CNC markings

[faulkdaddy]

Jay, don't be mad at me. But. In the famous words of My Really good friend and fellow builder.  I CALL BULLSHIT!!!!. Every 20 hours. Not in this lifetime at the cost of Titanium. Joe is right. Yet to be proven.  Hey Keith can you P.M. me what we talked about. I'm starting to like this thread.

Bruce Faulkner
SSG U.S. ARMY  (RET)

[cjshaker]

1-2 horsepower
I'd love to see a dyno that is that accurate, and repeatable.

[fekbmax]

Wow, I love this sight. You guys got a ton of passion and knowledge and I love it.
Thing is I in no way wanted anyone to think I wasn't happy with the heads because that is far from the truth. The valve pockets/bowls and the combustion chamber's look exceptionally nice and easy some of the best work I have seen. The heads I supplied him with were old 6005's and had been extensively hand ported twice before so I wasn't exspecting total perfect.  For what I gave him to work with and what I got back I'm totally satisfied.  I was only curious about the "few" CNC markings left in the runners and I'm going to take Jays advice and carefully smooth them out with 40/60 grit cartridge roll.
Thanks guys for all the vast knowledge. ..

[Autoholic]

Replacing every 20 hrs, with titanium valves... ouch. I also call BS on needing to replace them. I could see clean them, if you were racing. But replace? That's nuts and I smell greed / marketing. 1-2 hp increase, LOL. Even if you could prove this and say that they give each cylinder 1-2 hp, it won't do a darn thing for you and you would be better off just taking 50 lbs out of the car, or more. Make the driver a midget, fastest drag car.


While researching dimpling the intake manifold, I did run into some posts out there that say some racers do this. I suppose the only way to really know how well an intake performs would be to modify an existing one that you've already done a few flow bench tests on.

[Nightmist66]

Smoothing the combustion chamber and getting rid of any sharp edges in the combustion chamber helps to eliminate hot spots that may cause detonation. Jim

I agree with that. Something you can do if you want is smooth and polish the combustion chamber and exhaust port. I would leave the intake side with the sanding roll finish.

[Autoholic]

I take it you are wanting to leave the sanded, rough finish in an attempt to cause turbulent flow, so that the fuel is suspended in the air better?

[Nightmist66]

Yes. Unless that is wrong, that is the way I would do it. Again, no expert here, but maybe Joe-JDC or anyone else can inform me better on that. I just base that off my own understanding, but I would like to know what is ideal.

[Joe-JDC]

For the last 30 years or so, I have been finishing all my intake ports with a 60 grit flapper and polishing the exhaust ports with 120/180 grit flapper rolls.  I typically finish the combustion chambers with a rough texture around the intake valve and polish the exhaust side.  That was the industry standard until the CNC marks came into vogue, and like Jay said, if you carefully blend them out you may pick up to 15cfm in the intake tract, but not the exhaust.  Typically if you take them out of the exhaust port, you enlarge the port and change the flow characteristics, which can sometime kill the flow or at least not help it.  Last week I flowed a pair of aluminum sbc heads with 2.100/1.600 valves that were CNC'd from the supplier, and someone at a speed shop cartridge rolled the ports, and now the heads flow 284/168cfm at .750" lift.  Whoever modified the CNC program killed at least 40 or more cfm on each port.  Be careful when you listen to every new idea that comes along.  Not all of them are beneficial in the long run, and many actually kill the performance of an engine.  Joe-JDC

[Nightmist66]

Thanks very much Joe. I was hoping to hear it "straight from the horses mouth", so to speak. I appreciate all of your input.

[Autoholic]

What about using high 100's or even 1 or 2000 grit to polish the exhaust ports? Sure it will take a while but you won't be taking off a lot of material to polish a port smooth, you're more or less buffing it out at this point.

[Joe-JDC]

Ideally you do an initial cut with a carbide burr to get the shape close to what you desire, and then transition to a coarse cartridge roll, to refine the shape, and then move to fine cartridge roll to blend, smooth, and contour to close to the optimum size and shape.  Then you can polish to the final port shape or size with anything from 180-240 grit cartridge rolls.  If you want a mirror finish, you can achieve that with anything above 120 grit with a small dab of oil/grease/wd on your port walls.  It takes patience, and a light hand to polish without removing metal in the wrong place at this stage.  That is why I use a flapper roll for finishing out the ports, and I can get the finish as smooth as anything by simply adding water, or some type of oil/lubricant to the final polish.  That is a waste of time in the long run, though, for it does absolutely nothing for horsepower gains, just looks good until the first start-up and then the exhaust gasses start building up, especially if there is a poor shape in the port that causes a turbulence.  I often sandblast intake manifolds to restore the rough finish after I have the flow balanced and the flow I desire.  Then I pressure  wash the complete intake and store in a storage bag until ready for use, or shipping.   Joe-JDC

[Autoholic]

Thanks for all that info. Sounds like properly porting a set of heads and an intake is a black art.

[machoneman]

"...and someone at a speed shop cartridge rolled the ports, and now the heads flow 284/168cfm at .750" lift.  Whoever modified the CNC program killed at least 40 or more cfm on each port.  Be careful when you listen to every new idea that comes along.  Not all of them are beneficial in the long run, and many actually kill the performance of an engine.  Joe-JDC

Interesting too Joe and I had wondered about that. My local shop (D.S.S. Racing) states that yes, one can smooth the CNC ridges but one must be really careful since as you stated, an over-aggressive rookie can mess up a fine port job. Mies Van Der Rohe: less is more!

When CNC'ed ports first came out, some had mighty high ridges. Today, it seems that with more passes or fine tuning of the CNC progams, some ridges are visible but when touched with a fingernail, hardly any ridge is detectable. I'd tread lightly on those.   

[babybolt]

"1 or 2 horsepower" - you would get more from a slight touch up on the valve seats and valve faces.

I really doubt there is laminar flow anywhere in the intake track, combustion chamber or exhaust system of a running engine.  Its very difficult to obtain laminar flow on a freshly cleaned sailplane wing flying through clean still air.

[427Fastback]

Question for JDC..what does all your airflow testing tell you about the CNC marks on the intake ports ..Are they as disruptive as one would think ??