Technically long tube equal or un-equal lenth headers will let the engine "breath" the best, delivering more power. The down side is they can be hard to install, won't directly hook up to a stock mustang dual exhaust, possible ground clearance problems and there can be interior heat issues.
Shorty headers won't give you as much "breathing" as long tubes, but in most cases will hook up to a stock Mustang dual exhaust system and are generally easier to install than long tube headers.
The difference between equal lenth and un-equal are the lenth of each tube. On equal lenth headers all the cylinder tubes are the same lenth, so the headers will have tubes twisted in all sorts of configurations to make them fit to the collector. On Un-equal headers the tubes range from longer to shorter giving the appearance of a smooth tube arangement to the collector which in most cases makes them easier to install and change spark plugs.
The idea with equal lenth headers is that each cylinder will have the same amount of back pressure to the collector. On un-equal the pressure will vary from each cylinder to the collector.
IMO unless you're looking for the most power and plan on racing a lot than long tube would be the way to go. If it's mostly a daily driver with a couple trips to the strip per year than shortly un-equal would be better.
There are a lot of different thoughts on which one is "better", you just need to figure out which type will suit you best.
Depends on your motors RPM operating range and what you're using the car for. Long tubes are for high RPMS. They flow better at high RPMs but you sacrifice low RPM torque. Long tubes = racing.
Shorties don't flow as well as long tubes at high RPMs but do just as well at low RPMs (like less than 5500 RPMs for example). Shorties don't give up the low RPM torque. 90% of your street driving will be at lower RPMs.
Shorties = street.
Thanks a-lot guy's for your input. I really don't plan on hitting the track much, maybe twice a year? I was just looking for the best street set-up. My eng. is completely stock with 90-k on it. I was going to install a new timing chain and waterpump, would anyone be able to recc a good cam/rockers for a street set-up. I eventually want to build a 347/turbo combo for it but would like to have some fun with what i have in the mean time. Thanks, also my car is aod, any sugg. with trans, shifter, and rear gear??
Long tubes, don't waste your time or money. They work better on the 4.6 than the 5.0. For the street and ocasional track use, go with equal length. BBK's work great and will fit well weather you have stock H-pipe or aftermarket x-pipe. Long tubes have clearence problems also(starter)I have equal length and they were easy to install, sound good and work great.
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