Rember the intake port texture debates?

[digger]

gold ball dimples increase skin drag but modify the boundary layer so flow stays attached farther around the ball and the pressure drag is reduced

[user-23911]

Exactly.


Golf ball dimples on plane's wings?
No.

[pamotorman]

once everyone goes the direct injection this will go into the dust bin of history.

[cv67]

Could be what about the issue with all the carboning up of the valves backside mfrs are running into with them? Seems a legit issue
Not hijacking just curious
Seems the fuel spray keeps things a little cleaner

[lefty o]

No it's not, that is for objects that can't be streamlined like a wing.

edit: for trailing air on non streamlined objects

exactly, kinda hard to streamline an intake runner.

[Warp Speed]

once everyone goes the direct injection this will go into the dust bin of history.

That won't be happening anytime soon, ESPECIALLY in the NA performance world!

[BradH]

once everyone goes the direct injection this will go into the dust bin of history.

Sounds like my first marriage...

[BradH]

On two of three heads I applied "riblets" to on the SSR, both picked up about 5 cfm above .500" lift when flow-tested up to .700". One was a mid 9-sec. bracket car and the other was a mid 10-sec. street/strip car.

The third head I tried them on showed no improvement... even seemed to be a small step backwards for some unknown reason...

After some additional research, I believe that applying riblets on the 3rd head eliminated the "tripping" effect the original stepped CNC'd finish provided that helped to keep the flow from separating as much over SSR.

So, from my LIMITED experience on the subject, I'll hypothesize that "riblets" are not a "one size fits all" treatment.

[Rick Finsta]

The fuel puddling is seen very easily in EFI systems with datalogging. In fact, the best systems use OEM-style "wall-wetting" transient algorithms to account for the dynamic conditions that affect addition to and subtraction from the "puddle."

Could you expound on this a bit? PM if necessary.

Sure thing. When you look at transients, you can see that the commanded fueling (pulse width, duty cycle) does not match the amount of fuel getting into the cylinders based on the AFR. This is easily seen in fast transients because it takes time for the "puddle" to equilibrate but it is happening all the time as engine conditions change. The very basic way to see this is turn off any acceleration enrichment and decceleration fuel cuts, and stab the throttle on vehicle with a well-tuned fueling table, and you will see the AFR go lean on throttle opening and rich on throttle closing. The fuel table is commanding the correct steady-state fueling for the conditions, so what gives? The answer is that there is a change in the amount of fuel puddling relative to what is going into the cylinder, including the fuel being injected and the fuel evaporating out of the puddle.

The obvious reasons the amount adding to the puddle and the amount evaporating from the puddle would change are things like fuel flow, temperature (wall and air), pressure, air velocity (engine speed) and turbulence, things like that. So the more advanced strategies don't only measure the amount of fuel addition necessary under acceleration (think of a carburetor pump shot) to maintain steady AFR and prevent any stumble, they keep track of the size of the puddle under different conditions, as well as how transient conditions will add to or remove from the puddle.

The megasquirt guys actually have really good writeups on this - Google search for "x-tau" and "enhanced acceleration enrichment." In all honesty, I generally find that the carb pump shot strategy along with decel fuel cuts work great. I'm not trying to make emissions on any of my cars!

I just thought it pertinent to mention that, to my knowledge, all modern port fuel injected vehicles use some type of strategy like this to take the fuel puddling into account to keep AFRs steady during transients. So if the OEMs are doing it on highly tuned systems, that indicates to me that there is no getting away from puddling!

[pamotorman]

once everyone goes the direct injection this will go into the dust bin of history.

Sounds like my first marriage...

which part applies to your first marriage the direct injection or dust bin of history ???

[digger]

there has been discussion that the additional boundary layer thickness of a rough texture actually makes the port cross section seem smaller so if you have a little too much cross section maybe it makes it acts smaller

[GARY C]

As I understand the port texture and riblet technique is not about flow but getting the air to follow the port and atomizing fuel.

That is my understanding as well, but would one not see the "air following the port" on a bench?

I have never dyno tested this and have not seen a flow gain but my bench is small and may not be capable of showing small changes. I have seen mixed opinions as to flow gains, several say the textured port may loose flow but will show a power gain and visa versa.

I always do the riblet technique on the ssr and pr pinch because I can feel the radius with my finger while doing it and know that it's constant and that makes my brain happy.

[GARY C]

On two of three heads I applied "riblets" to on the SSR, both picked up about 5 cfm above .500" lift when flow-tested up to .700". One was a mid 9-sec. bracket car and the other was a mid 10-sec. street/strip car.

The third head I tried them on showed no improvement... even seemed to be a small step backwards for some unknown reason...

After some additional research, I believe that applying riblets on the 3rd head eliminated the "tripping" effect the original stepped CNC'd finish provided that helped to keep the flow from separating as much over SSR.

So, from my LIMITED experience on the subject, I'll hypothesize that "riblets" are not a "one size fits all" treatment.

I was talking to DV a few years back about all the articles and local guys talking about gaining cfm on the early AFR CNC heads by sand paper rolling the short turn and he asked me how many of them dynoed the head before and after, as far as I know none of them did, his reply was that they very possibly hurt the power with out even knowing it.

Then again if you modify the head and loose power it's probably not easy to get it back.

[GARY C]

there has been discussion that the additional boundary layer thickness of a rough texture actually makes the port cross section seem smaller so if you have a little too much cross section maybe it makes it acts smaller

That was one thing I questioned on Larry Maux's test, he base lined the head then added texture and gained power then sand paper rolled the head to remove texture and lost power...so what if the original head was a little to big to start with?
It seems like you would need to start with 3 sets of heads, very close in size for the engine but a small, medium and large base line and then apply texture and see if they all show the same power gain.

[MadBill]

i think if the texturing resulted in a 'virtual cross section change', it should be evident in the shape of the power curve, i.e. biased slightly to the top or bottom of the range.