If you made a 3.5 inch y pipe with round tubing on the right and BSR/Dr Gas oval tubing on the left to clear the "hump" under the drivers seat..would it hurt anything? Enquiring minds wanna know. It is funneled into a 4 inch Mufflex with a Magnaflow race muff on the end.....just in case you wanted to know.



David

 

Oval tubing, assuming it started its life as round tubing of the same diameter as the tubing on the drivers side, will have a higher pressure drop than the round tubing. The more you "flatten" it, the less cross-sectional area you have, and the higher the velocity/higher the pressure loss. What is the cross-sectional area of the Dr. Gas oval pipe? Even if the cross-sectional area is the same as the 3.5" round pipe, the wetted perimeter of the oval tubing will be greater. Whether its a significant increase will depend on how much its flattened.

I doubt it will be noticable. Keep in mind that pressure is also lost by adding length and adding turns. In any Y-pipe system, the banks of the engine are going to have a slight mismatch, because of these factors. I wouldn't worry about it, as long as the area of the two pipes is reasonably close.

 

P.S. If your talking about taking a BFH and beating the H out of it, that's a different story, but I think were talking about properly formed oval tubing.

Your going to have to post some math on this one. How does flattening the tube reduce the cross section. It does change the shape, but wether it's round, square, triangular, or oval it's still got the same cross section. Only if you reduce the ID, or in this case the internal circumference, would you reduce the cross section. So there should be no increase in velocity and no decrease in pressure. You are not creating a venturi by making it an oval. if you take two 1 foot section and cut them open and lay them out flat, they will have the exact same surface area. So there can be no increase in wetted area.

 

Although it might not be intuitive, changing the shape into anything other than round reduces the area (cross-section). The obvious demonstration is to flatten the tube completely and get zero area but sitll have the same circumference (wetted area).

Here's some math: Assume 3 inch ID tube. Area is (3 x 3 x PI/4) or 7.069 sq. in. and the perimeter is 3 x PI or 9.425 inches. Now divide that by 4 and make a square with a 2.356 x 2.356 inch perimeter. It's area is 5.55 sq inches or about 78.5% of the round shape. If you made a rectangle 1/2 inch high with that perimeter it would be 4.213 on the long side and would have an area of 2.11 sq. inches or 29.8% of the round area.

One of the reason many commercial airliner fuselages are round is that gives the most interior area for a given wetted area which causes drag. The other reason is strength: if you pressurize a non-round tube it will reshape itself round given enough pressure. That's because with a round the pressure is equal on each segment of the surface and the material only sees tensile loads and not bending. Oh, if you want the strongest pressure vessel, make it a sphere. Next would be a cylinder with spherical ends. But we digress...

 

Let's take an extreme example, but it illustrates the point that OldSStroker so clearly explained. The 3.5" pipe has a perimeter of 11.00". Flatten that so that it makes an oval approx 5.4" wide x 0.1" high. The area of such an oval would be PI x 5.4 x 0.1 = 1.70 square inches.

Let's take an alternate approach.... form the "ends" of the oval to match a 3" diameter pipe. That uses up 9.42" of the available 11.00" from the 3.5" pipe. That leaves you with 1.57" of material to form the sides of the oval, or 0.79". The area of the two semi-cricular ends is 7.07 square inches, the area of the space between them, defined by the 0.79" pieces is approx 2.37 square inches, for a total area of 9.44 square inches..... a bit less then the 9.62 square inch area of the 3.5" pipe we started with.

The term "oval" is not really mathematically defined. In actuallity, the closest defined figure would be the ellipse. While the area of the elipse can be easilly calculated with PI x A x B where A and B are the major and minor axes, it is impossible to calculate the perimeter of the elipse without getting into eliptical integrals. That's why I "approximated" the dimensions of the two examples I used, but I believe that clearly shows that the more you flatten the round 3.5" pipe, the less cross-sectional area you will have.

 

3" oval tubing is 2-1/4" high & 3-1/2" wide...... essentially a 2-1/4" pipe widened to add 1-1/4" in the middle.

