STi/LGT OEM manifold?

[65pontiac]

hey i searched thru about 8 pages and the search function pulled up nothing. I thought i read on another forum that the STi or the LGT (WRX also?) stock header/manifold will bolt up to any EJ25. is this correct?? im just curious...

[csweston]

I dont see why not. Their all the same 2.5l DOHC set up. (not literally the same obviously, but layout is the same)

[65pontiac]

yea i was thinking the same since they are pretty close. thanks!

[ouch1011]

Yes, they will work, but I think the stock turbo manifolds on the STI/WRX/LGT are smaller diameter than the stock N/A header. The uppipe internal diameter is like 2", its stupid.

Plus getting them to work without a turbo would require a custom exhaust setup from the manifolds back.

[65pontiac]

Yea i was aware of the custom header back exhaust which wouldnt be a problem. Thats very wierd its only 2inch...thats so restrictive especially for a turbo car. Now that i know that it looks like my 05 is getting a header before my 99 lol

[lord flashheart]

I'm assuming we are talking about exhaust manifold?if so the answer is not any ej seires. But will fit any dual port ej series.

If we are talking about intake manifold the answer is no. The manifolds will not work on any ej series.

[rougeben83]

Yes, they will work, but I think the stock turbo manifolds on the STI/WRX/LGT are smaller diameter than the stock N/A header. The uppipe internal diameter is like 2", its stupid.

Plus getting them to work without a turbo would require a custom exhaust setup from the manifolds back.

how is the 2" diameter UP stupid? Keep in mind this is pre-turbo, where building up the exhaust pressure is important to getting the turbine spooled up.

[65pontiac]

Then why do people use bigger up pipes?? Im a bit confused. What you said makes sense about spooling the turbo but arnt most aftermarket up pipes a larger diameter??

[rougeben83]

Then why do people use bigger up pipes?? Im a bit confused. What you said makes sense about spooling the turbo but arnt most aftermarket up pipes a larger diameter??

No, most aftermarket UP are 2in or slightly larger. The largest I have seen is 2.6in and these are for monster GT-series garrett turbos. Even most of the high-end (read, expensive) UP from japan keep the stock diameter to the UP. The gtspec UP I have in my car now, though having a 2.4in diameter pipe, has a restrictor built into it that is only 2in diameter.

Remember that the exhaust inlet of the turbo dictates how much exhaust will flow into it. You can run a 10in uppipe into a td04 all day, it's not not going to make a difference since the inlet is 2in (well it will, you'll have retarded lag and not go anywhere).

tl;dr. Its all about matching the flow characteristics of the turbo.

[Garrison]

I'm assuming we are talking about exhaust manifold?if so the answer is not any ej seires. But will fit any dual port ej series.

If we are talking about intake manifold the answer is no. The manifolds will not work on any ej series.
So Sti/WRX intake manifolds are specific to their respective makes?

[ouch1011]

Yes, they will work, but I think the stock turbo manifolds on the STI/WRX/LGT are smaller diameter than the stock N/A header. The uppipe internal diameter is like 2", its stupid.

Plus getting them to work without a turbo would require a custom exhaust setup from the manifolds back.

how is the 2" diameter UP stupid? Keep in mind this is pre-turbo, where building up the exhaust pressure is important to getting the turbine spooled up.

If your only desire is for quick spool up, then a tiny exhaust would be OK. But from a power aspect, the complete pre-cat exhaust on the WRX/LGT is incredibly restrictive, to the point of being stupid in my opinion.