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4" exhaust - yes or overkill ?

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Read it. "Aem EMS pulled a couple of degrees up top". Is this topic about exhaust systems or knock? Back on topic...
Edited


What you didn't read the sentence before that?
"Setting the boost back up to 29 psi, the larger 3.5-inch system started to expose the octane limits of our engine with pump fuel still coursing through its veins.

At 764 whp, the AEM EMS pulled a couple of degrees of timing up top"


Octane limits of pump fuel=pump gas
 
Got it. Thanks. the whole point of referencing that particular article was to show the gains made from switching to a larger diameter exhaust, which is the topic of this thread...
 
Someone brought up an idea of oval tube and got me thinking. On one episode of "How it's made" they were showing how a racing wheelchair is made. To build the frame they took plain round pipe, bent it into a J shape, and then placed it in a press to flatten it a bit to make it oval. Beauty of this technique is that cross-sectional area of the pipe stays the same while staying smooth (VS beating on a pipe with a hammer, that leaves lumps all over the pipe).
Another idea would be to take a pipe and run it through a tubing roller with flat rollers (or rollers with oval grooves instead of round). This will allow for bends, like for downpipe, where ovalness of the cross-section is perpendicular to curve of the bend.
Will any of this work with large exhaust pipe? Not sure, never tried it. Just thinking "outside the box" here.
 
No one says exhaust tubing must be round.

Too much thinking "inside the box" going on in this thread.

Hal


Or dual 2.5", which would be easier to snake around stuff.
 
If it were me, I would just run your standard 3" exhaust and if you need a little more, install a cutout. That will give you, realistically, all you ever need.
 
More important for flow would be a 4" down pipe. The exhaust gas is hottest, and has the highest volume for the first few feet after the turbo. I've seen cars gain 50hp from a down pipe, but only 3-4hp more when the rest of the exhaust was upgraded.
 
then placed it in a press to flatten it a bit to make it oval. Beauty of this technique is that cross-sectional area of the pipe stays the same while staying smooth

Except that the area doesn't stay the same. It gets less.
For a given perimeter, a circle has more area inside than any other shape.
That is, unless you are Dr Who :)
 
DSM Forums - View Profile: Tort9320g and this: DSM Forums - View Profile: johnnytsi

Way way more to find but i looked at a few on the first page. Most dont mention exhaust but these say full 3" TBack. I imagine either one of these cars (just random examples i found) would gain 20+ hp if they kept the same 3" pipe and cut it down to 3 ft long or just straight down from the turbo. Longer pipes create more backpressure correct?

Could do a 4" off turbo come down to smooth transition into 2 2" or 2.5" pipes. As the other fella said, smaller pipes easier to bend and fit in to place. The transistion itself would cause flow impedance but would it still be worth it is the question. This is interesting. We all know with turbos, bigger is better for exhausts. Space and weight are the limiting factors for a 4" full lenth pipe. 5" would be even better LOL, but i think id draw the line at 3.5 or 4 realistically.
 
Here's my 2 cents. If you have to ask then yes it is overkill. Sounds like you have a pretty straight forward build so why over complicate things and try and figure out a 4" exhaust. Either do a side exit or just run a true 3" turbo back.
 
Except that the area doesn't stay the same. It gets less.
For a given perimeter, a circle has more area inside than any other shape.
That is, unless you are Dr Who :)

What? How so? Air a tire up 50psi then place a load on it. Pressure didn't change because area never changed. Just the shape.

I'm confluzisssided now dammit.
 
Nherron: I was skeptical too. Circle area= piR(squared) Ellipse(oval) area is similar. piR(a)R(b) squared. radius A and radius B are the unknowns. That depends how far you smoosh the pipe but still, i have to agree, they HAVE to have the same area. Right? Someone flame me but in the process please educate me as to why im wrong.
I too looked at that and disagreed.
 
Two 2.5" pipes (round or oval) will weigh more, cost more, take more time and resources to make when you have to almost double the number of joints and connections, greater surface friction and they will still have ~20% less cross-sectional area vs. a single 4" pipe.. just food for thought.
 
3" is fine. I trap 163 mph with 3" piping. Just my $.02
 
Actually, an oval can have less or the same area. What happens when you crush it too much? It becomes a flat piece of metal with no cross sectional area. Also I don't believe the above formula is correct due to the fact that it would net a larger area than the circle LOL. The actual area would be 2* the integral from 0-diameter Given the formula for one side. Or turn it upright and it may work out to 2 parabolic formulas. I'm not 100% on it though.
 
I've got 3.5" round tube on my 1g with a good 2.5-3"+ of ground clearance below it. This is on a ~24.75" tire with Koni Yellows in the front, AGX's in the rear, and 8" springs/coil overs with perches set 1/4" from the lowest position (that was as low as the car could go and still clear a 26x9.5 racing slick).

