Camshafts, idle quality, driveability and LSA-REAL WORLD EXP and OPINION

318willrun said
Play'n devils advocate (helping folks understand)........ whenever you look at cam selection and see rpm's of a cams "sweet spot", the higher the rpm the lower the LSA.

For examples, I'll use the Mopar performance cams. The MP cam .484/284 will have a suggested rpm range of 2200-6000 rpm's, LSA 108.
The MP cam .474/280 (close in lift/duration) will have a suggested rpm range of 2000-6000, LSA 110. Power band goes down (upping the low end torque) with the greatest difference being the wider LSA.

Now check this MP cam which has a suggested rpm range of idle - 5800, LSA 115.
https://www.summitracing.com/parts/dcc-4452783/overview/

Do you see a pattern? wider LSA separation, rpm operating range goes down. Tighter the LSA, the higher the operating rpm range, leaving buyers to believe that tighter LSA moves the power band up, and killing low end torque.

Except in this case you overlook a very simple thing. Duration. Duration has a lot to do with operating range. While lower LSA will have a "tighter" operation range - I.E a 106 LSA might have 2200-5800 operating range. While a higher LSA will have a "broader" operation range I.E a 112 LSA might be 2200-6200. Duration will determine when that range starts and ends.

This is shown in your three examples. The MP 484/284 has 241@50 duration on a 108 LSA with a range of 2200-6000 RPM. The MP .474/280 has a 238@50 duration with a 2000-6000 RPM range. This range shows that to you. With that tighter LSA the range is smaller. BUT also lower, it's hard to see but it's there. It's only 200 RPM more than the smaller cam, despite the duration increase. This is further shown with your last example. It has 228/241 @50 duration. And look at how broad the power is, idle - 5800? That's only 200/400 rpm under the other cams. Assuming idle is 850, that's an additional 2000 RPM over the other two cams. That's one broad operating range, thanks at least in part to that wide LSA, the split duration also helps.

It's easy to see a pattern of "wide LSA = rpm operating range goes down" "tight LSA = high rpm range". And overlook the other parts of the cam. A wider LSA on a smaller duration cam makes sense. Helps broaden the power curve. Without a higher LSA the smaller duration cam's would give up before 5000 RPM. While a tighter LSA on high duration cam's makes sense. With a big duration, you are usually missing low end power, which a tighter LSA can fight. Also they generally have more power that comes on harder. The big duration guys are usually racers. So they want the most power they can get and they want it at a certain RPM they run at. They don't need broad, they need power between shift points. Tighter LSA provides that.

I think I mentioned it in this thread (or one of the other six cam threads going on right now), to pick a cam for it's entirety, not just one part. And remember, a good engine is built around all the parts. And how they work together.