[aktattoo]

Why does one advance the camshaft? For more cranking compression? What are the positive and negative effects?

[Tim Corcoran]

Normally it's best to install the cam per the cam timing card. If the cam card says 108 ICL then install it at 108. If you want to experiment with different installed positions I would install it per the cam card first and run it like that then if you make a change you can compare the performance from your baseline installed per recommended position. But in most cases you should just install it per the manufacturer's recommendations.

[Poncholvr]

I always liked this static/dynamic compression ratio calculator. If you use the dynamic compression calculator part, and play with the numbers, you can see how cam timing will effect the dynamic compression ratio by changing the intake closing point.

http://kb-silvolite.com/calc.php?action=comp

[72LuxuryLeMansLa.]

Originally Posted by Poncholvr

I always liked this static/dynamic compression ratio calculator. If you use the dynamic compression calculator part, and play with the numbers, you can see how cam timing will effect the dynamic compression ratio by changing the intake closing point.

http://kb-silvolite.com/calc.php?action=comp

Download and try this one. Use the advertised duration numbers. I find it to be very accurate.

http://cochise.uia.net/pkelley2/DynamicCR.html

Karl

[Lee]

To know WHERE to install a cam, you have to have a LOT of practical experience or some sophisticated software - or both. The safe bet is to follow the cam card - but if you talk to several different techs at the same company, you may get different recommendations.

If you install the cam and find out you have traction issues, then you might try retarding your cam a degree or two - which will typically trade a bit of low-end for more topend.

If the motor is soft off the line, than a bit more advance tends to improve the low-end a little.

A long time ago, a person who I didn't really care for told me that LSA and ICL are NOT design parameters for a cam. In contrast, they are simply byproducts of selecting the correct valve timing events. In the last few years, I've finally designed enough cams and seen how they work (on a chassis dyno) to realize that person was telling me the truth.

[ponyakr]

here's an idea that all the new age thinkers will scoff at. i always advanced mine 4 degrees--never less than 2 more than you want 2 run it--because unless they have come up with some new miracle chain that does not stretch, the timing chain will stretch at least 2-4 degrees almost imediately. i found this out accidentally 1 time when i had 2 take the timing cover back off for some reason, after only runnin the motor for a very short time. i knew i had used a new timing set, but there was allready slack in the chain. i think its unavoidable--but there are obviously many on here who know more than me--thats just my 2 cents.

[grrrrregg!!!]

Originally Posted by ponyakr

here's an idea that all the new age thinkers will scoff at. i always advanced mine 4 degrees--never less than 2 more than you want 2 run it--because unless they have come up with some new miracle chain that does not stretch, the timing chain will stretch at least 2-4 degrees almost imediately. i found this out accidentally 1 time when i had 2 take the timing cover back off for some reason, after only runnin the motor for a very short time. i knew i had used a new timing set, but there was allready slack in the chain. i think its unavoidable--but there are obviously many on here who know more than me--thats just my 2 cents.

any chance the cam manufacturers already have this built into their cam design

[ponyakr]

that may be--but i've heard several on this site say that they have run across cams that had the keyway in the wrong place by several degrees--so i guess you either trust the cam co to do it right or check it yourself. i've never used an offbrand cam, so i've never had a problem with it myself.

[paul s.]

Originally Posted by aktattoo

Why does one advance the camshaft? ?

For more low end power. MANY times it is done because of a low compression combination running too large of a camshaft and advancing the cam can regain some of the missing low end torque.

Originally Posted by aktattoo

What are the positive and negative effects?

Anytime you advance or retard a cam, you are changing ALL FOUR TIMING EVENTS and that, by and large, is contradictory. Let's say you advance your camshaft to get the intake valve to close sooner, looking to boost your low end power, but you are also OPENING the exhaust valve sooner... and that blows down your cylinder sooner which is good for TOP END POWER.

BUT, the most important timing event is the intake closing and that trumps the other three so you will still see a net gain.

To me the most negative effect is the need to go to a bigger cam just to achieve what a smaller cam can achieve in a better combination.

Now, if you are drag racing, you are going to want that valve opening ASAP and chasing the piston down the hole. You are also going to want a good 60' so advancing a big cam will work very well in that situation. But this IS the street section and it is very easy to open up a BIG can o'worms!

[aktattoo]

Cool thanks for the input. I always questioned that.

[Poncholvr]

Originally Posted by ponyakr

here's an idea that all the new age thinkers will scoff at. i always advanced mine 4 degrees--never less than 2 more than you want 2 run it--because unless they have come up with some new miracle chain that does not stretch, the timing chain will stretch at least 2-4 degrees almost imediately. i found this out accidentally 1 time when i had 2 take the timing cover back off for some reason, after only runnin the motor for a very short time. i knew i had used a new timing set, but there was allready slack in the chain. i think its unavoidable--but there are obviously many on here who know more than me--thats just my 2 cents.

After 30 years of doing this stuff, I've never had a performance timing chain stretch THAT MUCH "almost immediately". Heck, I've had race Pontiacs, that after 30K miles, I had to take the timing cover back off and the chain was still as tight as when I put it on in the 1st place. Of course, I always used a good Cloyes timing chain or others that were of high quality (large rollers in the chain). But just arbitrarily putting in 2 to 4 degrees of advance, "just because", may get you diminishing returns. But it really depends on the combination of course. Obviously its worked for you though

The other thing that makes me lift an eyebrow at is....crankshaft & cam bore centerlines. Anybody knows that blocks and heads suffer from "core shift' during the foundry process. Which is why I've always looked at the core shift on blocks before I would buy used ones. You could have a new block from the factory, and if the centerlines of where the cam or crank bores are off....well then, there you go. No timing chain will ever be tight. Unless you can get a timing chain with over sized rollers like for Chevrolet.