4" exhaust - yes or overkill ?

[boost97gst]

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

Gotcha bud. Thank you

 

[Hal]

The bottom line, overkill is relative.

I made 750+ (AWD dynojet uncorrected) on a full 3" turbo-back with a muffler.

Going any higher caused the slip joint (yes it had a sleeve clamp on it) come apart.

That tells me at 750, the back pressure is costing me power and it's hurting spool.

It's still fun to drive though.

Hal

 

[Morphius]

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.

Weight: I couldn't quickly find 4" weight, but 2.5" vs 3.5" is roughly 10lbs for a 10 ft stick. Assume to go up to 4" would be another 5 lbs. Then (2) 2.5" would be 38 lbs vs (1) 4" at 33lbs. So, 5 lbs neglecting joint hardware. Not significant.

Cross sectional area would be between a 3.5" and 4" pipe, which are both marginal for clearances underbody.

 

[LandSpeed-DSM]

As Hal stated.. "significant" like "overkill" is a relative term. Figures like 15% for weight and 20% for CSA however would definitely be considered experimentally significant.

There's nothing inherently wrong with 3" on an HX35, as I made sure to type out in my second post. Though both the on-paper numbers and real world results, including my own, show bigger to be beneficial. That part is not really up for debate. Turbines work on heat and expansion.

Go review the thermodynamic concept of enthalpy. Then try to figure out how that applies here.

 

[stunt2]

ok, thanks to all for replys guys