6G Celicas Forums

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

nothing you will notice!! honestly. unless you do the entire exhaust then maybe a bit. i did a header back. welded two high flow cats and now have me a magnaflow muffler and all youll get is a good sound. just my opinion.

From the 7a I wouldnt' expect more than maybe 5hp without revamping the entire exhaust (header only).

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

All of the headers for the ST Celica on eBay were actually meant for the Corolla. It'll fit, but you'll have a gap between the down-pipe and the secondary cat(94-95 anyway, not sure about 96+ having a secondary cat). You also have to deal with throwing off your downstream O2 sensor, since there isn't a cat in front of it anymore due to the header. That's if you even weld in a sensor hole for it into the new down-pipe. What I plan on doing is just removing everything past that downstream O2 sensor, secondary cat included, and replace with straight pipe and have a muffler at the end. Some marginal gains, sound being the main reason, and don't have to worry about throwing sensors off. Until they make a header that'll fit into place without having to remove the primary cat, I personally wouldn't bother. Not to mention the upstream O2 sensor only reads off one cylinder with the header, versus all four in the OEM set up. To me it seems to do more harm than good.

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.

Simply put, on the 7a with a header.

You will lose those take off bottom end, and gain some in the high end...mainly noticable around 3rd gear. That is it.

Thanks guys... dont really sound too awesome ro be honest lol. Guess ill start with exhaust... can anyone recommend an exbaust that sounds deep and not ricey at all? Wanted a greddy but i hear they are all gone

I was going to go with a Magnaflow stainless steel oval muffler myself. This one in particular: http://www.magnaflow.com/02product/shopexd...ain&id=9937 I've found them on eBay for under $80.

so for a 5sfe would the ebay header(at this point considered to be a mid rpm range upgrade only) increase highway mileage since highway cruising is at the middle of rpm range?

if so. what if there was a way to restrict it temporarily for low rpm power? or would a restriction not be enough would the primaries have to be shorter?

Longer skinnier primaries for lower RPM, though it should still resonate at multiple rpms.

you won't increase gas mileage with the ebay header, from what I've heard.
before I put a header on, and also the full header back, (stock) I was getting almost 400 to a tank. Now with the header and 2.25" exhaust with a muffler, no cats, and no resonator, I get about 300 to a tank depending on how I drive.
It's about 24 mpg on average with the aftermarket exhaust where as I was getting about 26-28 mpg with the stock exhaust.

hmm i definetley dont want my mileage to go down especially not highway. would leaving the stock manifold on but having the rest be more free flowing be beneficial for mileage or just performance or not much at all?

Had the obx on mine for 3 years now. Did notice more top end pull. It does change the torque curve. Cel didnt come on for 2 years for the seconary o2. Has come on sense i reset it. I had a parts car and just slapped a very very high flow cat from it on to fix the gap. Has worked well. Did have to wrap the section that went over the cross member because it was rattling along with the section towards the rear.yes i know not the best setup but it works just fine. I also cut it at the rear axle. Has a nice tone for what it is.

Dude...I have a full opened up high flow exhaust system, sri, ported and polished head, and the headers and I noticed a small increase in power at the upper rpm range. Let me emphasize, it was a small notice. NOW, I went and got custom grind cams and THAT's a noticeable change! Then, I got a SAFC II and had Presure2 wire it in and dyno it and THAT was an even bigger noticeable change. I say, safc, cams, and tune. That's the best you'll get before going turbo.

By the way, Manny, my celica is still running nice and strong man!!

This post has been edited by 6G96GT: Apr 26, 2012 - 8:16 PM

just installed my magnaflow and its lil deep. kinda raspy at cold but warms up and sounds good.