Thread: Vortec questions

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Originally Posted by techinspector1

The original GM L31 5700 Vortec heads that came on that block from the factory (casting numbers 10239906 or 12558062) flow better than any other PRODUCTION head that Chevy ever produced. Combustion chambers are 64cc's and intake runners are 170 cc's. The heads can be identified in a boneyard by the sawtooth design on the ends of the heads. To use them in a carbureted build, you must use an aftermarket "Vortec" intake manifold due to the different bolt angle and number of bolts used. I think the ports are a little higher up on the heads also.

Very respected professional engine builders such as Pat McCarthy on this forum have stated that most of the boneyard L31's that they see are cracked, so you may have to go through more than one set to find a set that is valid for use.

As produced, the valve lift limit with the stock springs, retainers and seals is 0.450" according to information published by GM. The problem is interference between the bottom of the retainer and the seal at lifts exceeding that. Some amateur engine builders have applied a "ghetto grind" to the bottom of the retainers to gain more lift, but you're still stuck with the stock, weak valve springs if you're planning any kind of agressive camshaft design. Anything over about 0.480" lift will require a larger diameter spring to be fitted to the heads if you're going to do it right, so you have to bore the spring seats with a cutter. Or you can chance it with the stock 1.250" spring seat and more agressive springs. The valve guide boss in these heads is quite large in O.D., so it's tough to put a single spring with damper on the heads unless you reduce the diameter of the boss. There just is not enough room between the I.D. of the damper and the O.D. of the boss. Comp makes a beehive spring that doesn't need a damper spring, so that spring fits without doing surgery to the boss, but they are pricey.

Keeping the rocker centered on the valve was accomplished with "rail rockers" that have a recess in the tip of the rocker to keep the rocker from sliding laterally off the valve stem tip. The 3/8" rocker studs are pressed into the head. Either the stock 1.5 rockers can be used or you can purchase rail roller rockers in 1.5 or 1.6 ratio. You can either drill and pin the studs to prevent pull-out using rail rockers or you can machine the heads for screw-in studs and guide plates so that you can use conventional rocker arms.

Racing Head Service manufactures a "Vortec" style head that bypasses all the negatives of the production head and is drilled for either the conventional Gen I manifolds or the aftermarket Vortec manifolds. Part #12410 is apparently available with the original GM intake runner configuration and 1.94"/1.50" valves or RHS runner configuration with 2.02"/1.60" valves and a little better flow. Both heads use a 170cc intake runner.

If I were going to build an iron head small block Chevy street motor, I might think seriously about using the larger valve 170 RHS heads.
http://www.racingheadservice.com/Cyl...st%20Iron.aspx

What I have learned through fiddling with the DynoSim dyno software is that you have to take any head manufacturers flow data with a grain of salt. For instance, if you look at the RHS data, it says that they flowed the heads using a 4.200" pipe. When's the last time you saw a 4.200" bore on a production small block motor??????? It also states on their site that different pipe sizes will yield different results. Well, DUH!!! Anyway, for what it's worth, I factor flow figures from the manufacturer by 0.9 or 0.85, depending on how much I think they're lieing to me. I'm not particularly picking on RHS. I think all of them lie, so like I said, I just factor the flow figures.

NLMoschitta, sorry I got off on a tangent. The point is, I would not use Hearly production heads on such a neat roller cam short block. They'll fit, but there are better heads available fairly inexpensively, considering the end results.

Here are the bare 2.02"/1.60" 170cc bare heads at Summit.....
http://www.summitracing.com/parts/CCA-12410/
I'd buy 'em bare, then use the springs recommended by the cam grinder for the cam I chose to use.

Not to hijack a thread but tech where do i find these vortec rhs heads drilled for conventional manifolds?

Summit lists them bare, but I haven't been able to find them assembled. It might require a call to Racing Head Service.
http://www.summitracing.com/parts/CCA-12410/
http://www.racingheadservice.com/Contact/

Originally Posted by techinspector1

Summit lists them bare, but I haven't been able to find them assembled. It might require a call to Racing Head Service.
http://www.summitracing.com/parts/CCA-12410/
http://www.racingheadservice.com/Contact/

THose are the heads I thought you were talking about. But at the bottom of the page it says: Notes Requires Vortec-style intake manifold for installation. I was wondering if there was one that had the stand gen I manifold holes.

Why not buy an Edelbrock 2116 intake....designed to fit Vortec heads? The Vortec intake gasket is vastly superior to the previous small block gaskets. The 2116 has no heat to the carb, etc....looks just like the other manifolds except for the mounting bolts.....and it is cheap.

mike in tucson

Sorry, my bad. Here are 64 and 72 cc models in straight plug design (easier to fit headers) that will take conventional intake manifolds. They're 180cc intake runners as opposed to the Vortec models with 170cc's and use 2.02/1.60 valves. Should do a great job on a street/strip 350 or mild 383.
http://www.summitracing.com/search/P...?keyword=heads

Originally Posted by techinspector1

Sorry, my bad. Here are 64 and 72 cc models in straight plug design (easier to fit headers) that will take conventional intake manifolds. They're 180cc intake runners as opposed to the Vortec models with 170cc's and use 2.02/1.60 valves. Should do a great job on a street/strip 350 or mild 383.
http://www.summitracing.com/search/P...?keyword=heads

Tech i may be wrong too. I looked at the 12410's on summit and read the entire description and it said it was able to mount to all different types of manifolds. (vtec, converntional)