I need to find the right cam for my 68. I want good power for my 454 (.030) from about 2000 rpm to 5000 rpm since I will rarely go over that. I'm also set on a good solid Roller cam, and I have 118cc open chamber heads. I want the car to be fast but I will not be racing it. And I'm shooting for about 9.5 compression. I have been reading a lot about cams and I know this is one of the hardest parts to decide on when putting together an engine. I have learned a lot of the lingo but maybe you could help me make a better decision.
I understand that:
LSA (Lobe Separation Angle) will effect the idle and 112 should be a good smooth idle but what else does LSA do for me?
The duration is basically the "size" of the cam but why is there an intake # and exhaust #?
Overlap is how much the intake and exhaust valves are open at the same time. What would a lot of overlap produce? A little?

If you don't have all the answers, thats fine I would appreciate your $.02

 

Howdy neighbor!

I don't have all the answers and there are many more rules, but I'm sure others will chime in with a few as important as these...

First rule of understanding cams; There is no perfect cam. So, don't be intimidated by all of this. The fact that you're asking questions is a good sign.

Second rule; Have the wisdom to stick to realistically matching the cam to the application and you'll maximize the satisfaction factor. Bigger cams aren't always better, as it's all too easy to "over cam" an engine (especially on the street) and end up with a dog. Duration is where most people get themselves into trouble here, but matching the type of cam (flat, hyd, HR, SR) is also important.

Third rule; The better your heads are, the less cam required to accomplish the same job. Stated another way, it takes less time for a high flow port to deliver the same volume of air, and that high flow port will deliver more air during a given time. Pretty straight forward when you think about it. BTW, you can only do so much for PoS heads with a cam before you get too far outside the box.

Fourth rule; Lift is your friend. Roller cams not only reduce internal friction, but they allow more aggressive valve opening rates which means more lift is possible for a given duration vs. flat tappet cams.

When you see separate intake and exhaust specs which are not the same, you're looking at a dual pattern cam. All that means is that intake and exhaust valve timing differ in duration and/or lift. BBC's typically respond well to having more exhaust cam due to the inherent flow differences between intake and exhaust ports.

LSA is easily confused with intake lobe center angle (ILCA). Make sure you know the difference. Narrower LSA's will increase overlap, which often leads to choppier idle and less vacuum, but usually increases peak torque and may lower the rpm at which it is reached. Wider LSA's decrease overlap, smoothing idle and increasing vacuum while broadening the torque curve, tho it tends to reduce the peak. With "big" cams, wider LSA's can become necessary to keep overlap from getting too large. Depending on the engine, ~110* LSA is the midway point for a BBC.


As for your specific application, you've left out a couple of important details, such as your transmission and final drive ratio, what type of induction and exhaust systems, what kind of driving is your intention, are you going to ever spray, does economy matter, how often do you want to crack the valve covers, and what kind of manners you are looking for... Knowing more would really help us narrow things down.

Also, as you've stated that you'll rarely rev past 5K, why are you set on a solid roller? (Don't take that wrong. I'm a solid roller guy myself.) They ain't exactly cheap and require more TLC than many owners wish to make a commitment to. If your engine isn't going to see anything very far past 6000 it's pretty hard to justify an SR cam, as there are plenty of HR's out there that hold their own up to that point. Remember rule #2.

Without knowing more and making a few assumptions, as a starting point I'd suggest looking at CompCams' (remember that they're virtually in our back yard here) Xtreme Energy XR270HR, which is a hydraulic roller with .510" intake and exhaust lift, 270* intake and 276* exhaust duration (advertised), 110* LSA (ILCA installed at 106*). Description reads, "Performance application, great mid-range torque, likes headers." Optimum operating range for this cam is 1600 to 5400 rpm. Depending on those unknowns I mentioned and where your CR ends up, you might step up a cam or two.

If you've just got to have a solid roller, I suspect you'll likely need help with a custom grind to meet your needs, but I wouldn't rely on cam techs too much as most of them freeze up with you go off the main menu.

Hope that's worth a couple of cents.


PS: The Tigers are still the best, just couldn't get the job finished (no thanks to Hightower, eh?)

 

I'm running Comps Xe-#268 on my BB n I'm very happy....Good sound n nice performance...Jerrylee///

 

Unless you like pulling valve covers to check valve lash from time to time and are willing to assume the risk that comes with a destroyed solid roller lifter and the subsequent engine damage, you might want to look at a solid flat or hydraulic roller. Solid rollers are considerably higher maintenance and much riskier. There's also no reason to run a solid roller if you're not going to rev over 5K. Solid rollers are built for max power and high revs, they're not really starting to shine until you pass about 6500. They generally want more compression, too.
I'd look at a hydraulic roller, 230-236 with as much lift as you can get. I'd get it on a 112LSA, it'll smooth the idle out a bit while still making plenty of power.
Rock On!

 

TheScunkWorks

Thanks a ton for the help. Let me give a little more info on my car:

T56 6 speed trans. from 97 Camaro
4:11 rear end
New World merlin oval port cast iron heads (small port)(118cc I think)
Exhaust Headers

Economy doesn't matter to much, just a weekend driver and I don't plan on installing NOS. My father has two with NOS and never uses it. We don't race the cars but do want them to be fast. As far as the cam, I really like the roller but don't want to pay for the HR (but I will pay if that gives me the desired results and it sounds like it may be a lot less work in the long run)

One more thing, why do people keep mentioning "advertised" next to the cam specs?

P.S. Tigers! Practice your darn free-throws but in all great season!

 

 

Advertised duration is a measurement of lifter rise that is not taken at a consistent point. For this reason, advertised duration numbers can vary greatly, and should not be used in the comparison of camshafts. Manufacturers determine the advertised duration by using the following formulas:

Intake:
Degrees BTDC intake valve begins to open + 180 degrees of crank rotation + degrees ABDC intake valve begins to close = advertised duration.

Example: 33 degrees BTDC + 180 degrees + 67 degrees ABDC = 280 degrees.



Exhaust:
Degrees BBDC exhaust valve begins to open + 180 degrees of crank rotation + degrees ATDC exhaust valve begins to close = advertised duration.

Example: 69 degrees BBDC + 180 degrees + 39 degrees ATDC = 288 degrees.

http://www.summitracing.com/streetan...dictionary.asp

 

Advertised duration is an indication of valve seat timing. However, since you can't rate a cam's duration at 0.000" lift, because nothing has happened yet, some point above zero must be used to define when the valves actually begin to open and finish closing. Thing is, as sperkins eluded to, that point may vary from company to company (and even from cam series to cam series within the same company). For example, one manufacturer may use 0.003" lift to rate hyd cams while another my use 0.006" (not uncommon). Not a huge difference, but when you start talking solids the variations become more significant.

Since virtually every cam's 0.050" duration specs are available, it is easier to compare apples to apples by using 0.050" specs. Also, it can be argued that not a whole lot of significant flow happens below 0.050" lift (IMHO that argument has a couple of gaps in it, but that's a topic for another thread), so 0.050" specs are felt to be a more accurate indication of a cam's performance potential.

Not to confuse matters, but as you learn more and more about cams you'll find that duration specs at 0.200" lift reveal a good bit about lobe profiles. But, you don't need to know that to make a sound decision.

If you don't want to go hyd roller and don't care for high revs, a good ole 268H may float your boat. Just a thought...