SMALL BLOCK VORTEC – Ported power for performance and
profit in today’s world
There are plenty of cast iron street heads to choose from but the Vortec is our best, least expensive way to get a good head that is readily available from many sources; new or used. Any GM dealer, car supplier, local junk yard, swap meet, eBay, or your buddy that just took them off his car can supply yours.
The advantage of the Vortec is high velocity intake ports, fast burning 64 CC combustion chambers, very little clean-up porting work needed, and price.
The most importiant area of this head is the throat dimension that drastically affects the velocity in both intake and exhaust runners. I always like the choice of small valves and smaller throat dimensions; 89 to 90% maximum on the throat dimension to the valve size.
A smaller valve in a 350 to 368 CI small block Chevy on the street with a Vortec head is a 1.940 intake and 1.500 to 1.600 maximum exhaust valve size. I only clean up the intake and exhaust port runnners. I do not believe in gasket matching, raising the intake and exhaust ports really helps the flow; only if there is enough material on the intake and exhaust, manifolds or headers allows you to do so.
The valve bowls, intake and exhaust are the most critical because this includes the short side radius blending. Be very careful in these areas; remember no larger than 89% throat dimension. Do not lay back the short side radius too much because this will affect high and low lift flow numbers dramatically.
The most important area is the throat dimension right below your last undercut in the valve bowl (this is the maximum valve bowl dimension area). I like to rough in the valve bowls then do the 3 to 5 angle valve job, then finally grind and blend in the final throat dimension. If you do not have between .080 and .100 of your 60° or 65° undercut width, you will be significally effecting your wet flow dynamics.
The surface finish on street performance cylinder heads is really not critical. A fine stone finish or 60 grit cartridge roll followed with 50 or 60 grit flapper paper finish is all that is needed.
The exhaust finish I like a little smoother; 100 or 120 cartridge roll, then a 120 grit flapper finish. If this is a quicky, down and dirty job, use a round nose tree, egg/oval, or flame shaped carbide cutter; this finish is OK as is. Use a reverse taper for the short turn.
After shaping the valve bowls with a carbide cutter, do a fine stone finish on the valve bowls and short side radii, very little work around the valve guide bosses is needed on the Vortec head.
If you are getting enough money for this job, you can reshape and taper the guide bosses for max air flow. Always remember when doing any heads, bigger is not necessarily better in most cases. Air does not like sharp edges or turns nor uneven surfaces on port walls and floors.
The sharp edges on the floor of the combustion chamber just above the top cut angle which I prefer to be 37° to 39° instead of the conventional 30° on a 45° angle primary seat. Fifty years ago using the Kwik-Way valve grinder with stones, I used a 33° top cut, 45° primary cut, 57° under cut; then with a hand-driven Kwik-Way 70° steel cutter I did my fourth cut for a better bowl blend. Nobody back then ever did more than a 45° primary cut. If it was too wide they would narrow or sink it with a 30° top cut.
In the late 70s they came out with a 3 angle racing valve job. My old four angle stone valve job set nearly every record in several facets of racing; quarter mile, dirt and asphalt circle, Bonneville, road and boat racing. Now with our 4 to 7 angle fixed carbide valve seat cutters we are really changing the name of high performance valve jobs to precision wet flow fine tuned maximum flow dynamic valve job!
We have come a long way in 50 years through our good old American research and development to come up with the great new automatic head centers, diamond valve guide honing, carbide guide reamers, ball hones, bronze guide liners, powder metal and alloy valve seats not to mention flow benches and especially our Mondello-cfm wet flow technology introduced to the industry in 1999.
On used Vortec heads the question that comes up is, “Do I need hardened exhaust seats?” When new they are induction hardened by heat treating. I feel this process is good up to about 75 thousand miles. You can test them with a stone or carbide cutter and usually can feel if they still have sufficient hardness. In most cases, I like to replace all used exhaust seats because of today’s unleaded fuel.
I am very fussy on these new thin casting heads and prefer to use a little shallower seat insert .200 to .215 maximum on these later heads. If you do any Buick, Olds, or Pontiac from the 60s, 70s, or early 80s, the maximum depth seat I suggest is .200. I prefer .188 as I have seen so may rare high-dollar BOP heads get ruined by non experienced machinests looking at a seat chart and putting a .240 to .250 depth seat in the heads. This totally destroys them and all you have left is boat anchors.
In the Vortec heads, the intake runner on the roof around the push tube turn wall there is a cavity just below the pressed-in rocker stud. This cavity, believe it or not, does not affect air flow. I have filled them and left them alone and there is no difference in air flow. The intake bolt pattern on the Vortec is different than a regular small block Chevy and there are plenty of intake manifold choices out there with tooling available to re-drill your Vortec heads to fit the standard 350 small block Chevy manifolds. A lot of people have a good supply of older manifolds laying around.
The final thing I want to mention on new or used manifolds, especially the cheaper priced ones made in third world countries, is to make sure you check the fit of all angles and bolt hole locations. I have seen some of these manifolds come twisted so badly it wasn’t funny. I like Dual Plane and Dual Plane Air Gapped manifolds along with the GM aluminum factory manifolds for street use. If you want to go racing, use an open plenum style.
Now, the valve job before final assembly… intake side 45° primary seat .040 to .050 wide 39° top cut angle, 65° bottom cut .080 to .100 wide, narrow 65° bottom cut by using a 75° straight cutter and adjust your throat dimension to 89% of the intake valve size. On the exhaust side I like a full radius below the primary 45° seat 1.1 to 1.4 mm 45° seat width 39° top cut full radius below 45°. To remove any sharp edges below your seat and adjust your 89% throat dimension, hand grind it on intake and exhaust by using a ½ inch diameter fine tooth (24 count) regular cut round nose tree carbide cutter on a 2 inch shank. Some machinests try to use a 90° straight blade cutter but it digs into the throat material below the final undercut. I have designed an 86° cutter that works well but I myself prefer hand grinding it. Always set a pair of inside dividers to 89% of your valve size outside diameter and continually check as you grind your final throat size.You will have to re-contour and shape your short side radius.
Good luck with this project. It is well worth 30 to 50 horsepower over a set of low performance smog heads. If you want larger CC runner heads there are plenty of them available and remember, when buying your heads make sure the throat dimensions are not larger than 89 or 90% maximum. If they are bigger than my recommended max you will not have good flow numbers and you will have low velocity after all your work is done. You are probably wondering why I haven’t mentioned anything about aluminum heads. I wanted this article to cover a great head for a reasonable price and made an effort to help you prepare them for great horsepower, torque, and performance. I will do an article on aliminum heads later.
One more thing I need to mention is heat coatings for iron combustion chambers, valves, piston tops and skirts, and exhaust ports. You can run ½ point more compression, use 4° to 6° less ignition timing and fight detonation by using heat coatings plus pick up more power and torque.
Joe Mondello has been involved in quality head porting and R&D at a time when Ed Iskenderian, and a few others started a high performance industry. Joe has been so successful that his tech manual was given a GM part number. Joe is an innovator and educator of the highest order. When he could have sat on his laurels, Joe chose instead to start a Tech Center in Crossville, Tennessee holding classes for any who desire to learn air flow secrets that took Joe a lifetime to find out.
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