[Half-Inch Stud]

Originally Posted by NHRASuperStock455SD

?..but this is for all the people...their ports are whistling Dixie because their ports are above Engine Mach requirements. RAV's will set you free!

I hear that.

[NHRASuperStock455SD]

Originally Posted by cgeise

LOL -- You didnt just say that last sentence did you ??????????

Yes.....err.....I did. We took two holes exactly the same square of 3 sq inches. The round flow flowed significantly more than the 1 x 3 inch square hole.

Conventional Pontiac guys have pushrod on the side of the port affecting their intake runner. This is why they cant really run a round intake runner. So, we will find out whether it makes power. Tony things that these ports going straight and round make power.

We have done 4 engines so far, and all 4 have exceeded our expectations. We are just now breaking ground on how to optimize things. It has all been so very interesting/eye opening.

Lynn

[NHRASuperStock455SD]

Originally Posted by Tom Vaught

I say, Let the engine tell you if it is happy. When JC dynos his engine and then runs it on the track we will know more than we do today.

ONE PIECE OF GOOD DATA IS WORTH MORE THAN 1000 OPINIONS

Tom Vaught

Ditto

[Half-Inch Stud]

Originally Posted by NHRASuperStock455SD

Yes.....err.....I did. We took two holes exactly the same square of 3 sq inches. The round flow flowed significantly more than the 1 x 3 inch square...Lynn

Super. I assume the round wins again in a 90degree turn?

[Tom Vaught]

On your little experiment, Lynn, did the round tube flow about 12% better?

Some comments about why it might have:

People might assume that a 2" tube (that they grab off the bench) has 3.14159 square inches of area or slightly more than the "3 square inches of area" in Lynn's "experiment".

Math Teachers often will tell you that a 2" inside diameter circle has 3.14159 square inches of area.

In order to get EXACTLY 3 square inches, the true inside diameter of Lynn's tube would have to be 1.95441". No metal tubing (sold as 2" diameter tube) comes in that dimension.

In order to get somewhat close to the 1.95441" dimension you would have to buy a piece of steel tubing that was sold as 2-1/8" tubing with a 14 gage (.083" wall thickness). Then you would have a tube with a true inside diameter diameter of 1.959".

You remember Lynn what the round tube diameter was that you tested with?

Now we need to talk about the 3" x 1" rectangular metal tubing. Common wall thickness on that tubing is .083" wall (14 gage) or .120" wall (11 gage).

So if we do an area calculation for the 14 gage (.083" wall) tubing 3" x 1" metal tubing we have the following inside dimensions: 2.834" by .834" or 2.363 square inches of area. The next rectangular tube size up is 3" x 1.5" which would give us an area of 3.78 square inches of area and would not be an obvious choice for a "layman" comparison of tubing areas. If you were trying hard to get closer you could select thicker .120 wall material but that would still give you 3.5 square inches of area so we can assume that Lynn used the 3"x 1" tube that he found on a bench.

To recap:

Rectangular Tubing:

Rectangular 3"x 1" tubing actually has a area inside of 2.363 square inches, NOT 3" as assumed. About a 21% hit from a true tested 3 square inch area square tube.

Round tubing:

People assume that a 2" pipe has a 2" inside diameter. That is wrong. A 2" pipe has LESS THAN a 2" inside diameter. Pipe only comes in certain sizes Like I said above Lynn probably just grabbed a piece of 2" tubing and flowed it. That tubing would have an area of 2.641 square inches.

So the difference between the two pipe areas works out to 11.7% difference.
The flow test probably had nothing to do with a round shape vs a rectangular shape, basically you were probably comparing different areas available in round vs rectangular sold tubing, Lynn.

Tom Vaught.

[cgeise]

Nice lesson in pipe and tube size-----so is your contention that IF we could get the two to be exactly the same size the would perform identically???? OR -- would the round -- or oval tube (port) be more efficient do to its more uniform speed gradient at all points in the tube???? And with that premiss will a round tube (port) being some what smaller flow and perform as well or even better than its square counterpart? Given that the arcitecture of the head to some degree will dictate port shape it is not reasonable to think all heads would be built that way -- but the trend is rounder not more square. Jmo

[BruceWilkie]

Originally Posted by Tom Vaught

On your little experiment, Lynn, did the round tube flow about 12% better?

Some comments about why it might have:

People might assume that a 2" tube (that they grab off the bench) has 3.14159 square inches of area or slightly more than the "3 square inches of area" in Lynn's "experiment".

Math Teachers often will tell you that a 2" inside diameter circle has 3.14159 square inches of area.

In order to get EXACTLY 3 square inches, the true inside diameter of Lynn's tube would have to be 1.95441". No metal tubing (sold as 2" diameter tube) comes in that dimension.

In order to get somewhat close to the 1.95441" dimension you would have to buy a piece of steel tubing that was sold as 2-1/8" tubing with a 14 gage (.083" wall thickness). Then you would have a tube with a true inside diameter diameter of 1.959".

You remember Lynn what the round tube diameter was that you tested with?

