head work any point

[Anonymous]

I have a 300 with 86 block and efi head. This is in a 4X4 and I don't expect this engine to see 3500 rpm,my question. I also have a good carb head is it worthwhile to port this head and install sbc or equivalent sized sbf valves. I realize I lose compression by switching to the older head.Will I gain anything at low rpms with the larger valves or would this gain if any be offset by the loss through dropping the compression(this engine runs on propane)?

 

[StrangeRanger]

The larger valves really only improve things above 3500 RPM. If you aren't going to run the revs, you won't gain much. You will gain from a cleanup of the existing ports and especially the bowls. There's a lot of excess metal and rough surfaces in there that it wasn't economically feasible for Ford to clean up on a production engine. Concentrate on smooth surfaces and clean transitions rather than removing large quantities of material. That combined with a 3-angle valve job and you should see some real improvements.

I don't know enough about the burn characteristics of propane to offer an opinion on which head to use, other than to say that higher compression (up to a point) is always a good thing.

 

[Anonymous]

SR is dead right, as usual

Your not trying to increase the quantity but the quality of the flow. The flow will have the same low end torque that you want but be capable of more velocity.
Result? An engine that feels better with a slightly higher rev range.

Now the bad news.
Propane loves compression, putting the EFI head on the '86 block was a good idea. Look around for a 240 head or another EFI head.

I think if I was rebuilding an engine for propane I would use the 351W flattops that I have. That would give between 10 and 11-1 depending on the head used.
Propane is a great fuel, if you take advantage of its qualities.

John

 

[rbohm]

8) one thing though when cleaning up the port is you dont want to polish the surface as you will actually take a step backwards. sr is right about smoothing things out though, but a slight roughness from the grinder you use will make the best surface.

 

[StrangeRanger]

He's running propane. No droplets of fuel to puddle out, no need for turbulence. Smoother is better, just don't convert back to gasoline.

 

[Thad]

SR,
Why is a golf ball dimpled, it function in a dry flow regime?
Could it have anything to do with parasitic boundary layer drag that forms between the stationary surface and a flowing gas column?

Can't go wrong with60 grit finish.

 

[Anonymous]

I believe this might provide some insights as to just why a golfball has dimples....
http://www.grc.nasa.gov/WWW/K-12/airplane/beach.html


-=Whittey=-

 

[xctasy]

Whittey :rolflmao: , you are on the dot again. Lets take this guy out with a four wood and see how good his areodynamics are!

Must be a bummer to find a white round ball in that snow you get there.

 

[Thad]

Read article twice, dimples are not mentioned.
The lift has nothing to do with dimples, the principle described make a curve ball curve yet it has no dimples. Rotation of the spheroid in a gas has a differential in gas flow relative speed across the spheroid, with the direction of rotation relative speed to surface is slower, against rotation relative speed is greater.
Rise, curve or sinker is dictated by which plane the rotation is in.

IIRC, Addo once posted about a Yella Terra racing head that had dimples in the intake ports which was immediately outlawed.

Whittey can you find an article comparing the aero coef of a dimpled spheriod vs a non-dimpled one.

 

[BB6Mustang]

I actually know why a golf ball has dimples! We studied this in one of my fluid dynamics classes. When a golf ball travels through the air it creates high pressure in front of it and low pressure behind it. This phenomenon is called pressure drag. Dimples are used to break up the boundry layer and reduce the low pressure area behind the ball. The dimples do create more surface drag by making the airflow more turbulent, but it is more that outweighed by the reduction in pressure drag.

Now, to interject something more on topic... IMO SR is right about polishing the intake. Since it is a propane engine there is no benefit to creating turbulence in the intake port. Think about it, why would people polish the exhaust port if turbulence was needed for better flow?

 

[rbohm]

8) one reason port polishing became popular was the added power it created, but further research has show that likely the added power came from the port just being larger. from everything i have seen a polished port tends to increase the drag on airflow and thus actually cost power. one of my college instructors, david vizard, found that when porting head on mini's, if he got a smooth surface then rattled the die grinder bit around in the port the engine made 5 more hp, this on a 1.4 liter engine. i realize that this was an engine powered by gasoline,but the flow priciples are the same. as for polishing the exhaust port, it is a wasted effort except on a race engine as they carbon up fairly quickly.

 

[Anonymous]

Of golfballs and baseballs and cheating:
http://www.phys.washington.edu/~wilkes/ ... ect18.html


-=Whittey=-

 

[Thad]

In class lecture Whittey posted at the very bottom;
Quote:
Lecture 18 Mainpoints:

Turblence in boundary layer can help reduce drag.

So the benefits of a rough port finish is independent of flow type, wet or dry.

In my 32 years as a oil field drilling fluids engr, often work with flow inside pipeor bore hole. Have computer models for differing rheological properties; Reynolds numbers, yield point, plastic viscosity, etc.

Boundary layer is a big deal in air flow. Look out the window of a passenger plane at the vortex generators on the wing roots. The USAF even experimented with an XRB-66 light bomber that had slits in the wing surface and a vaccum system inside the wing to remove the boundary layer. worked 'til the slits got dirty.

