Quote Originally Posted by 1978chevy View Post
I got a '78 chevy k10 4x4 4 speed 31" tires and 3.73 gears I'm currently building a 400 sbc to drop in it, it will be stock bore with stock dish pistons.
Heavy truck, big tires, not enough gear. Stock dished pistons will not have enough flat area on the crowns to facilitate a good squish, so you need to install pistons that will have enough flat area on the crown to mate up with the underside of the cylinder head to generate a good strong "squish" across the chamber. Not only that, but a 400 with stock pistons and 64cc heads will make close to 11.0:1 static compression ratio. You'll never get it to run on pump gas without using so much cam that you'll make power between 3000 and 7000 rpm's. There goes your towing ability.
Quote Originally Posted by 1978chevy View Post
I'd like a cam with a lobe at idle to
It's not lobe, lobe is the part of the cam that lifts the lifter. Lope is what you mean. Most of you fellows haven't enough experience to understand that lope does not equate to horsepower. It means that the motor is inefficient at the speed where the lope occurs. In addition, the word "to" is not what you meant here. The word "too", meaning "also" is the word to use.
Quote Originally Posted by 1978chevy View Post
I'll be using it for towing cars and stuff the truck hardly ever revs over 3,000 rpms
All the more reason to use a low static compression ratio, mated to a mild cam that will make power where you want it to, a cam that will close the intake valve at the appropriate time to make good cylinder pressure with the static compression ratio of the motor.

I just know that one day I'm gonna read one of these posts, pull out my revolver and dispatch this computer to another astral plane.

OK dude, listen up. Add up the stack of parts you will use. Half the stroke (radius) will be 1.875", the rods will be 5.700" (I don't use long rods on a build like this because it puts the wrist pin up into the oil ring land on the piston.) The pistons will be something like these, 22cc D-cup with a 1.433" compression height....
KB Pistons for Automotive Applications
Adding 1.875, 5.700 and 1.433 gives you a stack height of 9.008".
Take the block to the machine shop, have them check the mains for being round and parallel (align hone or align bore the main saddle to clean them up if necessary). Now, registering on the mains, cut the block decks to 9.018" block deck height. This will leave the piston down in the bore by 0.010" at top dead center. It will also equalize the block deck height front to rear on both banks so that the heads will sit level and be an equal distance from the centerline of the main bearing bore. This will also allow the intake manifold to seal up, preventing a vacuum leak from the crankcase to the underside of the intake manifold ports where they match up with the head ports. Buy the pistons in 0.030" oversize and have the shop bore the block to match the pistons. Hypereutectics need a very tight piston to bore clearance and a wider top ring gap, so pay attention.

Here comes the static compression ratio math.
Cylinder (4.155" x 3.75) 833 cc's
Chambers 64 cc's
Piston crown 22 cc's
Piston deck height 2 cc's
Compressed gasket 9 cc's
Fel-Pro Q1014 - Fel-Pro Performance Head Gaskets - Overview - SummitRacing.com
Add all the values together and find 930 cc's. Now drop out the cylinder volume and find 97 cc's. Now, divide the larger by the smaller and find 9.59:1 static compression ratio.

Now comes the part where you match up the cam timing events with the static compression ratio to set the cylinder pressure.
This is actually more cam than you need, but using the 64cc heads limits the static compression ratio to 9.59:1 and we need this much cam to be able to make the correct cylinder pressure to run on pump gas.
272 H10 Hydraulic Flat Tappet Camshaft and Lifters for Chevrolet 1957-1987 V-8, 262-400
The Dynamic Compression Ratio using this cam and 9.59:1 static works out to 8.565:1dynamic. Use any cam you want to, so long as you're closing the intake valve at 33-35degrees ABDC @0.050" tappet lift.

Bolt on a set of tuned, equal-length headers, an Edelbrock Performer RPM (not the Air Gap model) and a 600-650 carb of your choice. This combination of 406 cubic inches and the L31 heads will make an ungodly amount of torque from 1500-4500 rpm's and do it on crappy pump gas without detonation, thanks to properly engineered components that work together toward a common goal. That's the secret, a combination where everything compliments everything else. Having all these pieces work together also will allow you to feed in the proper amount of ignition timing.

If you go ahead with the stock pistons, be ready for a surprise when the motor won't run on pump gas without detonating. Then you find that you have to pull all the ignition timing out of the motor to get it to run at all and it won't make any power.

L31 heads, due to the very efficient chamber design, don't need too much spark timing, so I would curve the dizzy for 14 degrees at the crank and 20 degrees in the weights. Use vacuum advance with the hose plugged into intake manifold vacuum.

I really don't expect you to follow my recipe, but it is there for other fellows to use.