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Old 03-26-2017, 05:38 PM   #1
btucker_ss2
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Default Reading a cam

I have always taken someone's word on cams. However I would like to understand them a little more. Can someone please explain the following specs and why.
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Old 03-26-2017, 08:20 PM   #2
FDChappie
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Default Re: Reading a cam

Looks like a pretty big cam to me. The basics are lift and duration. Small cam 250-260, medium 260-270, big > 270. Your cam is split duration int 272/ ex 280.

There is a comp 252 in my Scout's 345. Idle is a bit lopie when cold, otherwise just a bit warmer than stock. And that's about the limit of my knowledge. For starters you can read the descriptions in the store here or maybe some of the really smart people here will chime in.

The real bottom line is that a 392 with a red line of 3200 rpm's will not spin fast enough to use a cam like that without extensive modifications.
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Old 03-27-2017, 12:47 PM   #3
jeff campbell
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Default Re: Reading a cam

I've gotta comp-cam 262 duration .440 lift on both int & exh, has a nice lope to it, 392,.030 over. Nice pullin power, sounds good, that 1 is just a might healthier. Its in my '71-1210 t'all 4x4. 3.73's.auto.
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Old 03-28-2017, 01:08 PM   #4
btucker_ss2
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Default Re: Reading a cam

Can someone provide me the specs for a stock cam?

I am currently working on building a 392. I have a set of ported and polished heads, aluminum intake, headers and .030 bored out engine. My goal for this engine is to drive it daily. I am looking for any input on this build.

I will either run a IH automatic or a nv4500. I want to make sure it stays in the power band when cruising down the highway.
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Old 03-28-2017, 03:38 PM   #5
Robert Kenney
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Default Re: Reading a cam

Stock sv cam details from measuring one my self.
Gross lobe cl 110
intake cl:112@.100, duration: 180* @ .050, lobe lift: .219
exhaust cl 108@.100, duration 181* @ .050, lobe lift: .225

only the @ .050 duration and valve timing is really relevant when power and torque are concerned.

In order to know if you will remain in the power band on the highway, we need to know the r&p ratios and what speed you expect to cruise at. In the 5 speed we should not consider the 5th gear for power calcs. Consider 4th as for hills you'll be in that gear.
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Old 03-28-2017, 05:13 PM   #6
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Default Re: Reading a cam

And tire size is important too. To really enjoy that cam lightening the rotating mass with lighter pistons and valve train components will get you into some higher rpm's. The oem pistons have steel inserts for the top ring land and that is a big rpm limiter.
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Old 03-28-2017, 07:39 PM   #7
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Default Re: Reading a cam

Current gearing 3.73 and the tire size will remain close to a 32 or 33 inch tire. The tire will be a metric size most likely but I will not go over a 33 inch. Due to rolling mass.
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Old 03-29-2017, 05:37 AM   #8
Robert Kenney
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Default Re: Reading a cam

4th gear @ 65-70 5th gear @ 65-70 mph you'll be turning 2450-2650 rpm

5th gear @ 65-70 5th gear @ 65-70 mph you'll be turning 1950-2120 rpm

that is close to peak torque rpm for a stock sv give or take a few rpm, depending on displacement. All sv's used the same cam, so the displacement increases from the 266 up, would lower the peak torque rpm and peak hp rpm.



A small correction on the information posted earlier regarding the masses that effect efficiency and hp in an engine are the reciprocating mass. The rotating mass doesn't change direction it just spins. The inertia of it will slow acceleration but will not effect the hp output of an engine.
The part of the piston and rod that are accelerating and decelerating with each revolution of the engine are critical because it takes a bunch of energy to push and pull on that weight 4000 times a minute. That wasted energy goes up as the the square of the velocity. So increases in rpm eat up increasingly enormous amounts of energy or hp.

The sv line of engines, being designed for low rpm and longevity wear very heavy pistons and rods. For example, sbc or bbc have pistons in the 3-400 gram range while an sv's are in the 1000 gram range. The rods are in the a similar predicament.
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Old 03-29-2017, 11:08 AM   #9
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Default Re: Reading a cam

Based on this information do you think I should get a cam just a little above stock? I already have a stock cam in the motor. One more thing: 345 heads will be going on this 392.

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Old 03-29-2017, 04:56 PM   #10
Robert Kenney
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Default Re: Reading a cam

Exactly where will your compression end up. You need all of the volumes to get the right compression calc.
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Old 03-29-2017, 08:50 PM   #11
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Default Re: Reading a cam

I guess the proper term would be reciprocating mass. Thanks Robert. Personally I'd rather deck the block, shave the heads and keep the bigger valves.
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Old 04-03-2017, 11:49 AM   #12
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Default Re: Reading a cam

I am estimating the compression will be just a little better than stock. 8.3 to 1. The only big advantage I can see is opening up the exhaust and the intake.
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Old 04-05-2017, 05:28 PM   #13
Robert Kenney
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Default Re: Reading a cam

You'll need to measure the combustion chamber volume as a guess is only a guess. Fdc is also correct on valve size. IH didn't up the valve size for kicks but because the redesign was an improvement.
Just remember that air flow is hp period. The increase in displacement demanded more air and the valve size was the proper decision. If you have the 392 heads I do vehemently recommend using them.
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