Hey guys...

This has been bugging me for awhile. CNC porting offers identical physical characteristics from port to port, while with a hand-port job, I would think that there would be some material and port variances between ports. Pretend I know little about porting, and explain to me why CNC porting would be better than a hand-port, or why hand-porting would be better than CNC?

Sorry if this isn't advanced tech, but I'd like some input. Thanks.

 

CNC would be more accurate than hand You just program how much you want to take off and where and start the machine. Almost fool proof. You can get exactly what you want done first try. Im no expert but i wouldnt imagine there is too much difference between someone like Lloyd and a cnc porter, besides the technology.

 

CNC port programs are built around master ports that were specifically designed to work well with specific car/tranny/engine combinations. The program is deemed a success and the port is digitized so as to replicate it if need be.

The CNC heads work real well but they are probably optimal so long as you don't venture too far from the original combination. Granted, you have a port that is well designed and is extremely uniform from port to port. That in itself is worth power. Not to mention, a port developed to that extent may have incorporated wet flow technology that many small shop porters can't afford. So there's more to it than just a CNC port copy.

There's a big enough selection, that if you talk to the right people, they can put you on the path to the right head for your combination.

-Mindgame

 

Are all CNC port jobs the same? I mean, having one person do it over another, will there be any real difference?

 

Sure there are differences.

If you look at Weld Tech for instance. They have a number of 18º portings with various cross section areas, port volumes etc. Many of those ports were developed by Ron Hutter (The HUT series) while some others were developed by the guys at Richard Childress Racing. Probably fair to say that there are some differences in the port, even though they're cut into the same casting.

Your differences lie in the talent of the porter who developed the master port. No two guys do it exactly the same way. I've seen the difference HP-wise from one porting to another with no other changes. Sometimes it's just a matter of the combination and what it likes but it's not usually as easy to see in the flow bench numbers.

-Mindgame

 

Ok both have their places/uses. For me when it comes to a SBC based casting I'm 100% hand port work. I've worked on SBC stuff off & on since the 80's, so I know what I want and how to get it quickly... besides for the most part we're not dealing with a ton of metal removal (that's the big thing). On LS1 based castings I start with a base CNC program that cleares out the "excavation" work. Compared to the average SBC head the LS1 & LS6 heads have a considerable amount of port area to work. The CNC program gets the "basics" out of the way and allows me to concentrate on fine tuning the port in a manner of speaking. Also the LS1 & LS6 castings are what is really in demand, so the quicker you can turn out the heads the better off you are business wise. As an added bonus starting with a base CNC head does facilitate a more consistent port to an extent when you're talking large ports.
Now straight CNC ports over hand finished... not on my motor! CNC is an awesome tool, but it does have it's limitations as to what the tooling can put out... or should I say leave on the table in an "all out" application.
CNC just one more tool to be properly used by head porters now a days...
Steve...

 

SAR2k,
What about having your best intake/exh combo digitized? If you're already going through the trouble to have the ports hogged out by the CNC, it shouldn't be any extra effort to have them machined to the finished dimensions. OTOH, if you're tweaking things between cylinders, maybe a hand port has some merit...

Andris/Z28tt

 

Very good points.

There is CNC porting and CNC porting and it's not all the same. To accurately duplicate an optimum port may require many cutting tools, lots of small cuts after the big cuts, as well as other machining that may demand more sophisticated CNC machning centers and/or more machine time. What determines cost is the total machine time and the hourly rate placed on the machine by the owner.

If "speed costs money", "good CNC time costs big money", so rarely will you get what you don't pay for on CNC machining. Really high-end heads (Nextel Cup maybe) might be CNC ported and take many times the machine hours to complete than "budget" CNC ported heads.

If the port shape is a good one, even moderate cost CNC machining can duplicate it fairly accurately, even given some machine/tool limitations and maybe get within say 5% of best flow, but that's still 15 CFM on a 300 CFM head. True a VERY good hand porter may achieve better flow numbers, but to do this well is very time consuming and hard work. Again, you probably don't get what you don't pay for, and the danger is that you might not get what you do pay for. Of course that also applies to CNC porting.

