The standard A15 exhaust manifold is a typical common tube 4 into 1 with no thought into tuned length. Mass production, cheap and does the job.Pictured here is a factory A15 exhaust I happened across, unknown origin, which has had a tiny bit more effort put into it. It's more of a header arangement being 4 into 2 - which leaves the rest of the system to complete the 2 into 1.
I ran around for a *long* time with the cheap and nasty exhaust manifold plumbed into the old 120Y exhaust. You can _feel_ the engine struggle to push the gasses at high revs out that old 1" drinking straw system. Yuk.
Factory headers from an unknown A15 model.
I finally snapped and put the nicer 4-2 manifold on (after getting a mate to knock me up a 1/4" plate with the right holes in the right places to act as a flange.) The exhaust boys put together the 2 pipes off the flange (1 1/12") and into a single 2" system with a nice turbo muffler to quieten her down.
Well I hadn't paid for a custom exhaust for a long time - since the Cortina which cost me $110 in about 1991 - and I just about fell over at the price. AUD$240 is what this system cost me in 1999 (the muffler alone was $75). If I hadn't already bolted up the manifold I probably would have not bothered.
But hey, exhaust is where your biggest performance gains are found for the cheapest price. Best bang for you buck. So it's done.
Is an almost stock A15 noisy and farty through a 2" system? Well mufflers must have come a long way since the last turbo muffler I used because there is only a minor low humm resonance at around 3000rpm and there is no back off farts at all. In fact it's not much louder than the old drinking straw system (which did have a hole in the muffler however).
So is it good? Lets just say that instead of straining past 4500 she now sings past it and wants more!
Original JAW, Jan 2000