|03-21-2013 06:56 AM|
|cobalt327||Poncho, feel free to delete my post directed at renjams and this post, too. Guys like that piss me off. It's like you're at your favorite hangout, then in walks some noob butthole putting his muddy feet up on the furniture and making himself 'at home', w/o so much as a how-do-you-do.|
|03-21-2013 04:51 AM|
|03-21-2013 03:41 AM|
|03-20-2013 11:37 PM|
|03-20-2013 05:39 AM|
for what c-n-c ported heads cost you could get the non c-n-c model of same head and bolt a turbo on it and get more flow.. cheating yes.. but my darts to buy the c-n-c ones where 2300.oo more..
and I'm sure it might be worth it as porting/testing/etc takes time and r&d isn't cheap.. but most don't need that extra 2-3% extra flow..as most of the good heads the as cast ports are not all that bad to start with..
|02-14-2013 09:58 PM|
I am a reader,in part of a life long study in performance engines,of Engine Builder mag.com.
It gives you a perspective of a insider of the business of manufactures/machine shops.
This link is a number of articles about CNC machining.
Search Results - Engine Builder
I do think it goes to the core question the O/P wanted.He could just skim over them.
|02-14-2013 08:31 AM|
This is all pretty good, but vastly over-simplified. CNC = "Computer Numerical Control". The aforementioned "5-axis" machine is similar to an old "Bridgeport" vertical mill, with motors and sensors doing the "work" instead of a machinist. In modern manufacuring of complex parts, CNC is used virtually everywhere. Those machines can do in seconds, what takes a human minutes. Imagine the labor savings in large production.
As for porting, there is a TON of misconception. IMO, the "best" machines are the Haas 7-axis jobs. Yes, upwards of a half a million to buy, program and train operators. But there's a "quirk" here. CNC machines require a "map" to follow. It's true, they are very "consistent'. The problem here is, if the human that did the orignal porting that is "mapped" made a mistake, or not a really GOOD port job, it will repeat that same bundle of errors. In one case we know of, there's a PILE of ruined iron heads where a very good "max port' job was mapped (pirated). I spoke to a CNC expert, and he said factory iron heads aren't consistent enough due to "core shift" to successfully "max port" them with the machine. Invariably, they break through bowls and runners. Another involves a popular imported aluminum small block head, that actually flowed less everywhere EXCEPT @ .600" lift, than the "as cast" version of the same head. They ruined the heads, as material was removed in the wrong places.
Pro race shops (like John Force Racing) buy semi-finished BAE heads, "roughed in" by CNC. THIS is where CNC machines offer the best service to engine builders. The crew chiefs of each team have their own "approach" to the ports and do the finish work by "hand". The Edelbrock "Pro Port" series are aimed at CNC porters.
CNC is advertised as the hot lick because it's so "consistent". When compared to an ametuer port job, they're right. But a professional porter will get the ports just as equal. Anyone that has "tried their hand" at porting knows how difficult this can be, and advertisers prey on that. They will also generally release the "peak" numbers aned not much else. Companies like Dart and Brodix, of course, have engineers "on staff" to optimize the ports. Peak numbers sound cool, but low- and mid-lift flow are MORE important to power production than peak flow.
The MOST important "negative" to remember is, machines don't "learn". Each set is the same as the previous one. So, if you want the same basic "engine" as the guy next to you, CNC heads are okay. If you want an "edge", you need to seek out a pro and follow instructions!
|02-13-2013 12:24 PM|
|1Gary||The cnc machines/programs come in different grades and older machines vs the newer versions.So the end result can be very different.The better machines with 5 axis porting are the better machines and can cost $250,000 on up.And the end result is a faster production time and is exact same result port to port. The better programs have the ability to do simulated porting and then apply that to a test mule for testing.Guys say cnc porting isn't worth the costs because it still requires a human to do the input into the program.No truer word could be spoken.It is that position that supports to purchase from a known name brand company that has been at this first old school way and now using top of the line cnc processes.It's that experience that counts.It's the same as it as has always been.How cheap and how good never mates up.|
|02-13-2013 11:12 AM|
Yes heads are cast then cnc cut to spec for valve cover and bolt holes. But most of the time they are not considered to be cnc unless they are cnc ported or cnc combustion chambers.
My procomps have cnc combustion chambers but the ports are as cast for the most part. CNC port work is a lot of money over the price of the head. but if your buying heads you can just buy the bigger ones and save the buck the cnc would have cost. Yeah its a little better but not worth the cost unless max effort racing. My procomps setup and ready to bolt on with 210cc intakes and 2.02 valves were 600 a set. Not 500 for a single head. If they flow a little less its ok I got the big ones anyway so still should be good. Exhuast ports do not look to be restrictive they seem open and well designed. But they have not been on a bench.
So yeah heads are made with cnc already. Larger production run heads are made with a single stage process. where the holes are drilled and tapped with the same machine all at once. it is not really cnc. But close enough they are made by computer/human on a machine.
|02-13-2013 10:14 AM|
Ford tried machined chambers on the First FE engines in 1958. The problems with those was the sharp edges at the angled spark plugs would cause pinging unless and octane booster was added to the fuel. With some die grinder work they were better than later cast chamber heads. just too expensive for production costs parameters.
|02-13-2013 10:14 AM|
|02-13-2013 10:02 AM|
|S10 Racer||In short, most production heads are cast in a mold and then machined. CNC'ing is a computer machined operation that mills the combustion chambers and intake runners to a specifc size. This is suppose to insure everything is the same size.|
|02-13-2013 09:40 AM|
CNC machining of heads
What are the head makers really saying when they advertise CNC machining? Aren't the heads made by CNC machining when they are manufactured? But when looking at a set of heads you'll see that they are CNC'd or they will offer CNCing at an additional price. Could it be that "CNC" has a different meaning in this case?