There is easily clearance for 4" if you wanted to go that route, although you'd need to be VERY strategic in your placement of flanges/v-bands.
 
I ran a 4" aluminum exhaust to the back of the car a year ago. It was nice because of the low volume levels compared to now, but it sucked to drive on the street with. There just wasn't enough clearence under my car even with a 26" tire and I would bottom out over railroad tracks etc. I now use just a downpipe that it just lower than my oil pan at its lowest point. I think that if it is a street car, you will be happier with a nice 3". Just my .02
 
they HAVE to have the same area. Right?

What they have the same is their perimeter or circumference. That is what doesn't change as you distort it from circular to ellipitcal or any other shape.

If you have a circle of some perimeter, and any ellipse with the same perimeter, the area of the ellipse will always be smaller than the area of the circle with same perimeter.

You could spend a good couple hours proving this to yourself with formulas. Because, unfortunately, the formula for perimeter of an ellipse is not a simple one.
Perimeter of Ellipse

So basically, you can start out with numbers for the a and b dimensions of an ellipse, any ellipse you want. Calculate the perimeter of that ellipse. Then go find a formula for calculating the area of an ellipse (same web site has it) and calculate the area of your ellipse.
Now take your perimeter number and figure out how big a circle you would have with that perimeter. Get the area of that circle.
Now you have the area comparison.
Do this as many times as you want, with different ellipses.
Take coffee breaks as needed :)
 
Except that the area doesn't stay the same. It gets less.
For a given perimeter, a circle has more area inside than any other shape.
That is, unless you are Dr Who :)

DSM Forums - View Profile: Tort9320g and this: DSM Forums - View Profile: johnnytsi

Way way more to find but i looked at a few on the first page. Most dont mention exhaust but these say full 3" TBack. I imagine either one of these cars (just random examples i found) would gain 20+ hp if they kept the same 3" pipe and cut it down to 3 ft long or just straight down from the turbo. Longer pipes create more backpressure correct?

Could do a 4" off turbo come down to smooth transition into 2 2" or 2.5" pipes. As the other fella said, smaller pipes easier to bend and fit in to place. The transistion itself would cause flow impedance but would it still be worth it is the question. This is interesting. We all know with turbos, bigger is better for exhausts. Space and weight are the limiting factors for a 4" full lenth pipe. 5" would be even better LOL, but i think id draw the line at 3.5 or 4 realistically.

What? How so? Air a tire up 50psi then place a load on it. Pressure didn't change because area never changed. Just the shape.

I'm confluzisssided now dammit.

Nherron: I was skeptical too. Circle area= piR(squared) Ellipse(oval) area is similar. piR(a)R(b) squared. radius A and radius B are the unknowns. That depends how far you smoosh the pipe but still, i have to agree, they HAVE to have the same area. Right? Someone flame me but in the process please educate me as to why im wrong.
I too looked at that and disagreed.

Actually, an oval can have less or the same area. What happens when you crush it too much? It becomes a flat piece of metal with no cross sectional area. Also I don't believe the above formula is correct due to the fact that it would net a larger area than the circle LOL. The actual area would be 2* the integral from 0-diameter Given the formula for one side. Or turn it upright and it may work out to 2 parabolic formulas. I'm not 100% on it though.

What they have the same is their perimeter or circumference. That is what doesn't change as you distort it from circular to ellipitcal or any other shape.

If you have a circle of some perimeter, and any ellipse with the same perimeter, the area of the ellipse will always be smaller than the area of the circle with same perimeter.

You could spend a good couple hours proving this to yourself with formulas. Because, unfortunately, the formula for perimeter of an ellipse is not a simple one.
Perimeter of Ellipse

So basically, you can start out with numbers for the a and b dimensions of an ellipse, any ellipse you want. Calculate the perimeter of that ellipse. Then go find a formula for calculating the area of an ellipse (same web site has it) and calculate the area of your ellipse.
Now take your perimeter number and figure out how big a circle you would have with that perimeter. Get the area of that circle.
Now you have the area comparison.
Do this as many times as you want, with different ellipses.
Take coffee breaks as needed :)

Thanks Hal. ;) :rolleyes:
 
The question is "would the 4 inch be too loud or have a drone sound cruising?" If your going to drive it everyday make sure you can live with a loud exhaust that drives you crazy and makes the car not a pleasure to drive. I had a 1986 Buick grand national drove it everyday ran 12's and I installed a 3 inch system which was not stainless steel (it rusted and looked ugly) but the noise was unbearable and became a in convince to drive or even cruise. Long story short, sold the car and started another project, and I was 19 years old. Anything over three inch is over kill. Do yourself and anyone who is a passenger in the car a favour and keep it as quiet as possible. You don't want to be like those honda losers. (no offence to honda drivers who have reasonable exhausts).
 
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