 

[Anonymous]

It's called the Coanda effect. Simply put, any fluid has a tendancy to adhere to a smooth surface it is flowing over. Ever tried that trick of holding a spoon under the faucet, and watching the water curve around the backside? For most physics applications, moving air is considered as a fluid. Therefore, air flowing over a smooth surface has a tendancy to adhere to it. That is what causes drag. Now, get rid of the smoothness, and the turbulance may increase, but the overall drag decreases. The reason why the exhaust gets outright polished is to keep carbon from sticking, and also to reflect some of the heat away from the coolant jacket.

Jared

 

[BB6Mustang]

You guys are talking about external flow and I am talking about internal flow. They are analysed in completely different ways.

Look at a Moody diagram:
http://www.ce.umanitoba.ca/~ugrad/ftp/23.279 Fluid Mechanics/Handouts/Moody Diagram.pdf

The relative roughness on the right corresponds to the lines and it is calculated: the surface roughness of the material (the larger it is the more rough the surface) divided by the pipe diameter (ft). I got 0.0058 using e=0.00085 (cast iron) and D=0.146 (1.75 inches).
The Re (Reynolds number) = fluid velocity (ft/s) times pipe diameter (ft) all divided by kinematic viscosity (1.64 x10^-4 ft^2/s for air). I got about 124000 using V=140 and D=0.146 (1.75 inches).
By finding where the Reynolds number and the relative roughness line meet you can get the friction factor on the left. I got about 0.035 using the two numbers above.

Here is a link for more in-depth explaination of the calculations:
http://ceae.colorado.edu/classes/aren2120/handouts/lect-2120-04.pdf

Now this is far too simplistic to actually model an intake port, but qualitatively it shows that for internal flow as the surface roughness increases the friction increases and therfore the pressure drop increases.

 

[Anonymous]

I love this stuff...!

I'm at work right now, so don't have access to my home computer files, but there's plenty of research to support the benefits of rough surfaces for enhancing internal flow. IIRC, the principle effect is to maintain liquid fuels in suspension. Therefore, as implied above, dimpling an intake will have little effect on a propane engine, since the fuel is already essentially perfectly distributed.

FWIW, at normal a/f ratios, one would expect a propane engine to produce about 15% less power than the same engine on gasoline. However, the superior fuel distribution of propane keeps this penalty to about 5% in the real word. Bump up the compression in this same hypothetical engine by a point or so, and even this penalty can be overcome. Don't go nuts with the compression, though. Propane's octane rating of ~104 looks deceptively higher than gasoline's, but doesn't benefit from the effects of evaporative cooling seen by liquid fuels. A good rule of thumb with propane is to use a max c/r of 10:1 for an iron head or 11:1 for an alloy headed engine. As usual, drop 2 points for mildly boosted engines. (These rules of thumb assume stock components and no special skills on the part of the engine builder. If you have expert assistance, obviously these rules can be stretched.)

 

[Anonymous]

Now You have me thinking. Ya, it's gonna hurt.

On an engine with a baddly designed short side radius that is to sharp of a turn, could the short side be polished and allow the flow to CLING to it and help it make the turn?

I doubt if it would be worth much, but it's something to think about.

John

 

[Anonymous]

No, John. If you leave the inside of the short side radius polished, you will make the flow separation worse, at least for a liquid fueled engine. That's because the boundary layer separates more easily from a polished surface, leaving a stagnant layer of air and fuel (puddling) at that point on the surface. As someone mentioned above, the answer is to roughen the inside of the curve surfaces with 60-grip sandpaper (or dimpling device) to help reattach airflow in those areas. The accepted technique is to attach a bit of sandpaper to one's finger, then reach in and carefully sand in a sideways motion, 90-degrees to the airflow, just enough to roughen the surface in that area. Start slightly before the turn begins and extend somewhat beyond where it straightens out. Cover about 1/3rd of the circumfrence with the scratch marks. That way you'll ensure a reattached boundary layer in those areas affected by the detached flow without unduely negating the polishing effort.

 

[Asa]

........ wow ...........
just when i start to think i can hold my own in a conversation around here i get shut down....
i'm bettin ya'll just have more experience than i, i could follow all that, just didn't know most of it at the beginning, gimme forty years and then we'll talk!
evan

 

[Thad]

BB6,
The area where boundary layer flow and parasitic drag occur has no relationship dependent to type flow; external flow, internal flow, whether the gas is moving over the solid or the solid is moving through the gas, the physics is the same. It is at the gas / solid interface and is dependent on the frictional attraction between the two. Surface finish can and does increase or weaken this attraction.

Boundary layer flow can effected flow inside a tube at the enter / exit points and at abrupt changes in tube direction, shape or size. The change in the boundary layer would be due to separation and/ or pressure changes which are directly related to pressure and velocity which changes flow rheology.

At the point of boundary layer separation in a tube such as at the short radius of an intake port, the EFFECTIVE cross sectional flow area at that point is reduced by the cross sectional area of the stalled gas.