HarleyTechTalk

The "effective" cross section is smaller?

Quote from: 1FSTRK on May 01, 2017, 04:01:02 PM

Quote from: TorQuePimp on May 01, 2017, 03:53:47 PM

Quote from: 1FSTRK on May 01, 2017, 06:54:28 AM

Quote from: joelp34252 on May 01, 2017, 06:39:03 AM
Are not the dimples increasing the boundary layer and by doing this increasing the port velocity?

I guess the overall surface of the port increases but because the flowing air does not travel down into and back out of each dimple, it skips across them the effective surface is reduced.
Or so I have read.

I have a program that I have ran over 200 times...using the same valves and seat cutter......simple generic port that just works.

doing nothing but adding dimples the CFM gains are maybe at most 1-4 cfm at any given lift point at some lifts nothing you might lose a CFM here or there.....airspeed usually picks up 11-15 fps.

I am trying to understand here and respect you taking the time to explain but how can you pick up FPS at a valve lift that has the same CFM or less CFM?

  I have two rear heads at my shop....same program.....same seat profiles....one dimpled one not

  the test results are what they are....dispute them if you feel the need

I have as of yet to run dimpled heads on a customers bike ill probably do a set for my own in time....its not like the technology is new or going away any time soon.

SO for all the input from those who talk AND WALK, The dimpling of the ports in a TC HD and using a carb is worth the $$$$. Very little gain when a fuel injection motor is use. Myself in reading all the posts may take the results as a more bottom end trq is drawn due to increase in port speed. Would the combination of the dimples and the correct port/TB length/AC length be a winner ? 

The dimple finish is definitely NOT going to hurt and it may do some good.
It needs to be done as part of a CNC program.

I'd say go for it. It sure looks trick!

Quote from: MCE on May 02, 2017, 05:33:02 AM
The dimple finish is definitely NOT going to hurt and it may do some good.
It needs to be done as part of a CNC program.

I'd say go for it. It sure looks trick!

Wonder  HOW MUCH $$$$$$$$$ "LOOKING TRICK" costs? Is it possible to dimple a set that has been cncd already? 
Gain to $$$$ to trq/hp is the question.

Years ago we tried this on an IHRA pro mod. The results were not conclusive. It didn't make any more power. Others it helped. But these were the best heads one could buy at the time. I think it depends on the port. The dimples band-aid a port that is not great??

I really don't know

Quote from: K4FXD on May 02, 2017, 08:27:18 AM
Years ago we tried this on an IHRA pro mod. The results were not conclusive. It didn't make any more power. Others it helped. But these were the best heads one could buy at the time. I think it depends on the port. The dimples band-aid a port that is not great??

I really don't know

It would have to be done while they were being cnc'ed.

Personally, I think it's a gimmick, but I don't know that for certain.

I'll have a better informed opinion on it later this year.

I can dimple any of the programs that I run thru the CNC
doing a set by hand would not be easy at all
doing a set that has previously been run would require the port to be digitized and ran.....both heads

not cheap

I can't quit thinking of that MASH episode when Col. Blake said " and I have dimples on my butt" 
Sorry, I couldn't help myself... That's funny "Potty mouth"!

Quote from: TorQuePimp on May 01, 2017, 06:41:45 PM

Quote from: 1FSTRK on May 01, 2017, 04:01:02 PM

Quote from: TorQuePimp on May 01, 2017, 03:53:47 PM

Quote from: 1FSTRK on May 01, 2017, 06:54:28 AM

Quote from: joelp34252 on May 01, 2017, 06:39:03 AM
Are not the dimples increasing the boundary layer and by doing this increasing the port velocity?

I guess the overall surface of the port increases but because the flowing air does not travel down into and back out of each dimple, it skips across them the effective surface is reduced.
Or so I have read.

I have a program that I have ran over 200 times...using the same valves and seat cutter......simple generic port that just works.

doing nothing but adding dimples the CFM gains are maybe at most 1-4 cfm at any given lift point at some lifts nothing you might lose a CFM here or there.....airspeed usually picks up 11-15 fps.

I am trying to understand here and respect you taking the time to explain but how can you pick up FPS at a valve lift that has the same CFM or less CFM?

