most cars don't run that high anyway.

Sounds like a decent cam for your run of the mill , street EFI 5.0, from mildly to moderately modified.

I still cant understand why you hate these cams so much. Why would they try to "compensate" for poor duration with valve lift? Why wouldnt they just give the cam more duration and less lift if that were to get them the same results? Maybe they like that particular group of cams to have mid duration, high lift because they work good in 5.0s with roller cams? Maybe, just maybe....

[Unit 5302]

Originally posted by Mach 1


Sounds like a decent cam for your run of the mill , street EFI 5.0, from mildly to moderately modified.

I still cant understand why you hate these cams so much. Why would they try to "compensate" for poor duration with valve lift? Why wouldnt they just give the cam more duration and less lift if that were to get them the same results? Maybe they like that particular group of cams to have mid duration, high lift because they work good in 5.0s with roller cams? Maybe, just maybe....

Duration and overlap mean more to higher rpm peroformance than lift does. If you look at Comp Cams XE slogan it's "more power than other cams with the same duration." That is true. The cams you would have to compare the XE series to are much milder in lift. The XE series eliminates a good few head combos from the ability to pick and choose, and the ones that they don't eliminate are generally more aggressive than the cam profile is.

The XE series on the basis of looking purely at the cam itself isn't as bad as I make it out to be. On the majority of heads available for the 5.0, it requires a lot of additional money to be invested, though. If the head is designed for a very high lift cam, most likely it's going to be a very aggressive head, and the XE series are not aggressive high rpm camshafts.

If you're willing to spend the money to put a valvetrain capable of using the XE series camshafts on a mild to midline 5.0 combination, the XE series should perform well. You could get the same performance for a lot less money if you were to go with a different cam with a little more duration and a drop in lift so the heads spring combination will work with the camshaft. All in all, I feel the XE camshaft line is kinda gimmicky. While they should work, there can be some hidden charges, and they shouldn't perform any better than the rest of the cams they go up against. I also see them as being quite inefficient in the way the go about making their power.

Lately the people I've seen asking about the XE cams are E7 and GT40P users. For them, the XE cam isn't gonna do much good. If the GT40P heads were stage 1, 2, or 3 job, then the XE cam would probably work with it because those heads usually come with better springs along with the porting work.

mysweetlx I am not, nor do I claim to be a camshaft guru. The real cam guru's are out there installing cams, testing them, and building them. All I'm doing is shooting a little theory your way. You can do a lot of research on the internet to learn about different aspects of how engines work. Just have to be careful as a good portion of the net has some "shady" articles.

[Mach 1]

Ill buy it.

later