1gary

Now look guys.Ya gotta start learning this stuff and learn about cams in general.You have the net access and a whole host of resources because of it.I think you should use it.Apart of Hot Roddding is learning it and not choosing parts by general consensuses or by jury.

Cam and compression ratio compatibility

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by: Cobalt327, Jon, Silver Surfer, Techinspector1
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Sometimes it's difficult trying to explain to fellows who are new to hot rodding that you have to match the characteristics of the camshaft to the static compression ratio of the motor along with the operating range where the cam makes power. The camshaft is not a stand-alone piece. It must be coordinated with other motor and drivetrain parts in order to arrive at a combination of parts that will all work together toward a common goal.
This chart is nowhere near scientific or definitive in its scope. Larger or smaller cubic inches, different lobe separation angles and other variables will alter these figures, but at least it's a starting point in the explanation of using a certain range of cam with a certain range of static compression ratio. The figures shown in degrees are camshaft degrees of duration measured at 0.050" tappet lift.
The chart will show why it is foolish to install a 230 degree cam in an 8.00:1 motor in an attempt to get a lope out of the motor. It might lope, but it will lack the power to pull the hat off your head. There seems to be an obsession with lope these days. Lope is simply the sound of the motor being inefficient at low rpm's because the ascending piston is pushing fuel/air mixture back up the intake tract through the still open intake valve and disrupting the metering abilities of the carburetor.
On the other hand, it's equally as foolish to install a short cam into a motor with a fairly high static compression ratio. You get into an area of such high cylinder pressure that no fuel short of alcohol or racing gasoline will prevent detonation.
You can move 1/2 point of SCR either way and be in the ballpark. In other words, if you have a 9.00:1 motor and you want a little more cam, you can move up to a cam that would be used in a 9.5:1 motor and be OK. On the other hand, if you wanted to go with a little less cam, you might use 1/2 point less compression, down to an 8.50:1 cam.
Crane says: Static Compression Ratio (SCR) Intake Valve Duration (degrees @ .050" lift) Power Range (RPM) 8.00:1 185º 500-4,000 8.25:1 189º 650-4300 8.50:1 194º 800-4,500 8.75:1 200º 900-4,600 9.00:1 204º 1,000-4,600 9.25:1 208º 1,200-5,200 9.50:1 212º 1,600-5,400 9.75:1 216º 1,800-5,600 10.00:1 221º 2,000-5,800 10.25:1 227º 2,400-6,200 10.50:1 233º 2,800-6,400 10.75:1 236º 3,000-6,800 11.00:1 240º 3,200-7,000 11.50:1 244º 3,400-7,200 12.00:1 248º 3,600-7,400

Orr89RocZ

iTrader: (20)

Pretty good guidelines assuming everyone has good 93 oct gas although it should run ok on 91 that some areas have. E85 guys can almost run a full point higher

Fast355

iTrader: (2)

Not only can we run higher compression, we can run proportionally leaner mixtures without detonating and have the benefit of the vaporization of the additional fuel cooling the intake charge more than gasoline would.

Orr89RocZ

iTrader: (20)

Yup superior for power making with its coolin effects and octane increase. Too bad its not available in some areas where pump gas is everywhere. Fuel system design for E85 should be abit more expensive to handle the alcohol

DeltaElite121

Here I was thinking I'd finally make a cam post so all the "what cam should I run" questions go away, hahah.

Gary, you beat me to it.

Fast355

iTrader: (2)

It is a phenomenal fuel for making power, especially midrange torque. I am not even running a high compression engine as its a flex fuel vehicle that still runs on ordinary gasoline. I lucked out in having a stock fuel system to handle it.

For a 5,350 lbs 4 door truck that came stock with 317 HP only adding a CAI, exhaust, tuning, and a few other free/inexpensive mods it flies.

Fast355

iTrader: (2)

It is a phenomenal fuel for making power, especially midrange torque. I am not even running a high compression engine as its a flex fuel vehicle that still runs on ordinary gasoline. I lucked out in having a stock fuel system to handle it I only wish I had 12:1 compression rather than 10:1, slightly larger cams, a slightly shorter runner intake manifold, and headers to make the most of the 104 octane E85.

For a 5,350 lbs 4 door truck that came stock with 317 HP only adding a CAI, exhaust, tuning, and a few other free/inexpensive mods it flies.

Orr89RocZ

iTrader: (20)

I know what you mean. Got a L9H 6.2 truck myself and with tune only it made 330 whp. Gas tune only never tried e85. Thats thru 6l80e and 14 bolt 2500 rear. It gets up quick

scoflaw

iTrader: (2)

Good basic guideline, but there are variables that can alter things a bit.

Without asking what cam should I run, I was thinking of installing what I want, spinning the engine on the stand , and using cranking compression as an indicator. If it's under 200, I'm probably good to go?

Orr89RocZ

iTrader: (20)

That probably will work, i have heard other motors running with well over 200 psi on pump. You can also dial in spark plug heat range and use timing and fuel ratio to bandaid everything else