Why an engine makes more power off a burr finish

[user-9274568]

Has anyone compared localized velocities, velocity gradients, to the same port, smooth vs burr?

You might be surprise. Since we are velocity managers, manipulation is a BIG part of cylinder head porting.

[GARY C]

I'd like to know what laws of physics it's defying?????

Comparing a F1 engine to a Cup engine to a Drag engine is absolutely lack of knowledge. Different animals requiring different demands.

Any fluid dynamics text book will indicate that surface roughness increases the boundary layer thickness, reducing cross sectional flow area.

ALL engines obey the laws of physics at ALL times. While there are differences in purpose and operation, they still behave the same when we are able to examine them very closely. Of course there may be differences in specific hardware, just as there are differences in opinion among experts.

A highly developed drag engine is an impressive accomplishment just as is a Formula One engine. But the air molecule does not know which engine is is taking it for a ride and doesn't care.

So why, specifically, does a burr finish improve performance?

I think you have answered your own questions.
Most race engines and the engines that show improvement from a burr (it's cold) finish are reworked versions of production engines that suffer from area change and tight turns in the runners.
An F1 engine is purpose built from scratch so this is addressed at the design stage.
My guess would be on other engines the better the runner is developed the less likely to see an improvement.

[John Wallace]

Larry Meaux has done many high horsepower engines and uses the rough burr finishes on about everything.

Don't know if he has done any F1 stuff, though.

He has many dyno tests where the burr finish has increased HP.
Both before polishing and tested after burr to polished.
(to get the naysayers who say the port has increased from burr finish)

I myself go by what actually works and not what some think should work.
(not a lawyer so don't know the law)

[Ron E]

Hero worship?...I see it more as respect . Respect that is derived from tangible results on the track. The sort that leaves no doubt of the strength of his methods. I don't have many heroes. Real results transcend chit-chat.

[Orr89rocz]

I'd like to know what laws of physics it's defying?????

Comparing a F1 engine to a Cup engine to a Drag engine is absolutely lack of knowledge. Different animals requiring different demands.

Any fluid dynamics text book will indicate that surface roughness increases the boundary layer thickness, reducing cross sectional flow area.

ALL engines obey the laws of physics at ALL times. While there are differences in purpose and operation, they still behave the same when we are able to examine them very closely. Of course there may be differences in specific hardware, just as there are differences in opinion among experts.

A highly developed drag engine is an impressive accomplishment just as is a Formula One engine. But the air molecule does not know which engine is is taking it for a ride and doesn't care.

So why, specifically, does a burr finish improve performance?

I think you have answered your own questions.
Most race engines and the engines that show improvement from a burr (it's cold) finish are reworked versions of production engines that suffer from area change and tight turns in the runners.
An F1 engine is purpose built from scratch so this is addressed at the design stage.
My guess would be on other engines the better the runner is developed the less likely to see an improvement.

I think this makes most sense. F1 tech is extremely developed. A 23 deg sbc is not in the same league. It makes sense that less developed ports that have less of a straight shot to the cylinder, maybe the more likely it is to see an effect of a burr finish

[David Vizard]

This summer in the heat I went to the track with a fully smooth ported manifold I had done. I took my tools and burr marked it out in his trailer after we got a base line. Put it back on the engine, AT THE TRACK, same day, and made more runs.

ALL of my manifolds are burr marked because it works.

Chad,
I have been in the habit of finishing manifolds and intake ports with a 60 grit roll. Why because Mr. Dyno tells me I should and I am very reluctant to argue.
I have seen your cuttered finishes and have tried replicating them but what I produce is way uglier than I care to show. Is there a trick I should know or, at 73, am I just too far past having a steady enough hand?

thanks
DV

[David Redszus]

Let me repeat my earlier question?

Specifically, why does a burr finish improve performance?

As I see it there are two general possibilities: increased air mass flow and improved fuel preparation.
The first should be visible as a change in a/f using a lambda sensor.
The second should be visible as a change in hydrocarbons in the exhaust gas.

