View Full Version : Cam Question
This question does not really apply to the N*, but I was wondering what kind of improvements a performance camshaft makes to an engine? I've heard its not really a power upgrade but an acceleration upgrade. Wanted to know how much power and acceleration it would imporve a car by, and if it is a good upgrade.
Thanks in advance.
02-16-07, 05:05 PM
More high end torque, less low end torque
You'll be hard pressed to get someone here to do a side by side comparison of camshafts, because nobody has one.
02-16-07, 05:29 PM
If you're talking about engines in general, think of the camshaft as the brains of the engine. Whatever you want the engine to ultimately do lies in the camshaft. Depending on lift, duration, and separation, you can take two originally identical engines and with a cam swap, make them do very different things. Depending on what you want to do, you can find a camshaft for it. If you want to tow, buy an RV cam. If you want a high-revving screamer with no low-end power, then you buy a huge cam with lots of overlap. If you want good fuel economy......well, you get the idea.
02-16-07, 07:34 PM
You can make a hell of a difference just by changing cam timing. Advancing cam timing improves bottom end torque. Retarding cam timing enhances top end horsepower. Mercedes was doing this on-the-fly in the 1930's. This is the reasoning behind Cadillac VVT engines. I've still got a drawer in my tool box with a handful of various offset woodruff keys.
02-16-07, 07:41 PM
Changing cams and choosing a grind is practically an art form.
Terms like lift, duration, degrees of separation, and profile all come into play and each little difference can change the performance of the engine itself.
Changing a cam requires more than just sticking a new cam in, often it requires re-tuning of the induction system, the fuel system and many other little nuances to make sure the engine runs properly.
The variable valve timing on most modern Cadillac Engines really enhances performance and adds to the complexity of the design of the cams themselves.
You can make or break an engine by swapping cams.
02-16-07, 10:04 PM
Back in the day I bought a fan to flywheel Z28 302 to put in my '66 El Camino. Chevrolet came out with a cam and spring kit for the Trans Am Z28's. I put that thing in it along with a carburetor off an L88 427 and AFR heads and it was like adding 2 more cylinders. That engine turned over 8000 RPM and when I held muster every horse answered up.
02-17-07, 06:10 PM
:alchi: Take an engine, any engine, and stick a wild grind cam in it. Without extensive tuning and intimate knowledge of what power ranges you're tuning for, and why, you will undoubtedly create a pig. No idle, no fuel economy, no power, no reliability. "Stick a cam in it" isn't close to the answer........
02-17-07, 06:54 PM
MAF cars almost tune themselves. You just have to worry about idle
^^ Yeah I had in mind computer controlled cars. When upgrading a cam do you need to tweek the computer at all?
02-18-07, 11:27 AM
The short answer should be yes.
Most of the sensors can make up for differences but to truly work properly with the grind of the cam you would need to change a few things in the calibration.
Technically it would run, but it might not "perform" the way you might expect.
02-18-07, 01:42 PM
About the only mods you can do to an engine that will improve the power throughout the range of operation is to raise compression and increase displacement, otherwise you are going to raise the output at higher RPM's at the expense of the lower and mid range. You are also going to narrow the power band and require more gears in the transmission.The rule of thumb is that the higher RPM you get the engine to peak at the higher the horsepower but the narrower the power band.
02-18-07, 01:45 PM
:want: Computer control systems are truly wonderful, but they cannot compensate for cam grinds unsuited for a particular engine, nor can they replace the MECHANICAL advance and retard installation options in a non-VVT engine. And just how good are we at degreeing DOHC heads? Is there any way to degree the cams in a N*? Who makes the parts? Do you stab them in advanced or retarded? What valve degree centerline/overlaps do you use with a DOHC setup? Will Comp or Engle or Edelbrock go to their cam suppliers and order you a special grind? Have you ever seen aftermarket chains or sprockets? What piston/valve clearance do you need at TDC for valve interference in a 32-valve N*? If you go from stock SLS to stock STS cams, you still have to reflash the PCM. As stated in the above replies, an advanced cam starts its power/torque band at an earlier RPM than a retarded setup, which is better for long-term pulling or midrange power. A retarded setup favors power at the top of the RPM curve at the sacrifice of low-RPM streetability. Rotsa ruck.......
02-18-07, 02:41 PM
^^ Yeah I had in mind computer controlled cars. When upgrading a cam do you need to tweek the computer at all?
Depends on the grind... Something close to stock won't need any intervention. Something like the 288 degree's from CHRF will require a lot of modifications (that can't currently be done with the stock computer)
The 3800 guys swap cams all the time, but they have power tuners that allow them to adjust their MAF tables at idle, raise rev limiters, change shift points, etc...
