FE Power Forums
FE Power Forums => FE Technical Forum => Topic started by: fekbmax on August 12, 2015, 06:58:20 AM
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So, I have heard so many different opinions on this but I figure theres some of the very best Fe engine builders right here on this forum so I have to ask.
To smooth out the CNC marks in heads and manifolds or leave them as they are ?
I remember reading countless articles back in the day about dimpling runners and combustion chambers and its benefits and effect on fuel/air tumbling. I would think if it was any real benefit that it would be a more common practice these days but you don't see much about it. I'm wondering if that's why some head guys leave the CNC markings in the ports but smooth and polish the combustion chamber's.
Hoping this isn't to dumb of a question.. uggh.. :o
I'm just curious
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Drawing from my experience with fluid dynamics, not engines specifically, I would say you want everything as smooth as possible. The surface friction will effect how the air moves from the intake to the combustion chamber and then to the exhaust. The least amount of resistance, the better. I know OE's today will dimple the sides of the skirt with lots of tiny holes, to reduce friction as these tiny holes will trap a spec of oil. They also are using super smooth and very hard coatings as well to reduce friction. Tumbling would only be beneficial if it was caused by a ram air scoop of some design, where incoming air slows down and increases pressure, ~1 psi. A rough air passage won't increase pressure all that much and you would benefit more from a smooth surface allowing the air to quickly get to the engine, in a laminar flow or as much as possible.
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I always smooth them out. I got a set of heads once and flowed them with the marks still in them, and they missed the claimed flow target by 30 cfm. Took a 40 grit cartridge roll and smoothed them out, and they picked up 15 cfm (from 330 to 345). Still were a little short of claimed, but much improved. There is always some discussion about the benefits of leaving the marks, but I've never seen them on any competitive Stock Eliminator or Super Stock car. You'd think that in those very competitive classes, if there was an advantage to leaving the CNC marks they would do it...
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CNC marks are different than dimpling.
Golf balls are dimpled, for a reason, but one with a scored surface, something like a CNC mark, would be considered flawed. Airflow is disrupted by scoring, but properly sized dimples helps.
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Dimpling runners might have a benefit but that would require either some very elaborate CNC work that will take hours if not days or to cast them into the part. Either way, you have have to create the part in a CAD program and do a lot of CFD work to find the best design. Trying to find the best design by creating multiple prototypes would get stupid expensive in a hurry. The only area I could see taking a look at this would be F1 where every tiny advantage helps but their runner lengths are probably too small for any of this to matter. NASCAR could benefit but if you look at how much time you would spend on this compared to the gains (maybe 5 hp?), it isn't viable when compared to just smoothing out the runners.
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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
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Keith, did you get your heads from Kuntz? I have a set of his CNC'd heads also. Can you give me a call please? 2 five 4- 5 seven seven - five 4 six two. I have a couple questions. Thanks
Bruce Faulkner
SSG U.S. ARMY (RET)
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I'm certainly not a professional, but I'd have to agree with Jay and Jim, look at anything from Top Fuel, F1, Nascar, Pro Stock, Pro Mod, pretty much any class you want to. They're all ported very smooth and many of the chambers are polished to a near mirror finish. Dimples MAY help with a less than ideal head in CERTAIN spots, but that hardly applies to todays heads and most likely would hurt most old heads if not done perfectly with a lot of testing. If there was anything to gain, it would most certainly be done by at least one of those classes of racing, but every Pro class you see has very smooth runners.
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Keith, did you get your heads from Kuntz? I have a set of his CNC'd heads also. Can you give me a call please? 2 five 4- 5 seven seven - five 4 six two. I have a couple questions. Thanks
Bruce Faulkner
SSG U.S. ARMY (RET)
PM sent.
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You all need to try a dimpled intake some time. ;)
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Apparently, it is still being done: https://www.google.com/search?q=dimpled+intake+ports&rlz=1T4GGHP_enUS533US533&tbm=isch&tbo=u&source=univ&sa=X&ved=0CB4QsARqFQoTCNuLvfiepscCFYmODQodF8oANw&biw=1097&bih=494
Long ago in the 70's, I do know many BBC shops (sorry!) were doing 2 runners on each head. IIRC, this came about since due to the GM layout, 2 runners were 'slow' and the effort was an attempt to equalize as much as possible all 4 runners. More common was some dimpling in the combustion chamber on 1st gen. SBC's (good pic in the link). Had no idea in the intervening years that dimpling was still in vogue in certain applications since I had thought modern CNC porting and flow benches took care of many head imperfections. Guess I was wrong! ;D
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The dimples question is still not resolved in real life. I can tell you one of the manifolds in those pictures is a real let down. There was a huge torque loss, and the ports have a variation of 65cfm between the highest and lowest port flow. Will be doing some dyno testing soon on that principle. Will report the findings later this fall. Joe-JDC
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I'm gonna toss another golf ball into the mix with what I found...
(http://www.williamsmotowerx.net/images/valve2.jpg)
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I would love to hear from the major engine builders on this topic. Dimpling a smooth intake port or sanding it to a consistent rough surface. The below link is an interesting read.
http://mototuneusa.com/homework.htm
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I'm gonna toss another golf ball into the mix with what I found...
(http://www.williamsmotowerx.net/images/valve2.jpg)
Wow, a whole 1-2 extra horsepower that needs to be serviced in only 20 hrs at who knows what cost. :o I think I would stick with a traditional valve and look for an extra gain in ignition/cam timing, fuel, whatever, before I drop a small fortune in "disposable" valves. Interesting though. Does have that golf ball look. ;D A quick look on their site shows that their prices start at $99.95 per valve. Ouch, that could get expensive.
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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)
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1-2 horsepower ::)
I'd love to see a dyno that is that accurate, and repeatable.
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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. ..
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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.
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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.
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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?
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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.
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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
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Thanks very much Joe. I was hoping to hear it "straight from the horses mouth", so to speak. I appreciate all of your input. :)
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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.
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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
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Thanks for all that info. Sounds like properly porting a set of heads and an intake is a black art.
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"...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.
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"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.
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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 ??
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Unlike Jay's experience, I have cartridge rolled several CNC heads for folks over the years and the flow remained almost exactly the same--less than 3 cfm difference, which can be attributed to exact placement on the flow bench fixture. I have bought CNC heads for myself on occasion when I needed a pair for an engine build, and I didn't have time to port them myself. I decided to do a quick cartridge roll to increase the flow like everyone says, and I wasted several hours when it was all said and done. I don't think it hurts anything, and if anything it actually is beneficial. I frequently get requests from a couple of shops in town to flow a CNC'd head for one of their customers, and give them an actual flow sheet on that head. It gives me a chance to see all kinds of heads from Pro Stock to heads like the ones I flowed last week that were DEAD. I have flowed the new Motorsports D-3 CNC'd heads that went 410 cfm on the intake with a 2.135" valve, and those ports still had cnc marks in places where the original shop did not think it necessary to completely blend the ports smooth. If you buy a set of CNC'd heads, run them with confidence after you thoroughly clean any loose chips from around guides, or valve stems. Some shops run their CNC program without the guides installed, and then install the guides afterwards and do the valve job. Those usually are clean enough to run as is. Joe-JDC
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Great answer..Thank-you........I had heard before that they don't disrupt airflow.That being said I understand peoples need/thought to blend them out..
My thought patterns are based around street engines not EMC stuff or sub 10 second cars..