Another method to consider is the use of in-cylinder pressure measurement such as the TFX system.

Improvements in performance are not the result of magic pixie dust; they are the result of some physical property that has changed. If we don't know what actually changed, we are shooting in the dark without a night scope.

We know that surface roughness combined with Reynolds number determines boundary layer flow resistance. At low speed laminar flow regimes, surface roughness doesn't matter. That is why we can't measure burr finish effects using a flow bench. At high velocity, turbulent flow conditions surface roughness becomes a much more significant factor; but it will always reduce air mass flow.

We also know that fuel films deposited on induction tube walls will reduce combustion performance. A burr finish might produce more turbulence, particularly in tube bend areas, that serves to reduce wall wetting.
A burr finish used with an external fuel source,(i.e.carb, entry point injector) might benefit performance. But it might not have any benefit when used with port injection, direct injection or diesel applications.

And then there are thermal considerations. What effect does a burr finish, on an induction tube or chamber surface, have on heat transfer? Could the same results be accomplished with a change of materials using stainless instead of aluminum or ABS?

[user-9274568]

This summer in the heat I went to the track with a fully smooth ported manifold I had done. I took my tools and burr marked it out in his trailer after we got a base line. Put it back on the engine, AT THE TRACK, same day, and made more runs.

ALL of my manifolds are burr marked because it works.

Chad,
I have been in the habit of finishing manifolds and intake ports with a 60 grit roll. Why because Mr. Dyno tells me I should and I am very reluctant to argue.
I have seen your cuttered finishes and have tried replicating them but what I produce is way uglier than I care to show. Is there a trick I should know or, at 73, am I just too far past having a steady enough hand?

thanks
DV

David it's just a double cut burr. The looks have changed over the years, I've tried many different methods. It comes down to speed and pressure.

Here is this years Engine Masters heads. Why did I do it? Give you a hint. 290cc port on a pump gas 406 from 3500-7500. Made 730hp/630tq w/240ish cam in the 20 pulls at home. And a manifold I shipped yesterday.

[user-9274568]

Let me repeat my earlier question?

Specifically, why does a burr finish improve performance?

As I see it there are two general possibilities: increased air mass flow and improved fuel preparation.
The first should be visible as a change in a/f using a lambda sensor.
The second should be visible as a change in hydrocarbons in the exhaust gas.

Another method to consider is the use of in-cylinder pressure measurement such as the TFX system.

Improvements in performance are not the result of magic pixie dust; they are the result of some physical property that has changed. If we don't know what actually changed, we are shooting in the dark without a night scope.

We know that surface roughness combined with Reynolds number determines boundary layer flow resistance. At low speed laminar flow regimes, surface roughness doesn't matter. That is why we can't measure burr finish effects using a flow bench. At high velocity, turbulent flow conditions surface roughness becomes a much more significant factor; but it will always reduce air mass flow.

We also know that fuel films deposited on induction tube walls will reduce combustion performance. A burr finish might produce more turbulence, particularly in tube bend areas, that serves to reduce wall wetting.
A burr finish used with an external fuel source,(i.e.carb, entry point injector) might benefit performance. But it might not have any benefit when used with port injection, direct injection or diesel applications.

And then there are thermal considerations. What effect does a burr finish, on an induction tube or chamber surface, have on heat transfer? Could the same results be accomplished with a change of materials using stainless instead of aluminum or ABS?

All this has been talked about in this thread. L E T IT G O!

It's about MANIPULATION! Measure that!

[David Vizard]

Let me throw my ten cents worth in here despite the fact it may only be worth five.

About a three years ago when F1 was all about screaming atmo-motors an insider friend of mine sent me a shot taken from inside an F1 intake port. There right before my eyes was a dimpled pattern that appeared to exactly replicate a golf ball. However what amazed me most was the extremely even distribution of the dimples. It was as if someone wrote a program to space them out evenly disposed on the surface no mater what the underlining contour was. It struck me that either the team had more manpower than they let on to or someone had more spare time than me by a country mile.

I will do my best to locate said photo but no concrete promises here.