02-18-07, 02:46 PM
:want: Computer control systems are truly wonderful, but they cannot compensate for cam grinds unsuited for a particular engine, nor can they replace the MECHANICAL advance and retard installation options in a non-VVT engine. And just how good are we at degreeing DOHC heads? Is there any way to degree the cams in a N*? Who makes the parts? Do you stab them in advanced or retarded? What valve degree centerline/overlaps do you use with a DOHC setup? Will Comp or Engle or Edelbrock go to their cam suppliers and order you a special grind? Have you ever seen aftermarket chains or sprockets? What piston/valve clearance do you need at TDC for valve interference in a 32-valve N*?
I'm not sure what the point of this post was...
Do you want us all to get VVT heads?
You ask a lot of questions that can best be answered by Alan Johnson at www.chrfab.com
You can have the cam sprockets drilled to any combination of advance/retard you want.
02-18-07, 05:41 PM
Well, since this question applies to all engines, it's not fair to say swapping a cam close to stock won't require a computer re-program. Engines with MAF sensors take to modifications easily, but other engines such as the L05 in my Brougham with a TBI engine won't run well at all if I was to change the cam. Even if you swap in a cam that's close to stock, a computer re-program is in order, to truly get the engine running as best it can. But then again, if you're swapping the cam, you're probably not gonna swap to another cam that's close to stock, a cam swap is usually to gain some decent power.
02-19-07, 08:08 PM
Eldo1......The point of the post was "there's a lot more to engine tuning than 'stick a cam in it' ". Sure, we've been there, but some of our new readers need the big picture before they spend a chunk of change on something that may prove detrimental to their wallet or engine........This is all fun and friendship, remember ? For the 100 or so N*/Cadillac owners that follow this thread/site, passing down a little knowledge or light criticism is a good thing. ........Now I'm obsessing about gas mileage on a trip to Virginia on Thursday..........
02-19-07, 09:54 PM
One of my friends is probably one of the best motorcycle tuner/builders in the business. I do know the '86 Yamaha FJ1200 I bought from him, has what he calls 'linear torque'. It's awesome!! He said he 're-degreed' the cams.
The engine increases power when your hand is only slightly opening the throttle.
I have no idea what the top speed is on this beastie, but it gets !!
02-27-07, 08:16 PM
Here's an article I found on the Car Craft website. In this article, Jeff Smith explains some cam basics.
By Jeff Smith, Car Craft Magazine
Performance may always lay heavy odds on power, but you also need the brains to go with it. The four-stroke internal combustion engine has been around for over a century, but we're still learning incredible things about using camshafts to make more power. That elliptical lobe may look simple, but it represents the brains for your engine's brawn. Let's take a look at what makes this simple eccentric device so powerful.
We'll start with the easiest concept involved with the camshaft--lift. A cam lobe starts off from a simple circle, called the base circle of the cam. From that circle, the designer creates additional lift using a ramp so that as the circle rotates, it converts rotation into a linear or vertical motion by using a follower or tappet. This lift eventually rises to its highest point beyond the basic radius of the circle. The difference in height between the top of the lobe and the radius of the circle is the lift component of a cam lobe. For most street-type cams, this will be roughly between 0.275 and 0.450 inch. This is called the lobe lift of the camshaft. But we don't generate this lift all at once--it's created by gradually moving the tappet from the base circle to maximum lobe lift. This is where duration comes in.
Lobe design can vary immensely, even within a family of camshafts. The key to selecting the right cam is to match it not only to the type of use the engine will see but also to the other components in the engine. The goal is to create a strong overall power curve.
Ideally, you could slam a valve open, hold it open, and then slam it closed, and many drag race camshafts attempt to perform this feat, but this harsh action is incredibly abusive on valvetrain parts, especially valves and springs. To make these parts live over hundreds of thousands of miles, the cam lobe lift curve must be gentler. The easiest way to measure the amount of time the lobe is creating lift is with degrees of duration. A long time ago, our cam-building forefathers decided to use crankshaft degrees to measure cam lobe duration. So a typical performance camshaft may have a duration of 280 crankshaft degrees. Keep in mind that a camshaft actually spins at half engine speed.
But this created confusion because all the different cam companies measured the beginning of the lift curve at different points a few thousandths of an inch above the cam's base circle. This is called advertised duration and it can get complicated because, for example, Comp Cams begins measuring its advertised duration for hydraulic lifter cams when the lifter rises 0.006 inch off the base circle. Crane uses 0.004 inch, which would make the same lobe "appear" a few degrees longer in duration because the duration would be measured over a 0.004-inch-longer distance (0.002 inch on the opening and closing sides added together). This difference between companies eventually led to the selection of 0.050 inch as the standard checking point where all the different companies' lobes can be compared. So now we have both advertised duration and duration at the 0.050-inch checking figure. Now that you have the basics, we can dive into a few more items that make camshafts complex, but also fun.
The best way to install a cam is to degree it into the engine so you know exactly "where" the cam is located. Advancing the cam will move all the lobes to open and close sooner in the cycle. Generally, advancing a camshaft will increase low- and mid-range torque at the expense of some top-end power.
