In general all cams (even stock) can lope. You simply lower the idle and take out some timing. When you increase duration you move the power band up included the required idle. If you have a small cam then all the nasty side effects of being cammed will appear.

A severe chop is also the result of the amount of fuel being dumped into the exhaust side on the overlap period. So the raw gas exploding part will be gone along with the smell of the raw gas being burnt in the exhaust.

The sound of a lopey idle with the chop is had even as small as a 224/230 114 cam. A 230/230 on a 115 will sound cammed and will have lope.

 

Your not hi-jacking. I want to know these things too. There are probably things Im not thinking to ask as well.

Thanks for the cam overlap formula Spin.

What exactly does lift do for a cam? I know that it is dependant on the size like a 228 xer lobe is a .588 lift but what exactly is the purpose? From what I know that means its how far the valve lifts off of the seat but is farther off the seat always better?

 

More is not always better as it depends upon the head. At certain lift the volume of flow may stall. Also the higher the lift, typically the more difficult it is to control the valve and hence the need for dual springs and other improvements.

From a practical standpoint, the lobes with higher lift also provide more duration at the mid lift because they ramp up faster. For example a 224 Xe lobe from comp has a lift of .568 (with 1.7s) and duration at .200 of 142. Switch to an XFI lobe and lift increases to .609 and duration at .200 increases to 149. I don't have the figures handy, but if you were to look at duration at .300 you would see an ever more dramatic difference.

For NA on LSx motors, I have seen 5 - 10 HP from using the higher lift lobes (e.g. Xer and XFI) and not seen anyone report worse results from using high lift lobes compared to low lift lobes.

 

Just like HP there is area under the curve and the average power of a H/C job that makes less peak HP and more average power in the range you use, makes the car faster.

For cams, The faster the cam gets to higher lifts, the more air it flows in the same time a slower ramping cam with longer duration can. A big intake runner is more efficient and you can use a smaller cam with more area under the curve for lift to make the same power. Its one reason the 260cc runner on the LS3 heads doesnt need so much duration for great power [but doesnt mean big duration doesnt make bigger power].

Heads have different flow ratings for each point on a lift lobe graph.

Lift is kind of a free way to get power since it doenst affect the driveability much. It does have a minor contribution to overlap at low lifts but its nothing major. This makes a 230XFI lobe pass as much air as a bigger slower ramping lobe. Although it does come off the initial ramp of the lobe slower than an XER it has more air moved using the same duration. Filling or emptying a cylinder then needs less time to do the job completely. Shorter duration cams with more lift, drive better and make better low end power too. Single pattern cams can take advantage of using XFI lobes on the exhaust side to limit overlap. I use the 230/230 115 on automatic cars instead of the 230xfi/234xer.

 

Ok I know we spoke about overlap already but Im still kina shady on it. What exactly does overlap effect? Is it only for driveability? Like a cam with 9 overlap will require more tuning for driveability than a zero overlap one?

 

Overlap is the time period in which both valves are open at the same time. It has a negative effect on low rpm efficiency. It causes what's commonly known as an "egr effect". EGR being EXHAUST GAS RECIRCULATION. What happens is you get pulse waves going different directions, and low manifold vacuum. The pulse waves are evident when viewing manifold pressure using a vacuum/low pressure transducer (or probe) and an oscilloscope. you can actually "see" the waves.

This is the root cause of bucking, trailer hitching, surge, whatever you wanna call it.

 

So basically a cam with big overlap is going to have more recirculation and buck more. With zero overlap there is no recirculation. Is there a point at which some overlap is good? I see pretty much every manufactured cam doesnt matter who the company is has overlap sometimes over 10 degress. So if it is too much why manufacter it with so much?

 

All cams have some overlap. You are used to seeing the specs at .05. At lower lift there will be some overlap, even in the factory cam.

Overlap contributes to making power. As you increase overlap you have the potential to make more power. The balancing act has several key variables: the rpm you want to make power at, the intake manifold design, the heads, and the exhaust. Adding overlap doesn't increase power uniformly. Increasing overlap at .05 from stock by 25* will make a big difference throughout the normal powerband on a bolt-on LS2. Add another 25* overlap beyond that and you should make more power, but the percentage increase in power is unlikely to be as great because of limitation of the intake manifold, heads, etc. You will also have a very messy bottom end because of the polluted charge.

Because of the tradeoffs, you see most aftermarket cams running from about -8 to +12 overlap. Yes there will be ones outside that range, and the better the tuner, the easier it is to run higher overlap.

 

Alright some of this stuff is actually starting to make sense. There is a lot of though involved in designing a good cam its crazy. Having an auto doesnt make it any easier either. It seems like the tune is so much more crucail for an auto car.

 

Hang in there brother. I dont know about cams but noticed they said that the right tunning MIGHT get you happier with your current cam. Worth a try as cams = parts = labor = spending scrilla

 

Labor is free cause its me! Spin has basically done the math on my cam for me and I know that its too short on the rpm power range and thats why It missing some action. I know I need a spinfast and he has given me some advice on a cam as well. Im the kind of guy that has to beat every decision to death though to figure out what I want. Thats why I have so many damn questions about what all this stuff does. I also dont wanna throw 500-800 at a tune to find out that my current cam selection is still incorrect. Might as well choose a cam I know will function change it out the get the retune I already need.

 

I understand man, Im the same way. I want to be happy with my mod so I try to learn what to expect so I don't get disapointed.The economy is bad and labor for me includes the Vette tax!

Keep on keeping on

 

so which one would be better for a stock ls2 manual trans with ported intake and TB with bolt ons that is daily driven
228/232 .595/.601 @112+2 cam
or 232/234 .595/.598 and 114lsa
would there be a big power difference?

 

I would guess the second one after all the learning Ive been doing over the past week or so. The second one would probably have a broder power band make more torque and have better driveability.