As for rough ports in a NA engine the positive results I have seen have be attributed to an improved mixture quality at the valve. If there were any gains in VE our instrumentation was not accurate enough to produce an indisputable answer. But here is the kicker. I have never seen a drop in output with a course finish intake manifold (I am talking of a finish produced by a new 60 grit emery) However I have in MOST cases seen a drop when the manifold gets a polished interior. Just how much the engine looses power mostly depends on the droplet size being received by the cylinder. If the fuel droplets are large as is often the case with carbs intended for heated intakes then the torque improvement can be significant. However in the case of a heated intake where the fuel in very much vaporized the difference in port finish is just about zero.

But we don't race engines with hot intakes and the typical carburated induction system does, in so many instances, like a rougher intake to reduce rivulet flow all the way to the cylinder.

Even with a wet flow test done properly (and most are not) it is quite horrifying to see just how poorly some systems flow an air fuel mix.

About 12 years ago I was consulting at Aston Martin's race arm on the development of the induction system and combustion chamber of the old in-line 6's (as per the Bond 007 AM) We had clear plastic intake for one of the three DCOE Weber to mount on. I cannot remember the exact before numbers but the motor went up from some 385 (give or take a two or three) to 408 (and that number i do remember). All this came about with close to zero increase in air flow. However (and as would be expected) both the BSFC and the BSAC got proportionally better.

The main improvements came from a really course surface finish on the lower half of the intake and a total redesign of the Webber's auxiliary venturi's (boosters in US speak).


While I do not claim to have all the answers by a long shot my experience to date tells me that without the aid of a dyno and back to back tests the average enthusiast is best served by a course intake manifold finish not a shiny one. Going this route also saves time and effort.

By the way Chad my cutter finishes are so much uglier than yours! If there was a prize for such you would loose big time!!!

DV

[Ken_Parkman]

Flowbench testing is always turbulent, never laminar, except at low lift and delta P. This of course is different topic from flow separation, which many refer to as turbulence. For understanding flow it's an important distinction.

A good theory to look at might be flow separation in context of level of turbulence near the surface due to finish. Might explain why a port that is less likely to flow separate (say F1) may have different results than others. Vortex generation to prevent flow separation is a pretty worthwhile topic to study.

if the results don't match the theory, it's the theory that needs work.

[Biteme]

I'm wondering how a back to back test between a burr finish and 40 grit would go.
Has anyone done any testing between those 2 finishes?

[David Vizard]

I'm wondering how a back to back test between a burr finish and 40 grit would go.
Has anyone done any testing between those 2 finishes?

I certainly have not but I think I will put this on my list to try. For what it's worth the cast finish on most manifold floors is a good place to be. If the floor is given a polish the power drops. If you modify manifolds for a living and have a typical customer they will perceive the unfinished floor as you having done a poor job. It could well be that a 40 grit saves the day.
DV

[jacksoni]

If you haven't read (recently) Larry Meaux's interview article here: http://hotrodenginetech.com/pipemax-cre ... d-porting/ It is probably worth another look. Was comparing a wobbly carbide to 60grit surface with A-B-A testing in at least one case. Doesn't solve the "why" question but interesting none the less.

[BOOT]

For a street carb I've always thought the roughest finish should be along the floor of the runner or anywhere the fuel will drop out, it's about surface area and heat. Dry vs wet.

I jut skimmed some but I saw golf ball mentioned, plus vortex generators and the only way a dimpled surface helps is if the trailing edge is poor, otherwise smooth flows better. One factor I never hear discussed when people talk vortexes n such is the effect of the expanding fuel off the surface on flow. What about the flow around steams of injected fuel or pooling fuel? Most have seen that vid of the guy sticking his finger into the plastic intake, well I also saw streams/ripples/waves/peaks of fuel being made on the walls, so the surface texture is fluid(changing all the time). I would imagine with high amounts of fuel it'll smooth any rough surface, layer it. The needs of a runner changes from low to high flow.

https://www.youtube.com/watch?v=7Iq1B-2paCs