M117 Intake Refurbishment

[Niclas]

Well, improving the finish of the manifold's inner surface wasn't that bad job. A couple of hours work maybe, probebly a lot less of you have a good rotating tool (electric grinder).
I'm pretty sure this will prevent carbon build up as well.

/Niclas

[TJ 450]

Maybe it is time I got a dremel... I would like to see all that carbon gone.

Tim

[WGB]

Love my Dremel - you gotta get one.

[pez]

While I am far from a fluid dynamics engineer, I can share some semi-educated thoughts on the M117 intake system...

I had mine apart a couple months ago for a good cleaning. The interior surface is quite rough.  I would suggest cleaning it using a high speed drill, solvent, and a wire brush attached to the drill.  After the cleaning, I think you could smooth out the interior roughness using a flex hone [again, attached to the drill] or you could just take it to a machine shop and have the insides made smooth.

I personally believe that smoothing out the interior of the manifold would increase airflow volume.  While it is true that turbulent air does create more torque, the length and diameter of the plenum has more effect on the torque vs. equation when it comes to intake systems.  And my understanding is that the value of highly turbulent air diminishes before 2000 rpm on most vehicles.

I also think that getting the interior surface of the plenum totally smooth would cut down on build up, too. Mine was totally gunky from 33 years of use.....on a K-Jet system [I cannot speak for the D-Jet], the cold start injector squirts fuel in to the manifold, and any oil burn-off from the crankcase also goes into the manifold....this makes for the potential of sludgy mix that cannot be burned off or cleaned out in any other method than removal and physical abrasion.

While you are in there, install all new rubber seals, and gaskets, and new intake manifolds gaskets. Be sure to use Hylomar when installing.

[koan]

Not much on fluid dynamics either but not sure about the wisdom of polishing intake runners.

Polishing head passages and ports was the thing years ago then it went out of favour. I think because it was realised that the fuel in the fuel-air mix would cling to the smooth walls of the ports and separate out which didn't happen with a rough surface.

This doesn't apply to injected engines where the fuel is introduced close to the valve head.

But I also seem to remember reading somewhere that high speed flow is greater through a pipe with a rough rather than a smooth surface. I know that goes against logic but it is something to do with a rough surface forming micro eddies that separate the flow from the walls reducing the attachment of the flow to the walls.

As I say I know little about the subject,  a wikipedia search might turn up something.

koan

[Big_Richard]

Has anyone ever custom designed their own intake manifold for the mercedes v8's of this era? Id imagine this would be the ultimate answer to the massive shortcomings of the woeful factory intake manifolds.

Perhaps our resident billionairs should investigate and design something that also uses a modern, easily available larger bore throttle body - or 2 

[OzBenzHead]

On the idea of smoothing the inner surfaces of the intake manifold ...

Years ago, when Rolls-Royce adopted the GM 4-speed Hydramatic (in place of the 2-speeder that it was developing, which eventually became the GM Powerglide), their engineers thought it a good idea to smooth the sand-cast-textured hydraulic passages in the valve body.

This they did - only to discover that the transmission wouldn't work. It needed the rough texture to help the fluid run at correct pressures.

Smooth isn't always good, and I figure if M-B made the insides of the inlet manifold rough, they did it for a good reason.

[Niclas]

These engines were probebly not built to have high output in relation to their volume. They have long intake manifolds, bad angles of the intake and exhaust valves due to only on cam, non ideal radius at the exhaust port - and som more minor stuff. They just added som volume to get the power they needed. This gave them a wery durable engine that ran 2-3 times longer than most other seventies engines.
I think the raw casted surface is there for one reason only - to save some money at manufacturing.

Airflow is generally better at smooth surfaces since this couses the flow to be laminar for a longer time, this is very crutial at airplane wings where even very small rougness from rimice can cause the flow to be turbulant and generate more drag.
The only exception i can think of is vortex generators (also used on wings) they are a small fins mounted on top of some wings in a angle to generate a controlled "coil" of air. This is done to keep the flow laminar.

/Niclas

[TJ 450]

Could a rough surface delay separation of the boundary layer, also allowing the flow to be laminar for a longer duration?

BTW, OBH, I recall hearing about the polishing of the fluid passages some time ago. They thought they could improve the design, but they didn't realise that it was a fundamental part of the design!

Tim

[koan]

Just did a quick search on a few words relevant but couldn't find anything concise.

Seem to recall it's the boundary layer that causes the problems. In a pipe flow velocity isn't constant across the diameter, highest in the middle but slower the closer to the wall and at the wall very slow due to the attached layer. 

Anyone out there with some real knowledge?

koan

[TJ 450]

In a pipe flow velocity isn't constant across the diameter, highest in the middle but slower the closer to the wall and at the wall very slow due to the attached layer.

The same holds true with electron flow in a conductor. Anyway, it would be good to hear from an expert on the matter, I concur.

Tim

[koan]

Not relevant to port flow but this here about golf ball dimples is interesting.

Shows just how unintuitive this area is.

koan

[Niclas]

I'm an ex-pilot, I think they mentioned boundry layer, laminar flow and other stuff a couple of times in aerodynamics class in flight school  

I found this (here http://images.google.se/imgres?imgurl=http://www.free-online-private-pilot-ground-school.com/images/boundary_layer.gif&imgrefurl=http://www.free-online-private-pilot-ground-school.com/aerodynamics.html&usg=__HYsWeQWBQhU4t25xIfV5SoVNlfk=&h=176&w=732&sz=7&hl=sv&start=41&um=1&tbnid=5qpELbHpWoNI7M:&tbnh=34&tbnw=141&prev=/images%3Fq%3Daerodynamics%2Blaminar%2Bflow%2Bturbulent%26start%3D36%26ndsp%3D18%26um%3D1%26hl%3Dsv%26rlz%3D1T4GGLR_enSE240SE241%26sa%3DN)

There are two different types of boundary layer flow: laminar and turbulent. The laminar boundary layer is a very smooth flow, while the turbulent boundary layer contains swirls or "eddies." ], but is less stable. Boundary layer flow over a wing surface begins as a smooth laminar flow. As the flow continues back from the leading edge, the laminar boundary layer increases in thickness. At some distance back from the leading edge, The laminar flow creates less skin friction drag than the turbulent flow the smooth laminar flow breaks down and transitions to a turbulent flow. From a drag standpoint, it is advisable to have the transition from laminar to turbulent flow as far aft on the wing as possible, or have a large amount of the wing surface within the laminar portion of the boundary layer. The low energy laminar flow, however, tends to break down more suddenly than the turbulent layer.

I'll keep looking to see if I find it a bit better explained somewhere else on the net.

/Niclas

[Niclas]

We want this:
http://www.youtube.com/watch?v=KqqtOb30jWs&feature=related

We dont want this:
http://www.youtube.com/watch?v=NplrDarMDF8&feature=related

They are probebly made with different fluids with different Reynolds figures and does not really show the difference due to different surface roughness but it would look the same.

/Niclas

[OzBenzHead]

Not relevant to port flow but this here about golf ball dimples is interesting.

Shows just how unintuitive this area is.

koan

Wow - I could almost (yawn!) find golf interesting after that!