L31 Vortec Heads
When GM Performance Parts released the L31 Vortec heads for small-block Chevy engines in 1996, they were an instant hit with the hot-rodding crowd due to the great flow numbers (outflowing the venerable Bow Tie heads), efficient 64cc chambers, and great price (under $500/pair, assembled).
I bolted a pair onto my Nova's 350 engine in 1999 and really enjoyed the performance and efficiency of the castings. I ran a 13.49 ET with my mild setup and it was as reliable as the sunrise. However, installing Vortecs on a basic small-block Chevy engine isn't a simple, bolt-on proposition. Also, there are additional costs involved that are not immediately apparent when you plunk down $500 at the Chevy dealer and walk away with two heavy boxes.
I've been asked many, many times what's required and recommended to install the L31 Vortec heads on a small-block Chevy engine. The following was written in 2001 and reflects prices and parts availability from that year. Be sure to look at current prices and parts before making your decision. Also, if you do get used Vortec heads, be sure to avoid casting number of 10239906. These come from heavier-duty trucks and have a flow-limiting exhaust seat installed.
- The biggest issue in my opinion is the maximum lift these heads can handle when
stock. I did some checking on mine and found that I had only about .460"-.470" total between
the stock positive valve seals and the retainer. Add the recommended .060" clearance at max
lift and you can see the problem with anything other than a near-stock .400" lift cam.
Some sellers will tell you that stock Vortecs can handle .470" lift without any problem. Be careful. I don't know where they get that measurement unless they've decided they don't need any margin of error, I know my heads couldn't handle that.
To gain more room for additional lift you need to add +.050" keepers and/or replace the stock positive seals with umbrella seals and/or machine the guides down for additional clearance.
- You must use a Vortec-specific intake manifold. This disadvantage is purely a financial one. You can drill Vortec heads to accept standard intakes but the intake ports don't line up well, you're inviting sealing problems, and you'll reduce the power potential of your engine.
- The stock valvesprings are weak. The cams in stock Vortec engines are quite mild and don't need much pressure, but on the assumption that you're putting these heads on for increased power, you'll have a non-stock cam in your engine. Buy the recommended springs to match the cam; don't risk valve float by using the stock Vortec springs. They only create about 80 pounds of pressure on the seat and that's just not enough for performance cams.
- Vortecs come with pressed-in rocker studs. Sure, most stock heads are like that and they're fine up to about .500" lift, but if you plan to really rev the motor regularly or go over .500" lift, you should machine the heads for screw-in studs.
- You must use self-aligning rocker arms. No big deal, right? Not until you compare prices. Individual stock, stamped-steel, self-aligning rockers from a GM dealer will run you about $15. That's EACH. Multiply that by 16 and you've just added $240 to the cost of your project. You can get the old-style rockers from many sources for a buck or two each. High performance, high quality, full-roller, self-aligning rocker arms are about $300/set compared to about $150/set for non-self-aligning. You do the math. When I set up my Vortecs I scrounged the junkyard and bought a set of used stockers for $10. One solution is to machine the heads for screw-in studs. Doing so will allow you to use pushrod guideplates which will eliminate the need for self-aligning rockers, but the machine work and price of guideplates does drive up the overall cost as well.
- You must use center-bolt valve covers. Not so much a disadvantage, but it's something you need to deal with. I like center-bolt valve covers better than the perimter-bolt style because they seem to clamp more evenly and leak less, but unless you can find some in a junkyard, be prepared to spend some dough. The cheapest stamped-steel aftermarket covers I've seen are about $60/pair.
- You must use dedicated intake gaskets. Again, these gaskets are great pieces of engineering and are far superior to standard intake gaskets in my opinion, but they cost $22/set. The silver lining? They work great and are reuseable. They're made of a rigid plastic with some Weatherpak-connector-seal-like rubber stuff around the ports.
