Author Topic: Cam suggestions.  (Read 1232 times)

Offline Sheriff_of_Rock_Ridge

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Cam suggestions.
« on: August 17, 2018, 04:53:26 PM »
Guy i work with had a 97 vortec motor rebuilt 30 over and needed to sell it.  It’s short blocked at his shop.  I was going to have him long block it.  I’m a newbie and am having a little trouble communicating with the mechanist.  Short story long I want to use this motor in an 84 k10, 700r4, 10 bolt rear, Carbureted no computer.  This is the 1st non stock addition to this truck. 
He has the factory cam but it’s my understanding (Wikipedia) the 97 has the computer timing thingy cam. 
So, new cam...  I see the term roller cam thrown out there in my research.  Also see things like internal/external balance.  I’m not trying to build my forever motor but don’t want to miss an opportunity to get something a little nice.   I’m looking for some advice on cam selection.  Also any pros and cons of the balance.  It seems like internal balance is the way to go but idk.  Does it even mater that much?

I’m more worried about just getting this thing built and not missing an opportunity.

Things I know about it are:
.030 over
Slight dish pistons
Vortec heads
It was built to be stock type motor for a work truck.

Any help on cam or anything that might be easy to do now would be great advice.  I know the machine guy will appreciate it too.  Thanks


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Offline 75gmck25

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  • 1975 GMC K25 Camper Special, 350/TH350/NP203
Re: Cam suggestions.
« Reply #1 on: August 18, 2018, 06:45:19 AM »
If its a true '97 Vortec motor (L31), its a great starting point for a build.

- Internal vs. external balance are based on the crankshaft installed.  If its stock Vortec, it should use a stock SBC balancer, but will need a flywheel for a one piece rear main seal. 

- Vortec iron heads seem to be prone to cracking, so make sure they have been checked before they are installed. 

- Stock Vortec heads only support cams with limited lift (about .420) before the springs bind.  The heads can be modified by grinding down the spring seats and providing more clearance, or you just have to choose the right cam.  I think one manufacturer also sells a different set of springs that allow a little more lift.

- With dished pistons, I hope they kept compression to at least 9.5.  You could use more, but 9.5 is very forgiving when you use cheap gas.

- Stock Vortec heads use pressed-in rocker arm studs.  This works fine for most cams, but can be an issue with agressive cam profiles.  Some folks pay to have the heads tapped for screw in studs.  Probably not worth it for your application.

-The original L31 cam is about 191/196 @ .050 duration. For your truck I would just swap in an upgraded roller with about 214/218 duration, which would provide more power while keeping the low end torque.   It will still idle well and be a very good street cam.  Don't get carried away with rump-rump sounding cams that sound tough but are poorly matched to your truck. 
I like the Howard's roller cams myself, but there are many other brands available.

- Use a good dual plane Vortec intake (Edelbrock, etc,), and at least a 650 CFM carburetor.  Long tube headers and full duals are also best.

- You probably have a stock 700R4 with a fairly lame rear end ratio (3.08?).    Swapping in a set of 3.73 axles would really wake the truck up, and with overdrive it would still be fine on the highway. 

- If you go with a much more aggressive cam you may want a higher stall torque converter.  However, I would leave that mod until much later, and its probably not even needed if you stick with a reasonable cam.

Bruce

Offline Sheriff_of_Rock_Ridge

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Re: Cam suggestions.
« Reply #2 on: August 20, 2018, 06:36:35 AM »
Thank you Bruce.  That’s really good information.  I’ll talk to the guy today.   


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