  I have two rear heads at my shop....same program.....same seat profiles....one dimpled one not

  the test results are what they are....dispute them if you feel the need

I have as of yet to run dimpled heads on a customers bike ill probably do a set for my own in time....its not like the technology is new or going away any time soon.

I am not trying to dispute it, my intention was to understand it. I was under the impression that there was a formula to calculate port speed from CFM and cross sectional area as well as one to calculate CFM from port speed and cross sectional area. That would make them directly relevant to each other so I could not understand how one could go down when the other went up in the same port. 

It was brought to my attention that you may have been referring to pitot tube readings in a particular area of the port and if this is where the port speed increase is coming in then it would seem another part of the port must loose speed for the CFM to stay the same, A more balanced port and maybe better for tq but still running out of air at the same CFM so the HP would remain the same.

I will drop it if you want, not looking to challenge or stir, just like to learn when and where possible.

I think the theory is,

The dimples cause the boundary layer to be larger, this causes the effective port area to be smaller. So the faster air speed keeps the same CFM delivered to the cylinder.

Now that you've thrown that out, how about an increase in the outside and a decrease on the inside turn. Would the quicker outside turn air speed help build the low pressure area on the short side and pull the air down to that side of the valve and cylinder?

This is an interesting tread and it is not the first that I have read on this subject. I am a boat racer who had raced outboard runabouts. These are small boats with flat bottoms that weigh 475 lbs including boat, motor and driver in the class that I ran. We ran in the 60 mile per hour range with a 33 hp motor. Of course in a racing environment a half a mile an hour advantage is huge. So guys and gals are looking for any advantage.

Dimpling was tried by a few in hopes of gaining that 1/2 a mph advantage. The results were not favoritable, in fact a few who tried it saw a slight loss in speed but most saw no difference.

Common practice with this type of race boat is to get the bottom as flat and straight as possible. We use epoxy resin do do the final finish and get it as smooth as possible with no dimples of any sort. But this is not the ultimate either as it creates a kind of stiction situation with the water. So the final step is the sand the bottom with a 320 grit sandpaper on a straight edge. This creates a surface that is very similar to a honed cyclinder but with no pattern. This surface has been determined to be the fastest through many years of trial and error by many boat racers. 

For what it is worth Donny Peterson wrote an article in American Iron recently on porting. His feeling were that an intake shouldn't be polished but have a rough finish for maximum flow. He also said it was ok to polish exhaust ports, it didn't help with flow but might help with helping against build up of deposits. I am only saying what he said to the best of what I remember.

I added this to the discussion because I thought it was along the same lines but it is probably irrevalent but may be interesting none the less. 
kk

Quote from: 1FSTRK on May 02, 2017, 07:00:30 PM

Quote from: TorQuePimp on May 01, 2017, 06:41:45 PM

Quote from: 1FSTRK on May 01, 2017, 04:01:02 PM

Quote from: TorQuePimp on May 01, 2017, 03:53:47 PM

Quote from: 1FSTRK on May 01, 2017, 06:54:28 AM

Quote from: joelp34252 on May 01, 2017, 06:39:03 AM
Are not the dimples increasing the boundary layer and by doing this increasing the port velocity?

I guess the overall surface of the port increases but because the flowing air does not travel down into and back out of each dimple, it skips across them the effective surface is reduced.
Or so I have read.

I have a program that I have ran over 200 times...using the same valves and seat cutter......simple generic port that just works.

doing nothing but adding dimples the CFM gains are maybe at most 1-4 cfm at any given lift point at some lifts nothing you might lose a CFM here or there.....airspeed usually picks up 11-15 fps.

I am trying to understand here and respect you taking the time to explain but how can you pick up FPS at a valve lift that has the same CFM or less CFM?

  I have two rear heads at my shop....same program.....same seat profiles....one dimpled one not

  the test results are what they are....dispute them if you feel the need

I have as of yet to run dimpled heads on a customers bike ill probably do a set for my own in time....its not like the technology is new or going away any time soon.

I am not trying to dispute it, my intention was to understand it. I was under the impression that there was a formula to calculate port speed from CFM and cross sectional area as well as one to calculate CFM from port speed and cross sectional area. That would make them directly relevant to each other so I could not understand how one could go down when the other went up in the same port. 

It was brought to my attention that you may have been referring to pitot tube readings in a particular area of the port and if this is where the port speed increase is coming in then it would seem another part of the port must loose speed for the CFM to stay the same, A more balanced port and maybe better for tq but still running out of air at the same CFM so the HP would remain the same.

