I have been reading all the threads about exhaust pipes. since I have a had a "flex" system on my car for a year I am spoiled with the sound and "no" kinks or bends. Is there much difference in a 2 1/2" mandrel bent system vs. what mid america sells? Is the extra price to have a custom system installed worth it? $300 vs. $600. My engine is basically stock, headers, airgap manifold, holly 600cfm, pertronix coil. I will be putting on a set of vortex 64cc heads soon and a new roller cam set up unless I can find the $$$$$ for a 383 crate engine.
Tom

 

 

There would be absolutely no noticeable difference.

You might even do better if you go to a local exhaust shop and ask how much they would charge to bend up a 2.5" system. I took a picture of a 2.5" exhaust with an X-Pipe to a local Indi and he bent up a superb system just like the picture.

 

Just do a 3 inch system straight back from the headers using a modded cross member or the cross member that can be purchased from BTO.

Then you don't have to worry about bends, or lack of flow, and a three inch system makes a nice deep sound.

 

Talk about a waste!!!

 

So there is no difference in using a crushed bent system that reduces the pipe size the bends, than using a uniform system with the mandrel bent pipe.

 

Ya, that's exactly what was said!!

 

if there is no diff then why would anyone pay for a mandrel system?$$$$$

 

I don't buy the argument that there is no difference. The kinked bends in your exhaust creates a smaller "effective" diameter, as do many other factors... length of pipe, number of bends, etc. The point is to size your system just larger than the breathing needs of your engine from an effective diameter standpoint. There's a chart someone posted in another thread that tells size vs. horsepower requirements. Try searching for it, I think it might have been DurangoBoy.

So what does that all mean? Well if you have a kinked bent system and are right at the limits of your engines horsepower in terms of nominal size (let's say 2"), then you should probably go with at least a kinked 2.5" or a mandrel bent 2". In other words if you're operating near the limits, it's best to err on the size of bigger effective diameter, so as not to create high backpressures and breathing inefficiencies.

So you might ask, why not just go crazy big? Well the bigger you go the less velocity you'll have in your exhaust. While that's not a huge deal it will probably have some effect on your pumping work in your engine. The bigger deal is the cost. You want to be able to size a system as small as you can but as big as you need.

 

One of the wheels at flowmaster in one of the rags said the crimps equal a 1/4 inch loss in tubing size, another words a 2 1/4 size mandrel system would flow as good as a 2 1/2 system with crimps in the bends. Think you should use at least a 2 1/2 mandrel system.

 

Those crimp-bent sections are going to cause turbulence and reduce diameter. I don't buy any claim that there will be no difference.

 

pws.....
My original 2" system sounded awesome with just an "H" pipe and a pair of Turbo mufflers at the rear... Sounded tough, but too loud, especially on full throttle; and a loud resonant drone occured at 1300 to 1400 rpm.

So I decided to get a new system to make the car more friendly on long cruises.

I fitted a 2.5" stainless system with an X-pipe and 2.5" bore Magnaflow mufflers.... It is certainly quieter at full throttle (in fact, it sounds like a late model LS1) but I have a significant exhaust drone now from 1200 to 2000 rpm. Don't like it at all.

What mufflers have been fitted to your system, and does it drone?

Can anyone suggest a good 2.5" setup which is drone free...

I am considering removing the X-pipe and putting back a traditional "H" pipe for maintaining an original muscle car V8 sound, and fitting a couple of round 4" resonators in the mid section to reduce the droning... will this work?

Or should I toss the magnaflow mufflers and put in a pair of reverse flow type mufflers at the rear along with the "H" pipe.

Sometimes I kick myself for being so pedantic about the little issues.... Maybe I could have lived with the old system and saved myself a wad of cash and lost time

Arghhhh!!!! the joys of hot rodding

PS: there was a noticeable difference in the buttometer readings between the old 2" system and the new 2.5" system... the new system does NOT have mandrel bent tubing.

 

There is quit abit of difference in the mandrel bent compared to a local bent system with crushed pipes, I a good 15-30hp in a system with alot of bends, thats why they sell mandrel systems and people big money for them, and if your upgrading go to 3 inch exhuast while your there

 

Which one flows better on a Corvette - 1-1/2" mandrel bent or 1-1/2" regular bends? The 1-1/2" mandrel bend setup is clearly BETTER than the given alternative but still not optimal.

Which flows better on a Honda Accord - 4" mandrel bent or 4" regular bend? It won't make a difference because either one is more than enough.

