Would a smaller LSA such as 108 vs. 112, give the effect of a higher DCR?

I would think it would be the opposite with a higher LSA building torque earlier in the powerband? I know forced induction guys tend to like cams with higher LSA.

From what I've observed DCR is depended only upon where the intake valve Closes and tweaked by the Degreeing the ICL position; however, Vacuum is affected by Overlap such that: The Greater the Overlap which occurs when the LSA Angle is Small accompanied with a Long Duration the Vacuum will Drop and the engine will be less manageable at lower RPMS. That is not able to pump enough air to Siphon Fuel and atomize the mixture. It seems the only way the engine can build Compression with a Rich enough Charge with say a Short 108 LSA Long Duration Cam is to wind it up as there was nothing there to compress at Low Revs and Low Vacuum no matter what the DCR was. I suppose Fuel Injection could alleviate most this syndrome with these radical cams to provide some throttle response at low revs.

Hi-Compression 11:1 or better 327's with a Muncie and low Gears used to thrive with such Cams at the Strip; for instance, the Sigerson F296-1 3800-6800RPM Range, Adv 296/302, 258/264@.050, .563"/.563", 108 LSA.

DCR is only about the intake valve closing event.Lobe seperation angle has nothing to do with the calculation.That said,if a cam with a tighter lobe seperation angle were also ground with a shorter intake centerline{often the case} then the intake would close sooner and that would raise the DCR.

I would think it would be the opposite with a higher LSA building torque earlier in the powerband? I know forced induction guys tend to like cams with higher LSA.

You need cyl pressure to make torque.With two identical grinds..the tighter 108 lsa closes the intake valve sooner than a 114.You can not build cyl pressure until the intake valve seats.
The forced induction crowd typically spread the lobes apart more to decrease overlap.N/a engines rely more on exhaust scavenging than blown units.The hot outgoing gasses helps to pull on the stalled intake charge n/a.With positive manifold pressure..you have flow with the intake valve .001" off its seat vs say .015" n/a.To much overlap with positive manifold pressure has a large portion of the boosted charge blow right clean past the exhaust valve during the overlap period.This obviously is a waste of boosted charge that could have been trapped in the cyl for higher cyl pressure/torque.

You need cyl pressure to make torque.With two identical grinds..the tighter 108 lsa closes the intake valve sooner than a 114.

That's the reason I recommend 112LSA Marine Profiles for Rides that use higher gear ratios say 331 to 273's ,especially with manual transmissions that see a lot of HWY. All though you loose some DCR these Profiles have less overlap using longer durations that provide sufficient vacuum and excellent scavenging and has a distinct Exhaust Note. You have better throttle control where you can slide into gear without feathering the clutch by synchronizing the engine with the drive line and Torque on Demand, suited for a Road Warrior.

There is a little bit of misinformation in the answers in this thread so I'll hopefully be able to clear some of this up.

The Intake Centerline is what actually controls the closing point of the intake valve (assuming duration is constant) which is what primarily affects DCR and cranking compression.

Now the intake centerline is usually set up based on what the lobe separation angle is so indirectly the LSA does affect the DCR. The wider the lobe separation angle, the later the ICL typically is and the lower the DCR and cylinder pressure.

The opposite is true as well, the tighter the lobe separation angle, the earlier the IVC is and the higher the DCR and cylinder pressure.

Hope that helps clear things up.

The wider the lobe separation angle, the later the ICL typically is and the lower the DCR and cylinder pressure. We are saying the something with different words ;o)

By ICL I'm correct referring this to the symmetric or asymmetric Center Line of the Intake Lobe Profile and yes, as the LSA Widens the intake lobe closes later decreasing DCR but you can tweak to maximize the DCR by advancing the cams recommended installation position a few degrees providing you have the Valve to Piston Clearance.

The Wider the LSA, the less the Overlap on cams with similar profile lobes, stronger the Engine Vacuum and although the DCR maybe lower the Torque Curve Broadens with better Scavenging. You can run longer durations with a Wider LSA without sacrificing Vacuum. Scavenging is why, in most cases, the duration is allotted to the Exhaust.

