Why an engine makes more power off a burr finish

[1980RS]

Last year I ran my peanut port engine that I put the burr finish in the intake ports, the chambers and all through the intake manifold. I don't know if it made the car any faster but I do know one thing, it had the cleanest intake ports and head runners I had seen in a long time.

[David Redszus]

Over 960 posts from smart people and we still don't know WHY a burr finish works?

[digger]

A bump for 2021. Darin Morgan gave a webinar on 01/20/2021 and durning that discussion he concurred with what Nick, Chad and Larry have been saying...burr the intake and intake port...and he said he didn’t think you can make it too rough.

Surely, Darin isn’t a liar or a stooge. He certainly wouldn’t waste his time propagating an error.

Of course, you all should watch the webinar for yourselves and hear what he says.

Certainly, if I have said something that Darin did not say, or if I have inferred something which he did not infer, I apologize in advance to all of you and more importantly for making it appear Darin said something he did not say.

I’ve watched both his PERA webinars, and IMO he is very clear on intake runner and port finish.

i watched it and to paraphrase he said with fuel injection only downstream from where fuel is introduced and a couple inches or so up should be rough the rest can be non smooth.

Based on this the answer to the following question.

Over 960 posts from smart people and we still don't know WHY a burr finish works?

it is to do with fuel and the amount of heat release due to changing additional amount of fuel from liquid to vapour so it burns more efficiently. I guess this stands to reason certain fuel are likely to benefit more.

if it was somehow changing airflow then it would show up on the flow meters on the dyno, has anyone seen this ?

it is also plausible that certain port layouts are on the edge for "stability" for lack of a better term that the texture is enough to help but this would be dependant on the port so may not be applicable for a modern downdraft 4V which has lower velocity gradients .

its not that hard to detect change in air flow, fuel flow and/or BSFC on a dyno the answers will be all there IMO

[Erland Cox]

Over 960 posts from smart people and we still don't know WHY a burr finish works?

Because it activates the boundary layer among other things.

Erland

[SchmidtMotorWorks]

if it was somehow changing airflow then it would show up on the flow meters on the dyno, has anyone seen this ?

it is also plausible that certain port layouts are on the edge for "stability" for lack of a better term that the texture is enough to help but this would be dependant on the port so may not be applicable for a modern downdraft 4V which has lower velocity gradients .

its not that hard to detect change in air flow, fuel flow and/or BSFC on a dyno the answers will be all there IMO

If the fuel is better suspended and that raised cylinder pressure/more exhaust blow-down, there would likely be more airflow.

[williamsmotowerx]

if it was somehow changing airflow then it would show up on the flow meters on the dyno, has anyone seen this ?

it is also plausible that certain port layouts are on the edge for "stability" for lack of a better term that the texture is enough to help but this would be dependant on the port so may not be applicable for a modern downdraft 4V which has lower velocity gradients .

its not that hard to detect change in air flow, fuel flow and/or BSFC on a dyno the answers will be all there IMO

If the fuel is better suspended and that raised cylinder pressure/more exhaust blow-down, there would likely be more airflow.

I've found burr finish is down 2ish CFM on the flowbench than a cartridge finish. But I have been using a burr finish before it was in vogue.

[David Redszus]

Over 960 posts from smart people and we still don't know WHY a burr finish works?

Because it activates the boundary layer among other things.

Erland

Erland,
What do you mean by the term "activates the boundary layer"?
David

[David Redszus]

Over 960 posts from smart people and we still don't know WHY a burr finish works?

it is to do with fuel and the amount of heat release due to changing additional amount of fuel from liquid to vapor so it burns more efficiently. I guess this stands to reason certain fuel are likely to benefit more.

I also watched Darin's video. My sense is that he referred to dry air, as with a flow bench, not air flow containing
wet fuel. Wet air flow (air containing fuel droplets) will flow more air than a fully evaporated mixture due to
the fuel vapor displacement of air. The phase change (fuel evaporation) will cool and increase air density
but not enough to overcome fuel vapor displacement of air.

