Camshaft for 400 B block

[hoss]

I have a question about camshafts. I'm a diesel mechanic by trade, but trying to get into performance mopar in the spare time. I want to build a 400, and with all the dfferent combo's of cams It's hard for me to decide, but first I need to understand exactly how duration, lobe lift etc. effects the entire engine performance. I persally like the sound of engine lope. Could someone explain how these combo's effect idle sound, and overall performance?

[Christopher]

As a diesel tech,you probably know this,but I'll explain it anyway for anyone who might not know.Duration is measured in degrees,and a circle has 360 degrees,so if a cam is advertised at 280 degrees,you get the idea of how "long" it's duration is.Valve lift is in inches and that is how far it's raised off the valve seat.In other words a 280 deg duration cam with 470" lift Intake and exhaust means that the valve upon opening will be raised .470" off the valve seat(or Open)for a period of 280 deg of cam rotation.Now overlap is where the intake and exhaust valve are open at the same time and this too is measured in degrees.A longer degree overlap is what gives a engine it's "lope" A stock 340 cam has 44 deg of overlap,but the 280/480 has 60,hence it "lopes" more than the stocker cam.So a long duration cam,at 300 degrees and valve lift at .750" with a 68 degree overlap,means those valves are staying open a long time and off the seat almost 3/4 of a inch and both valves are open at the same time for 68 degrees out of 360,That's a pretty big cam!!! As far as picking out a cam,regardless of manufacturer,it depends on what you are doing with the car and some of what the engine is or will be equipped with.

[hoss]

Thanks Christopher, you really know your stuff. I understand duration in degree's as the time period valve is open, but didn't actually know what made the engine lope. Your professionalism is greatly appreciated!!

[451boy]

Actually Christopher made a mistake there in confusing cam degrees with crankshaft degrees. A cam with 300 degrees of duration means 300 degrees of CRANKSHAFT rotation, not camshaft rotation. The cam rotates at 1/2 crank speed so 300 degrees at the crank is 150 degrees at the cam.

[Christopher]

You are correct,however I'm sure Hoss understood what I meant.

[PRO]

So why build a 400 when a 440 cost just as much to build?What do you want to do with it?4x4,2x4,towing,muscle car,race car?You got some good explanations on cams,one thing to remember is total duration does not indicate the actual time that the air/fuel mix is filling the cylinder,flow doesnt actually occur until the valve is approximately .050 off its seat(with 45* valve seat)so real cam duration is represented @.050.For instance the 280* cam in MPs catalog has 238*@.050 so it takes 42* to open and close the valve to and from .050.Mopars have an excellent design in their valvetrain,the base of the lifter measures .904,this is the biggest base dimension in a gas engine and for good reason,the lifter has to rotate up an down the lobe of the cam,the bigger the base of the lifter the easier it spins,its like having a longer torque wrench.This allows for faster opening and closing ramps,this helps to keep your vaccum up while adding overlap w/o sacrificing low speed response.Compare this to some of the gm cam specs and youll see as much as 80* difference between advertised duration and duration at .050.Let us know what your going to build and I'm sure people will be glad to give you advice and share what they're currently running.I have a question for you diesel mechanics,go to diesel truck chat and look for...PRO..

[340king]

The responses you have gotten are all real good. I must mention however, a little tid bit of info.

Advertized duration is commonly listed using two different methods. Method one is the Society of Auomotive Engineers(SAE) method. It uses .006" of lobe lift to start counting duration. The explanation I was given was that there was/is about .006" of compressability in the common valve train. Therefore it takes that much lobe lift to start valve movement. (They actually went into rocker ratios and called it .010" at the valve typically.) Most OEMs use this method.

Most aftermarket cam manufacturers use .020 of lobe lift to determine adv. dur. While this seems like a simple point, it can get real confusing in a hurry. Most engine builders talk about duration in degrees at .050" lift. This more acurately depicts the actual duration an engine sees with respect to flow as PRO stated.

Now if all manufacturers and engine builders used the same method all would be great. Crane at my last checking still used the SAE method for advertised duration. Crower, Reed, Comp and others use the .020" to the best of my knowledge.

P.S. I did the SAE method from memory so don't kill me if I missed it by .001" or .002". The trick for displaying the ° symbol is pressing the ALT key and typing the number 248. This is ASCII code from way back and your computer remembers it. So much for my tid bit being little. Sorry

[Christopher]

I appreciate the info, especially on how to put the degree symbol in!!