Can someone explain to me why aftermarket heads are better that just porting the stock ones? I know that they are lighter which is a plus. The reason I want to know is if you look at my sig. I need to do something about the stock heads. (Headers on the way, so no comments about the stock manifolds )

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88 Formula 350
Upper and Lower SuperRam, 1000 CFM Accel Throttle Body, ZZ4 cam, 24# Motorsport Injectors, Larger Gutted Mass Sensor, Homemade Cold Air induction, Custom Burned PROM, MSD 6a box, MSD Distributor, Accel SuperCoil, Taylor 8mm wires, TB Bypass, B&M shift Kit, 160* Thermostat, Flowmaster Muffler,

 

I assume you are looking at aluminum heads. They are different in many ways. Simply put, they flow better. They have larger valves and ports (in general). With an aluminum head you can also run more compression (more hp). It is hard to answer your question, but your car DEFINETLY needs some heads. Im glad you have headers on the way because those logs are killing you. Think about the flow of air in and out of the engine. If it is restricted (heads, manifolds, stock exhaust) you will loose horsepower. You've already taken care of the intake restriction, but the intake doesnt do much good if the heads/exhaust cant flow well. You would see huge improvements if you slapped heads on with the headers. What heads are you looking at? How much do you want to spend?

 

I'm interested in a head upgrade also. Looks like most of the aftermarkets are in the $1000.00 price range. Anyone had success at significantly lower cost?

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87 TA, 305 TPI, Custom CAI, K&N, ACCEL 8mm wires,ACCEL Super-coil, ACCEL Plugs, JET TPI Airfoil, Cherry Bomb Muffler, 160* thermostat
The Phoenix Project..click to see my project car
Trans Am stuff and GIRLS, GIRLS, GIRLS!!!!!

 

The stock heads can be just as good, if not better than the aftermarket heads.
When the factory designed the heads, they were designed with the idea of mass production and driveability of the car in mind. Things such as core shift, casting flash, screw in studs, high lift springs were not as critical in the mass production environment.

Aftermarket heads are designed for performance. They use high lift valve springs, screw in studs, bronze valve guides, a more efficient combustion chamber design and an emphasis on gross cfm flow. Core shift and casting flash etc... are still present, but the effects on overall heads performance are greatly reduced due to design/quality control/ etc...

Factory castings are also referred to as cheaper castings because the factory purposely didn't use as much material in the heads.

Consider the Dart Iron Eagle's versus steel L98 heads. Dart Heads have intake runners ranging from 165 to 220 in the same head casting. They can do this by suspending different cores in the head during casting. In order to make sure that the intake runner for the 220 cc head isn't too thin, they design the head with a 220cc runner in mind. They relocate the water jackets for porting and add extra material where machinists typically concentrate their porting efforts. This design concept is then applied to all other intake runner sizes. Factors such as the size of the short side radius and casting finish are large concerns.

The factory wants knows that maybe 1% of the owners of cars will port their stock heads, so water jacket relocation and porting areas are not design concerns. They cast the heads with as little material as possible to maximize profits. They design their intake runners for economy. Consequently, after light porting, a factory head may very well be able to perform just as well if not better than a comparable aftermarket head out ofthe box. For reference, Lingenfelter ports the corvette L98's for use on all his tpi crate engines.

In conclusion, people buy aftermarket heads because they offer better flow numbers out of the box, along with the potential for better performance after porting due to superior design. They also offer features such as screw in studs, bronze valve guides, stainless high flow valves, high lift valve springs, locks, retainers. All of these features combined make the aftermarket heads a better alternative to stock heads.

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355 c.i.
Dart 180 Heads
Lunati 224/224 cam
Harland Sharp 1.5 rockers
Performer RPM Manifold
Holley 600 cfm double pumper
Hooker Super Competition Headers
Flowmaster Exhaust
Competition Engineering Sub-frame connectors
Tremec TKO
Pro 5.0 Shifter
GM posi 3.42 rear
Hurst Roll Control
13.9@102