ok, well i race circle track and i need good heads. The rules wont allow you to run vortec, so camel humps are the obvious 2nd choice. But i can get a set of 993 heads for free rather then spend hundreds on a set of camel humps. So does anyone know how many CC's the intake and exhaust runers are?? I need to know CC's not cfm.

Thanks in advance,
If you have any input, email me at Mooredell7@yahoo.com because i wont check this site much, if at all.  

This is probably a discussion more appropriate to Circle Track Magazine, but for a lot of reasons Hot Rodders are more forth coming with information than sprinter crews. Something to do with competition I imagine.

Anyway the 993 is the trusty, tried and true SMOG head that saw the light of day back in 1972 and soldiers on in the Mr. Goodwrench 350 replacement engine for pre 1987 trucks.

Its ports got shoved around a bit thru the years and they will vary from about 150 to 160 cc, so I guess the average would be 155 on the intake and the exhaust cruise in the range of 105 to about 110 cc.

These heads were Chevy’s first attempt at thin wall casting and all of them, particularly the early ones, are given to cracking between the exhaist and intake seats, seats to spark plug, or inside the ports from the seats upward especially the exhaust is subject to this. I suppose part of this problem can be attributed to the induction hardened seats which makes a spine thru the length of the valve seats that's stiffer than the rest of the casting. So where I'm going is since these are free look the "gift horse in the mouth" with die penetrate or magnaflux before committing them to use on a circle track engine as they tend to run pretty hot, especially when the yellow or red flag comes out.

I think you'll need to crowd some advantages your way if you use these heads so if the rules in your class or at your track allow or at least don't forbid, I'd make these suggestions.

1) If you can run either a flat top of "D" dish piston rather than a circular dished piston. These heads have poor combustion characteristics and are detonation prone. Depending on what you want/need for a compression ratio or what the rules allow a "D" shaped dish or a flat top will provide improved combustion by vigorously forcing the mixture over to the spark plug side of the chamber and the larger quench band provided by a flat piston surface in close proximity(not to exceed .040 to.060 inch, lesser is better) to the head's flat quench deck will provide superior anti-detonation/pre-ignition characteristics. Try not to recover warped surfaces or compression by milling, these heads are thin to start with and become boat anchors when milled and treated meanly on a real race engine.

2) Cooling a circle track engine is a real pain, and these heads don't like to be cooked. If you can run an oversized radiator do so. If there's space, fair the edges of the radiator to the air intake so any air movement is assured to go thru, not around, it. If you can by the rules, run some external cooling lines around the outside of the heads. Jegs and I'm sure others sell a kit that adds an aluminum spacer to the manifold’s coolant return which includes a couple fittings and some braded hose which attach into the side of the heads where the factory puts the temp gauge sensor. These help make the temps inside the heads from chamber to chamber more uniform and reduces cracking problems especially on the right side as this hole is more rearward on this “flipped around” head. The ultimate of this type system is to drill and tap into the back of the heads for a fitting and where the "JEGS" kit attaches to the sensor holes put in a tee fitting. Then run a braded hose from the back of the head to the tee, then from the tee to the coolant return. This does a lot to balance the internal heat load and does much to flood out steam pockets that form above the chambers.

Another cooling trick, if you can use it, is to take the heater coolant return on the top of the pump and reduce this to fit a ¼ inch tube and then route a tube from there back into the coolant return on the front of the intake. At high speeds the belt driven pump cavitates and this little trick takes the gases and froth that forms to the top of the housing and returns it to the radiator, keeping the pump impellers wetter.

3) If the rules allow, clean up the valve pockets. The 993 has horrible globs of metal under the seats. Cleaning the pockets back an inch from the seat does a lot to improve flow past the valve. Carefully blend from the seat ID back to the port wall. This reduces cracking in this area. Don't carve on the walls even if the rules allow, the 993 is mighty thin in this area and even if you don't break thru, the thin wall will never survive the thermal and dynamic beating a circle track engine hands out.

4) When you have the money and if the rules allow a substitute stock head the DART Iron Eagle is the only way to fly. Something to watch is cost, the cost of making a sow’s ear in a set of competition heads can run within a few bucks of really good aftermarket stock replacement (SR) heads.

Bogie