3-1/2" oval is 2-1/2" high & 4" wide.

these dimensions are per Spintech & Dr. gas websites

Hope this helps.

 

The dimension of the 3.5 inch oval tubing on BSR's site is 2.5 high 4.5 wide if this helps.

Dr. Gas makes a 3.5 inch "frame notch" that we are also looking at to help the situation.

The reason I asked this question is GM made the LS1 Y pipe the same way, flat on drivers side, round on passenger side. And I am sure they investigated it's drawbacks.

Nascar uses this tubing, so it cant be too bad.



Thanks for the info guys.

David

 

The equivelant oval for 3-1/2" round is 2-1/2 x 4" as they advertise for close to the same cross section. The Dr Gass :frame clearance tube has an expanded center to keep the same cross section.

 

If oval tubing is what you need to get the clearance then you have your answer.... use oval tubing. I just don't see the difference in perimeter being that big a factor in regards to airflow. I agree, more surface area is more head loss but we're talking maybe 2% more area here.

-Mindgame

 

I can see where you would say that if we used it on BOTH sides, but I considered doing oval on the left and round on the right, like a LS1 car.



David

 

When we put the frame clearance piece in the left side it will leave about 4" of collector. The flattened piece WILL BE the collector and it is about 12" long.
I am not to worried about the length of the pipe after the collector 'cause both sides will be different lengths. I am concerned about the flattened piece on one side and a full collector on the pass side. I would rather see the flattened frame clearance piece on both sides as it will represent the collector and I want both banks doing the same.
To use flat tubing on one side and round on the other doesn't represent "equal" to me.

Anybody know the math to figure this out. The frame clearance pieces are swollen in the middle under the flat spot to equal cross section of a 3-1/2" round pipe.(supposedly)There is a size change so the collector will act different if they aren't the same-- I think.

 

hmmm, I thought if you had a 7" rope and had it in a circle, then changed it into an oval, it was still 7" of rope........ The inlet circumfrence is still the same, thus the flow rate would be too. Cross section diameter has nothing to do with capactity, rather than inside circumfrence. If oval was that restricting, I dont think NASCAR would use it with their motors. -Tim

 

Nascar builds their's to whatever size it takes.. If it's 5" flat then that's what it takes and they don't have any frame clearance issues like this '94 does or have existing collectors that are 3-1/2" they build what they need from the head back and then dyno it a bunch to see if it's right.
Don't have that option,moneywise or time wise here,mostly money.

Flow doesn't act the same in an oval as in a round and when there is a reduction in size and back to the normal size. There is a pulse issue to consider when ya put a partial choke down collector on it. Don't know how much though,Or weather it will/how much it will effect performance.

 

I'll explain it one more time, and hopefully you will understand the concept. Make your 7" loop. Form it into an oval. Expand the major axis, and reduce the minor axis. The open area of the "loop" approaches "0" as the major axis approaches 3.5". Its still a 7" loop, but it has no open area, and it will flow "0". Flow is determined by pressure loss, and pressure loss is related to both open area and wetted perimeter (or circumference).

 

Couldn't get an image to come up.

Fred,
Ya got any ideas on using the frame clearence tubes in the link as the major part of the header collector? They are 12" long with the flat being 6".Would ya put one on both sides to make it "equal"or will just one side (all that's needed for clearence) be OK. I feel because of the flat this would do "things"to the pulses,as it could be seen as a size change.
I am not sure the collectors would function the same and the two banks might be running different. They are 1-7/8 headers with 3-1/2" x14" collectors with the 3-1/2" "Y" pipe after that to a merge then 4" out the back



Frame Clearance Tubes

Frame Clearance TubesFrame clearance tubes start and end as a round shape. The center of the tube is ovalized from the top side. The entire bottom side of the tube will lie on a flat surface. In order to maintain cross sectional area the tubes taper up to a larger dia. middle section which, is then ovalized asymmetrically. They are made to accept 2 ½", 3", and 3 ½" dia. tubes. Call for custom oval sizes made to your specifications.



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