How to determine cam duration?

[SilverXJ]

Hypothetically, one has a cam with out a grind card and no way to get a grind card. How does one determine duration? I know if you can find the VC and VO events you can add those together + 180 and get the duration... but how would one be able to find those?

[dwg86]

The only way I know how would be to have the cam profiled by a cam company. I had Reed Cams profile the Mopar 30AB cam. They charged $25.00. They are close to my house so I didn't have to pay shipping. They can tell you lift, advertised duration, duration @ .050, lobe separation, and valve timing events(when they open and close).

[SilverXJ]

The how do they do it?

[dwg86]

The how do they do it?

I'm not sure. I am assumung they have a special machine to do it since they grind cams.

[SilverXJ]

I am trying to find a way to check it myself without sending it to one of them.

[dwg86]

You should be able to check it with a degree wheel with the cam insatlled in the engine.

[yuppiexj]

You should be able to check it with a degree wheel with the cam insatlled in the engine.

and a dial indicator to check the lift events

[SilverXJ]

You should be able to check it with a degree wheel with the cam insatlled in the engine.

Wouldn't that only work if the cam was installed 100% straight up? And you need the IVO and IVC to determine that.

[gremlinsteve]

its called a cam doctor.
one way is to remove cam and check p[art number/serial number engraved on it.
call that company and have it looked up.

second way is to send the cam to a company like comp ect...that allows them to put the cam on the machine called a cam doctor. will tell you everything about that cam. cost is usually 25 dollars. not a machine thats common to find...


steve

[SilverXJ]

its called a cam doctor.
one way is to remove cam and check p[art number/serial number engraved on it.
call that company and have it looked up.

You didn't actually read the whole thread nor the initial post, did you? I said with out any identifying numbers on the cam.

second way is to send the cam to a company like comp ect...that allows them to put the cam on the machine called a cam doctor. will tell you everything about that cam. cost is usually 25 dollars. not a machine thats common to find...

I don't want to send it to a company. There has to be a way to do this manually.

[RAPTORFAN85]

Couldn't you put the degree wheel on the engine and a dial indicator or the rocker arm or top of the spring retainer and turn the engine over and when the rocker opens the valve .050 note the degrees on the wheel. keep turning the engine over until the valve starts to close again and when it reaches .050 again, note the degrees again. The difference should be your duration at .050 lift.

I don't see why this wouldn't give your a pretty good idea were you stand for duration.

If I understand correctly,the valve events only tell you when the valves are open in relation to the crankshaft, The duration tells you how long they are open so you wouldn't need them to tell duration.

[yuppiexj]

Couldn't you put the degree wheel on the engine and a dial indicator or the rocker arm or top of the spring retainer and turn the engine over and when the rocker opens the valve .050 note the degrees on the wheel. keep turning the engine over until the valve starts to close again and when it reaches .050 again, note the degrees again. The difference should be your duration at .050 lift.

Don't forget advertised duration is generally .006" lift, if that's what you are seeking.

[SilverXJ]

Couldn't you put the degree wheel on the engine and a dial indicator or the rocker arm or top of the spring retainer and turn the engine over and when the rocker opens the valve .050 note the degrees on the wheel. keep turning the engine over until the valve starts to close again and when it reaches .050 again, note the degrees again. The difference should be your duration at .050 lift.

I don't see why this wouldn't give your a pretty good idea were you stand for duration.

If I understand correctly,the valve events only tell you when the valves are open in relation to the crankshaft, The duration tells you how long they are open so you wouldn't need them to tell duration.

What I did was put the cam on a V block, with a dial indiactor on one lobe, and a degree wheel on the other. When the dial hit .050" I started counting degrees and stopped when it hit .050" on the other side. What I got was 192*, when the cam actually has a 251* duration. Something isn't right.

[RAPTORFAN85]

you need to measure it at the valve. The duration is going to be longer at the valve because of the rocker ratio.

Also is the 251 advertised duration or at .050? If you want advertised duration you need to measure from .006 like previously noted.

[SilverXJ]

it was .050", but 251 duration is at .050". Measuring it at the vale will only cause it to open to .050" sooner and close later. So, pretty much the engine needs to be assembled and measure the crank degrees and lift at the valve? I wonder if there is an equation of sorts I could use if I know the rocker arm ratio to convert from lift at cam to valve lift. I doubt it.