I have an 86 f150 4x4 with a 351w in it and want to put on headers and a 650 cfm or so carb. But, with all the headers and carbs on the market I don't know what kind of pairings I need to go for. what's the difference between shorty's and long tube headers and how do I determine which I should use. any help would be appreciated.

 

Equal-length long- tube headers return power in the rpm midrange.
Equal-length shorties move the power increase band upward towards the high end of the rev range.

It all has to do with sound pressure waves moving back and forth in the tubes. When a reflected negative pressure wave arrives at an exhaust port during TDC valve overlap the increased differential pressure across the combustion chamber pulls more fuel/air into the chamber, thus increasing power. It's a bit like supercharging in reverse: Instead of intake pressure you have exhaust vacuum (more or less).
Any equal-length header should have a good collector into which the tubes feed in order to develop the strongest pressure wave reflection. Any well-designed major-brand header set will have the proper collectors. And an exhaust cross-over, or H-pipe, must be installed to get best performance.

The NASCAR Chrysler 426 hemi back during the middle sixties had both intake and exhaust tuned. Volumetric efficiency of the engine at 6000 rpm was 104%. In comparison, the non-tuned Ford OHC 427 VE was 90%.

 

kattumaram
thanks for the information. I'm looking for the low/mid increase so the long tubes sound like the way to go.
cheers!