Camshaft

[76_Scottsdale]

I filled out the form on Comp cams website to suggest a camshaft for my planned motor build. I filled it out for my K20 and a 383 with Vortec heads on it like I plan on building. They suggested the Comp Cams #12-207-2. I looked it up and it doesn't really seem like a performance cam. I want something with tons of low-end torque and HP, as much as I can get without having one so lopey that I have no idle vacuum. Does anyone have any suggestions?

[VileZambonie]

I would run a hydraulic roller. Keep the max lift under .510" and the duration under 230°

[Lt.Del]

You have chosen the correct engine for the low end high torque engine.  I love mine.  I have the RV cam installed in my stroker to take advantage of the lower-end, versus the higher rpms, which I never see.
I'll see if i can dig up the info on my cam--i don't have the vortec heads though.

update: here is my cam info.  They advertise cam for a 1.5 rocker.   I have 1.6 rocker (tall valve covers), so the cam lift has been adjusted.

Hydralic Flat tappet Cam
Advertised Duration is 280 Duration @.050" 214 .295" cam lift X 1.6 = .472" Valve lift
Ground on a 110 Lobe center.

This puppy flies!  It has a slight lopey idle.  I like a low idling engine--like 600 rpms.  My wife thinks the engine is getting ready to cut off.  I laugh and tell her that sound is music. 

[76_Scottsdale]

So the duration of less then 230 degrees will give it lots of low end torque and HP correct? I've noticed the higher duration cams have tons of high rpm horsepower which i really don't want. my motors almost never see above 4 grand. I'm still learning what exactly what all these cam specs mean.

[Blue 82]

there are 2 different ways to compare duration
one is advertised duration
one that counts is the amount of degrees the valve is open above .050"

for example a cam with 230 degrees duration at .050" lift has an advertised duration of 280 degrees (Comp 280 Magnum)

If you are looking to make good torque below 4000 and still get decent economy, then Comps recomendation is dead on the money

Check these dyno sheets out (these are for 356 cu in engines, you can add about 35 lb/ft for a 383)
The XE250 makes more torque the hotter XE256
an XE250 would be my choice but you will probable give up 1 or 2 mpg over Comps recomendation

http://www.compcams.com/technical/DynoSheets/

[VileZambonie]

Build as much lift into the cam as you can and stay with the 1.5 rocker ratio, spend the xtra on a roller set up if you can afford it. If you do it right the 1st time you will love it. If you are running a non roller cam http://store.summitracing.com/partdetail.asp?part=SUM%2DK1105&autoview=sku is a good cam that will still have good torque

[eventhorizon66]

Don't forget to carefully check your retainer to valve guide clearance with any performance cam you choose, especially with L31 heads.

[gary82]

my cam is a crane cam 282 duration 480 lift it has tons of lope and i have great low end torque 700r trans with 2600stall and 3.73 gears does the lope come from the duration or lift

[76_Scottsdale]

I'm not quite sure if I currently have a roller cam or not. I have the cam card and I'll look it up tomorrow. I was planning on buying the 1.5 roller rockers that are the only ones (They claim) that work with the vortec self-aligning heads. I will build it piece by piece because the motor I have now was rebuilt only about 50,000 miles ago and runs good. I'm starting to understand the basics of cams a little more. How can you retro fit a roller cam into a flat tappet cam engine if thats what I have?

[eventhorizon66]

Every cam manufacturer makes retro-fit roller cams designed for old non-roller blocks.  The big money for these is spent on the lifters themselves, which must have some sort of linkage, connecting each pair, to keep them from rotating in their bores.  This means they are a different design from OEM roller lifters and thus more pricey.  At Summit a set of Comp's entry level retro-fit lifters #853-16 will cost you about $460, the nicer Lunati's run $570.  To completely retro-fit an older SBC with new roller valvetrain you can expect to spend in the neighborhood of $1000 (cam, lifters, pushrods, valvesprings, retainers, locks, timing chain).  That's why flat tappets are still alive and well.  Here's an example of a complete retro-fit roller kit from Comp.  Also you are going to need a wear plate and thrust button to keep the cam from "walking" as roller cams don't have a taper machined into the lobes like flat tappets do.