PontiacFreebird

Hey all. As the title says l swapped the LG4 305 in my 87 Formula to a 350 crate engine that is built around the design of the old L-82 camshaft. I've got a summit aluminum intake manifold for a Q jet along with shorty headers attached to 2.5" dynomax superturbo exhaust and was looking to use the original computer controlled carburetor. The engine is in and it runs and drives but is running rough. I've heard the ECM and CC carb will be at war with the L-82 camshaft and it will never run right. Should I pull the CC carb and distributor to replace them with a non CC carb and vacuum distributor? However I've also heard I should try messing around with the metering rods on the CC carb to meet the demands of the camshaft and that might solve the problem. What do you guys suggest? Any assistance would be greatly appreciated my F body Bros!!

sofakingdom

iTrader: (1)

What cam is it EXACTLY? Part number or EXACT specs only please.

PontiacFreebird

Lift: 0.450"/0.460" hydraulic flat tappet
Duration @ 0.050" : 222/222

Thanks for the reply and hope this helps!

sofakingdom

iTrader: (1)

Those specs look similar enough to the old L-82 stick.

What is the LSA? What ICL was it installed at?

Apart from all that, "running rough" isn't something that the CC Q-Jet is likely to be the cause of. Usual symptoms of "too much cam" for it to handle are more like, impossible to get it to idle, dies when you put it in gear no matter what you do, and runs TERRIBLE in general at low speeds. On top of that, that cam is pretty lightweight overall; well within a decent tuner's ability to work with the CCC system.

Describe "running rough" in more detail, after you post the rest of the cam & installation specs.

Also, what is the rest of the motor? What pistons? What heads? What was the deck clearance of the pistons after installation?

vorteciroc

Without the LSA and the Installed Position relative to the ICL...
The Specifications that you have Posted are almost worthless.

We do not know when the Valve-Events are taking place.
Just so you know, the Duration at 0.050" only means something when the LSA and Installed Position are known.

I HATE the way that Camshafts Specs are listed/ advertised.
But I understand why they do things that way...
It is for people that have no idea what the Valve Events are, and can only relate to Numbers being smaller or larger than one another.

I suspect that the majority of people who purchase Camshafts, never view the Valve Events with a Degree-Wheel installed...
and actually visualize what the Camshaft is doing (moving the Valves) relative the Crankshaft and Camshaft Positions.
This makes up the Science of it all, and is the FUN part of Degreeing the Camshaft.

Once the Valve Events have been visualized and understood...
It becomes very clear as to how changing when the Valves open/ close affects Power Output.

sofakingdom

iTrader: (1)

^^ This ^^ ... although I wouldn't be quite so harsh, myself. I'd describe the part of the specs you posted as "the beginning", and important, but it's possible to make VERY different cams that have those specs identically in common, if those other specs are allowed to vary.

LSA - lobe separation - describes how early the exh valve action is, relative to the int valve. Larger #s mean the exh valve opens earlier as the piston nears BDC. In general, smaller values tend to make the motor more "peaky", wherein the peak torque RPM and the peak HP RPM are closer together, which in racing, IFF you can assure that the engine ALWAYS runs in THAT SPECIFIC RPM range by way of converter & gears, will make it faster. Idle will be rougher (more "lope") and the engine will "feel" like it has more torque. "Area under the curve" is about the same regardless of LSA. Larger values OTOH tend to sort of "smear" the curve out, mostly in the upward (RPM) direction: neither peak will be as high, but they are farther apart, with the torque peak RPM not affected very much but the RPM peak at a higher RPM. That peak will be a lower value but at a higher RPM. Idle will be smoother, and torque will be more evenly distributed across the whole operating range. A pure street car will generally work better with a wider LSA than a race car, which is one reason that even the highest-performance factory cars nowadays are set up that way, but it's dangerous to carry that generalization too far. Wide LSA also is better for emissions, which is why so many factory cams have seemingly outrageously high LSA. Ordinarily you'd see anything from 108° up to 117° or so, with typical off-the-shelf "performance" cams these days around 112°: back in the day with carbs they were overwhelmingly at 110°, but EFI gets harder to tune if it's too close. The original L82 cam was about that, maybe as high as 114°, I can't recall exactly. It's been 30 some years since I used one, it's not exactly "state of the art" anymore if you catch my drift, and wasn't particularly popular even when it was, because it just ... wasn't ... particularly ... anything. The L82 itself is largely forgettable today. The name is more of a feel-good buzzword in 2021 I'd guess than anything "performance" as such.

Intake center line aka ICL is controlled by the installer by the use of timing gears that either advance or retard the cam's events with respect to the crank. Generally, advancing the cam lowers the RPMs at which all the peaks occur, and retarding it moves all those RPMs upwards. Again, be careful of over-generalization, but that's the general overall pattern. Retarding the cam provides a sort of built-in exh gas recirc (EGR) and in that respect is helpful to emissions. Large #s mean the int valve is later (retarded). Typical for a "performance" application is something like 108 - 110° ATDC.

However all that may be, "rough running" in unlikely to be a byproduct of any cam that could realistically bill itself as a "L82 replica". But, post the specs, we'll make our best guess.

vorteciroc

So Duration...