Now we need to talk about the 3" x 1" rectangular metal tubing. Common wall thickness on that tubing is .083" wall (14 gage) or .120" wall (11 gage).

So if we do an area calculation for the 14 gage (.083" wall) tubing 3" x 1" metal tubing we have the following inside dimensions: 2.834" by .834" or 2.363 square inches of area. The next rectangular tube size up is 3" x 1.5" which would give us an area of 3.78 square inches of area and would not be an obvious choice for a "layman" comparison of tubing areas. If you were trying hard to get closer you could select thicker .120 wall material but that would still give you 3.5 square inches of area so we can assume that Lynn used the 3"x 1" tube that he found on a bench.

To recap:

Rectangular Tubing:

Rectangular 3"x 1" tubing actually has a area inside of 2.363 square inches, NOT 3" as assumed. About a 21% hit from a true tested 3 square inch area square tube.

Round tubing:

People assume that a 2" pipe has a 2" inside diameter. That is wrong. A 2" pipe has LESS THAN a 2" inside diameter. Pipe only comes in certain sizes Like I said above Lynn probably just grabbed a piece of 2" tubing and flowed it. That tubing would have an area of 2.641 square inches.

So the difference between the two pipe areas works out to 11.7% difference.
The flow test probably had nothing to do with a round shape vs a rectangular shape, basically you were probably comparing different areas available in round vs rectangular sold tubing, Lynn.

Tom Vaught.

So if a head had only enough room to make a port 2.5" tall by 2.5" wide a 2.5" round port wouldnt have as much flow area.

A 2.5" square equals 6.25 square inches. A circle of 2.5 inches only equals 4.90859375 square inches.

Chances are the round port flow might transition to and exit past the valve better. But can it make up ALL that difference in area?

[Tom Vaught]

Curt, Actual flow area obviously has a big contributor to accurate testing.

In Lynn's pipe test using steel pipe we could assume that the surface finish (boundary layer) would be the same between the two shapes.

Straight pipe is straight pipe as far as flow down the center of the pipe so the edge shape might have some contribution or loss to the testing.

You go around a bend with a pipe of either shape you have some differences like the flat floor of a "D" port Exhaust (turned on its side) is better than a round port because the round port has a dead spot at the bottom of the exhaust port.

Lynn was comparing two pipes with similar surface finish (assuming that they were the same length for the test) but missed the fact that Rectangular Tubing and Round Tubing of the same gage and reported size do not have the internal area so his test was flawed.

Tom Vaught

[cgeise]

agreed

[Tom Vaught]

Originally Posted by BruceWilkie

So if a head had only enough room to make a port 2.5" tall by 2.5" wide a 2.5" round port wouldnt have as much flow area.

A 2.5" square equals 6.25 square inches. A circle of 2.5 inches only equals 4.90859375 square inches.

Chances are the round port flow might transition to and exit past the valve better. But can it make up ALL that difference in area?

If you had a Port Fuel Injection set-up, Bruce, you might see that a rectangular port would package well and the air would follow the shape in either case, round vs square. When you add a Carb to the puzzle the how fuel flows around a bend or in a corner radius comes into play. That is where the Porting experts have figured out the best way to deal with a given port and still have a good port for fuel and air mixture.

Tom Vaught

[Elarson]

Another minor factor enters in here. The round port has the smallest perimeter and so has the smallest surface area and the smallest frictional loss (assuming identical boundary layer velocity and surface finish). The further you go toward an extreme rectangle, the worse the problem. (5) ports, all 3.0 in2 area for example:

1.955" diameter round = 6.14" perimater

1.732" square = 6.928 " perimater

1.5 x 2 rectangle = 7.00" perimater

1 x 3 rectangle = 8.00" perimater

0.25 x 12 rectangle = 24.5" perimeter

Eric

[J.C.you]

Another variable is that some have the opinion the pushrod tube and the valve stem have the same influence on flow in the port. I disagree with this assumption.

The pushrod tube is at a 90* angle, or vertical across the port. At the valve stem the air, fuel mixture is not flowing at a 90* angle across the stem, but rather follows the contour of the port around the stem. (In an ideal scenario.)

Imagine two stationary logs in a fast flowing river. One from bank to bank across the river, the other, anchored in the center, parallel with the flow.

I'll take the rectangle shape river with no log from bank to bank, rather than a round river with the log across the middle.

[Tom Vaught]

Good Point Eric, How far do you go with the analysis, i guess is the question.

Not arguing that a round port isn't the best from an engineering standpoint goes, but then you get those 'package guys' in there who add all kinds of stuff to screw up your perfect port: bends, pushrod bulges, pushrod tubes, "s" turns, fuel, etc

Tom Vaught

[NHRASuperStock455SD]

Originally Posted by Half-Inch Stud

Super. I assume the round wins again in a 90degree turn?

Interesting you would ask this 1/2. We did some work where we took the short side radius and curved it with three distinct turns rather than just a typical Pontiac cliff. This significantly increased flow. We then curved the corners for approach angles and got more flow.