I like the idea of hogging out most of the material with a CNC and then finishing the final shape by hand, as long as the hand holding the grinder is connected to a great porting brain. Recently I've seen some awesome hand porting and the appropriate flow numbers all across the curve. I've also seen some excellent porting by WeldTech on similar SBC heads. Both were fairly expensive, but the customer got what he paid for in both cases, IMO.

The caveat is just because is says "CNC ported" doesn't make it a good port. Consistent, probably, but that could be consistently mediocre, or it could be consistently awesome. "You pays your money and you takes your choice." There's really no free lunch in this business.

My $.02.

 

just "re_dyno " tested a Racer's BBC with 18 degree Big Chief heads
as heads came with $800 CNC porting made 842 HP ...pretty bad numbers
but the CNC was just "eye cosmetic" porting. looked very good , but heads didn't flow much more than out of box numbers

after re-doing valve job, hand-porting Intake bowl and just short turn areas, the same BBC made 983 HP => gained 141 HP
983 HP is still pretty weak...theres 1100 to 1200 hp potential +
in a Full port job
----------------------------------------------------------------------

Chrysler SuperStock heads=> one of my customers sent his Heads off to get digitized and CNC ported/duplicated from his best running head....the 1st results were about 40+ HP down from the original set, 2 tenths ET loss and 3.5 mph loss...all that for a $5500 CNC ported head (complete assembly)

they tried another CNC digitized/duplicate (another $5500)
results were closer this time...came within 15 average HP thru out the Power Curve and 20 less Peak HP...ran within 1 Tenth ET of my hand ported heads

the problem is the SS heads are cast-iron with very small ports and a ton of valve guide boss in the port ...along with a ton of epoxy on the floor
the CNC tooling just can't get into a long narrow port and mill across a material like cast-iron then go across softer epoxy during the same sweep
so the $5500 heads needed more rework after they were done.

if you put the Epoxy in "AFTER" the CNC work..its sort of defeating the original purpose of CNC !!

-----------------------------------------------------------------

SARK=>
>>Now straight CNC ports over hand finished... not on my motor! CNC is an awesome tool, but it does have it's limitations as to what the tooling can put out... or should I say leave on the table in an "all out" application.
CNC just one more tool to be properly used by head porters now a days...
Steve...<<<

i've had about 5 or 6 of the top "name" CNC'd LS-1 / LS-6 heads in my Shop
and so far, theres "still much more HP to be gained" by Hand-porting and
Hand-finishing on these type Heads . So far the best CNC programs out there are still not capable of porting the Short Turn correctly, as this is the hardest area to get to by a machine !
--------------------------------------------------

i've seen very good CNC heads...and very bad CNC heads
your just buying some one else's "Idea" of what a port should be

CNC can make you 8 "perfectly Bad-Ports" or 8 "perfectly great Ports" ??
[(1) V-8 head]

usually 95+ PerCent of the time, you can still pickup a lot of HP/TQ hand finishing a pair of CNC'd heads
---------------------------------------------------------------

you have a 1/4 to 1/2 Million Dollar CNC machine that can "duplicate ??"
a Cylinder Head "perfectly" ....the problem is a Cylinder Head is a "casting" that varies all over the place ....another problem is "Setup"..if a "Perfect Casting" is setup slightly off in a "Perfect CNC Machine"..you get 8 perfect bad ports ! Hand-finishing allows to to "adjust" your Porting to try and correct any casting or setup problems

CNC is potentially a great Time Saver..but if you want real HP, you'll have to spend more Time Hand-finishing these heads

 

Ok...

OS, did you renege a statement? I thought I saw you post something last night and I was too tired to read through. Tell me I aint losing it.

-Mindgame

 

You ain't losing it...

(This from someone who lost it a LONG time ago, according to many folks. )