For each lobe there is an opening and closing point. Let's say you are measuring an intake lobe on a camshaft in the engine using a dial indicator and a degree wheel. Once the lifter rises off the base circle 0.006 inch, let's say that the degree wheel reads 20 degrees before top dead center (BTDC) and closes 90 degrees after bottom dead center (ABDC), then you can add those two numbers together along with 180 degrees and come up with the advertised duration: 20 + 180 + 90 = 290 degrees. This same formula can also be used to determine duration at 0.050 inch tappet lift.
Duration is a major contributor to the torque curve and where it occurs in the engine's rpm band. Generally speaking, as you increase the amount of intake lobe duration, this makes for an earlier-opening and later-closing intake valve. This additional duration also extends the rpm point where peak torque occurs. This tends to increase peak hp (depending upon the other components used on the engine) while sacrificing low- and mid-range torque. Conversely, a very short duration camshaft opens the intake valve later and closes it sooner, reducing the potential for high-rpm horsepower but increasing torque at a lower engine speed.
Now that you have lift and duration mastered, we can move on to more of the measurement values in camshaft design. Imagine looking at a lobe with a vertical line running right down the middle as viewed from the end. This line would represent the centerline of the lobe. If this were an intake valve, this would be the intake centerline of the lobe. Cam designers and engine builders use this centerline to establish where the lobe is located relative to the piston. For example, a Comp Cams 268 Xtreme Energy cam has an intake centerline of 106 degrees ATDC. This means that the midpoint of the lobe (which may or may not be maximum lift, since some cams are asymmetrical in design), will occur when the Number One piston is positioned at 106 degrees after top dead center.
The camshaft spins at exactly half crankshaft speed, which is easy to tell with the timing chain and gear, with the cam gear twice the size of the crank gear. Performance gear and chain sets often allow you to easily advance or retard the cam with optional slots on the crank gear.
When installing a camshaft in an engine, performance engine builders and the blueprinting process demand that you measure or "degree" the camshaft to ensure that it is installed where the engine builder desires. It's not enough to merely line up the dots on the cam and the crank gear. This way, if the engine builder would like to change the phasing of the camshaft, he can use that installed point as a reference. It's tough to know where to go if you don't know where you are.
This phasing of the camshaft is important because when the valves open and close has a serious effect on engine performance. This is where we get into advancing or retarding the position of the camshaft relative to the Number One piston. All references to positioning a cam are always around the intake lobe for the Number One cylinder. So if we wanted to advance the previously mentioned 268XE cam with its 106-degree intake centerline by 2 degrees, this would open the valve earlier in the cycle. It would place the intake centerline at 104 degrees after top dead center (ATDC).
Conversely, if we wanted to retard the camshaft by 2 degrees, this would move the original 106-degree centerline to 108 degrees ATDC. This is an important point that many people get backwards, so take a minute or so to study why these numbers are correct by looking at the cam timing graph.
Advancing the camshaft means that you are starting the opening and closing process sooner in the cycle. It generally improves low-speed torque and mid-range power while sacrificing top-end hp. Conversely, retarding the cam detracts from low- and mid-range power in order to help top-end power. Generally, moving a camshaft a couple of degrees will not make dramatic changes to the engine's power curve.
The camshaft is only one part of the overall valvetrain. Rocker arms are also important players in the overall engine performance scheme. From the left is a stock stamped steel rocker followed by a roller-tipped rocker, and then a series of different design true roller rocker arms.
Lobe Separation Angle
Here's where we get into some meaty stuff, so stay with us. If you look at the lobe graph, you can see the relationship of the intake and exhaust lobes. One of the variables that make cam designing such a challenge is the relationship of the intake to the exhaust lobe. The number of degrees between the intake and exhaust lobe centerlines establishes what is called the lobe separation angle. As an example, many Crane street camshafts are built using a 112-degree lobe separation angle. This means there are 112 camshaft degrees between the exhaust and intake centerlines. This can be determined from a cam card by adding the exhaust and intake centerline numbers together and then dividing by 2. So if you add a 111-degree exhaust and a 113-degree intake lobe centers and divide by 2, you'd get a 112-degree lobe separation angle. Keep in mind that often the intake centerline and the lobe separation angle will be the same number, but they represent completely different functions.
Valve overlap is a function of both duration and lobe separation angle. If the lobe separation angle remains the same but you increase the duration, the amount of overlap will also increase. Overlap is the time, measured in crankshaft degrees, when the exhaust valve and intake valves are both open. Overlap helps improve engine performance by starting the intake cycle before the exhaust cycle has ended. As overlap increases, this tends to make the idle quality more erratic, or lumpy, while improving midrange and top-end power. This is a very complex subject that we'll just touch on here, but even slight changes in overlap and intake opening and closing points can make a big difference in engine performance.
02-27-07, 08:26 PM
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