When choosing a cam, you also have to consider valve lift. What type pistons do you have?, dished, flat-top, domed?. Make sure you have enough valve to piston clearance. Of those three, the third one (942),looks like a good choice. Just for reference, the factory cam for a 76 390 C7AZ-6250-A :Adv. duration 256/266. Valve lift .427 int. .431 exh.

 

I am far from an expert on cams, but do have a general idea of how which should work, but really we need more info. What heads and intake are you running, going to assume you will run hedders? I get the vibe you are focus on dynamic compression, opinions vary but I would not focus to much on that, be aware of it, but it's not the end all be all. Big difference in selection for stockish heads vs worked iron heads vs Trick Flows etc. Intake plays into that because if you have a crappy intake then you will hit the wall early. Without more info, you are not going to get a good answer.
I looked at those cams, I like the last one the most for me but not quite enough to say pick it....the first two, I don't like anything about them.... depending on the rest of the build and your intentions it could be a mile off. Also, low end power is like an oxy moron....unless your truck has road gears it will spend its life at 1800 RPM and up if not idling around town....I ran a comp XE262 in a wore out 360 FE, 75 F250 4x4, RPM intake, Hedders, 750 Holley, D2 Iron Heads....never even put new springs or pushrods in it...just wanted to see what it would do....that combo pulled a load better than my 03 V10 4x4 F250 minus stopping and would walk the dog on it to about 45 MPH....the V10 never could beat it to 60 MPH HAHA....Had that been a decent CR motor, fresh, and the correct stuff for the cam it would have been pretty mean. That same cam in the same build in a 390 would small in my opinion. I beat the hell out of that combo until the front main bearing gave up...it was about shot from the start. A good point of reference may be to find some dyno info, combos....the info is there if you want to hunt for it.

 

Thank you for your input! I'm most likely going to be using stock iron heads. It has the 2v intake on it right now, but I will be installing a 4v intake along with a carb right around 600 cfm. And yes, truck has headers. So I'd probably want to stay more on the conservative side of things with the heads. This engine was put in the truck in the early to mid 90s, and from memory the casting number is C8AE for the heads and the intake manifold is a similar vintage, so nothing is original to the truck.

 

Pistons are dished. And that's good info, I was never sure of the stock can size in those engines.

 

C8 heads are about the same, maybe better flow wise to D2's. If you buy, or have an intake get a Performer RPM or Steetmaster(used). The regular Performer hits a wall at around 3,800 rpm....I ran one of those too....only use it if you have nothing else. Given your calculated CR I suspected dish pistons, another thing to check but you are likely fine until you get around .6 lift OR a lot of duration....

 

OP, you’ve definitely put some time and thought into this. Out of the listed cams, the Crane 901 would be a great driver and near-invisible in terms of idle. The Crane 942 would be a good hot rod cam. It might be a little soft off idle depending on gear, converter, and tire diameter.

Another option would be a Comp Xtreme Energy like the 33-234-4 with 212/218 @ .050, .487/.493 lift 110+4. That’s a 32* IVC @.050 and 54 @.006. This would be a nice match with a stock converter.

If you don’t mind a stronger idle note, take a look at the Comp 33-238-4 with 218/224 @ .050, .513/.520, 110+4. It has a 35* IVC @ .050 and 57 @ .006. It would pump up dynamic just a bit versus either of the two larger Cranes. It can work with the stock converter but would be best with a 1800+ rpm stall. Some 3:55+ gears would be a benefit as well.

 

So the truck actually has a NP435 4 speed manual rather than the C6 auto. I have 4.10 gears and 4wd

 

So the truck actually has a NP435 4 speed manual rather than the C6 auto. I have 4.10 gears and 4wd

 

recommended the same cam I said would be a tad small for a 390. Good stuff...not a bad selection but not a great one. 4 speed will allow you some wiggle room on your cam in a way...they are low geared, the 4;10s are a big help too...get a little wilder on your cam, the added cubes will take more "cam".
The XE cams have some agressive lobes, I would recommend better springs, but talk to Brent, do not just go with what they recommend....even if you do not go the custom route. Measure for pushrods too just in case, and he can hook you up on those even if you don't get a cam from him.

 

Alright so I did a bit more research and came up with these other options. How do these look? I know I'm probably beating a dead horse, but do one of these look better than my other ones?

