Advanced Engineering Tech - Aftermarket Casting VS Stock Casting
01-12-2006, 08:16 PM
now what aspects of an aftermarket head would truely make it better than its stock counter part? im talking the design changes in the casting itself not nessecarily jus the ports and flow numbers. i mean im a believer that any reputable company that releases its own version isnt just copying a stock design but improving upon a design that was already decent to begin with. on another forum theres a debate that discussing the justification of an aftermarket casting? what do you all think? what makes the after market hunks of aluinum better?
01-12-2006, 08:40 PM
More meat to work with for one. The thicker deck and thicker casting gives you more options and can support more power.
I'd look for more port bias for swirl, or a nicer approach to the valve, as in improved valve position & angle, and a nicer short side approach in the intake port.
Combustion chambers can be improved for power as well. Shallow angle heads are especially good IMO. They allow you to unshroud the valves, give you more squish area, and allows you to easily have higher compression at the same time. They can also give you more piston/valve clearance as compared to a stock angle head. 11* is shallower than 14-15* valve angle heads.
Another thing to think about with a head is the meat around the spring pocket. Some people need to run much larger springs. Others want to raise the intake port roof a lot with porting. Having more meat around the spring pocket allows this to a greater extent than the stock head.
01-12-2006, 09:10 PM
Depends on who you talk too....
Of the very good head porters I know that work with LS head castings....
1. is a big fan of the 243 GM castings no matter what, said he likes how the ET heads look.
2. is a big fan of the Darts.
3. is a big fan of the All Pro's but does some good work with 243's but has only found 1 set that can fit a big enough valve in it.
4. is a fan of the edelbrock castings for the applications he's using them for.
Aftermarket castings should be made with improvements over the factor stuff, does that mean they should be smaller? Not IMHO.... If they are made smaller then they should be made for porting.
01-12-2006, 09:43 PM
Yes, somtimes it's just a matter of providing more to work with. I don't know about the current rules, but some years ago Pro Stock had to use 'factory' heads. After years of adding 20 pounds of weld to a head and then grinding 19 out, the racers got GM to release a "head" that was little more than an 80 pound aluminum ingot with a GM part number cast in, leaving them all the scope in the world re valve locations and angles, port size, shape and location, any chamber size and shape you wish, etc...
01-13-2006, 06:51 AM
i horses for corses though isn't it????
GM dont need to prdouce heads that can handle 1000+bhp and 30psi of boost! they are more concernd with fuel econamy and emmisions than outright power! then when you start to think of cost (BA saved £1million by severing 2 less olives on first class in flight meals!!!!) you see they wouldn't even if they could!!!!
on the other hand the aftemarket guys can make the head that GM should have made! they can do what they (read you guys) want! and as said above, if racers that need to use GM stuff want something better, GM will make a small "production run" for them!
just my sinical opinion, Chris.
01-13-2006, 06:09 PM
I just scanned an article on the Gen III Small block by Will Handzel in Truckin' Magazine. He heads up GM Performance Parts as I recall. Anyway, in this article Will said that the valve spacing was optimized for the 4.8 and 5.3 L engines because they were destined to become the highest volume Gen III versions. This limited the stock versions of the 5.7 and 6.0 L engines by an estimated 15 to 25 HP. This issue is apparently being addressed in the Gen IV engines with 6.0 L and larger displacements by the head redesigns (intake and exhaust runners), offset rocker arms, etc.
Also, on aftermarket heads, the methods and materials used are not so constrained by unit production costs. Also, the aftermarket developers get the advantage of learning the issues related to the production design and addressing those shortcomings.
01-13-2006, 10:18 PM
Better is a relative term. Here on LS1 Tech it generally refers to power output performance, not emissions output reduction. (Although in some cases they can both be accomplished). Given the power performance goal, the aftermarket most always uses the factory parts as the standard to reference to. The aftermarket automotive industry then applies variations of current racing engine designs to suit the intended applications.
As mentioned above, issues such as valve angles and position in the chamber are optimized to suit airflow demands of engines that lift the valves in a range that are far from production requirements. These are fundamental changes that in some cases can cause major engineering issues with the castings.
We're about to begin working on a program for the AllPro 13º LS heads. There were a number of factors that helped us make the decision to choose the All Pro head. One of the major improvements over the factory LS7 head is in the rocker boss area. The extra material that was added by AllPro makes it a far more suitable racing head than the LS7. Aftermarket valve gear will make our customers happier. Valve train stability is a major issue in the harsh enviroments of modern racing engines and AllPro has addressed it by reinforcing this critical area.