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Tatterone

I have a question about the cam I put in my 350

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I have a 1986 3/4 ton 4x4 long wheel base GMC that I rebuilt a 350 for. It has 202 heads, headers, and .30 over flat top Pistons. I put a small lunati voodoo cam in it. ( advised duration 256in262ex. Duration @ .050 tappet lift 213/219 with .454/.468 lift ). The truck has really good power from idle to 3000rpms, but then kind of slowly climbs from there. (spinning 37 inch military tires in dirt) I am wanting to put a bigger cam in the motor without changing valve spring, and other things. Would going to a cam with an advertised duration of 262/268. Duration @ .050 219/227. With a lift of 468/489. Make a big difference? Seems to be the next cam in line.
I'm afraid if I go bigger I will loose vacuum to my brakes and transmission, or have to run a stall converter.
Also what is the difference between advertised duration and duration @ .050 tappet?

Edited by Tatterone

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I've been there before and read some of it this time too. Starting to get a little more familiar with some of the specs, but it still looks mostly like Chinese to me. I was hoping someone would have had similar experience with small builds.

Would just degreeing this cam wake it up some, or just going to the next cam in line

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The answer to your question about duration is on page 8.

 

Degreeing the cam would at least tell you if it's installed correctly.

 

You still haven't answered the questions about the rest of the engine.  Compression ratio, engine management, timing (maybe you just need to set the ignition timing correctly), etc.  The very basic stuff.  No point in swapping cams without addressing the basics.

 

That's all I have.  Good luck.

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It's difficult to believe that an increase of one increment in cam-size in one manufacturer's catalog would either result in substantial gains or in substantial ruin of an otherwise well-sorted combination.  My recommendation would be to (1) study any of the principal books on small-block Chevy performance (such as those by David Vizard), and (2) look at an engine-simulation program, which estimates the torque-curve based on inputs regarding the various engine components.

 

The key unknown is tuning; carburetor, ignition, and how it all goes together.  Engine simulation programs assume a best-case scenario.  In practice, it is quite likely that the main problem is less about poor choice of components (unless something outlandish is selected), than in suboptimal tuning.

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