Mike - thanks for the sticky. :cool:
I'm sure anyone interested in Vortec heads will find this thread to be quite useful and informative for their own Vortec engine build and questions concerning using the same. The idea is for anyone with Vortec experience and/or info to post here in this thread so as to pool our Vortec knowledge. Anything Vortec-related is welcome.
So -- without any further ado, I'll start things off. :cool:
What exactly are "Vortec heads"?
Beginning in 1996 to '00, L-31 Vortec heads were installed from the factory on GM truck and van 350 engines. These newly designed for 1996, state of the art heads are made from cast iron and replaced the former swirl-port TBI heads that had been previously used on the GM truck 350. Instantly the HP rating increased 55HP to 255 HP primarily from the power of these cylinder heads.
What makes Vortec heads any different from other GM steel heads?
Pretty much everything. Beginning with the intake port, which is 170cc with a cast-in 'ski jump' on the port roof which is there to increase port flow velocity, port flow was designed to be high in the .300"-.500" valve lift area to make power with relatively low-lift truck camshafts. The bowl area is wide around the guide - much wider than the old 'camel-hump' heads from back in the day - and the intake valve seat has a 3-angle grind from the factory. The intake valve is also back-cut as is the exhaust. The exhaust port, considered to be the "weak" part of the otherwise steller-flowing Vortec head, actually does not flow that bad but because the intake port is so good, responds better to port work than does the intake and there is a strong feeling in some camps that these heads make best power with a split-duration camshaft because of this aspect. The exhaust valve seat also comes from the factory with a 3-angle grind and back-cut valve (except as noted below). The combustion chamber design was a radical departure from anything GM cast in iron prior to the introduction of these heads, and is of a 'double-quench' design. Highly efficient, best power is made with 32° total timing, although these heads can make power with timing reduced to 29° when used with short-duration camshafts.
How many versions are there of 'Vortec' heads?
Realizing that today, several manufacturers have tooled-up their own reponses to GMPP's highly successful debut of the L-31 Vortec for the budget small block crowd, thus far we have several versions to choose from in the performance aftermarket:
GM L-31 Vortec
GMPP 'small port' Vortec Bow Tie
GMPP 'large port' Vortec Bow Tie
GMPP 'Fast Burn'
Edelbrock E-Tec 170
Edelbrock E-Tec 200
Dart Vortec replacement head
RHS Vortec
EQ Cylinder Heads Vortec
L-31 Vortecs -- there are two castings with two versions of one of these castings (#906). The two castings are the #062 and #906. The #906 is the same as the 062 with the exception as noted below. Using the 906 heads myself, I can safely say do not worry about any percieved weakness in HP potential in comparison to the 062. They both make the same amount of power. The 062 is the head you will get when buying the Vortecs from the dealership/GMPP.
- Vortec heads were designed based on the 1996 Caprice 9C1/Impala SS LT1 cast-iron head castings. The only difference is the water jacket revision so these heads could be used on conventionally-cooled small blocks. The 1996 LT1 cast-iron head was the highest-flowing LT1 head used by GM. These heads outflowed the Corvette/f-body aluminum LT1 heads reportedly by 20 cfm on the intake side. The cast-iron head was in development 6 months longer than the aluminum head and during that time GM engineers tweaked the ports for the additional flow.
- Two Vortec castings were used from 1996-99 on GM CK trucks ('00 in vans) and SUV's utilizing the Vortec 5700 350 engine. The #906 and #062. The #906 casting head was available in two versions. One has an Inconel exhaust seat with a single angle grind, and the other has the conventional 3-angle grind on the exhausts as per the #062. The #906 with Inconel seat does not intrude into the exhaust port. It was used primarily on the HD and 1-ton truck applications where sustained towing of heavy loads & weight up inclines could cause eventual damage to a standard induction-hardened exhaust seat from excessive heat.
- The only difference between the #062 and #906 Vortec head is in the exhaust seat of the HD/1-ton truck #906 version, as described above. The #062 has a 3-angle grind on a standard induction-hardened seat, as does the non-HD #906 head. The 062 does flow slightly better on the exhaust side at low lifts but the advantage over a 906 is very slight. They both utilize back-cut exhaust valves. They both have 3-angle grind seats on the intakes with back-cut intake valves. Both heads make the same power in stock form.
- Vortec heads were used exclusively in trucks and SUV's. No passenger cars were equipped with these heads.
- Stock out-of-the-box Vortec heads have approx. 480HP potential naturally-aspirated. Fully race-ported flowing 275 cfm @ 28" water with 2.055/1.60 valves, potential is approx. 580 HP. There are reports of some shops getting close to 300 cfm out of these heads in fully-ported form.
- Retainer to guide clearance is the primary Achille's Heel of the Vortec. For valve lifts above .460" they need to be checked for R-G clearance. This varies from head to head. Some find they can get .480" and slightly more valve lift fine. Others will find .460" about the limit. Always check R-G with any performance cam above .460".
Great, I'm interested in Vortec heads, but am concerned about retainer to guide clearance. What can be done about this, and, are there any places I can buy Vortecs already modified for use with high-lift camshafts?
Good question, easy answer.
Scoggin-Dickey sells Vortec heads already correctly modified for use with high-lift performance camshafts. They also sell a complete kit which has the modified Vortecs, intake manifold (Edelbrock Vortec), rocker arms, etc to basically bolted on your existing short block.
Sallee Chevrolet has an interesting solution to this problem (from their website):
The Sallee Chevrolet solution is to use Crane Cam’s 10309-1 drop-in valve spring and retainer kit which is good for .550” lift with no machining. The installed height for this Crane Cams kit is taller and the lower part of the retainer is shorter. The “AVERAGE” clearance between the retainer and seal is .575” for this kit. We have found that some of the Vortec heads, coming from the factory, do not have the valve seals driven on all the way. You need to check that they are before installing this kit. If they need to be driven on all the way, we have found that a 3/8” drive - 1/2” socket fits the valve seal just about perfect.As with all modifications to performance engines though, you should always measure to assure that there is proper clearance and fit.
Comp Cams sells a tool that will cut down the size of the Vortec valve guide and is around $50 or so.
Another method is the infamous Vortec retainer "ghetto grind". If the camshaft being used only requires a stock 1.25" diameter single-wound valvespring, it is possible to only need to grind off approximately 3/32" off the bottoms of the stock Vortec retainers with a grinder or on a grinding wheel to achieve enough R-G clearance to run up to approximately .530" -.540" safely. I must caution here that R-G clearance must ALWAYS be checked to verify that there is in fact enough clearance - also include allowing for coil bind. One other thing - you must remove the dampner in this modification. Don't worry -- the stock Vortec valveguide being much larger in diameter than other SB heads will act as sort of a dampner and I never noticed any RPM issues related to lack of running one when I did this mod. Although myself and others who have done it this way have had no problems, I must caution this basically for those on a strict budget and cutting down the guides either with the Comp tool or at a machine shop is the best way to go. However, I'm of the opinion that since it works well within the noted constraints, then you're really only out your time to grind down the retainers. The choice is yours.
More to follow. :cool:
