Hello folks it is your old pal GEE OTTO here to post about the mythical and elusive LGT stock manifold modified to fit the 2.5i platform and other useful information about the rest of the exhaust.
Many years and many, many hours of research and trial and error were put into getting this done right. I made a thread 2 or 3 years ago to float the idea and gather feedback, which came in the form of positive and negative responses. I understand both sides
So first let’s clear up some complete garbage about this project/mod:
1. You don't lose bottom end power
2. You don't lose top end power
3. Your cars acceleration is more linear
4. You car sounds like a stock LGT afterwards
5. It does not impede the oil filter in fact it makes oil changes 10x easier
6. Your second cat IS sufficient to keep the CEL off and your fuel mileage the same
7. It will not melt your water pump outlet
8. It does fit under the stock splash tray with plenty room to spare
9. You do not get the sewing machine sound under load
10. You don't have to fab a new mid-pipe
11. You only have to extend your rear (gray) O2 sensor
12. The LGT manifold fits the EJ253
13. The stock flange is a 3 bolt 2.25" NOT 2.5" flange !
In terms of difficulty this would be a 7/10. You will need these parts:
- 05+ LGT/WRX/STi manifold
- 2.25" three bolt flange with ROUND holes and a set of Grimmspeed THICK cross-pipe to elbow gaskets see my diagram below:
- A Casper Electronics Rear (gray) 36" O2 extension
- Two standard O2 bungs
- A thick 2.25 inch three bolt gasket
Photo of the parts (notice the thick GrimmSpeed gaskets installed btwn the cross pipe and collectors)
The most difficult part of this process is finding a shop that will chop and weld the manifold. Cast Steel scares many a welder, so ask around and explain to them what you want done, take a picture with you
So far LM24 in the Tristate area and Mach V in the greater DC Metro area will do it for a good price and do it right. Once you find a shop they will be able to do the entire project for you.
Some tips from me after three UEL attempts:
Try not to splice the O2 sensor(s) if you have to move the AFR sensor (orange) reroute the wiring harness back through the intake manifold and down the back of the engine first! Then connect the orange and place it where you or your fabricator sees fit. If you do splice them make sure to use the proper braided wire not the solid copper stuff.
Buy the rear (gray) O2 extension! Trust me there is nothing better than having a Bolt on UEL setup that you can swap out to your stock setup with the turn of a wrench and unplugging of a sensor. There is also much to be said about peace of mind
DO not rush the process! Don't settle for a old beat up Stock manifold, I bought a EJ20K manifold it was in bad shape but cheap it wouldn't even fit my block, and I ruined the bolt flange b/c it was so rusted together I had to use a torch and cutting wheel to separate the three parts. Well trust me when I say: grey iron doesn't like the heat an Oxy/Acetylene torch puts out
Keep a look out for a clean EJ255/7 (05+) stock manifold. Also buy a good thick flange as well for the new connection to your stock mid-pipe. You will find plenty of 1/4" flanges but you want at least 3/8" and preferably a 1/2" or greater. This insures during the welding process you don't experience any warping.
Do some research on the rest of your exhaust well ahead of time as well. I like mellow tones and overall quiet operation SO I went with stock LGT cans and my stock Y pipe. For now this setup is as quiet as the stock 2.5i system. Most of us that have/will done/do this mod want to have something to show for it so naturally a CBE is in the mix of future additions.
I would suggest the more tame SPT/BOSAL exhaust first if you can't find that look for an exhaust with a resonated mid-pipe like the Invidia Q300, this is essential as things get loud once you go un-resonated. Custom is an option but I would stick to 2.5 inch piping and neck down to 2 inch for the split to the mufflers.
I say that b/c typically a shop will fabricate the exhaust with thin walled mild steel instead of thicker 304 grade steel. Thinner steel has issues like, poor corrosion resistance, emitting mechanical sounds, lower crush tolerance, and the interior has a higher coefficient of friction. However it is cost effective and with a few coats of Hi-Temp header paint you will have a durable custom setup.
I would also go for an 18" minimum resonator, you want to go with a double walled, fiberglass packed resonator. If you cheap out on this component you will suffer from drone and rasp, so look at brands like Vibrant, Thrush, Borla, etc.
Along with custom piping comes your choice of mufflers I would avoid a straight through muffler i.e. FlowMaster 40's or Super 44's, cheap 115mm melon cannons you find on eBay or cheap exhaust shops. Instead look for chambered and well packed mufflers like a Flowmaster 60 Series, Thrush Hush Super Turbo, MagnaFlow Universals or any other well flowing well insulated muffler.
And now some pictures of my recently completed setup as reference for your own project should you choose to follow.
As you can see the stock splash shield fits perfectly and will not melt. The stock size oil filter clears easily. You can also see how I positioned the rear O2 sensor so it isn't directly exposed to road elements (snow, rain, salt, debris). The front sensor is placed in a similar fashion for the same reasons and because there isn't much slack with the connector in the stock location under the intake manifold.
Keep an open mind about the end result and be willing to change components as needed to achieve your desired effect.
Be clear when approaching a shop or welder to do this project, print my pictures, take them with you, show them. This is a big part of getting a yes versus a “nah I can’t do that.”
I wish I went with this setup three years ago it is as quiet as stock and I have the option to go LGT CBE or back to stock at anytime. Oil changes are easier and there is no degradation in fuel mileage or vehicle behavior. Also this setup is solid, compact and durable.