- GM L31 Vortec heads - fully assembled ($480/pair)
- Dedicated intake manifold for Vortec heads ($175 for Edelbrock Performer RPM Vortec)
- Special Vortec-only intake gaskets ($22/set)
- Center-bolt valve covers ($15/set used, minimum of $60/set new)
- Self-aligning rocker arms ($10/set used, $300 for new full rollers)
- Standard head gaskets
- Center-bolt valve cover gaskets or RTV
- Thread sealer
- New valvesprings - follow your cam manufacturer's recommendations ($55-up)
- Depending on lift requirements you may need +.050" keepers ($35/set), umbrella seals ($16/set), or you may elect to have the valveguides machined down ($65 or so)
- Machine for screw-in studs ($65 for machining, $29 for studs)
- New head bolts ($20+/set)
If you've read this far you may be wondering if these heads are really that good to warrant the expense and hassle of setting them up to work properly. It depends on your goals and the intended use and expected performance from this engine.
These heads are capable of supporting 400 hp on a relatively mild 350 engine and they work great on the street and actually can help provide some acceptable fuel economy. Chevy High Performance magazine did a series of articles based on a Goodwrench 350 and Vortecs and made some good power (just over 400 hp with some mild port work). They really are great street heads.
The down side? These heads are pretty much maxed out right out of the box. CHP only gained a few horses by doing the port work and proclaimed that GM apparently did their homework when they designed these heads because they're nearly perfect as is. In other words, you won't likely be able to do anything to them later on for increased performance.
To summarize, if you're looking for a very streetable small-block Chevy engine capable of producing nearly 400 hp for street use and occasional drag racing, Vortecs are a great choice. If you ever plan to go for more power or add a blower, however, you'd likely be better off with one of several other head choices. Some choices worth considering (among others) are Trick Flow Specialties 23-Degree aluminum heads, World Products Sportsman heads, and RHS Pro Action heads. When considering bang-for-the-buck, the Trick Flows appear the most attractive of the bunch, so I'll compare them below to the Vortecs.
If you've got a fairly solid, typical setup (350, Edelbrock Performer intake, Comp XE268 cam, headers, performance carb, etc.), let's look at the cost involved in going from stock #882 heads to Vortecs or TFS heads on your engine:
- Vortec heads - $480/pair
- Intake manifold - $175
- Intake gaskets - $22
- Rocker covers - $15-$60
- Rocker arms - $10-$300
- Valvesprings - $55-$85
- Either +.050" keepers ($35) and umbrella seals ($16) or machine guides ($60) and umbrella seals ($16)
- (Optional but recommended) Machining for screw-in studs ($65), screw-in studs ($29), guideplates ($24)
- Engine gasket set - $22 (FelPro KS2600 - their low-end gasket set)
- Total: $830 (minimum) to $1220 (with everything)
Compare that to swapping to a set of Trick Flow Specialties 23-degree aluminum small-block Chevy heads:
- Heads - $999 (up to 0.480" lift, $100 extra for 0.540" lift)
- Engine gasket set - $22 (FelPro KS2600)
- Rocker covers - free-$30 (free means reuse parts you already have)
- Rocker arms - free-$150 (free means reuse parts you already have)
- Valvesprings - free (included with heads, as are guideplates)
- Total: $1021-$1201 ($1121-$1301 for 0.540" lift)
- high-efficiency chamber may give better fuel economy
- durability, reliability, and quality of factory parts is generally great
PORT SIZE: 170
VALVE SIZE: 1.94 / 1.50
FLOW@.100: 70 / 48
FLOW@.200: 139 / 101
FLOW@.300: 190 / 129
FLOW@.400: 227 / 140
FLOW@.500: 239 / 147
- Aluminum saves weight from the front end of the car
- As-delivered they're ready to go with good springs, screw-in studs, guideplates, and can accomodate 0.480" lift (0.540" optional)
- Trick Flows intake flow numbers are very close to those of the Vortecs, exhaust is significantly better
- They can be improved through port work
- Aluminum is much easier (and therefore cheaper) to port than iron
VALVE SIZE: 2.02 / 1.60
FLOW@.100: 65 / 70
FLOW@.200: 133 / 102
FLOW@.300: 188 / 140
FLOW@.400: 226 / 164
FLOW@.500: 250 / 183
If I were to buy something right now, it'd be the Trick Flows. That said, I do miss my Vortecs! I hope you take the information I've given and do further research and make a well-informed decision. Feedback and questions are always welcome, please click the "Contact" links if you'd like to leave some.
Copyright © 2009 Bruce Johnson and Craig Watson