Crower 16241
Advertised duration: 280/286
Duration at 0.050": 222/228
LSA: 112 degrees
Intake Valve Closing Angle: 68 deg ABDC
DCR: 7.15:1

Lunati 10330703
Advertised duration: 268/276
Duration at 0.050": 227/233
LSA: 110 degrees
Intake Valve Closing Angle: 60 deg ABDC
DCR: 7.61:1

 

OP,

In your initial post, you mentioned wanting low-end power under the curve. We based our initial recommendations on that and the given combo. We like that you're not just settling on a cam, but digging into this. Something that hasn't been covered is what you're looking for idle wise. When we start creeping up into "larger" cams the idle quality is generally going to suffer. With poor idle quality comes poor engine vacuum. Things such as power brakes and difficult carb tuning become a concern.

By the same token of "larger" camshafts, you might start seeing the exhaust valve closed later. This increases overlap which increases power. The problem is if we're using a restricted street exhaust system we can start allowing exhaust reversion. You already have headers so that's a plus. Knowing what the rest of the exhaust system consists of would be beneficial for picking out a cam.

Let's lay out how we like to look at a cam. That's with individual valve events @ .050.

Crower 16241 with specs of .538/.552, 222/228, 112+4 with 1* of overlap.

IVC: 39* ABDC
IVO: 3* BTDC
EVO: 50* BBDC
EVC: -2* ATDC

Lunati 10330703 with specs of .552/.564, 227/233, 110+4 with 10* of overlap.

IVC: 39.5* ABDC
IVO: 7.5* BTDC
EVO: 50.5* BBDC
EVC: 2.5* ATDC

These were all calculated using the manufactures specs and our cam timing calculator.

Individual valve events explained

IVC: Is building compression and torque down low with closing the valve early. Or using inertial charge longer after BDC and closing the valve later to increase power higher in the rpm range.

IVO: Is basically idle quality..the earlier you open the intake, the more air you're taking in on the downstroke (at the expense of idle vacuum).

EVO: Is blowdown. Most of the blowdown occurs even before BDC because of high residual cylinder pressure. Earlier = better evacuation and less pumping loss on the piston upstroke at high speed vs. slight loss of pressure on piston during last degrees of power stroke for low end

EVC: Is in conjunction with overlap. Most useful with open headers, equal length headers, and primary lengths wave tuned to the intake runner and rpm. We don't place much emphasis on extending this event later as it produces reversion with street performance exhaust systems.

With what we know at this time with your combo we like the Crower 16241 the best. With the 39* IVC we're going to give up the off-idle low-end grunt. However, with your 4:10 gears, it's going to have a tremendous mid-range and good top-end. The 3* IVO will provide a steady lopey idle. The EVO is good at 50*. The EVC of -2* would play nice with more of a street exhaust system.

The lunati 703 is going to be a little much in our opinion in a heavy 3/4 ton truck. It starts with the 7.5* IVO. That is going to be a very rough idle and isn't going to play nice with low cruising speeds or stop and go traffic. Then the later 2.5* EVC. As long as you have a fairly open exhaust with the headers this shouldn't be an issue. The combo of these brings us the 10* of overlap which coincides with the low speed and tuning issues.

We would like to throw another cam into the ring. The Lunati 10330702 with specs of .540/.552, 219/227, 112+4 with -1* of overlap. Maybe the duration looks small but we like the valve events and lift for a heavy 3/4 ton truck.

Valve Events

IVC: 37.5* ABDC
IVO: 1.5* BTDC
EVO: 49.5* BBDC
EVC: -2.5* ATDC

We really like these events for this combo. The IVC is a little earlier and will help with low-end power. The 1.5* IVO will provide a nice steady lope but not be too choppy. EVO is in a good spot right around 50* for good efficiency. The -2.5* EVC is favorable if we have a street performance exhaust system. It would be a little more subtle than the other two above but will be plenty enjoyable in a heavy 3/4 ton truck with the 390.

Sorry to make a long post but we wanted to explain how we come up with recommendations and the reasoning behind it.

 

Hard to give camshaft advice without knowing for sure the rest of the specs of the engine. What cylinder heads are on it? Any port work? What intake? Where would you want the peak hp rpm to be if you could choose? What's the tire size on the truck? Are you towing with it?