to CNC or not to CNC

[rrubel]

Was reading an interesting older article in Corvette Fever (http://www.corvettefever.com/techarticles/18459/) which basically has them upgrading an older C4 using the same plan I've got. One thing they did differently was buying Trick Flow heads instead of the Lingenfelter I've been looking at, for about half the price. Summit Racing has these heads, about $1050 for normal and almost $200 more for a CNC version of the same thing. So... my question is - what's CNC and why should I (or SHOULD I) pay $200 more for it? I thought it was a finishing process but the Summit blurb says "CNC profiled' which makes it sound like something else.
Thanks...
[RICHR]

 

[oldace84]

Did you already order those head's??
thanks
tony

 

[rrubel]

Not yet. I'm doing some pricing/comparison shopping for the few major parts I still need - heads, SuperRam base, roller lifter retrofit kit.
[RICHR]

 

[-=Jeff=-]

go here

http://www.totalengineairflow.com/

if you want CNC porting. It is worth it depending on gains from stock and your plans for performance

 

[rrubel]

Thanks, Jeff. I emailed them with some questions. Still not sure, though, exactly WHAT it is - just a different process?
[RICHR]

 

[pauld]

CNC basically means the operation is controlled by a computer, an operator writes the program on a computer and the machine carries out that task. In the context described, it means that the milling operation is carried out by a CNC milling machine or lathe, or possibly a machining center containing a 'bank' of tooling.

 

[rrubel]

So essentially the specs are fixed and there is a better consistency between consecutive runs. So your left and right heads are definitely going to be the same grind.
Thanks for the info.
[RICHR]

 

[rrubel]

I asked my question to Total Engine Airflow, as someone suggested. The response from Brent:

"CNC porting is porting by a machine and not by hand. In my opinion cnc porting is far superior than hand porting. The machine never messes up and can port from hole to hole within .005 where the human eye can't even see that difference and port to port variation is far greater than .005 when done by hand. "

They have what seems like an awesome deal on Trick Flow heads - $925, or $1075 CNC ported. Including valves/springs/etc. That seems to be less than what it'd cost me to buy used stock aluminum heads and get them reworked.
[RICHR]

 

[sothpaw]

Rich,

CNC machining is not new, it's pretty standard now. It was up and coming when I was in engineering school, it would be a project for a grad student to program the machine and play around with the process variables.

Almost all machining now is CNC, or as we call it, 'NC.

What it does for heads is about CONSISTENCY. It means they can put out much more product faster with little variation. We would not dream of having machinists make our radar, those parts are all NC machined.

It is not, therefore, inherently better for you the consumer, except that it should be cheaper. NC machining is only as good as the database the machine is using (the drawing, if you will).
That will depend on how much testing this place did.

 

[vette-dude]

Computer Numerical Controlled machining basically is as everyone has said previously. However, the workpiece, or heads in this case, must be set-up by the machinists. The resulted machining is only as good as the set-up. True the machine is consistent but if the set-up is incorrect then the machining of the ports will be incorrect not once but eight times per head. Second, the accuracy of the machined part will only be as good as the accuracy of the machine. Sure the control can comp for some of the slop in the screws and such but it can not comp for worn out ways and pitch or yaw in the table. Therefore, before investing extra $$ I would want to know the machinist capability, the machine it was going to be machined on and when the last time that machine was calibrated (laser checked for accuracy and physically aligned). It would seem to me that CNC machine porting should be less expensive than hand porting due to the labor involved to flow check for consistency and remove material while hand porting a head. I have hand ported many heads and it is indeed labor intensive. Using a CNC machine with a jig and fixture for the set-up and the programming already developed would be a piece of cake in comparison.

Randy

 

[8388]

Also important, especially on new heads, make sure they pressure test them. Casting flaws do happen, and this can become a serious issue.

 

[grapeknutz]

go here

http://www.totalengineairflow.com/

if you want CNC porting. It is worth it depending on gains from stock and your plans for performance

Thanks Jeff it's now booked marked!