The biggest issue with the RAV was the cross sectional area(CSA) at the turn. Stock OEM RAVs neck down signficantly before the turn thus increasing velocity before the turn. Since we were trying to decrease the overall CSA we made the approach smaller, the flange smaller, but we could not justify this OEM design. In this area as Jim R. pointed out, is much larger in CSA. The prevailing thought is that since the density of fuel is 17ish times the density of air, you slow down the velocity just before the turn so you can turn the short side radius and minimize the fuel split. This gave us a tested number of 360 to 370cfm as cast depending on the seat angle used. The 5/8 raised port was still 1/2" lower than other aftermarket heads keeping the valve length at 5.75 inches. We say it is smaller, but it is bigger where it needs to be bigger.

End result smaller flange CSA and down the runner, but larger at the turn. Smaller port than OEM and about 60-70 more flow. Our test bolt together engine 755HP/650TQ. With better valve springs over 800HP(but not streetable). This was to represent what you could bolt together in your garage with just regular stuff.

[twinturrbo406]

Originally Posted by cgeise

Nice lesson in pipe and tube size-----so is your contention that IF we could get the two to be exactly the same size the would perform identically???? OR -- would the round -- or oval tube (port) be more efficient do to its more uniform speed gradient at all points in the tube???? And with that premiss will a round tube (port) being some what smaller flow and perform as well or even better than its square counterpart? Given that the arcitecture of the head to some degree will dictate port shape it is not reasonable to think all heads would be built that way -- but the trend is rounder not more square. Jmo

... you are on the right track Curt, but there is much more to it then the hole simply being an oval ...
... the layout of the head has everything to do with how the port is able to be shaped, and located, many heads will simply not allow the correct oval shape to be put into it due to pushrod locations, and head height ...
... another limitation is convergence angles, the port cant just be oval, the roof & floor has to come in on the correct angles to the apex ... this is very important, but sometimes can be a real pain to pull off ...
... then the other factor is valve size, depending on its size could very easily put the needed area in certain parts of the port out of reach, and not just due to material limitations ...
... but yes, if the head can house it, the oval should make more power ...

[NHRASuperStock455SD]

Guys,

We simply did flat pieces of board, and yes Tom V we did as close to matching 3 sq in as humanly possible no radius, just holes.

We introduced no variables just shapes flow flows. 1 x 3 in square 323 cfm, 3 sq in round hole 376 cfm. 12.5% better

I am very conscious of inside and outside diameters as I designed air/hydraulic systems out of college. I had the pleasure of working on the hydrostatic steer for the X1100 tank transmission for Allison Transmission that went on the M-1 tank.

[NHRASuperStock455SD]

Originally Posted by J.C.you

Another variable is that some have the opinion the pushrod tube and the valve stem have the same influence on flow in the port. I disagree with this assumption.

The pushrod tube is at a 90* angle, or vertical across the port. At the valve stem the air, fuel mixture is not flowing at a 90* angle across the stem, but rather follows the contour of the port around the stem. (In an ideal scenario.)

Imagine two stationary logs in a fast flowing river. One from bank to bank across the river, the other, anchored in the center, parallel with the flow.

I'll take the rectangle shape river with no log from bank to bank, rather than a round river with the log across the middle.

Yes that is a good point JC. However, what about turning the corner while you are trying to flow around the tube? Also you have varying velocities as the air/fuel has different densities trying to turn the corner at the valve stem. Most of the flow will hug the back side of the sport and split the log!. It will spit also as the fuel splits. What a cluster F^&$. We improved or area by making the casting thicker so all the guide could be eliminated from the port sticking down. Many heads do not do this.

At the pushrod, we can compensate by bulging around the tube to maintian speed, but most heads are maxed out on bowl area, not so easy. The square port is smaller, flows less, and has to tube in the way creating a corner to flow around. It is an argument which is better, but those are all three negatives any way you look.

A good engine builder accentuates the positives and minimizes the negatives. I like to focus on all the positives of the RAVs. Ford Racing was commited to its design and spent years developing it before the BBC guys took over. We will see where it takes us. I am very pleasde so far.

[zeebo]

so are they finally recasting RA1V heads? in iron or aluminum?

[Don Chapman]

Originally Posted by zeebo

so are they finally recasting RA1V heads? in iron or aluminum?

They been out a couple years, Heres a link to the current ones available.
http://www.wix.com/lmc3470/ramairv

[Half-Inch Stud]

Lynn, that was a lucid and informative short turn description. Your cross-section photos revealed to me that you SOLVED the short-turn flow with the long-ledge short-turn. It's intuitive by eye now. Excellent.

Grumpy discussed the short-turn in his "building power" book, but it never sank in well.

Blacktopr had some relevant discussions on short-turn-to-valve seat slope causing flow separating from the metal. Fuel separating out (wet-flow) being an earlier fallout. Wishing I had a better recall of all the details to type a succinct and correct summary.


Yea, cast iron RA V heads sound exciting.