Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Incredible Exhaust System (repost)

If that was true, just about every car built by Ford would have crush bends, since I assume mandrel bending is a more costly process (higher tooling charges and development costs when compared to crush bending). When it comes down to it, if Ford is doing something that costs more, it definitely has good reasons behind it. At an auto manufacturer, people fight (and I mean everything short of fisticuffs) over pennies per vehicle. Guys make careers out of shaving a few cents here and there from every aspect of manufacturing.

Well, I can't speak dyno, cause i never did dyno my car yet, but i can tell you this : the cardoc system sounds great. Period. I do have a slight drone at 3150 rpms, but its gone near 3300. Lovely burble on idle. Throaty sound below 3300, lovely multivalve melody after that. The lack of rasp and low drone are the results of removing tye rear y IMHO.

BTW, my two rear pipes on mine are 2.25, with "nasty" crush bends. But then , if you add up the total area of those 2 pipe, you end up with plenty for a 2.5L engine now don't you...

The biatch is heavy, but if I really wanted light, I would of gone for a nice single setup...

Except air flow does not work that way. Every time it is squeezed down due to a crush bend it slows down in velocity & adds more turbulence.
Repeat this process for every crush bend. Then double it for having 2 pipes. It adds up very quickly!

Crush bending is a cheap way to build exhaust and you get cheap results.

I choose performance every time!

demon, I'm no physicyist, but when a a diameter decreases, doesn't flow speed increse? A simple question from a guy who took High School physics a long time ago in a galaxy far far away.........

http://www.atlans.org/elements/fluids/pg11.html of course this is a stupid attempt to explain what I almost remember - and may apply only to liquids as air is more easily compressed than liquids(proven by the Beer Consumption - Flatulence/Belching/Urination studies - which incorparated input and output diameters - completed as the basis of my Phd) .

Finally, IMHO, mandrel bending is superior to crush bending, but like so many things in life, it is (in our Contour Exhaust Example) a very steep point of diminishing return versus cost.


Mark

Actually, the exhaust speeds up in the crushes (CFM= Area x Velocity, when CFM is constant, a decrease in area {crush bend} means the velocity must be higher. [Actually, the CFM decreases as the exhaust cools and the volume of gas is reduced, but we can ignore this for this calculation, since the decrease in volume is the same for otherwise identical length exhaust systems]) .
When you increase the speed , the resistance goes up by the square law, I.E.: 2x the velocity is 4x the resistance 2^2. So the resistance goes up in a crush bend. In addition, curves (bends) mandrel or not, increase resistance. A mandrel bend (say 8 in long 90 Deg.) is probably about the same resistance as 5 to 10 times the length of straight pipe. So 8 in. mandrel bend is like 40 in. to 80. in straight pipe in resistance (This varys depending on the roughness of the wall and other factors). A crush bend is more likely a 15 to 25 times difference. This is because the increase in velocity requires energy. Resistance and velocity increases both absorb energy.

So you are right that crush bends are less efficient than mandrel. Just wanted to get the engineering right.

No Dyno numbers yet, but the "mmars exhaust" is the best..
mmars True-Dual Exhaust

--Matt

It's not the actual crush that reduces overall flow, it's the portion directly after the crush that flares back out to the original diameter that is the turbulent restriction. The low pressure void created by the expansion after the crush bends causes backflow, if only for an instant. It is possible for this design of exhaust to be better than the stock SVT system because of the differently designed split, but it would not outperform the same Cardoc type system with mandrel bends.

Richard, you have all of the numbers, formulas, and results, but you miss one very important thing to add... Exhaust gas isn't a constant. It's a series of pulses.

mmars, very impressive duals man!!! I'll be doing something very similar!!!

Thanks! I think it sounds great and I can definitly feel a difference in power.

--Matt

Nope just the opposite assuming smooth angled reducer/enlarger the following is true. Necking down the diameter reduces pressure and incresses velocity. Necking up the diameter increases pressure but reduces velocity. Check out a book on fluid dynamics, as it's been years since i got out of school and i don't remember any of the equations.