DeTomaso Mailing List: October 98, Message #106

> Subject: Yet another head porting opinion (part 4: CNC)
> 
> Now that I have told you that good valvejobs and bowl ports are great
> for street cars, we'll get to the meat of the discussion: who actually
> cuts on the heads.  When all is said and done, the machines don't
> develop the heads, humans do.  And humans that are specialists at that. 
> One gentleman challenged a CNC to duplicate his craftsmanship and
> accuracy.  He's right.  A CNC will not do it.  All a CNC can do is be a
> workhorse that duplicates efforts very rapidly and increases
> productivity by a bunch if used right (a whole nother discussion in
> itself).  The problem here isn't that of accuracy of a CNC versus a
> human though, as it is the limitation of the number of humans that are
> capable of doing the work that is needed by so many.  CNC to the rescue
> closely duplicates the work of a craftsman head porter to the point that
> it can be touched up by hand to make as much horsepower as the last 50
> sets of heads, without working that poor human for 2 years straight. 
> The scenario is that someone will develop what they feel is a very good
> port and then they will get a CNC program that duplicates that work for
> a certain application.  These modern 5-axis machining centers are very
> fast and accurate _enough_ for this kind of work.  So, while that CNC
> machine is hogging out heads and accomplishing 99% of the cutting for a
> job, that porter is free to continue development on the port for another
> generation program rather than wasting his life away making big piles of
> aluminum shavings.
> 
> Here is the skinny: the CNC port job is only as good as the development
> work that went into the program initially.  Winston Cup and Indycar
> engines are getting heads bolted on that car CNC only ported.  A lot of
> them never get touched by humans again.  There are only 'development'
> ports and CNC'd race heads.  The difference is that their CNC programs
> are proprietary and unaffordable by mortals.  They don't use .015 or
> .020" step overstep when they machine the heads, it's more like .005"
> and
> they take a long time to machine.  It's fine for a street car or even a
> bracket drag racer to have 'general' CNC ported heads that have
> noticeable machine marks in the ports.  Again, diminishing returns. 
> After they are pulled off the CNC, a good porter could probably find
> some flow and likely some horsepower, but it's probably not worth the
> effort if the CNC was developed from a good port pattern.
> 
> I don't know about the people in Florida. They have great claims and
> talk the talk, but I would have to take a set to my couple of expert
> friends to get their opinion.  I know where I get my heads ported and
> for good reason.  I bought a set of CNC'd AFR heads and ended up wasting
> a ton of money because the original portwork was absolute crap.  The
> heads flowed very badly and needed a lot of work.  They have a lot of
> potential and are working as well as any other 23 degree SBC heads out
> there, but it cost a lot of money to get them that way.  I  would have
> been better off buying castings and getting all the work done piecemeal
> as it turns out.  Thought the CNC was the answer for me, but it wasn't. 
> Might be for someone else though.
> 
> I hope I didn't put anyone to sleep or step on anyone's toes with this
> dissertation, but just wanted to give a little perspective to the
> discussions.  I try to not get too specific since every application is
> special and has specific needs.  This whole thing is more food for
> thought than anything else.  Remember that advertisements are there to
> lure you into buying a product.  Try to talk to someone technical and
> not a salesman when you are investigating headwork (bonus if someone
> technical is playing salesman for the day).  Often they will not want to
> take the time because they are busy and it sort of wastes a valuable
> porter's time trying to sell his work to a person with a street car that
> would be better off with a bowl port anyway.  I know that the many times
> I have called LPE (Lingenfelter), I have only been allowed to talk to
> salesman, though there are ones with different levels of expertise. 
> Even they get most of their package heads CNC machined and have their
> own programs...for all I know they could be using the people in FL to do
> the work.
> 
> Later dates.
> - -- 
> Scott Knight  mailto:sknight@mich.com
> http://www.mich.com/~sknight IRC:SS396man ICQ:8353618
> '95 Black Impala SS
> '94 Ducati 900SS CR
> 
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