I will drop it if you want, not looking to challenge or stir, just like to learn when and where possible.

Airspeed....yes

pitot tube yes I also have a swirl meter in the bench....

an increase in airspeed does not always mean an increase in CFM

Dropping it not needed I just have not tested a set that I am happy with ,making someone a guinea pig

Quote from: TorQuePimp on May 03, 2017, 12:41:13 AM

Airspeed....yes

pitot tube yes I also have a swirl meter in the bench....

an increase in airspeed does not always mean an increase in CFM

Dropping it not needed I just have not tested a set that I am happy with ,making someone a guinea pig

Could you then help me with the formula to calculate this?
Everything I find states that if pressure, temp, and humidity are constant then speed equals CFM divide by CSA. This is what I was taught when I went to school and it is what I have always used. I wonder if the dimpling has a pressure effect in the area your speed is being sampled causing the difference in the two readings?

Quote from: Moparnut72 on May 02, 2017, 09:27:38 PM
This is an interesting tread and it is not the first that I have read on this subject. I am a boat racer who had raced outboard runabouts. These are small boats with flat bottoms that weigh 475 lbs including boat, motor and driver in the class that I ran. We ran in the 60 mile per hour range with a 33 hp motor. Of course in a racing environment a half a mile an hour advantage is huge. So guys and gals are looking for any advantage.

Dimpling was tried by a few in hopes of gaining that 1/2 a mph advantage. The results were not favoritable, in fact a few who tried it saw a slight loss in speed but most saw no difference.

Common practice with this type of race boat is to get the bottom as flat and straight as possible. We use epoxy resin do do the final finish and get it as smooth as possible with no dimples of any sort. But this is not the ultimate either as it creates a kind of stiction situation with the water. So the final step is the sand the bottom with a 320 grit sandpaper on a straight edge. This creates a surface that is very similar to a honed cyclinder but with no pattern. This surface has been determined to be the fastest through many years of trial and error by many boat racers. 

For what it is worth Donny Peterson wrote an article in American Iron recently on porting. His feeling were that an intake shouldn't be polished but have a rough finish for maximum flow. He also said it was ok to polish exhaust ports, it didn't help with flow but might help with helping against build up of deposits. I am only saying what he said to the best of what I remember.

I added this to the discussion because I thought it was along the same lines but it is probably irrevalent but may be interesting none the less. 
kk

didn't see or read the article,but if this is what Peterson said,its hardly cutting edge news.

Mythbusters did a gas mileage test on a car, the dimpled car got better.

I wonder if dimpling the bottom of the boat would help more than the rough surface, or along with it?

Quote from: K4FXD on May 03, 2017, 04:29:28 AM
Mythbusters did a gas mileage test on a car, the dimpled car got better.

I wonder if dimpling the bottom of the boat would help more than the rough surface, or along with it?

If you read up on golf ball technology, you can discover some interesting facts on dimpling and increased air speed. I realize this is a round sphere traveling thru air but interesting just the same the increases in speed of travel and also straightness of travel. Not sure it even applies in a port application or not.

At school, in a V8 with whatever intake you can put on a v8, CNC tooling marks are always left in the port even when they don't need to be. The engine dyno consistently shows 5-8 more with the tooling marks. I'm not allowed to put the twin on the dyno even if I build the proper fixtures, so I can't speak on that.

Tooling marks aren't sexy though, so there's that.

Not apples to apples, but maybe apples to pears?

I use someone else for a guinea pig from time to time (with their permission).
If I'm pretty confident with something, and all I need is a test subject, it's not hard
to find volunteers. 

Quote from: build it on May 03, 2017, 08:30:27 AM
At school, in a V8 with whatever intake you can put on a v8, CNC tooling marks are always left in the port even when they don't need to be. The engine dyno consistently shows 5-8 more with the tooling marks. I'm not allowed to put the twin on the dyno even if I build the proper fixtures, so I can't speak on that.

Tooling marks aren't sexy though, so there's that.

Not apples to apples, but maybe apples to pears?

So if I understand :just cnc job on a oem head SHOULD produce a better graph/seat of the pants ride as long as the tooling marks are left and the intake TB is left rough. bigger everything in the same heads but cnc will be the ticket? Forget the dimples? 

