headers..., what will they do for me? Options

[celicaluva79]

Was looking at headers on ebay for my st. Would just headers give me any extra power at all? If so, how much?

[95CelicaST]

Why were you looking at multiple manifolds? The 4-cyl motors only have a single header, not headers.

[Special_Edy]

Why were you looking at multiple manifolds? The 4-cyl motors only have a single header, not headers.

I guess it could be plural considering its four header tubes running into a single collector and mid pipe. Lol who knows whether its plural or singular.

This entire process with the exhaust is similar to how a well designed intake system and intake manifold will actually FORCE air into the cylinder and create a high pressure wave at the intake valve. Optimally, you want a vacuum on the exhaust valves/ports and high pressure on the intake valves/ports, though on most any Naturally Aspirated engine the opposite conditions exist.

Headers add power through a few different processes. A manifold usually runs all the exhaust ports into a single pipe in as little distance as possible. They are cheap to manufacture and provide backpressure which is somewhat beneficial with low rpm torque, but at mid to high rpm it is very restrictive and the exhaust pulses start to fight against each other because of the uneven length from the exhaust port on the head to the exhaust pipe.
A header has individual pipes for all the exhaust ports(four for our 4cyl), called primaries that all join together at tbe collector to run through a single exhaust pipe. The key with headers is the primary length and diameter. All four primaries are usually the same length and diameter. The theory is that the exhaust gas leaving the cylinder head comes out as a pulse once every exhaust stroke of the 4 cycle combustion process. This high pressure pulse traveling out the exhaust system can be used to create a low pressure vacuum behind it, which will actually suck exhaust gas out of the cylinder(this process is called exhaust scavenging).

What is important to acheive good scavenging is a low backpressure and high velocity in the exhaust system. If the primaries and exhaust system in general are too small then the backpressure will increase(bad) but the velocity will increase too(good). If the exhaust is too big and too freeflowing, then the backpressure will become negligible(good) but the velocity will become too slow(bad). So you dont want to go too big or too small on the pipe diameter. Another thing to note is that the frequency of the exhaust pulses increases with RPM, so every component of the exhaust is only optimal for a certain RPM.
As for the primary pipe length, the longer the pipe the better low rpm performance, and the shorter the pipe the better the high rpm performance. It actually has to do with the frequency of the exhaust pulses, so the header length is actually tuned to a certain harmonic(just like a musical instument ). A lower rpm(lower frequency) needs a longer pipe to resonate, and a higher rpm(higher frequency) needs a shorter pipe to resonate. If you are good with music you know about harmonics and so a good header will actually hit its harmonic at several rpms at different points points across the operating range of the engine.

Most of the headers will probably be tuned for a higher rpm and higher flow than stock but you should see a mild performance and efficiency gain as well as a better sound out of the exhaust. Thats the last part of the headers is a much better exhaust tone, incase you like listening to the engine growl and sing.

Unfourtunately the stock exhaust and intake manifolds are not a major restriction on the 5SFE and 7AFE engine as might be the case with a 3sgte or a larger displacement engine. The performance gains will be slight until you add forced induction or increase the volumetric efficiency of the engine(the head and camshafts are probably the single most restrictive components on our engines). But headers always have a very positive impact on the engine in all conditions over the stock manifold unless you go outrageous with them.