The Cam Thing

[Woodward_Dreams]

Can someone give me a proper explaination of what "adding cam" means. Does this throw off timing? How do you know how much cam you need? I probably sound pretty stupid, but i have never heard a proper explanation. I have only rebuilt 2 engine in my life and dont fully understand how this works.

[revolutionary]

Re: The Cam Thing

I would suspect they are talking about changing to a camshaft with more duration and lift. This will absolutely affect camshaft timing but confuse that with ignition timing that you can adjust with a wrench and a timing light.

[squirrel]

Re: The Cam Thing

A camshaft with more duration will move the "power band" up in RPM. So if the stock cam makes the most torque from 1500 to 4000 rpm, you can "add more cam" by replacing the cam with one with more duration (and lift), and it will make more power for two reasons--the added lift will usually increase torque, and the power band will move up in RPM to (for example) 3000-6500 rpm. Since HP is the product of torque and RPM, you get a lot more power.

The problem is that you have to make the car's drivetrain work in the new RPM range, which means you need to change the rearend gears to get cruising rpm up, and raise the stall speed of the torque converter (or slip the clutch more) so the engine is not loaded until it is in the power band.

Also there are other things that will need to be changed, such as improving exhaust, carburation, intake, heads, valvetrain, bottom end strength to handle the higher rotating speed, etc. So it's not a simple change.

[DanStokes]

Re: The Cam Thing

As usual, Jim's hit it on the head. Engine performance is a function of an integrated SYSTEM working together. So more cam doesn't necessarily mean more power unless the rest of the system is optimized to match. Cam timing is fixed into the cam design and the installation specs. The cam is timed "straight up" when the cam marker and the crank marker are in their stock locations or the cam can be advanced or retarded depending on the characteristics desired for the combination (there's that word again). Once installed, this is fixed unless you take the front of the engine apart and retime the cam. Ignition timing is independent of cam timing, and is the relationship of when the spark is delivered vs. the location of the crankshaft to TDC at the time of spark discharge - usually something like 34 degrees BTDC at, say, 3500 rpm or so in a SBC. Each combination likes different spark timing to run it's best.

The reason people say "more" cam is that stock cams are compromised to run smoothly at the RPM range that they will usually see. Performance cams are compromised for more power at the expense of smoothness, especially at lower rpm. As the cam increases in power output, the numbers describing the cam (duration, lift) increase. Notice that, in any case, it is a compromise. Duration is how long the valve is held off the seat and lift is how high it comes off the seat. There are a whole bunch of other variables including overlap, rocker arm ratio, and more. Cam design is a whole field of study in itself. If you want to know more, you likely want to but a good book on it and read up.

Hope this helps
Dan

[Ron Ward]

Re: The Cam Thing

Can someone give me a proper explaination of what "adding cam" means. Does this throw off timing? How do you know how much cam you need? I probably sound pretty stupid, but i have never heard a proper explanation. I have only rebuilt 2 engine in my life and dont fully understand how this works.

Excellent question!

I have found that for the most part, the information you require can be had by calling the cam manufacturer and following their advice as per what you will be doing with the car (or truck) and what intake, heads, exhaust, gear ratio etc. you will be using. Seriously, they will get you in the ballpark quicker than asking any of us!

Ron

[JeffMcKC]

Re: The Cam Thing

I have found that for the most part, the information you require can be had by calling the cam manufacturer and following their advice as per what you will be doing with the car (or truck) and what intake, heads, exhaust, gear ratio etc. you will be using. Seriously, they will get you in the ballpark quicker than asking any of us!

Ron

In the Parking lot for the Tailgating, but not the ball park, unless you have a cookie cutter and just want close. Call anyone of them, on 3 different Mondays, they will say 3 different cams

[Woodward_Dreams]

Re: The Cam Thing

Thanks guys, that helps explain things a little

[WindsorDlx440]

Re: The Cam Thing

I have found that for the most part, the information you require can be had by calling the cam manufacturer and following their advice as per what you will be doing with the car (or truck) and what intake, heads, exhaust, gear ratio etc. you will be using. Seriously, they will get you in the ballpark quicker than asking any of us!

Ron

In the Parking lot for the Tailgating, but not the ball park, unless you have a cookie cutter and just want close. Call anyone of them, on 3 different Mondays, they will say 3 different cams

From experience, I can concur. The only consistency I've found is with Comp Cams CamQuest software....but then, for example, it only asks generally specific questions relevant to the engine and you have to determine approriateness of transmission, rear end, etc. But I still like it for playing around with possibilities!