Originally Posted by AirGoya
Can someone explain the difference between shorties and long tube headers. I mean obviosly shorties are shorter but what do they do differently and why would this make GM offer shorties?
In F-bodies, shorties as of late have typically just been a replacement for the OEM manifold, keeping the cats' in their original location(s). Hooker, Edelbrock, and possible a couple others (I can't think of for sure at this time) are a couple of the companies who have spent resources to test their shorties to pass CARB laws. GM would make shorties in order to pass CARB laws because there are no CARB-legal long tubes (LTs) (for at least 4th. Gen. F-bodies) because they don't light the cats' off quick enough and get them and keep them hot enough to burn all the emissions they're designed and supposed to. I have validated this by testing my own LTs with an infrared digital thermometer and found at idle the temps' just aft of the exhaust ports were around 700-800*s but when I check just in front of my cats', temps' were already down to around 400*. Cats' are designed to run hot (although they can run too hot a burn up - not litterally) in order to burn off more emissions. In addition, LTs are usually more difficult to install because they usually take up more space than shorties. Another thing to consider is that 02 sensors are designed to run under certain conditions to send accurate signals to the PCM and if you move them downstream of the their original location(s) they may not be operating under the same conditions and send false information (voltage) to the PCM (i.e. having already said the further you go down the header (or exhaust) the cooler the gasses get and if you move the sensor(s) further away from the exhaust port it may not be operating within the range it is supposed to.) I know this from experience with mid-length and LTs and have had my tuner disable the PCM from referrencing the 02s. There are people on both sides of the fence on whether or not this is the best approach, in this regard, but I'm just going by experience and with my tuner.
Power-wise, shories can produce really good power if you rev' the engine high enough but you can have a more power under the curve with LTs because they scavange the exhaust and actually pull more spend gasses, after combustion in the engine, so the new air-fuel mixture will be less polluted by the previous combustion event. Think about it like flushing your toilet - shorties would leave more of your waste in the bowl than LTs because LTs will evacuate the bowl better leaving clear water there.
I could go on more, and this is all off the cuff, but I'd be happy to clarify. There's a lot I left out and some I'm sure I'd revise, but that's the sum of it