Bigger is not necessarily better, (it's actually better to error on the small side) especially for a street driven vehicle where you're wanting a nice flat TQ curve. Less is more.  A small port that's efficient will win out every time.

A CNC port is only as good as the port it was mapped off of. Just b/c a machine does it, doesn't make it "better".
I've seen (tested) CNC ported heads here that were just average. fwtw.

Quote from: Templer on May 03, 2017, 06:54:43 PM

Quote from: build it on May 03, 2017, 08:30:27 AM
At school, in a V8 with whatever intake you can put on a v8, CNC tooling marks are always left in the port even when they don't need to be. The engine dyno consistently shows 5-8 more with the tooling marks. I'm not allowed to put the twin on the dyno even if I build the proper fixtures, so I can't speak on that.

Tooling marks aren't sexy though, so there's that.

Not apples to apples, but maybe apples to pears?

So if I understand :just cnc job on a oem head SHOULD produce a better graph/seat of the pants ride as long as the tooling marks are left and the intake TB is left rough. bigger everything in the same heads but cnc will be the ticket? Forget the dimples? 

The schools CNCed ports are developed ports, not OEM. What I'm saying is, if you develop a good port and have a set of heads CNCed, leave the tooling marks alone, the tooled finish is good for 5-8 in a v8. Not sure about a twin, and I'm not going to guess or give an opinion that can't be proved out in a timely manner.

I don't know if this (tool paths) correlates with dimples or not, only that the school as a whole doesn't do any purposeful dimpling in any application, v8 or otherwise. If they wanted to, they could put any finish you could dream of in a set of heads, yet they don't do anything.

I have yet to see a CNCed intake so I can't speak on that, only guess and I won't bore you with that.

Good luck Templer.'

Quote from: build it on May 03, 2017, 11:23:41 PM

Quote from: Templer on May 03, 2017, 06:54:43 PM

Quote from: build it on May 03, 2017, 08:30:27 AM
At school, in a V8 with whatever intake you can put on a v8, CNC tooling marks are always left in the port even when they don't need to be. The engine dyno consistently shows 5-8 more with the tooling marks. I'm not allowed to put the twin on the dyno even if I build the proper fixtures, so I can't speak on that.

Tooling marks aren't sexy though, so there's that.

Not apples to apples, but maybe apples to pears?

So if I understand :just cnc job on a oem head SHOULD produce a better graph/seat of the pants ride as long as the tooling marks are left and the intake TB is left rough. bigger everything in the same heads but cnc will be the ticket? Forget the dimples? 

The schools CNCed ports are developed ports, not OEM. What I'm saying is, if you develop a good port and have a set of heads CNCed, leave the tooling marks alone, the tooled finish is good for 5-8 in a v8. Not sure about a twin, and I'm not going to guess or give an opinion that can't be proved out in a timely manner.

I don't know if this (tool paths) correlates with dimples or not, only that the school as a whole doesn't do any purposeful dimpling in any application, v8 or otherwise. If they wanted to, they could put any finish you could dream of in a set of heads, yet they don't do anything.

I have yet to see a CNCed intake so I can't speak on that, only guess and I won't bore you with that.

Good luck Templer.'

So at the school you see between .625 and 1 hp per cylinder gain, what is the average engine displacement and what hp level are they?

One thing to remember is the school is run by people and people have personal likes and dislikes as well as habits so just because they do not test the dimples does not have a lot of meaning. If someone at the school believes in the untouched cnc finish as better then his teaching will be in a manor that supports that belief. The trouble with even back to back testing on single components is most things in an engine work in combinations. Like cams and compression, port shape and surface finish go hand in hand so the testing becomes more difficult. You see this with people that try to test coatings, and it also can depend on agenda. Are you testing to prove it helps, prove it hurts, or is the test designed to be unbiased and gather data so you can go where the data takes you.

Many well known head porters in the Harley world have had CNC ports for years now and many of them offer at extra charge a "premium CNC head" that is hand finished and flow bench tested after being CNC'd. They will tell you these head heads, in their testing, flow more and make more power on the engine and came into existence because the raw cnc'd heads did not perform as well as the hand made prototype they were copied from.

Every CNC head I've ever tested, responded favorably to some hand finishing/touch up. (Especially
in the high airspeed areas)