I guess, for this reason, why 114LSA cams that drop the DCR somewhat are preferred for NOS and Super Charging without going overboard with overlap and maintain a Hg of Vacuum or 2 for low end power while loafing around at low speeds.

There is a little bit of misinformation in the answers in this thread so I'll hopefully be able to clear some of this up.

The Intake Centerline is what actually controls the closing point of the intake valve (assuming duration is constant) which is what primarily affects DCR and cranking compression.

Now the intake centerline is usually set up based on what the lobe separation angle is so indirectly the LSA does affect the DCR. The wider the lobe separation angle, the later the ICL typically is and the lower the DCR and cylinder pressure.

The opposite is true as well, the tighter the lobe separation angle, the earlier the IVC is and the higher the DCR and cylinder pressure.

Hope that helps clear things up.

That is what I was thinking in more complex terms!

With Wider LSA and Longer the duration the closer the Piston the Valve incident and less room to Tweak the position of the Cams ICL; which limits the amount the Cam can be Advanced to close Intake Valve sooner and increase the DCR. It still leaves the position of the ICL to determine the event closing of the Intake Valve and the Main Factor controlling the Length of the Dynamic Stroke. These cams are generally Street Mannered as they produce more Vacuum because of less Overlap and have a much broader Torque Range.

DCR is not the only factor for determining Torque, particularly at higher revs and running low gears and you don't care about street manners; for instance, a Cam with a 108 LSA has Torque because the DCR is easily Tweaked with longer durations but because of the greater Overlap vacuum is lost and you have to wind the engine up to build Cylinder Pressure before the Torque becomes effective.

There's lots of ways to say it and I find I have to juggle the words around a few times in order to understand a specific event in the in the Combustion Cycle.

The Wider the LSA, the less the Overlap on cams with similar profile lobes, stronger the Engine Vacuum and although the DCR maybe lower the Torque Curve Broadens with better Scavenging. You can run longer durations with a Wider LSA without sacrificing Vacuum. Scavenging is why, in most cases, the duration is allotted to the Exhaust.

I guess, for this reason, why 114LSA cams that drop the DCR somewhat are preferred for NOS and Super Charging without going overboard with overlap and maintain a Hg of Vacuum or 2 for low end power while loafing around at low speeds.

I think you will find that most street blown engines loaf around with more than 15Hg not 2Hg.Crutching the exhaust side on a blown unit is cyl head dependent.Todays raised exhaust ports flow much better and require less exhaust lobe duration as compared to a lesser head from the past.
The scavenging effect during the overlap period aids n/a engines...gets that stalled out runner charge moving prior to the pressure drop introduced by the descending piston in its bore.
Keep in mind..a supercharged engine may not indicate backed up pressure in the manifold at a given throttle angle and load ..but will move more air vs n/a until it exceeds the engines ability to injest it...and then you read boost.No where does it depend on the negative pressure scavenging effect to accelerate the incoming charge.Thats why we bolt on blowers with minimal overlap and large by huge carbs and big tube headers.

maintain a Hg of Vacuum or 2 Vs more than 15Hg not 2Hg.
I thought my statement would be interpreted as meaning less over lap maintain that "extra" Hg or 2.

Very true raised Exhaust Ports are not our old OEM heads - Look at the narrow angle between the Valves of a Hemi-Desmo Design where the Exhaust Port exits the Cylinder Bore at almost 90 degrees to the Cylinder Head. Cams profiles are complex and ground for all sorts of engines and applications. It's takes a good deal of understanding to pick one that matches the engine design and maximizes power in the range we intend to use the engine.

I do not use after market Hi-Flowing heads or Super Charging and do not Drag my Camaro as I am into Long Distance Cruising, Endurance and Road Courses using old OEM Castings. In this application, the Wider LSA and Longer Duration Exhaust Lobe benefits our Old Engines.

I agree a Blown Engine built around Hi-Flowing Aftermarket Heads do not need that long Exhaust Duration. If anything the Wider LSA which supplies that "extra Hg or 2" would probably be best used to extend the Intake duration. I would also think Big Cube engines would benefit from a Wider LSA and Longer Duration Intakes.

I think we understand one another quiet well when it comes to discussing the complexity involved with choosing a cam. At least you are using examples and not just saying something without backing up your point ;o)