Quote Originally Posted by Bowtiepickups View Post
First off, thanks for the replies. Tech, you really seem to know your stuff but I'm not really interested in building a 383 or anything near 470hp 490 ft/lb torque. That's more power than I need and I'm not looking to beat my dad in a race... yet. I see the general consensus is to get a leak down test done on the motor so I will have that done. I don't know if the previous owner played around with the gearing so I'll pull the cover off the rear end and check the rear gears and then go from there. I'm not sure what it's like for oil pressure and I won't be able to do a leak down test or check compression until spring time because it's in the back of a barn blocked in by another 20 cars. I also have another option. It has vortec heads on it right now. Do you think I could make solid ponies and torque with those heads and new cam, intake, carb?
What you got was my signature approach, to come galloping in like Caligula, lopping off heads and taking no prisoners. I guess that's because I have always built stuff by the old hot rodder's axiom...."If some is good, more is better and too much is just right." I may not always be right, but I will always be opinionated.

There are lots of copy-cat, so-called "Vortec" heads out there in the aftermarket, but the only ones that are worth fooling with, other than the RHS heads I linked in my first post, in my opinion, are the genuine Chevrolet production RPO L31 heads off a 5700 Vortec motor that was in the '96-'99 Chevy trucks and vans. Same motor that I suggested using the block out of to build a 383. These heads can be found under casting numbers 12558062 (induction hardened valve seats) and 10239906 (separate pressed-in exhaust seats in some, but not all of these heads). Some people will tell you that there is a "good" head (induction hardened seats) and a "bad" head (pressed-in exhaust seats). Builders who have flowed both heads will tell you that the heads flow the same after you clean up some sharp edges at the seat and blend them in.

These L31 heads flow better than any other PRODUCTION cast iron head that Chevrolet ever cast up, but they have several weak points as well. It takes some work and some money to get them to the point where you can bolt them onto a motor and get close to the same results as you can from the heads I linked, which come out of the box ready to bolt on.

First, they are thin-walled castings. If you are pirating a set of used heads from somewhere, the first thing you want to do is clean them up and have them magnafluxed for cracks. You might want to make a deal with the guy you're getting them from that you can exchange them for another set or get your money back if they fail magnaflux.

Secondly, the rockers are "rail" type rockers that have an area on either side of the rocker that shrouds down around the tip of the valve to keep the rocker centered on the valve stem tip. These rockers will work ok for short and moderate lift cams and the aftermarket has come up with "roller rail" rockers. Use caution and buy only narrow body rollers so they will clear the inside of the L31 center-bolt valve covers.

Thirdly, the heads have pressed-in rocker studs that might tolerate up to around 250-260 lbs of pressure across the nose of the cam, but any more than that will begin to pull them out of the heads. You can pin the studs into the heads with a low-buck Mr. Gasket kit to prevent pull-out.
http://www.summitracing.com/parts/MRG-806G/

Fourth, the valve guide boss is extremely large on the O.D. because Chevrolet used only a single spring on these heads. There is no room to install a 1.250" spring with damper because the damper I.D. will not clear the boss O.D. And if you're going to use more cam, you're going to need more spring. So, you must cut the O.D. of the boss if you plan to use a 1.250" spring, or cut the seats in the heads for a larger diameter spring to clear the boss. The other main problem is that the bottom of the retainer will crush the valve guide seal at valve lifts exceeding 0.430". I know there are those fellows who will tell you that you can run 0.500" lift with the stock arrangement, but Chevrolet says 0.430" limit. You have to leave a safety margin to account for valve float and that is usually around 0.060" minimum.

Crane Cams makes a spring and retainer that will clear the seal and the O.D. of the boss, drop right in on the seats in the heads and will allow more lift, but they are pricey.
http://www.summitracing.com/parts/CRN-10309-1/

Some fellows have done a "Ghetto Grind" on the bottoms of the retainers to gain some clearance between the retainer and the seal. I have heard of cutting 0.080" off, but have never done it, so have no experience with what works and what does not work. If I were going to do this, I would mount all the retainers on the table of a surface grinder and take off the material that way, instead of trying to do it with a hand grinder.

So, there's the skinny on L31 heads. By the time you get through doing machine work and buying new parts, you could have bought a set of RHS thick-wall casting heads complete and ready to bolt on for less money.