I have a fairly decent drive home and it always gets me pondering engine and car improvements. I'm convinced my old rusty exhaust system is choking the life out of my 914. Having put SSI HE's and an M&K muffler on my 911, I noticed what an improvement to performance changing one's exhaust can make.

I've looked at all sorts of options for my teener ('74 1.8) and that got me thinking. Why do headers have so many curves and HE's have more subtle bends to them? Couldn't headers just go straight back to the muffler? For a two in and one out muffler. I know there's a reason. And I'm sure it's performanced based. I'd sure like to know. Thanks.

first of all you want all the tubes to be of equal length, hence the ones towards the rear tend to go towards the front before coming together with the front ones.
second of all the length of the tubes has an impact on HP and torque and what RPMs they come in at. also the length of the tube after the collector has an influence on HP and torque and what RPMs it comes in at.

I am sure someone will come up with a more eloquent response...but thems the basics

I see...far more complicated than I thought. Thanks.

Stock and SSI HE's are curved for axle vertical range of motion clearance.

the exhaust gases exit the engine resonating. meaning, they move as a wave.
the wavelength changes with the rpm and you can shift the powerband of the engine by using different length headers that match a certain resonance frequency.

the bends are usually in there to archive equal length for the pipes and to clear other items, like axles etc.
Andy