Pick powerband ratings? Seems like some companies are either making the greatest cams alive or full of it?

They are based in reality, but some are a little more realistic than others... ;)

Pretty much a factor of duration, overlap, and timing. Compression enters into it somewhat and you'll see the grinders recommend a certain CR for a cam selection. No voodoo with this, just goes with the specs. From what I've had over the years, the more radical the cam, the harder it is to get the engine to run like it should. If I only knew then.........

I tend to go by this....

250 = 8 to 1 CR.;

260 = 9 to 1 CR.;

270 = 10 to 1 CR.;

280 = 10.5 to 1 CR.;

290 = 11 to 1 CR.; and finally

300 = 12 to 1 CR.

Or thereabouts.

Read Pat Kelley's great DCR site at least three times and it will tell you about picking a cam for a specific CR for pump gas use.

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

I've read it at least three time's too!!

pdq67

ehh, with some of the new promises I 've seen advertised, I'm leaning to the full of it side of opinion.

thanks guys, me have no hair and ride little kid motorcycles.

You also need to consider the effect of cubic inches of the engine when selecting cam specs, as that also has an affect on the useable power band.

As well as lifter foot diameter too!

B/c a .904" dia. MOPAR and AMC lifter foot can be ran on a much more aggressive lobe than can our .842" dia. lifters.

pdq67

ehh, with some of the new promises I 've seen advertised, I'm leaning to the "full of it" side of opinion.

AMEN!!!!

After 55 years of R&D, I think we've taken the flat tappet hydraulic cam about as far as possible and I don't care who's springs you stack on top of them!

Todays market is the ricer that believes a sticker and a fart pipe makes a 20HP gain. If you can't beat em.........

Back in the "Dark Ages", there were;

Stock, 1/4 race; 1/2 race, 5/8 race, 3/4 race and finally full race cams b/c we didn't know a whole lot about cam tech so the makers used this lingo to tell us how far off from stock an aftermarket race cam was.

Now the lingo is totally out of date, BUT the same principal still holds true to this day if you think about it.

Like a stock at say 250, a 1/4 at 260, a 1/2 at 270, a 5/8 at 280 a 3/4 at 290 and the ball's out full race one at 300 or more duration!

And compression and engine size AND stroke play a good roll here too!!

Stroke is a bigger power producer than bore!! As long as the valves aren't shrouded so much it plain CAN'T breath up top!!

Don't laugh at that old man that said he had a 3/4 race cam in his old Ford or Chevy back then!!

pdq67

marv and pdq,,,you 2 guys are starting to show your age!!!!!!!! ha ha!! ditto with that info!!

heard once from "those with the know" that it actually takes about 14* duration change with a 350 chevy to show a true 500 rpm change. and that it changes progressively (grows) with cubic inches added.

Take a copy of D2k and run an engine combination through it and holding everything the same except run it for.......................

A 302, a 327, a 350 and finally a 377 w/ a 3.75" long 400 crank in it and watch the power curve peaks drop in rpm's as you do it!!

Interesting to say the least to me!!

pdq67