Thread: Cam Choice help

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Originally Posted by Ranch

So if I moved to say 10-1 SC where would that put me as far as DC?

That would put the DCR at 8.3:1, but the problem with that is that you're using iron heads. Word on the street caps iron heads at 9.5:1 and aluminum heads at 10.5:1 for use with widely available pump gas. Now, you may get away with it if you tightened up the squish/quench to 0.035" to 0.040" and/or maybe used water injection. Then again, you might be just fine with 10.0:1 and iron heads. It's just that I don't want to counsel you to do something that I myself wouldn't do.

Originally Posted by Ranch

Sorry I’m completely lost with cams.

Me too, I know just enough to be dangerous, so I tend to lean to the conservative side of the issue because I'm dealing with other folk's time and money and I want everything to turn out well for them, even if there is a little left on the table. I figure it's better to leave 10-15 hp on the table and shoot for the sweet spot in the middle than it is to create a motor that is on the edge with what I would consider too much cam for the application and have a soggy bottom end that would have to be crutched up with more converter and more gear. If you feel you need more power, change pistons and bolt a 3.98" arm into the block, then invest in some aluminum heads that will breathe far better than those iron relics you're using now. I don't intend for that to sound mean spirited either, I'm just being real with you.

Originally Posted by Ranch

I’m looking at 9.5 SC to give me some ignition timing room using 93 octane, but the way this sounds I may have the room using this 282S at 10.1 SC.

And I absolutely agree with that thinkin', but you'll have to watch closely for signs of detonation. Purchase a Longacre loupe and find a place (dragstrip being the best) where you can make a full-power pass, then go to neutral and chop the ignition. Coast to a stop and pull the plugs right there. Idling back to the pits will re-color the plugs and give you an erroneous reading. The first signs of detonation will be little black spots on the insulator that look like someone sprinkled pepper on them. That will be oil that is jetted out of the top piston ring lands from the sledgehammer blows of detonation. If allowed to continue with that tune, the next thing you will see is silver-colored specks on the insulators. That would be part of the pistons that melted from the excessive heat of detonation.
LONGACRE 50884 Spark Plug Viewer

Originally Posted by Ranch

Not trying to tell you anything Tech just very confusing since Comp Cam sez 9.1+.

I won't attempt to argue with CompCam techs, they know their products far better than I do, but I looked at similar specs from a couple of other grinders and they seem to favor 10.0:1 to 11.5:1 for cam timing in that 282S range. And another thing, as I've said on here and other forums many times before, I dislike the idea of yanking the valves off their seats with a numerically low Hydraulic Intensity in a street motor. The 282S cam has a HI of 46 and I would want another 10-15 degrees of difference between advertised and 0.050" for a street motor. If you are building a race motor, yeah, yank 'em open and slam 'em shut and get all the valve lift as quickly as you can and put up with noisy operation, but this application is a street motor, where longevity and quiet operation trumps horsepower in my opinion. Harvey Crane used to grind all his cams on a HI of 62 and Harvey knew one hell of a lot more than some of these yahoos grinding cams today in my opinion.

Originally Posted by Ranch

As far as the C4AZ –D cam that Jerry mentioned, I don’t know much about that or if it’s even still available

The C4AZ cam had 324 degrees duration and 112 degrees overlap and might want SCR on the order of 12.0:1 or better, so it may be a little too healthy for a street motor that has to operate on pump gas. Jerry has probably forgotten more than I ever knew, but that's just my opinion.

Originally Posted by Ranch

Thanks guys all help is greatly appreciated

You're welcome, keep those cards and letters comin' in.

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