1968newport

How do you where to set the cam timing? Cam with reference to crank. I don't even understand ignition timing. What's the difference between the two? Am I right to say that ignition timing is when the spark happens, and cam timing is when valves open and close? If so, what effect does cam timing have? How do you know where to set it? And in relation to cam timing, where is ignition timing set?

Thanks.


Again, 383 stroker, with 6-71 blower at 6-7 psi.

440roadrunner

There have been books written...............LOL

The basics of cam timing are that any given cam, if advanced a little, gives you more bottom end, while retarding give you more on the top end

There are some performance cams that seem to "run better" for many if advanced or retarded from the "factory marks."

In addition to the above, it "seems" that either or both, cams or cam drives are not as accurate as they once were. So this leads to huge discussions on "degreeing" a cam. I just ran into that the other day.

A newly made friend had one of Mopar's "purple" cams in a pickup. He says it was a dog We discussed it over at FABO, and everybody "thinks" you should advance the cam some

The cam seems to be made with an intake lobe center design at (if I remember all this) at 108*

We checked, and it was at 110

The guys say run the cam at 104--106, maybe even more advanced. In a heavier vehicle, and or with higher gears, you WANT "low end."

So we pulled it apart, used an aftermarket multi--key cam drive, and advanced it 6* from the new drive "factory marks." We ended up at 105 + / - our inaccuracy in reading this

Google stuff like "how to degree a cam." There are websites and Youtube videos. All the major manufacturers, Comp Cams is one, have tech info on their websites.

So CAM timing affects where the power band comes out, regardless of the original cam design.

=======================================

Ignition timing. You set ignition timing AFTER you install the cam, because changing the cam timing changes ignition time. Ignition time is ALSO a huge can of worms. All cars federally since 68, and Califrootia cars since 66 had to have emissions controlls, which GENERALLY means retarded ignition timing at idle, and a long slow mechanical and vacuum advance. Some of the 70's cars were actually timed at idle at zero (TDC) or AFTER TDC a couple of degrees or so. This is NOT what you want for performance.

There is so many things that affect ignition timing, that again, BOOKS have been written.

Compression ration, design of the compustion chamber, type of fuel, weight and gearing of the vehicle, and many other factors come into play.

GENERALLY on a performance car that you want timed to "run" instead of "keeping the smog inspectors happy" you want LOTS of initial timing, a short mechanical curve, and somewhere in the 34--40 range for total mechanical advance. Vacuum advance can run out to as much as 55--60* total, depending.

Vacuum is only "light cruise," "part throttle," so it's for fuel mileage. The more throttle you give it, the less vacuum

1968newport

Sweet. That actually clarifies things up for me. Huge help. I thank you for this info. This is my first build, and am pretty new to motors and such. I have done ton of research but sometimes not knowing what to google makes it impossible to get info. Thanks again, you are a HUGE help!