Which cylinder heads do I have and what are the component specs for the valves and springs?
All the heads we make have cast-in letters and codes under the valve cover. It is important to note that World is not affiliated with Dart or Roush although very early castings may have some of these markings. When calling customer service, first reference the markings on your head. A code such as  "I-037 ” or "WOR-070B" determine the family of head. Ford iron heads have  Windsor (200cc runner) or J/R (170cc runner) cast in place. The numbers stamped on the end pads of a head are the abbreviated World part number. If the spring and valve size/type is desired, you must first measure the diameter of your spring and then the World rep can provide more complete specs. We cannot determine the chamber size by any markings so that must be measured by the owner.

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Which pushrods should I use?
We advise that you acquire an adjustable checking pushrod to get an exact spec. Variables such as rocker ratio and valve length cannot be accounted for.

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Which spark plugs do I need?
All World head combinations and crate engines (SBC, BBC, SBF) use either Accel 276* (iron heads) or 416 (aluminum heads). Any variation of head or engine components requires a check of spark plug manufacturers' recommendations. 

* Accel 276S for crowded header installations.

Why do I have distributor trouble or engine misfiring if you ran this engine on a dyno?

All our crate engines are dyno tested - however, the only time 12 volt battery power is in effect is actually starting the engine. The ignition system is powered by the dyno's 110 volt AC system which generates a constant 13.7 volts DC to the distributor. If a distributor was defective we would know it immediately and replace it to continue the dyno run. Every engine that leaves here has an operating ignition system. The trouble is usually due to a system in the vehicle which is faulty, such as a poorly functioning alternator, weak battery, poor grounds or an old or damaged wiring harness. Check your system carefully and test for at least 13.5 volts at the distributor before calling for tech help.
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I have a rear main seal leak, why did you ship the engine to me that way?

The truth is, we didn't. As we complete the assembly of an engine, we add a leak detection dye to the oil. After an engine completes it's dyno test we inspect with black light to check for leaks. Only then is all oil, gas and water drained and the engine packed for shipping. If oil leaks are found, the engine never leaves until they are corrected. The major cause of rear seal leakage stems from poor crankcase ventillation. Many times, for appearance sake, a new owner will change the valve covers we supply which sometimes negates the breathers we include with our covers. Be sure to provide sufficient crankcase breathing and rear seals will not leak.
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Why do aluminum heads make more power?

They really don’t make more power-by themselves. Aluminum can dissipate heat better than cast iron heads, allowing the temperature in the chamber to be lower. This permits the compression ratio to be raised without raising the octane level in your fuel. The raised compression is what makes more power. Raising the compression still higher requires a switch to higher octane race fuels.

How can I determine valve lift if I change rocker arm ratio?
Using the advertised valve lift of your cam, divide that figure by the current rocker ratio. This figure is your theoretical lobe lift. Multiply that figure by the new rocker ratio and the result is your new valve lift.

What does “Racer Special” porting mean?
These procedures consist of matching the port opening to the required gasket by slightly hand grinding the port entry and exit. Then the “bowl” area of the valve pocket is smoothly blended to meet the valve seats. If any burrs are present in the chamber or port edges they are removed to avoid hot spots.

When should I be concerned about piston to valve clearance?

As an engine builder, you should check this clearance anytime a parts or machining change is made which may affect piston / valve clearance. Changes to rod length, piston design or pin height, deck height and cylinder head milling are among these factors. The procedure is; with the head removed and the piston at TDC, attach a small piece of clay to the piston top. Re-install the head, without the gasket and move the valves to max lift of your cam or rotate the engine. Measure the thickness of the clay at the contact areas. The addition of the gasket thickness should be taken into account. Safe numbers are .080” on the intake side and at least .100” on the exhaust.