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

Pressure only drops very locally at the constriction. The fact that the flow has to constrict and then expand causes energy losses which can be thought of as friction in the flow, reducing the ease by which the exhaust leaves the car.

So, NO the crush does not slow the flow at that bend, it speeds it up, and YES this is not a desirable characteristic because more upstream pressure is required to force out the exhuast at a given rate.

From the point of view of this aerospace engineer, it does not seem that crush bends would be the way to go simply because they add additional losses to the flow.

It's not rocket science!

Your correct, the bending does not cost more. The equipment does!

WERD

Uhhhh...velocity of gases through a "nozzle"...I think it is rocket science!

Here's a test we did in fluid dynamics...

Take a normal straw and blow on a piece of paper and maintain a constant deflection of the paper.

Bend the straw in the middle to a 90 degree angle and try to make the same deflection. It becomes harder and harder the further you bend it.

Now take a corrugated straw and you can bend it all the way around to blow back at you and the deflection of the paper is still as easy as if the straw were straight. It's elementary, which is exactly what Professor Ryan wanted it to be.

You don't see crush bends on pipelines, you don't see them on race cars, you don't see them on high quality headers, you see them on garage mechanic's cars. You see them from Midas and Pep Boys...

Why? Because it is cost effective and quick.

Design elements being the same, mandrel bent is better.

Weight is always a factor, luckily the weight is down low, but it is still weight and it still detracts from the performance gains when the gains are in the 3-10 whp range.

If the sound is what you are after, get a Borla.

Ed

Blue WRX,

Your straw analogy is not correct. When you bend a non-corrugated straw the ends bow out and the center collapses... (That is NOT what crush bending does to an exhaust pipe...) A corrugated straw just adds stress relief points for the straw to bend, Hardly the same thing. A real crush bend does NOT crush the sides nor the outside wall of the pipe. In all reality it stretches it out some. The inner part of the pipe is pressed (while smoothly) and stretched to make the crush bend.

You people make it sound like you bend it over a bench and bend it. Hardly the case at all. I've seen actual mandrel bent pipe that has that corrugation in the bend - That would hurt performance even worse than using crush bent pipe (think turbulence) crushed pipe interiors are smooth - No sharp transitions and no eddy's for the exhaust to get divert off of.

OK - The basic theory is this:

The disadvantage of mandrel bending is that it is relatively expensive, because of the costs involved in operating a mandrel bending heat machine. A popular alternative is to get piping with larger diameter and then have it crush bent. This way, it kind of evens out the differences in air flow ease, especially if that particular exhaust pipe configuration has a lot of bends and 90 degree bends.

Does that sum it up for you retards? Really... One pipe that was crush bent vs. one that was mandrel bent same pipe diameter. A maybe 5% difference in flow (which would equate to possibly a 1 or 2 hp loss). But with Cardoc's system - That is not a reality. Remember the principal behind his system is (2) 2.25" pipes. Crush bent yes, but hardly enough to underflow ANY aftermarket system. PERIOD

Now you almost forget about the inlet of his system and the type of muffler he uses. He uses a Cherry Bomb Vortex muffler. This muffler is designed for the most possible throughput (Almost similar to a Dynomax UltraFlo) but it has a center channel that absorbs the sound waves and evenly distributes the flow two ways without disrupting it. The dimensions on the muffler are 2.5" inlet and (2) 2.25" outlets. Do you think there is a restriction there? Not unless you put a cork in it.... Reason why this is important??? Here ya go:

A straight through muffler design would allow exhaust gases to be expedited out as efficiently as possible, although the muffling abilities would not be as efficient as that of the reverse flow design. Therefore it will be inevitable that the exhaust will sound louder than before, but as mentioned before a couple of times, an aftermarket straight through muffler uses noise suppressing material that tones down the sound to that of one that's deep and throaty and not irritating. Hence getting rid of the factory completely restrictive resonator and factory rear mufflers he is effectively making the optimum flow design for the exhaust. Those that use some type of resonator and dual mufflers are still not flowing as much as he is ... You have 3 points of disruption (compared to his 1).

Now, that school is out - I asked Cardoctor for a pic of his pipes out on the ground. He is staying away from this thread and most of the "opinionated" CEG'ers for obvious reasons...

You hate him?? Gee, it must really feel nice to be him and get constantly ridiculed by idiots that don't really have a clue. No wonder he doesn't have any opinion on CEG or it's members... Probably figures it's not worth the trouble to say, and I guess he would be the bigger man for staying clear of this.. Because some of you I think are just waiting for him to show.

Well, I've said my peace. I've had the Cardoctor system (actual system I bought) for almost 10 months and I love it. If you like the deep European sound and gargle on deceleration... This is the exhaust system for you! But if you like the sound of rasp (especially with systems with the factory Y still intact and the resonator removed) this is not the system for you. If you haven't heard it for yourself I would strongly suggest hearing it in person before putting your foot in your mouth. His sound clips don't even come close to the actual sound and also the system gurgles and rumble like no Borla or Bassani could ever do. I've heard them all - And I'm still not impressed.

Sincerly - John

P.S. I almost forgot - Cardoctor was nice enough to give me a link where I could view the early prototype system laid out. These pipes I was told were sold to Mike in NY. I think he said his name is "fuseface" or something on Ford Contour. So look over, study, turn your nose up or whatever.. But don't knock what you don't understand.

Well, it sorta looks that way in the pic...
Time to give it a rest. You summed it up well when you said Cardoc did not design it for performance but for sound. I trust that it sounds good.

Ratchie, you clearly do not have a full grasp of fluid dynamics, and flow in pipes especially.

You have posted some dyno numbers that were initially incorrect, then when corrected completely incompatible w/ other dyno results posted by other, and no copies of plots, only peak numbers.

The simple fact of the matter is that given the choice, mandrel bends provide far less loss of flow energy than a crush bend, ultimately giving a far more efficient method of transporting a gas flow.
Does this mean Cardoc's exhaust setup is useless? no, it just means that others feel it to not be the value he makes it out to be. Does it make crush bends a horrible evil? No, many people use crush bends on custom setups for the sake of convenience and expense (heck my own custom quai-dual system uses crush bends)
The reason Cardoc ended up having to defend himself all of the time, is he would make claims, and then when technical questions were asked regarding them, he would not respond, or would whine about having to defend himself. He and I have gone several rounds on several different subjects. He is certainly not someone I would go to for technical advice, especially on engineering matters. (Note that engine/powertrain modifications are inherently an exercise in engineering)

All that said, I still would like to see dyno plots of Cardoc's exhaust, and another, relevant plot to compare it to (ie a basline dyno of the same car, or with a different exhaust or whatever)

And finally, last time I checked, "Cherry Bomb" was not known for being the high quality exhaust component leader, but rather a Pep Boy's special.

Your right, However at the price that you guy's are paying for these catbacks all they have to do is sell 4 catback systems and the bender is paid for!!!!

Wow... those pipes are really crush-bent. I mean REALLY bent. Geez, there are indentations in the pipe where the pipe is supposed to be straight anyway! :rolleyes:

Oh well, it's all about the sound right? :p