[BogiesAnnex1]

Cam number one is at the limit of a stock stall converter, not that all GM converters are at the same stall but they are a family that stalls pretty much between 1200 to 1800 RPM.

Cam number two will demand more stall somewhere like 2200 to 2800 RPM.

Usually stall is thought of as a racer thing that allows the engine to be brought up on its torque peak or more when staging for a drag race or coming off turns on a roundly connected track. On the street it is an issue of ‘tug’ that is big cams demand a high idle speed and the bigger the cam the higher the idle speed. This combined with a stock stall converter can become physically exhausting applying enough brake pedal pressure to wait out a traffic light combined with the unpleasant habit of the vehicle leaping from every stop. Imagine this with a cop behind you, smells like a speed exhibition ticket to me.

Cam number one will sound aggressive at idle; cam number two will be choppy or staggered at idle.

Max lift on the L31 Vortec head ranges from .450 to .470 inch. This wanders from head to head and intake to exhaust on any given head. So you will have to address this for either cam and keep in mind SBC cams rate and advertise lift at the valve with a 1.5:1 ratio rocker. Changing the typical 1.5:1 rocker to the common hot rod ratio of 1.6:1 increases the lift by 7 percent so what lift might squeak by with a 1.5 rocker may not with a 1.6. The issue here is clearance between the bottom on the spring retainer and the top of the valve seal as it mounts on the top of the valve guide. There are several things that can be done from remachining the too of the guide to lower it to using beehive springs and either Comp 787-16 retainers or the special retainer from Alex’s Parts for vortec heads. There needs .050 inch clearance measured at peak lift to insure the bottom of the retainer does not collide with the top of the guide or it’s seal, however you decide to get there.

Cam number one can be run with GM production LS engine beehive springs and proper retainers that adapt the locks from production 8MM valves to the classic SBC 11/32’s inch valve stem. Cam number two could, also, be used with beehives but will need a higher pressure that stock GM. These are my go to for high performance street builds Howards Cams Electro Polished Beehive Valve Springs, 1.280" O.D., 115 @ 1.800", 354 @ 1.225" - Competition Products

I‘d say 380 HP with cam number one is conservative representing a pretty conventional build of not ported Vortec heads and a more than less factory style valve train with a moderate intake and 650 carb using 1-5/8ths long tube primary headers and not much if any collector length. For careful builders seeking to max cam one there’s probably another 30 horsepower and torque numbers hiding in there for a carefully built valve train bigger carb, Edelbrock Performer intake and larger primary tube headers with a 20-24 inch collector before the exhaust pipes and some mild porting.

The number two cam will get there with more brut force that results in poor low speed driveability. There are ways to tame this or at least build into it with higher stall converters and stiffer rear gearing so the engine is operating in an RPM range it likes on the street.

Frankly the 383 is such a torque monster that it quickly gets crazy in a light weight vehicle.


Bogie

 

[BogiesAnnex1]

These are factory heads on a 350 I have that needs rebuilding. So they will need to be worked

Something to consider is rebuilding the Vortec’s can start to tease the price of import or even lower performance end of domestic aluminum heads. Not a bad idea to put together some comparative cost estimates.

Bogie

 

[BogiesAnnex1]

First the Vortec’s need to be cleaned and inspected. Unfortunately modern thin wall castings are very crack prone and Vortec’s are no exception. So disassembly, cleaning and very close inspection which can include did penetrant with black light or Magnaflux to be sure before you pour money into them they are worthy. Cracks mostly were a result of overheating from failed cooling systems using Dexcool. People that didn’t pay attention got into an issue where there was leakage which both lost coolant and introduced air. The latter oxidized the coolant and things got really bad forming a sludge that interfered with cooling so this and the former loss of coolant quickly spiraled out of control overheating the heads in particular.

Once past that point comes the decision to port or not, here again these are thin wall castings and porting, if any, should be minimal clean up and no shape changes. The stock Vortec flows very well especially the 062 casting. The 906 is a bit more robust as it was intended for use on the larger trucks, industrial and marine engines. These heads are a little restrictive on the exhaust side where there is added material for a hard seat insert which may or not be there as many were simply received induction hardened exhaust seats just like the 062 head.

The next standard operation is seats but leading into seats is the condition of the valve guides. If out of spec these need to be renewed. The shop classic is to knurl the guides the ream them to size, this is not a long lasting fix. Another is to ream the seat oversize then use new oversized stem valves. This works well but adds new valves to the budget that might not otherwise be needed. Another that in part is similar in that the guides are reamed oversized but a thin wall metal sleeve is pressed in and honed to finish size and similar to this is to bore the old guide with a larger hole then press in a thick wall guide and finish it.

Following any of these operations, other than oversized valve stems, either the current valves receive new seats or are replaced with new if there isn’t enough seat depth left. The operations of refinishing the head seats and refacing the valves themselves sinks the valves deeper into their pockets. This reduces compression be enlarging the combustion chamber volume and degrades flow past the valve. This raising of the valve relative to the spring and valve train affects spring tension and push rod length which affects the contact angle of the rocker to valve stem. Generally the extent is not to extreme to cause problems with grocery getter engines, but seekers after hot rod power need to fix these things and of course this introduces more cost.

Then you arrive at having to deal with more lift of performance cams. The Vortec head uses a tall guide to improve stem and guide wear but this interferes with lift. So there are fixes to be employed from just taking an angle grinder and whacking some of the top off the guide to buying a tool to do this with more precision at home or have the head rebuilder do it in their shop. Then there is the Alex’s short depth retainer which essentially is a retainer with the bottom edge below the locks taper removed since the locks are loading against the sides of the cup in the retainer so the base of the cup while reinforcing the hoop loads at the bottom of the cup is not directly carrying the load of the locks. Then beehive springs and the Comp retainer buys about .050 inch without doing anything. Then this can also be finessed with offset locks that raise the retainer relative to the spring then chase the added spring to retainer length with spring shims.

I point al of this out so that you can visualize the problems hence cost that modifying Vortec heads can get you into. So it’s easy to put as much wealth into fixing a set of Vortec’s as you would invest in a set of Speedmaster’s stuffed with parts and ready to go, these of course will cost you at least .1 inch longer pushrods. Plus the use of an aluminum head either works better with a decked block or a raised compression height piston. Either of these being a process to get control of the squish/quench clearance without going to super thin shim style head gaskets. The makers of aluminum heads love for you to use composite gaskets that are .040 to .053 inch thick which when combined with a chevy’s nominal piston crown to head deck clearance of .025 inch simply adds too much distance between the top of the piston and the step of the combustion chamber.

So if you’re unfamiliar with building these engines you need to grind through understanding what impacts what in both a technical and cost sense or you can get yourself into a batch of unpleasant and costly surprises.

Bogie