Camshaft 101

[Ridgerunner]

Ok I understand nothing about cams or any of the info on cams. Like this. What does it all mean?


http://store.summitracing.com/partdetail.asp?part=EDL-2106&autoview=sku

 

[Mil1ion]

Those numbers are degrees

a circle is 360*

The longer duration allows for more of something

More intake of air
More exhausting of exhaust .

ie: The 8 lobes of a intake valves of the cam start at 65* and end at 350* which equals 285* of duration sucking air into the combustion chamber.


This cam per link

* = degrees

Intake Duration at 050 inch Lift: 194*
Exhaust Duration at 050 inch Lift: 204*
Duration at 050 inch Lift: 194* int./204* exh.
Advertised Intake Duration: 272*
Advertised Exhaust Duration: 282*
Advertised Duration: 272* int./282* exh.
Intake Valve Lift with Factory Rocker Arm Ratio: 0.460 in.
Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.480 in.
Valve Lift with Factory Rocker Arm Ratio: 0.460 int./0.480 exh. lift

 

[UNRULEE]

Dennis did a good job, as usual.

Too simplify (anyone,correct me if I'm wrong here). The two numbers that are always first taken into consideration with a cam are the intake and exhaust duration.

In one revolution an engine makes 360 degrees of rotation, hence one revolution. The numbers stated for duation of ex/intake are "how long" during one revolution of the engine that one exhaust valve and one intake valve are open. The larger these numbers are, the longer the valve is open. Larger numbers also equal the desireable "lumpy" idle. It's tempting to go overboard here but bear in mind that as the duration goes up so does the power curve of the engine, in hp and up the rpm range. Your bottom end torque will diminish as the duration numbers go up.

If you're building a high rpm drag motor, more duration is your friend. A high stall torque converter will help compensate for the lack of low end torque.

For most truck motors that see the day to day grind of grocery getter, trailer pulling duty and offroading cam duration should be kept fairly mild. Most of the time (keep in mind I'm used to shopping for 400's, other engines may vary slightly) duration for these type of vehicles won't be over 255-270.

I run a CompCams 265Deh in my 400 with good results. It's given me good torque at low rpm that is helpfull in getting my 35's rolling, even with the stock 3.54 gearing. It also makes decent top end power.

Valve lift is important as well. With the cam that I went with in my 400 I had to change the valve springs out. The stockers would have "went solid" (ie, completely compresed to the point of no longer being a spring). This will add cost to the cam swap process.

To avoid all hassle I went with a Comp Cams K-kit. This is an entire valvetrain upgrade that comes in one box, all of the homework is done! In the kit I recieved the cam of my choice, matched valve springs, valve spring hardware and seals, lifters and a double roller timing chain.

 

[Ridgerunner]

Thanks Lee I'll give ya reps later

 

[Mil1ion]

http://auto.howstuffworks.com/camshaft.htm[/url http://auto.howstuffworks.com/camshaft.htm

 

[miottimouse]

hi snake a 260 rv cam is a good "all around cam" very good throttle responce lots of tork smooth idle desent mileage 268 or 272 are a little more aggressive cams and you get the power in the higher rpms [1500+] and they will give you that "rap sound" and a little shake but lack some tork off idle and should have some mods to work well [headers/duels/intake/carb] check the rpms that these cams run best at and be honest to what you are useing the truck for are you running lots of highway or city/stop&go i have run all 3 in 390s and 460s and woudnt go more than a 268 my self point of caution do not go too big or aggressive mileage and power will suck
regurds joe

 

[Bob Ayers]

With the large duration, there is also overlap, the time the intake and exhaust valves are open at the same time. You will loose vacuum and torque at idle, and low RPMs, causing the lopy idle, but there will be scavanging at the higher RPMS, increasing the high RPM power.