222 Degrees of Duration (0.050") is essential an amount of time in Degrees out of 360 Degrees.
...222 out of 360.

That is like saying that you have a 1-Hour Lunch-Break, when someone asks you: When do you have a Lunch-Break?
You did not say when it is, you said how long it is.

The LSA and ICL provide the rest of the information that tells us when the Valve Events will occur.

naf

iTrader: (7)

if we had the equation for the curve we could calculate the area under the curve using the integral.

with a cam's lift we're probably not going to have a formula for the curve

peruse: https://eng.libretexts.org/Bookshelv..._Under_a_Curve

the length of the cam's curve is measured in degrees, the height in inches of lift. by measuring the lift at some defined interval of degrees along the length, we can estimate the area under the curve by summing the area of each of the little rectangles we've divided the curve into. this is numerical integration, or the numerical method.

the smaller our defined intervals are, the closer our estimate comes to the actual value. as our intervals approach zero, we're in calculus territory and that can be a frightening place for me.

in reference to the above, it's easy to imagine two different cams, one with a high peak but short length and one with a low peak but longer length, having approximately the same 'area under the curve'.

well that's 'area under the curve' in only a few sentences. don't know if I've helped or hurt.

aliceempire

iTrader: (14)

T.L. -the term 'area under the curve' is used for graphing in general but typically when talking camshafts it's about a lobe where the values have been graphed out. Sometimes people use it when talking about a torque curve on a dyno graph too.
this helps visualize what naf has nicely laid out

sofakingdom

iTrader: (1)

In this case I was referring to the area under the HP and torque curves. (those are the same curve function at its core, since you can easily convert from one to the other, linearly) Exact same math, just applied to a different relationship.

In the case of, say, HP, imagine that the engine's curve is near zero until it reaches 3000, as the RPMs increase the power increases to its max at 4000, and it returns to zero at 5000. Not that any real-world engine would do that; but...

Using the integral of its function, or in the absence of knowing the function of the curve, just the tedium of breaking it up into hundreds of tall narrow rectangles (which is what the integral really is at its root), the area is easy enough to calculate.

Now imagine a curve that starts at 1000, rises gently to a peak at 4000, and slowly tapers off and back to zero at 6000. Again, use the integral of that curve to calculate the area under it.

Now consider the total output produced by each of these engines, if they ran through their respective RPM range in the same time. If it took, say 5 seconds for the first to go from 3000 to 5000, which would be controlled by the load on it (gears, converter, weight, etc.), and the 2nd one 5 seconds to go from 1000 to 6000 as controlled by its load, then at the end of each event, the same energy would have been produced. This could readily be measured by the speed of the vehicle, since energy = mv²/2. On the other hand, the driving experience would be very different.

Now imagine taking those same 2 engines and putting them through any kind of real-world exercise, for example, a drag race. If the first engine was geared such that it left the line at, say 3800 RPM, and shifted at 4200, and when it hit the next gear the RPM returned to 3800, then it would be at or very near its peak HP at all times; and the maximum possible amount of energy that it can produce, or nearly so, would be transferred into vehicle motion. Then imagine the 2nd engine, which since the area under its curve is the same as the 1st which since the curve is "wider" would require it to not be as tall, leaving the line at 3000, shifting at 4800, and recovering to 3200; in a word, a normal-ish street-ish gearing and load setup. Since the curve would be nowhere near as "tall" during the run, and the engine would only be covering part of it, considerably less energy would be produced over that same exercise. The 1st car would be MUCH faster.

The effect of cam LSA is like that. The closer together (smaller number) the exh is in relation to the int, the more "peaky" the engine will be, i.e. more like the 1st; and the farther apart they are, the more like the 2nd. In theory, if everything about the motor was "static" (no inertia of the moving air anywhere), 90° would be ideal. But such a motor, in the real world, would have trouble running more than a few hundred RPM; it'd be a tractor motor. The int needs to stay open later, and the exh open a little earlier, to promote better high-RPM properties. Which is why the #s are usually in the low 100s somewhere. 105° sometimes for certain racing applications, and as much as 118° for some "stock" passenger-car uses. 110° used to be the "standard" LSA for "performance" cams, because that's just about right for car with about 4:1 rear gears that rolls out about 7' per tire rotation, a transmission that has a ratio between gears of about 1.33, and a weight-to-HP ratio of about 8-10 lbs per HP. I.e., yerbasic muscle car. That LSA gives about the right "width" of the "peak" of the curve, to work best with the load characteristic imposed on the engine by such a vehicle.

sofakingdom

iTrader: (1)

Not necessarily.

Forget "power" or "lift" for a minute, and just imagine a curved line on a piece of paper. Like, a gentle hump, that goes most of the way across. Imagine that there's an area of 4 sq in under it. Now imagine a narrower curve that's also taller, that also has 4 sq in under it.

That's all there is to it.

In terms of "power", "area under the curve" refers to the total amount of energy output coming from the engine at all RPMs. For any given amount of "total power", some engines might produce it spread out all across the full RPM range, and some others might produce the same amount except concentrated into a narrower range. Clearly if the range is narrower, then to have the same "total power", the peak would have to be taller.

Re. cam lobes, compare these 2 cams here.





Imagine that these 2 cams had identical lift and.050" duration specs. Which one do you think would have more "area under the curve"? Which one would likely make more power than the other, even though the "specs", such as they are advertised, are the same?