What I am trying to say is that you can be undersized where your exhaust system does not flow enough to meet the needs of the engine, and you will loose power. More flow IS better but you will quickly run into the law of diminishing returns. If going from 2" to 2-1/2" gives you a 15 HP improvement it does not mean going from 2-1/2" to 3" will give you another 15 HP.

If your C3 is a basicly stock L-48, a typical non-mandrel bent 2-1/2" free flowing system is pretty darn good. I doubt you will see much of an improvement going bigger or from better bends. Put the money elsewhere. That has been my experience.

Take that same C3 and add a 500 cube solid lifter big block then you probably will benefit from a bigger set of pipes and/or mandrel bends.

-Mark.

 

Some of the posts in this thread make it all sound so simple and that 3" pipes are better than 2 1/2". For a C3 350 ci engine that is "basically stock", 3" mandrel bent pipes are not better because you're losing some scavenging effect. Velocity hasn't been discussed much here. Don't forget that air weighs something - 38 tons for a 100x100x10 cube. It takes energy to stop and start the air in your exhaust system, and that energy comes from your engine. The faster you can keep it flowing, the less energy from your engine will be used on accelerate/decelerate cycles.

For some engines, 2 1/2" crush bend pipes will perform better than 3" mandrel bend pipes. For other engines, the difference between crush bent and mandrel bent pipes might measurable on a dyno but not noticable on your butt-o-meter yet noticable on your budget-o-meter.

 

- OzzieTom -
Yes, I do have a 'drone' somewhere around the same area you mentioned - I just make sure I stay out of that RPM range! I believe that, in general, X-Pipe's are conducive to droning to some degree regardless of the mufflers. I am running Delta Flow 50's - pretty quiet at "normal" driving speeds/RPM's but certainly can get your attention when you stand on it.
---

To all of the Piranha's that took my comment "There would be absolutely no noticeable difference. " completely out of context, please reread the original post. For HIS particular car (which is what HE cares about, no??) the statement stands.

As another poster stated, 3" (IN THIS APPLICATION) would most likely REDUCE performance. His "basically stock" configuration certainly needs SOME restriction.

Clearly, in the right situation, mandrel bent pipes WILL perform better than poorly "crush bent" pipes. The system I have has very nice bends (no, not mandrel bent) and highly doubt that there is much "turbulence" robbing power. The car runs like a scalded banshee.

Once you go over the 400-450 HP area, things like mandrel bends, pipes greater than 2.5" diameter MAY become worth considering, but I would need to see Dyno results for any particular configuration before accepting claims of "huge" differences.

Edit: I just noticed that sting69 said most of this already!!

 

OK let me see if I understand this. Size doesn't really matter and sometimes smaller out performs bigger?
Try telling that to the girls!

 

No. Restriction means backpressure. This means power lost trying to push out the spent exhaust, and more residual exhaust gas mass retained in the cylinder. Neither are good things.

 

I gotta disagree with a few of your comments. You are not making a functional distinction between header pipe diameter/length and exhaust pipe diameter/length. Tuned length and diameter is fine for the headers (primarily when uncorked), but adding an exhaust system to the headers changes the dynamics appreciably. Given the existence of a fancy "cork" (muffler) at the end of the system, we no longer have a pulsed flow type of environment in the exhaust system. The exhaust system performs more like a plenum, which temporarily absorbs the exhaust mass dumped into it every exhaust stroke. A larger plenum volume will produce less backpressure restriction to the exhaust pulses traveling down the header pipes. The major decision is whether the additional volume (via pipe diameter) reduces backpressure (and increases horsepower) more than it inconveniences the driver by the additional cost, weight, and reduced ground clearance inherent in a big tube system.

 

Lots of different opinions here. what about the discussion that a certian amount of back pressure is good on a typical non race engine!!! all the nascar and nhra boys run big tube open pipes for lots of flow at 8500 rpm. My harley has shorty pipes without a crossover. lost some low end torque but she screams on the interstate. My h-pipe I thought was to supposed to even out the pressure in the pipes? at least that was what I have been told. I have hedmam coated full lenght headers, 3" collectors, 2 1/2" flex pipes, a h-pipe and flow tech mufflers. yes there is a drone but I can work around that. with maybe 275hp she still will light the tires and haul ***. since I am gonna put on another system the question still remains.......bent vs mandrell. will I see a change from my free flowing 2 /2" flex pipe when I install a bent 2 1/2" system? great discussion though!