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

[318willrun]

The torque should be more and at a lower RPM.
With a tighter LSA you should have more torque at lower rpm.more at a lower rpm.
.

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.

 

[Lustle]

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.

 

[318willrun]

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.

very well explained, sir. this single post prompted by the right questions and examples that real general folks see/ and read and draw conclusion explains the LSA. So many questions and arguments on cams lately, but when asked the right questions as how most folks see the cam listings, we get the right explanations easy to understand that hopefully will clarify to many readers the correct explanation of LSA. these couple of post should be a sticky, because it helps.

 

[yellow rose]

The torque should be more and at a lower RPM. I'll post charts below.



With a tighter LSA you should have more torque at lower rpm. Might not be more OVERALL torque, but just more at a lower rpm. For example (and im pulling this outta my butt) 112 LSA might have 200 ft lbs at 3000 RPM, the 106 will have 200 ft lbs at 2600. It will at least make the same torque, just lower. But generally tighter LSA cams make more overall torque as well. It just all gets moved earlier and ends sooner.



While YR may have his problems with these articles. They give you a general idea of tight vs loose LSA. With the tighter LSA cams you can see how while they generally make more power/torque, it's earlier in the power band. You can also see how they fall off sooner. The crane article is especially good at showing this.

View attachment 1715001173

Look at the 104. Peaks torque between 5100 to 5200. While the 110/114 pull to 5400. Horsepower it's very evident. With the 104 plateauing at 6100-6200 then falling off. The 110 falling at 6900. The 114 still going flat at 7000.



That's part of why they chose it. 110 is the middle of the road and does offer a great compromise between max power and streetability. BUT it's also easier to mass manufacture cams when they are all ground on the same LSA core. Easier for mass production and such.

Lustle...did you read the article? Just curious.

 

[Lustle]

Lustle...did you read the article? Just curious.

Not in it's entirety. Mostly just looked at the cams they picked then jumped straight to the graph. What I did see there are some thing that could have been improved. I would have really liked to see more cam choice (104, 108, 110, 114). As 104 is not as common on the street as 108. While 114 is out there (ls engines I think? I dunno I don't touch GM). Maybe throw in a 120 to really show the difference.

Honestly if I ever won the lotto. I would just build a dozen really common engines (318's with minor work. 360's with XE series cams and 10:1 on iron heads. Stroker 408s. Eddie heads vs iron heads, etc etc). Then swap just cams, or just heads, or headers, carb. Etc etc etc. And dyno and document it all. And share it with everyone on here. So they could see real world, no BS results. And get a good look at proven power from a certain common combo.

 

[yellow rose]

Not in it's entirety. Mostly just looked at the cams they picked then jumped straight to the graph. What I did see there are some thing that could have been improved. I would have really liked to see more cam choice (104, 108, 110, 114). As 104 is not as common on the street as 108. While 114 is out there (ls engines I think? I dunno I don't touch GM). Maybe throw in a 120 to really show the difference.

Honestly if I ever won the lotto. I would just build a dozen really common engines (318's with minor work. 360's with XE series cams and 10:1 on iron heads. Stroker 408s. Eddie heads vs iron heads, etc etc). Then swap just cams, or just heads, or headers, carb. Etc etc etc. And dyno and document it all. And share it with everyone on here. So they could see real world, no BS results. And get a good look at proven power from a certain common combo.

And that was my point. The test was to show trends of LSA's with no other change. The problem I have with these tests is:
1. They don't give enough info. I'd like to see all the dyno sheet. Not just HP and TQ.
2. They didn't articulate where each cam was installed. Who knows, the 104 LSA in at 100 or even 98 would have packed more at the bottom. But we know it would have been more prone to detonation. How about the 104 at 106? Would have helped power past peak. When you don't test for ICL you really have no idea what the engine wants. And testing is expensive.
3. Why a split pattern cam? They either wanted to extend the RPM by adding exhaust or add bottom by reducing intake timing. That head is plenty good enough to not need help on the exhaust side. You could have reduced exhaust timing put it on a 108 and it would have killed all the other cams and had more vacuum at idle.


For what it was you could learn something from it.

My point is there is only ONE set of timing events that is correct for any givin combination. LSA is product of that. To move the cam more than a couple of degrees means you have the wrong timing to begin with and you leave power on the table. There is no de facto LSA.

 

[Lustle]

And that was my point. The test was to show trends of LSA's with no other change. For what it was you could learn something from it.

That's kind of why I like it. It's a very simple test that clearly shows LSA effects on power. There may be problems with it. But it does clearly illustrate what affect a change in LSA will usually have.

 

[yellow rose]

That's kind of why I like it. It's a very simple test that clearly shows LSA effects on power. There may be problems with it. But it does clearly illustrate what affect a change in LSA will usually have.

Exactly. If you look at a that test it will show you the typical direction an LSA change will go. But I stand by my original statement that LSA should be based on events. Looking at the cam in that Crane test, it looks to me like a single pattern cam on a 108 would have beat then all, all over. So it's more important to get the right LSA than to just pick an LSA out of thin air, or because you want your idle to sound a certain way etc.