If 2 cams with the same specs, but different LSA...say 107 on one cam and 112 on the other...what effect does switching from the tight LSA to a greater LSA have on the compression?

really just worry about when the valve closes.

tighter lsa ,=more overlap=less dynamic

LSA has nothing directly to do with the dynamic compression of the motor. The compression will be affected by the closing point of the intake valve, which is altogether independent of lobe separation angle and depends on the position of the intake lobe. Overlap occurs at the end of the exhaust stroke and will also have nothing directly to do with the dynamic compression

tigher lsa build cylinder pressure, at least that is how I see it.

How does that happen?

Well, l'm a novice at this. However, I base my answer on Pat Kelleys DCR calculator.

Lets take a 350 SBC with 10.2 compression. Lets cut two cams. Both will have the same duration and lift. Both will be on different LSA's.

Duration is 280/288 on a 110 lsa and the other 280/288 on a 108 lsa.

Both are cut with 4* advance.

Here is the results of the 110

Intake opens at 34 and closes as 66. Exhaust closes at 76 and 32. Overlap of 64.

Here is the results of the 108

Intake opens at 36 and closes at 64. Exhaust opens at 76 and closes at 32. Overlap of 68.

Now when you run these cams through Pats program will get the 110 to produce a 8.11 DCR.

When you run the 108 you will get a 8.24 DCR.

Based on that I state that the 108 helps build cylinder pressure.

However, I may be totally wrong here, but this is how I see it.

Does it build cylinder pressure because the LSA is 108° or because you install the 108° LSA cam on a 104° ICL and the 110° LSA cam on a 106° ICL? What if you install the 110° LSA cam on a 104° ICL? What if you had a cam that had 114° LSA ground with 10° advance. Would this cam have different cylinder pressure than your 108° LSA cam?

Does it build cylinder pressure because the LSA is 108° or because you install the 108° LSA cam on a 104° ICL and the 110° LSA cam on a 106° ICL? What if you install the 110° LSA cam on a 104° ICL? What if you had a cam that had 114° LSA ground with 10° advance. Would this cam have different cylinder pressure than your 108° LSA cam?

OK, I try to do the best I can here.

If the 110 lsa cam was advance from 106 ICL to 104 ICL to a total of 6* then it would have the same DCR as the 108/104 cam.

To answer the final question of the 114 lsa cam. It too would have the same DCR as the 108 cam.

The how far you advance the cam (depending on the lsa) would help build cylinder pressure.

So, I would say that both work hand and hand.

Ok, My turn,

A cam with an LSA of 112 is considered "straight-up" at an ICL of 112

A cam with an LSA of 107 is considered "straight-up" at an ICL of 107

A wider LSA will build more cylinder pressure, thus more power, at the lower and upper areas of the power band

A narrow will build more cylinder pressure, thus more power, around peak torque

The "sweet spot", as far as cam advance goes, doesn't really change a lot when changing LSA, even though the ICL changes, unless peak torque is considered the bottom of the RPM range:D ,from my experience atleast.

So I would say that the wider LSA, installed at its "sweet spot" would produce a lower DCR. Wonder what Harold thinks?

OK, OK, OK!!

Make these cams BOTH straight up!!

I would use solid lifter cams so the upper rpm ranges can come into play here too!!! Just use GOOD valve springs is all.

say 112/112 and 108/108 and then run them through Pat's program as well as through D2k AND the power curves through DRAG holding both sim's 100 precent constant EXCEPT for cams and you will have an answer from a sim program that I figure WILL hold up in the real world as far as a trend!!

pdq67

Ps., and fwiw, Ron Isky once said in an old mag cam test that a 100/100 cam or thereabouts will make the MOST power, BUT he wouldn't sell one b/c of driveability issues!! End of conversation.

I have the mag somewhere too!

OK, so if a cam that is ground on a 108 lsa and 104 ICL for a 4* advance and is installed "dot to dot" is not straight up?

Would you have to advance it 4* to get it "straight up?"

Most cams are ground with 4 deg advance built in. Any way tightening the LSA [lobe separation angle] will create more cranking compression because you open and close the intake sooner and open and close the exhaust later which allows more time to build cranking compression which is exactly why tighter lobe centers build more torque at low and mid range rpm's . Ofcourse it also increases overlap which effects idle quality and fuel milage therefore when running a tighter lsa its more critical to avoid speccing the cam with too much duration.

OK, so if a cam that is ground on a 108 lsa and 104 ICL for a 4* advance and is installed "dot to dot" is not straight up?

Would you have to advance it 4* to get it "straight up?"

The cam doesn't care about the marks on the timing gears. It only cares about the position of the piston. Therefore you should ALWAYS degree in a new cam. In the real world, lining the dots up doesn't always work. Most cams SHOULD be ground with 4*s advance. but I've seen cams with as much as 12*s advance/retard!!! :confused: Of couse, with an adjustable timing gear or offset key, there fine. Installing it dot-to-dot just won't do.

The cam doesn't care about the marks on the timing gears. It only cares about the position of the piston. Therefore you should ALWAYS degree in a new cam. In the real world, lining the dots up doesn't always work. Most cams SHOULD be ground with 4*s advance. but I've seen cams with as much as 12*s advance/retard!!! :confused: Of couse, with an adjustable timing gear or offset key, there fine. Installing it dot-to-dot just won't do.


I know that, my question is when installing a cam "dot to dot" does this mean it is installed "straight up?"

straight up means a cam on 108 lsa would be installed on 108 lca [lobe centerline angle] dot to dot on a lot of cams would be 4 deg advanced like i said earlier. the reason is most engines run the best with 4 deg advance

Ok, My turn,

A cam with an LSA of 112 is considered "straight-up" at an ICL of 112

A cam with an LSA of 107 is considered "straight-up" at an ICL of 107

A wider LSA will build more cylinder pressure, thus more power, at the lower and upper areas of the power band

A narrow will build more cylinder pressure, thus more power, around peak torque

The "sweet spot", as far as cam advance goes, doesn't really change a lot when changing LSA, even though the ICL changes, unless peak torque is considered the bottom of the RPM range:D ,from my experience atleast.

So I would say that the wider LSA, installed at its "sweet spot" would produce a lower DCR. Wonder what Harold thinks?
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Hi Michael the Master Grinder,,, :)

DCR as used around here or low speed cylinder pressure is controlled solely by the intake closing point,,,,
Personally I like Effective compression ratio but we won't muddy the waters or rock the boat,,,, :D

So,,,,
Yes given the same advance of two cams with the same lobes the DCR would be lower with the wider LSA
But,,,,
LSA does not effect it if,,,,
you have the same intake lobe in the same place.
In other words a 112 LSA cam advanced 6° will have the same DCR as a 106LSA cam straight up ;)
The intake lobe is in the same place.

However,, as you know the engine will be a somewhat "different animal" with this scenario,,,