headers suggestions please

[Mattheww044]

hey guys im just curious what headers everyone is running ATM how it sounds and performs, cost range, and what to look for; will Sti headers fit? etc... thanks guys!

[93forestpearl]

All single scroll turbo subaru exhaust manifolds are the same, essentially. The older up-pipes are also the same as newer 2.5L up-pipes.



You really aren't going to gain much of anything by going to a tubular exhaust manifold until you've over doubled the stock power, or are going to a twin scroll manifold and turbo. Spend your money elsewhere.

[Mattheww044]

well my car has alot done to it, ive got kelly's old red SS, go to the link on my sig. I was just curious cuz my friend said that he was lookin under there and noticed that it still had the stock headers... so i figured upgrade!!! lol

[93forestpearl]

The factory manifold is fairly efficient. People make 500whp on that manifold with little trouble.


Its just that my opinion is that unless you are changing to a twin scroll manifold and turbo, its not really worth it. The factory manifold keeps the most heat in the exhaust compared to any un-equal length tubular manifolds. From what I've seen tubular manifolds will shift some power to the right at the expense your midrange. If your turbo doesn't hit until 4500 rpm, this could be advantageous.

Otherwise you are looking to be efficient across the board, and with the turbo you are running, I'd say stick with the factory manifold. Maybe get it coated and wrapped.

The exhaust system before the turbo and the turbo itself have a greater effect on backpressure than the exhaust behind it. You want the least restriction after the turbo as possible for both top end power and quick spool-up. Careful attention has to be paid to keep velocity high before the turbo and in the exhaust housing of the turbo to spool the turbo up as quickly as possible while not choking off the exhaust gasses on the top end.

The header can be simpler in some ways than a non-turbo header. Bigger dividends can be had by getting the exhaust gasses to the turbo with the least amount of restriction, highest velocity, and the most heat rather than worrying about a tuned equal length design. It would be optimal to make an equal length header, but the packaging of the WRX make a tuned equal length header difficult to design. This helps explain why we usually get near identical results from a factory header when compared to the aftermarket ones we have tested thus far. The factory header gets the gasses to the turbo as quickly as possible and goes a good job of keeping the heat in. Aftermarket headers tend to take a longer path and loose quite a bit of heat in the process. Also, most have a poor collector design that is s a byproduct of the unique packaging of the WRX. In this case a good collector does play a more important role than the length of the pipes. If all of the gasses ram together at a steep angle it causes a lot of turbulence, creates backpressure, slows velocity, and tends to make a mess of things before the turbo, which is the worst spot for inefficiency on a turbo charged car. A good header design would be something like a 4 into 1 design that uses castings or good thermal coatings as much as possible to keep heat in and would also get the gasses to the turbo as quickly as possible. The collector would have to be longer than the ones I have seen and the transitions nice and smooth. The main problem comes from trying to make it package well into the constraints of the turbo Subaru. A well designed header would likely require the header to up-pipe connection to have different flange points than factory, so it would not be as easy to sell in header and up-pipe pieces. The WRX is a hard car to design a proper header for, to say the least. It is very hard to improve what the factory has already done.

The up-pipes duty is to get the collected gasses from the header up to the turbo. The best size is the smallest that does not create excessive backpressure for the intended use. Again, the goal is to keep the gasses moving as quickly as possible while flowing enough gasses to make the desired power. There also needs to be a small amount of flex in the system to avoid cracking, warping, and blown out gaskets. The exhaust before the turbo has a lot of heat differential from one point to the next and adding to that is the fact that different metals have different expansion. This leads to a system that wants to twist, pull and push quite a bit. Without some give, something has to go. The gaskets and welds are usually the first victims. One problem lies in getting flex without having a flex section that is prone to cracking, splitting, and leaking it's self. It is not wise to cure a problem with a part that causes the exact same problem. That would be like sun screen that causes skin cancer.