With all things remaining equal, what will a larger or smaller LSA do to a cam?

Reason I'm asking, I've been talking to a few cam folks, and it seems they can't agree on what higher or lower LSA does, or how it affects things. I'll share with you what a couple of guys have told me.

**************************************

1) "The only thing LSA does is affect idle. It doesn't do anything else."

2) "Lower LSA will move the power band down in RPM's, higher will move it up. It doesn't do anything else to the cam's characteristics."

3) "Lower LSA makes the power band narrower, whereas a higher LSA will make it wider. That's all it does."

**************************************

So you can see why I am confused.

Anyway, let's say I wanted something like the Lingenfelter GT2-3 cam....207/220, .573/.580, 117.5 LSA. How would this behave as compared to the same cam on a 114 LSA?

 

add in:

lsa will affect your valve events. higher lsa will equal less overlap, and lower lsa will equal more overlap

overlap is when both valves(exhaust and intake) are open for the cylinder.

 

That Lingenfelter cam is VERY similiar to a 02 Z06 cam. It will make solid power from 4500-7000, and wants to shifted at 7100 with open exhaust.
It will be no more powerful than a stock LS1 cam below 4500.

If you changed the LSA to 114, it would make the cam "smaller" in terms of degrees between Intake Open and Exhaust Close. It wouldn't rev as high, it would make more power in the midrange, get worse fuel mileage, and higher emissions.

Here's the thing... Cams actually only have 4 timing events:

INT Open
INT Close
EXH Open
EXT Close

LSA, Duration, Advance, Retard, Overlap are just simple calculations based on those 4 numbers to make it easier to interpret.

Cams used to sold using the Overlap value instead of the LSA value. But it's easier to just use the LSA.

Unless you want to spin your car to 7000+ for best ET's, you'll want the 114.

 

PS - A Z06 cam is not a good choice for an automatic truck. You probably won't rev it high enough to take advantage of it. Yes, you will go a little faster, but not much.

 

Okay, I'll get more specific then.

I want my powerband between 2000 and 6200 RPM's. The two cams I am considering are a 206/212 and a 208/214. From what I understand, both of these will give me more low-end power.

In spite of what Comp states in their literature, I've heard that their 212/218 won't make good, usable truck power until about 2500-2600 RPM's. Fine in an F-Body, not so good in a truck where I'll want to do some towing in addition to daily driving.

Anyway, let's say I go for the 206/212 - what will be the effect if I get a 114 LSA, over a 116.5 LSA?

 

Uh... Is this a Supercharged application? Just read more of your signature.

 

Yes, I have a blower. Would like to keep the stock TC, but also considering the Trailblazer TC or the Yank TT2600 (if I have to...I'd like to keep it mild, so I can tow and keep the truck driveable).

 

[QUOTE=Naked AV]
In spite of what Comp states in their literature, I've heard that their 212/218 won't make good, usable truck power until about 2500-2600 RPM's. Fine in an F-Body, not so good in a truck where I'll want to do some towing in addition to daily driving.[QUOTE]

The stuff you read in CompCam's description is probably meant for 5.7 liter LS1s. A cam will act "bigger" when you have less cubic inch (centimeter) displacement.

To reply to your first post, #3 is the closest to being a correct answer. LSA affects the torque curve. The narrower (tighter) LSA, the more peaky the curve gets usually gaining torque at the peak area while losing torque in the flank area. Thus, on the low rpm-side of the curve flank, less torque or should I say less cylinder pressure causes less idle vacuum, lopey idle etc. (the characteristics that would cause you to fail an emmisions test). On the high rpm-side of the curve, the power drop off becomes more severe. You'll be able to feel when the cam just doesn't want to accelerate enthusiastically anymore. Within the middle of the curve, you'll feel a much stronger pull. Only drawback is that the strong pull occurs over a shorter powerband.

The wider LSA will flatten the torque curve by decreasing torque at the peak area while increasing torque in the flanks. More lowend torque (cylinder pressure) will give a better idle, blah, blah, blah. The high end torque will make the cam feel like it wants to pull and pull and pull. The midrange will be uneventful and kind of "linear" in power output. You never really feel the cam "hit". This makes for a very useable wide powerband.

OK, I forgot what else I was going to say, anyway I typed too much....hope this helps.

 

Ignore everything I said (my wife does anyways).

Supercharged applications have different rules than NA application. Small LSA's make it hard to build boost down low.

I would try and get more boost at lower RPM first. Not sure what your setup is, but if you want more "grunt" with a blower, you need to optimize your existing setup.

 

what he said^^ plus with a blower, u want a higher LSA... also, Yank makes specific truck converters, so u don't lose towing capabilities, and would really wake up a blown 5.3 with a cam... maybe a custom cam like a 210/220XE on a 114 would be good...

