what exactly is it about the long tube header that gives an advantage over a shorty?
what are the differences other then length?

 

Oh, Goodie! Lecture Time!

You have to realize that there are wo key factors in header dimensions. Length is one, like you mentioned. The other is primary diameter. You also have to figure in collector type.

The key dimension for a header is going to be the diameter of the primary piping. Exhaust flows through there, right? At higher RPM's, there's going to be more flow, more volume per second/minute, whatever. More volumetric flowrate (volume per unit time) in the same diameter means more velocity (speed, distance per unit time)... up to a point, and then it becomes a restriction. So, the larger the diameter, the more flow it can handle before being a restriction. However, too little velocity means that the exhaust gasses can get sucked back into the cylinder before the exhaust valve closes (the piston is already heading down...), which results in loss of power This is know as reversion, and is the reason people still get hung up on the ancient myth of "backpressure"... different lecture... In short, the diameter of the piping is the primary factor that determines where you peak torque is going to be in the RPM band. Assuming you keep the number of cylinders and displacement the same, then a header with a larger diameter pipe will peak at a higher RPM. There are calculators aplenty out there for your piping sizing enjoyment...

The second factor is primary piping length. If you've studied physics, you should know all about wave reflections in open and closed systems. If you haven't, fear not. When the exhaust valve slams shut, a pressure wave goes down the pipe, just as if you had dropped a pebble in water. The wave has a high point leading a low point, which we'll call a "positive" wave which is going to "push" particles (exhaust gasses) in the same direction. When the wave reaches the end of an open pipe, the wave is going to reverse direction, but now the low point is going to lead, which we'll call a "negative" wave which is going to "pull" particles in the opposite direction (away from the cylinder). Timed correctly, the wave will get back to the exhaust valve while it is still open and pull any remaining particles out of the cylinder. This is called "scavenging". The length of the primary pipe is going to determine how long it takes for the wave to get from the exhast valve, to the end of the pipe, and back again. Since the wave travels at the speed of sound (for the exhaust gas mixture at its temperature), then a longer pipe will obviously take longer. So a longer pipe will tend to scavenge better in the lower rpm range. On a dyno chart, you can see the effect of changing pipe lengths. The peak point will stay the same (may be a higher or lower value, but still at the same RPM), and the rest of the band will rotate around it. With longer pipes, the bottom end (below the peak RPM) will tend to lift up, and the top end (after the peak RPM) will tend to drop. With shorter pipes, it's the opposite. Again, there are a ton of calculators out there...

So, why do people go with shorties or long tubes? In general, companies are not going to make a available-to-the-public part that is going to be considered illegal in all 50 states. So relocating the catalytic converter is a big no-no (Federal law, states haven't had a say-so in overriding Federal laws since the Civil War). So shorty pipes make sense. The diameters tend to be stock (or smaller) so the peak is fairly low, and the lift comes after the peak (it's not much, but it'll do). With long tubes, the diameter is usually larger, so the peak is near the very top of the useable RPM band, and the lift comes in the bottom end (pretty much everything else). In every dyno, the long-tubes like Blackdog, Kirk, AFX, and Fast Fabs have always, ALWAYS, made more power overall than any shorty (Pacesetter, Mopar, etc.). The good long-tubes that have a merge collector (Blackdog, some of the Fast Fabs) have made more power at every point in the RPM band than any shorty and any dump-collector header (Kirk, AFX). Tri-Y headers do tend to pick up a little more bottom end torque at the sacrifice of overall peak torque. Makes for a nice flat torque curve though for folks that use the entire RPM band...

Good enough answer?

Best of luck!

 

ok so the shorty headers arent exactly bad but it depends on where you want the power at?
i have a pacesetter on one of my cars and was thinking of geting a knew one, just thought that it would be nice knowing the difference.
thanks

 

Just be aware that the Pacesetter's for the Neon don't have a great reputation. I have one on my car, but it has beend ground down and properly rewelded where the primaries meet the head flange. That's the most common break point, the welds were crappy from the factory. And they were sloppy, sticking up into the flow area causing a restriction.

 

the flange on mine only lasted less then a year until it rusted through and broke. ever since i put it on my car a couple years ago and havent been able to get rid of the exhaust leak. until now, i removed the old flange and welded a piece of 3 inch pipe to it, now it wont leak. the flange pacesetter gives you doesnt sit high enough on the hedder.

 

what about a ceramic coated shorty? are they any good against rusting and breaking?

 

yeah radar is right, I just had my pacesetter header put on and I took a look at the job they did and was pleased, the exhaust shop that hooked up my header just gave me back the pacesetter collector and used a better one and weleded it up when the snow stops and i get some light outside Ill take a pic or two. and go with the ceramic coat, they are better and last longer as well has puts out less heat then non ceramic coated headers