Darin was speaking only of dry air flow, or so I assumed. Please correct me if I am wrong.

if it was somehow changing airflow then it would show up on the flow meters on the dyno, has anyone seen this ?

Flow meters and dynos are crude methods of air flow measurement. Flow bench data is based on
steady state flow while engine air flow is both pulsed and compressible. Big difference.

it is also plausible that certain port layouts are on the edge for "stability" for lack of a better term that the texture is enough to help but this would be dependant on the port so may not be applicable for a modern downdraft 4V which has lower velocity gradients .

If burr effects are port specific, then air viscosity, air density, and piston speed would be contributing factors to
be considered. Since piston speed is variable within the induction stroke, mass flow rate would also
be variable at each crank angle.

Air mass flow is determined by: area, flow length, pressure ratio, air density, and viscosity.
But the above factors are for incompressible flow. Engines see compressible, turbulent flow.

If surface roughness contributes to mass flow, then we should see a change in one or more of
the above listed variables. We do not know local air density, viscosity, pressure; we know area
and flow length. But we have ignored an important factor-surface friction. How can increased
friction improve air mass flow?

As Erland has indicated, the answer might lie in changes to the boundary layer due to
turbulence at the wall surfaces. But these are micro vortexes to consider and measure.

Somewhere within the vast library of SAE technical white papers, this issue must have been
addressed before. Perhaps well before our time.

[hoffman900]

The wet fuel debate might be clarified by running a carburetted burr finish inlet manifold and head combination, then swapping on a similarly burr finished efi manifold with injectors and tuneable ecu - - has anyone tried this?

I don’t think there is any debate. Look at the ports of a F1 engine and other factory programs. Honda has a white paper on looking at fuel adherence in the port using a fuel with a staining component, from their F1 program over a decade ago.

Carbureted engines have problems with fuel puddling that a properly set up injection system doesn’t have. Just takes a different approach.

I haven't seen the Honda data. What's their view on this? Is it a direct smooth to rough comparison?

It was due to port velocity issues and the fuel falling out od suspension.

Granted they are running fuel pressures and injections that atomize much better than you’re going to get off the shelf.

[4vpc]

The comparison to F1 ports must be examined very carefully, any I've seen are quite smooth so you have to ask why.
It could be down to port or engine speed, lack of sharp turn (large SSR). Although who would let a highly developed head, bulging with expensive and hard won secrets into the public domain for everyone to see? You wouldn't of course. If it had rough ports and they were working you'd smooth them out before selling on to Joe Public.

The other thing is this, if smooth ports worked then that is what you would be seeing on modern cars, yet you don't.

[GARY C]

Over 960 posts from smart people and we still don't know WHY a burr finish works?

Because it activates the boundary layer among other things.

Erland

I think the A B A tests done show that the boundary layer fixes an already to big induction system, there for making the burr finish look like the power improvement.

I don't recall ever seeing a test where a burr finish increased power significantly on a small or properly sized runner application.

[GT50]

One thing that makes sense to me and Larry M has mentioned, is this simple test: If you put fuel on top of sand paper and blow with air it will eveporote if you do this test on top of a glass it will not eveporote and it is just pushed away. In my point of view the burr finish is more related to fuel eveporation than airflow, also it works better on engines that have carburetors because on these there is always wet fuel.

[GT50]

I don't recall ever seeing a test where a burr finish increased power significantly on a small or properly sized runner application.
[/quote]

If it is on a carbureted engine there always a benefit even if it is BSFC.

[SpeierRacingHeads]

I had customer with a 565 and a blow thru carb and pro charger. The inlet charge of the pro charger totally was making the manifold wall stained with fuel, it was ugly. The builder asked me what I though. Told him I'd fix it. Burred it up, made it really rough in that area.

Went from 6.32ish to 6.teens. He won many races and Divison.

Call Richard at Kroyer Racing Engines and ask what the results were he backed to backed it on the dyno.

[SpeierRacingHeads]

Remember, at the wall the air velocity is zero or near zero. The viscosity of the air is holding onto the wall so, the faster the air gets, the thinner the boundary layer gets. Regardless of surface texture.

So it's all about wet flow.