 

Oh yeah, I remember what else I wanted to say. You can get a killer lowend by picking a short duration, tight lsa cam. The short duration will keep the overlap to a minimum thus the lowend will be strong. This cam will die-out quickly in the upper rpms though. So don't choose too small a duration if you want to retain some usable upper rpms. Well theoretically, you could retard the cam a bit and regain some of the upper rpm range back (I have not tried this yet).

 

Could you give an example of what you are saying? Thanks!

 

Check out my resp #19 in this old thread:
https://ls1tech.com/forums/generation-iii-internal-engine/170903-short-duration-tight-lsa-cams.html

I ran a computer simulation on some torquey cams. That might help illustrate what I am saying.

BTW, I didn't extract my understanding of camshafts from playing around computer simulations. Most of what I know is what I personally experienced or learned over the years from people far more knowledgeable than I. The computer simulation stuff has just confirmed my learned knowledge. I still trust my own instincts over the computer sim though

 

Some cam designers dislike it when we (LS1 community) talk about LSA.

I have had a few interesting conversations about duration and LSA with some top folks in the industry.

Here are some generalizations to keep in mind (very general):

-Duration makes power
-Duration makes power but as duration increases your low/midrange will suffer at the expense of peak power AND you might make peak power at an rpm you cannot use
-Lots of overlap is not ideal for boosted LS1's. A cam that has 3 degrees of overlap at .050 might work as well as a bigger cam with 8 degrees of overlap. It becomes a matter of efficiency.

So you could run a 230/240/112 cam in an FI engine but it's total output with boost might be the same as a 224/230//114 camshaft because it works better and does not have as much boost blowing out the exhaust.

My 348ci with my setup peaked at 6900 rpms thru my unlocked T400 with my 230/236//3.7 @ .050//115 lsa camshaft. Could I have made the same power with a 224/224//117? Very hard to say. Probably not. In the end I don't currently have a lot of overlap so 3.7 degrees of overlap might not be a big deal compared to zero degrees of overlap. So in the end duration is power.

But what about for you.

I would not do the GT3, I don't think it will give you the midrange increase you want.

212/218 might be interesting, but I always like big so I tend to look into stuff like 218/224 but I don't know how that would work in a truck.

 

Yeah, my 'raceweight' is about 1.25 tons more than yours...so I thing that changes things a little bit.

More than one place has told me that 212/218 is too much cam if I want to retain any low end. But who knows, if I did, I wouldn't be asking questions...

 

I hope that is not part of the reason why LS1Tech people are confused.

One more comment to add since PSJ brought up duration. Duration will shift the torque curve up or down the rpm range. The following are numbers I just pulled out of my ****, but I want to illustrate a point: If you have say 350 ftlbs peak torque within a 3500-4500 rpm range with a 210/210 cam you can make more horsepower by increasing that cams duration to 225/225 and moving that torque curve to 4500-5500 rpm range. Because horsepower is a function of rpm, that 350 ftlbs of torque made at a higher rpm will give you higher horsepower.

Way back when, it used to be shunned upon to throw around torque and horsepower figures without saying at what rpm it occurred. Nowadays, it is all too common to leave out that valuable piece of information. That is bad practice! Spawns dyno queens, lol! I'm done.

 

Keep in much of the advice you are getting is from NA engines, maybe in lighter vehicles, maybe more cubes.

To make a vehicle go quicker, the best tack is to "fix" problems. Find your week spot, then attack it. Then find the next one and attack it. Guessing that your cam is too small for your goals with a blown engine is not a good method for better performance. You can make INTENSE power with a stock cam with a blower. You can double your engine output with 15psi.

 

Okay, well my 'problem' at this point seems to be anemic performance from off-idle to about 3000 RPM's. So that 'symptom' might steer me toward an other-than-stock torque converter as a first 'fix', but I don't really want to lose towing capability or driveability around town. So that's why I was moving toward a cam to give me low-to-medium-end grunt....

 

hmmm... try a 6.0 liter swap .... seriously though, a magnacharger should make good low end, so maybe it's a problem other than your cam? Intake restriction maybe? Tunning? How's your a/f?

 

****, my truck only spins to 3200! But I'm making some good torque.

If it was my truck...

I would look into what it would take to increase the boost at low RPM. But boost = fuel, so your mileage will suffer if you increase boost (or HP) at cruising RPM. If you don't care about mileage, you might want to shrink the blower pulley first. It will make more boost at low RPM. With a cam, you will want to decrease your overlap, yet leave your INT OPEN and EXT CLOSE events at the same point if you are happy with your top end performance. This would mean a "smaller" cam with a larger LSA.

Your stall rpm will go up when you start adding low end torque. What's your current stall rpm? You really don't need to add HP below that number. If you need more HP below your stall RPM, you push the pedal down. If you are 3.73 or smaller, you might want to increase your gear size first. Some of your "off-the-line" punch has been eaten up with your wheels.

Best choice would be turbo-diesel IMO... Punch off the line is a non-issue. 2.1 60' with a 7500lb raceweight on 3.73's.