cam question

[Omie01]

If a cam comes from the factory 4 degrees advanced, do you have to take that into account when setting initial timing? So if you want to set it to 12 degrees, do you only set it to 8 on the balancer? Might be a dumb question, but I haven't done this before.

 

[barnett468]

If a cam comes from the factory 4 degrees advanced, do you have to take that into account when setting initial timing? So if you want to set it to 12 degrees, do you only set it to 8 on the balancer? Might be a dumb question, but I haven't done this before.

no, the timing mark will always be in the same place until the cam chain stretches.

 

[Don C]

To change the cam timing you have to use an adjustable sprocket or offset keys.

 

[jbojo]

I think what Omie01 is asking is if the factory set the cam timing 4* advanced does he have to compensate for it when setting the engine timing, I think that the answer is no and you just set engine timing to the timing data that was recommended, so if it was 12* then you set 12* and don't compensate for that 4*. I believe because of emissions in the later years Ford stated to alter the cam timings to meet the federal reqmts. Of course if he wants to remove that 4* advance he would need to use an adjustable sprocket to accomplish that as Don C mentions.

Omei01, please confirm what you are asking here.

 

[TommyK]

I am far from an expert on these things but I think perhaps cam timing is being confused with ignition timing.

When you advance or retard a cam you are changing the relationship of the valve events to piston position.

When you are advancing or retarding ignition timing you are changing the point of spark plug firing spark to piston position.

While both can effect when and how much combustion pressure is made I don't think there is any direct relationship between the two, but I acknowledge I could be wrong about that.

A change in cam timing may necessitate a change in ignition timing to optimize the performance of the engine or it may not, just as it may necessitate a change in carburetor calibration.

 

[barnett468]

.

optimal performance is achieved when peak cylinder pressure is made a 14 degrees after tdc.

 

[TommyK]

.

optimal performance is achieved when peak cylinder pressure is made a 14 degrees after tdc.

Yes and the goal of ignition tuning is to achieve that.

 

[c9zx]

Tommy's first post is spot on. Chuck

 

[Omie01]

Yes, I'm talking about cam timing affecting ign timing. My cam is 4 degrees advanced according to the cam card, I'm asking if that affects the ign timing process, but after further study it sounds like it does not. Tommy I think is right, it's just the valve events happen a little sooner, and I time my engine as usual.

 

[Don C]

The cams came advanced from the factory for emissions, not performance. The 71s and 72s have the same cam profile, just the 72s are 4* advanced.

It looks like you may have an aftermarket cam, if so please disregard...

 

[barnett468]

I time my engine as usual.

that is correct.

If a cam comes from the factory 4 degrees advanced, do you have to take that into account when setting initial timing? So if you want to set it to 12 degrees, do you only set it to 8 on the balancer? Might be a dumb question, but I haven't done this before.

no, the timing mark will always be in the same place until the cam chain stretches.

 

[Mister 4x4]

Yeah, I never did get the whole "degree the cam" thing. The cam is designed to work with the crank, which has a key slot on the balancer (that has the timing mark indicator - typically) with a sprocket using the same keyway. The cam has a sprocket with a key slot as well... meaning, it can only go on one way. The timing chain has specifically spaced slots for the teeth of the cam sprocket and crank sprocket - making single degree changes really hard to do.

Regardless of how the "degreeing" gets done, the timing is set by moving the distributor around to find the sweet spot for the application.

I'm just saying "I don't get it." I don't really need an explanation either, because I know it does good things for people trying to squeeze everything out of their engines... I just accept it as one of those "F.M.*" kind of deals - kind of like automatic transmissions. rofl

* F.M. = Freakin' Magic

 

[Omie01]

We did my cam degreeing yesterday, and as far as I can tell its to verify that your cam is what it is supposed to be. 3 ways I know of to fix an out of phase cam is with a multi-key sprocket or Hex-adjust cam gear. Or send cam back and get new one. My engine builder says he see's a bad cam every once in a while, usually wrong cam in box situation. Even after going step-by-step through the cam degreeing process, all I came away with is its for verifying the cam. PS: My Comp Cam was "right on"!!!

 

[73mach1]

I just accept it as one of those "F.M.*" kind of deals - kind of like automatic transmissions. rofl ,i what you mean ,love it