Help educate me on the language of cams

[Martin]

Hi all,

Just trying to learn a few things - not necessarily looking to understand all the details, just the language so I know what I should be asking and thinking about.

On the compcams website it lists these items in the specifications:

RPM Range - is this the range that it is designed to run it? i.e. "2000-5800". Does this mean it drops off heavily after 5800? Red line is at 5800? Below 2000rpm it will be sluggish?
Valve timing - e.g. 0.006 ??? Is 0.006 good? What does changing this to 0.008
Lobe separation - I think this has something to do with engine vacuum. EFI engines need something like 112-114 degrees? Carb'ed engines can be anywhere from 107-112? Does this have anything to do with the engines ability to support a vacuum based power brake? I think the higher the degree, the less overlap you have so the engine is going to idle smoother and have less lope?
intake centreline - e.g. 106 degrees. Again, I have no idea, what does changing this mean? 104 degrees? 108 degrees?
valve lash - e.g. Hydraulic
duration - e.g. 282 intake, 288 exhaust?
duration @ 0.50 lift - e.g. 230 intake, 236 exhaust. Again, I have no idea, what does changing this mean? 104 degrees? 108 degrees?
valve lift - e.g. 0.51
Lobe lift - e.g. 0.301 intake, 0.307


Does anybody have a dummies guide to cam selection? I guess I am more interested in how a change in each specification item affects the overall

Martin

[sharkx]

Start here:
http://www.chevyhiperformance.com/techarticles/49158_camshaft_engine_basics/index.html

Camshaft design and selecting a camshaft is always a compromise between competing goals.

There are many factors but here is a simple explanation of just one factor.

For a low RPM application, we want the intake valve to close before the compression stroke.

At a high RPM, air is rushing through the intake system and it has considerable momentum. By leaving the intake valve open a little longer, the momentum of the fast-moving air/fuel continues to force air/fuel into the cylinder even though the piston may have started its compression stroke. So the faster the engine goes, the faster the air/fuel moves, and the longer we want the intake valve to stay open.

Similar factors apply to the exhaust valve too. It's factors such as these that influence the design and hence the RPM range of the cam.

I'm sure lots of others will chime in shortly.

Bruce

[Hankl]

valve lash - e.g. Hydraulic There is a "Preset" for Hydraulic liftes, not actually a "Lash"
valve lift - e.g. 0.51 The distance in inches that the valve lifts from the seat, in this case, .510 inches, just over 1/2 an inch
Lobe lift - e.g. 0.301 intake, 0.307 The distance from zero lift, to max lift, that the lifter travels. In this case, the cam moves the lifter up .307 inches, that movement is multiplied by the rocker ratio to give you the lift at the vale 0f .507.


Hank :cool:

[AJ Roadster NJ]

Martin, you are obviously at an extremely fun part of the build -- at least it was for me -- and I really educated myself about these things before making my engine choices.

This is the best book I bought while planning the build, even though it is not specifically about Ford smallblocks;

http://www.amazon.com/Engine-Blueprinting-Practical-Rebuilding-S/dp/1884089267/ref=pd_bxgy_b_text_c

A good reference for various combos, including various heads;

http://www.amazon.com/Dyno-Proven-Small-Block-Ford-Performance-Design/dp/193249474X/ref=sr_1_fkmr0_3?ie=UTF8&qid=1309129993&sr=1-3-fkmr0

By FAR the best smallblock Ford engine book out there IMHO;

http://www.amazon.com/How-Rebuild-Small-Block-Ford-Engines/dp/0912656891/ref=sr_1_3?s=books&ie=UTF8&qid=1309130091&sr=1-3

Read these. Study them. These are complex topics you're asking about, with no clear "right" answer, and you aren't going to get the information you need from quick questions and answers on this forum, much as I love it here. You need to buy these books. The authors address the very questions you're asking in thoughtful and well-written chapters that are heavily illustrated with pictures to help you really understand what they're talking about.

Best advice I can give.

AJ

[Martin]

AJ - that last book you posted is the same book I bought a year ago that convinced me not to try building an engine. I read it, read it again and decided it was just too complicated.

Wife got on my case a few weeks back and told me I wasn't allowed to build the car without building the engine so looks like I am back to studying again.

Martin

[AJ Roadster NJ]

Building the motor yourself is certainly challenging. And there are risks of course. Not to mention that I could've bought a crate motor for significantly less money than building my own.

But I have to say, every time I start the motor for people to hear, I feel great satisfaction at having built it myself. I really do. It is a strong motor, it was fun building it, and I can always say, "I BUILT IT!!!"

I studied all those books just as you have, and I found that there were no surprises as I went through the motor. I did have some questions along the way -- as just one example, the way that the timing chain actually gets oil is by a measured "leakage" from the front cam bearing, which has to do with the cam thrust measurement -- but that's why we're here to answer your questions along the way.

AJ

[Fifty-Two]

Wife got on my case a few weeks back and told me I wasn't allowed to build the car without building the engine so looks like I am back to studying again.

Nothing like having your wife threaten your "man card" during the build. Too funny! ;)

- John

[Martin]

Before we got married my friends hassled me because she was whining about not taking her to the drag strip one day. Little did I know she would turn around one day and tell me she wanted to build a car together with me.

:o

I can handle having my man card threatened when it means I all I have to do is put up with that kind of thing :)

[AJ Roadster NJ]

Wow. I had SUCH a difficult time selling my wife on this project. What finally did it was to let her see the Factory Five open house. I drove the three of us (my son was 4 years old at the time) up to Providence RI on the Friday. On Saturday we hit the open house early, the cruised around the upper cape and ended up at a B&B in Newport. Great weekend, and it let her associate pleasant memories with FFR.

So Dave, if you're reading this, we're one of those sales that is a direct result of an open house. :cool: She had serious doubts about whether I could actually do this and, being a CPA, she was very concerned that I was going to flush a very large pile of cash down the toidy. After talking to a whole bunch of nice people at the open house, every one of which said, "Yeah, you can do this," she softened up a bit. I interpreted the attitude adjustment as implicit permission and placed the order that fall during a sale.

It's all good now. I'm almost done, driving a go-cart and working the body.

AJ

[Martin]

I think I'll be lucky to turn a wrench with my wife around. I'll probably be relegated to holding the heavy stuff while she does the fun stuff.

So far we've agreed, she will do all the electrical work, the fuel/brake lines etc. I'll do the body work and suspension. The rest we will figure out as we go.

Martin

[Someday I Suppose]

Martin,

I was just going to add to what Shark and Hank had said, the comprimise of a single cam engine. You will sometimes hear the term overlap which is what Shark is talking about where the intake valve is still open even though the compression stroke has started. At low RPM's a cam with a lot of overlap will have that thumpy sound to it and also can make it fun to pass an emissions test.

The other thing to mention, when you hear of newer engines multiple cams, etc they are trying to get rid of the comprimise there by having more adjustability in the system. The new Ford Coyote is a good example, not only multiple cams, but the seperation is infinatly adjustable by the computer. This allows the engine to get good fuel mileage and good low end torque, but then also make great power on the higher end. Really cool stuff.

_Scott

[Martin]

Given the emissions laws are tough over here in the UK, having a lumpy idle is almost impossible if we use a new block. The alternative is to get a really old block and hope for the best.

Personally, I don't like the sound of a lumpy idle on a street car so it works out OK for us.

Martin