Indexing Cams

[cgrey8]

I've never had to index a cam before. I've always seen the indexing wheels, but never knew what to do with them. Reading around on the NET, I can see a few articles on HOW to index a cam, but nothing really explains why.

Any thoughts of expereince out there that can detail out exactly what indexing is, when you want to index, and why it's important?

[MercuRanger]

Degreeing a cam is mostly to verify everything's OK (unless you're advancing/retarding the cam). IMHO, in these days of computerized manufacturing and ISO9000, if you get a cam & timing chain from a respectable company, degreeing a cam to "straight up" is a waste of time. Just my $0.02, and I'll probably take some flak for it.

Mike

[cgrey8]

That's sortof what I figured, however I just wanted to be sure.

Every engine I've ever helped build, we just slapped the cam in, put the sprokets on, and wrapped a chain around'em after aligning the sprokets to their marks. I should also add that every engine build I've ever had my hand in has been a "shade-tree" operation and thus I can't assume that everything I've ever seen/learned from my experience was the right way to do things. That's why I asked about this.

So unless I'm draggin' with major horses, Indexing is not needed?

What about cam advance or retard? I seem to remember a thread someone made mention that 302s like a slighty retarded cam, where 351s can take a little advance on the cam to improve performance. Why would you ever want to alter the timing of a cam? What's the effect of advance/retard of a cam?

[2lo-rngr]

ADVANCED: Increases the time the intake valve is open during thedownstroke of the piston, therefore inhaling a greater fuel/air mixtureand allowing more compression time, which is especially noticed at lowrpm. I don't believe this is as rpm dependent (as retarding the cam)and low rpm power is increased by the timing at which the mixture isdrawn in. However, at high rpm, the exhaust valve plays a larger rolein power. Since you also have closed the exhaust valve earlier,diminished scavenging and top end power will Decrease.

INCREASED: Low end power
DECREASED: Top end power


RETARDING: By diminishing the time at which the valve is open on thedownstroke and essentially slightly lowering the compression, you willdecrease low end power, yet increase top end power by a greater amountof scavenging at high rpm.

INCREASED: Top end power (A good exhaust is mandatory)
DECREASED: Low end power

[cgrey8]

Are these cam-games people played before there were as many different options in cams as there are today or do people still do this on street cars?

Obviously, if you are into serious draggin', all bets are off. If you can think of it, they've probably tried it. You do and test whatever to find what's optimum, including custom ground sticks.

[stranger]

the duration determins how long the cam is open.advancing or retarding cam is to adjust your lca(lobe center angle)cubes determine an optimum lca.more cubes,lower lca.factory stock is about 114-118 on a 302.optimum
for a efi is about 112-113.so advancing cam 2-4 deg depending on original lca spec.all stock cams vary slightly so checking with a degree wheel will varify actual lca. then adjusting crank sprocket for optimum lca.

example lca chart
302 112-113
351 109-111
393 107-109

so an e cam at 110 lca is perfect for a 351
retard 2 deg for 112 on a 302
advance 2 deg to 108 for 393


there are many other factors in cam/cube reccomendations.
but advancing or retarding only affects lca not profile or lift or lsa,or duration

to low of an lca gives you low vacume at idle,to high robs power.hope this helps you understand degreeing
you check #1 intake at max lift(center lobe) check degree wheel position
exhaust center is also important but effects driveabilty a little less.

custom cam is usually best when done by a great cam grinder.however good results can be had from an off the shelf cam degreed ptoperly