squealingtires

iTrader: (14)

Straight from MTI: "CNC PORTING CANNOT MATCH THE PERFORMANCE OF OUR HAND PORTED CYLINDER HEADS"

Doesn't make a lot of sense to me to say that CNC porting cannot match MTI's porting is saying an awful lot.

3.4camaro

iTrader: (1)

the reason they say that is because they CNC port then hand port. CNC is very accurate, but it leaves little ridges which hypothetically can disrupt airflow. MTI goes the extra step and smooths these ridges out.

and MTI is badass.

Sean Collins

Depends on the cutting quality of the machine. I would say a top notch top of the line machine would be 1000x the finish quality of the Hand porting if the program was properly done. In fact they are finding particular wall finishes with the CNC reduce boundry layer air volumes and improve velocity.

3.4camaro

iTrader: (1)

i guess they outflowed a CNC a couple years ago by smoothing out the edges and called it a win over all and any CNC mills.

thehammer69

iTrader: (2)

technically, most CNC porting is porting that has been designed by hand and then CNC mapped then duplicated again and again using CNC machining. So yes, hand porting can beat CNC. What hand porting can't do is consistantly produce identical ports over and over with speed and consistancy.

Hammer

WYD-01

iTrader: (2)

Definately the cnc is alot faster and proven fail proof. But the program to run the cnc has to be written off of something ie a hand port job. So hand porting would definately be better, but it just takes a bigger time frame to complete the task.

squealingtires

iTrader: (14)

Ok so MTI "hand finishes" their port jobs. This would make a lot more sense.

3.4camaro

iTrader: (1)

thats it. they claim to use a CNC, so that makes the most sense

Adrenaline_Z

Those little ridges are there on purpose. They can help break up the mixture
for improved atomization, and improve the flow near the boundary layer among
other things.

Having a glass smooth surface is not desireable from the porters I have talked
to; however aggressive ridges are not optimal either. I'd like to see back to
back dyno and track testing of identical heads with this criteria in mind.

A CNC is just a machine which is programmed based on a human design. If the
human design sucks, the CNC job will suck.

A good head porter can take a CNC head and improve areas as well as fine
tune the port shape and surface texture to a degree that a machine cannot.

DRCE

Nothing more is needed on this topic, that sums it up right there. Point blank and period.

SStrokerAce

iTrader: (2)

Depends....

At PRI there was a TRD Cup Head that almost every head porter I talked to said that was as nice of a CNC port that they have ever seen. IF you have the machine spend the time, have small cuts and short distance between the tool paths you can make a better product than a hand ported head. Also if the CNC copy can be digitized and the CAD file of the orginal and the copy are exactly the same then your really not going to get any better than that.... in terms of copying. The master port is the key to everything.

Bret

Brian Tooley Racing

iTrader: (13)

This is true to a point, most people when they first start programming 5 axis CNC's from the master port, they tend to do a poor job at copying it.

With time a good programmer will be able to duplicate a port within a percent or two.

With enough time and pratice the top programmers will be able to actually make the port flow more air after it is digitized. Take the TFS 215 head for example, if you sand the intake port surface smooth....it will flow less air, if you sand the seat area....it will flow less air. Pretty much anything you do to it, will make it flow less air. Of course most people that program will never spend the amount of time it takes to make a CNC port that good, they can't afford to take the time to.

GuitsBoy

iTrader: (4)

Ive grown up my whole life around CNCs in the aerospace industry (thanks dad!)

When you clamp the head down into the machine, youre reliant on GM's tolerances for where they installed the valve seats and guides in relation to the outer dimensions of the head which youll be using to hold it with. If their tolerance is .010 in either direction, that means youve got to program your machine to leave up to .020 extra meat so you dont wind up getting too thin. When touching up by hand, you can view your progress and gauge your work, and adjust it in real time. The CNC has no idea if its .010 too close or too far away from that valve guide. All it cares about if cutting whatever's in its path. Due to clamping variances, casting differences and GM tolerances, youd have to set up your CNC program conservatively.

TXZ28LS1

iTrader: (5)

i dont know much bout the whole process on heads and all that, but all i can say bout mti is that they probably have been in the business longer than most sponsors if im not mistaken. im looking at mti 2e heads also. my thing is, that they must have a really bad a$$ head porter because they dont run any other elses heads!! so no afr, patriots, or trickflows.. so that must mean something.

Studytime

iTrader: (15)

On race motors you'll be very hard pressed to find a CNC ported head that's not hand finished. What does that tell you? Also, there is no reason for there to be ridges in the runners. Actually a smooth intake runner wall provides the best power. Makes sense? No. I've taken fluid dynamics and this should not be the case, but also according to engineering calculations a bumble bee would never be able to fly.

CNC heads are fine for street cars, but in the super competitive racing world it's a different case.

Thanks to CNC companies you can buy heads for a street car that cost a grand instead of a hand ported set for two grand. When the GTP heads were the only ones on the market those were 2400 a set. You're probably getting comparable results to the CNC

Ben T.

1997bird

iTrader: (2)

Isn't the real question how well the CNC ridges vs the hand ported heads, leave behind the best boundry layer for flow?

Studytime

iTrader: (15)

No CNC marks and a perfectly smooth finish gives the best power. As for as emissions, possibly something else? A slick wall shows the best power on an engine dyno. There are also companies that coat the intake runner at the same time they're ceramic coating the chamber and valves. The smoother the better. Besides the master head for any CNC head is slick in the runners because that slick surface digitizes better.

It contradicts fluid dynamics I know, but which one do you believe? Theory or a lying engine dyno.

Ben T.

mullenh

iTrader: (1)

hmm all nascar engine porting is finished by hand

Bo White

iTrader: (59)

Center up on the valve guide itself even creates possibilty of a thin head in areas. This topic is way to broad to be taken care of in one thread

Richard@WCCH

iTrader: (3)

All the Gen 3 heads are machined on very modern CNC machine transfer lines. The tolerances they hold are exceptional as compared to the older 23º heads and that goes for the valve guide to head/block dowell dimension. I have no problem holding the critical tolerance for valve guide lineup. It is extremely difficult to hold these tolerances when hand porting. Hand finishing a CNC ported head can in some case improve net airflow, but as Brian mentioned in his post sometimes it's not possible to improve the port no matter what gets smoothed. CNC's definitely have the speed and also have the consistency to make more ports flow exceptionally well. At least my hands don't go numb and I don't rust my T shirts as much when I port with a mouse

Richard