Header Design Theory & Turbo EJ Headers

[bhazard]

Okay well I guess I shouldn't emphasize fuel economy. I like to have my fun too but the car is/will be a daily.

 

Fuel economy it definitely not it's hallmark but I'll be making up for today by not having a huge car payment anymore. It's replacing my dieselgate TDI. Bonus is that I only paid $1300 for it. Needs a short block though.

[covertrussian]

The info listed is for the GDB STI twinscroll header. The listed weight for the stock header changed on the large pipe page, but I can't account for that.

 

STOCK JDM STI ------ 9.0mm 4-2-2 Φ42.7 Φ42.7 Φ42.7 1.5mm 12kg/13.1kg

TOMEI #193081 SS304 8.0mm 4-2-2 Φ38.0 Φ42.7 Φ42.7 2.0mm 8.5kg

TOMEI #414001 SS304 8.0mm 4-2-2 Φ42.7 Φ45.0 Φ45.0 2.0mm 9.7kg

 

Agreed that thicker is preferred, but keep in mind that the OEM stuff comes with insulation and heat shielding for retention.

 

At one point Tomei had released a technical report regarding their development of the twinscroll manifold. Essentially they pointed out that while the bends and collector could be improved, it yielded little improvement due to other systemic restrictions. I'll keep digging and see if I can find it.

 

Ah, you made it sound like there were bigger pipes in the STI version of the header then the measurements you posted.

 

If OEM header is 304SS then adding insulation and heat shields will actually reduce the header's life since they will contribute to overheating the 304. But heatshields to help prevent cold dipping the hot header (rain splash or snow), which also can lead to cracking.

 

It makes sense that the smoother bends wouldn't help too much with a stockish turbo, the back pressure is just too high to matter. With bigger turbos start requiring better engineering overall .

 

So what's the general consensus on the best setup for a stock turbo daily driver? Drivability, torque, fuel economy are the priorities.

 

I personally just bought the TOMEI EL header, primarily for fuel economy reasons and for engine reliability/longivity since Cylinder 4 will no longer be treated as a second rate citizen in the flow department.

 

Stay stock stay happy. Just get a stage 1 tune to smooth everything out and give you a little more torque. Don't change any hard parts. Don't floor it, stay out of boost. The XT / GT is the wrong car to care about fuel economy.

 

Once you start changing out hard parts there is no general consensus. Sure switching out the downpipe will give you more torque, but drivability is the same. Fuel economy is worse (because it's fun to floor it).

 

Depending on who you talk to there is no reason to change out your header until you get to a larger than stock turbo.

 

If you read covertrussian's thread, you can see he made changes to the ECU map and his turbo (to delay boost) to help him with fuel economy, but how long will it take to recover those costs? Probably a couple years.

 

Your best mod is your own feet.

 

While I understand where you are coming form, I respectfully disagree. I like having a fun turbo car that can get out of it's own way but still gets great gas mileage the 90% of the time it's not at full throttle . It's only a compromise if you make it be. It's possible to have your cake and eat it with these cars, you just need to spend some cash.

 

All things equal, I didn't start dipping into 30mpg territory until after I replaced the downpipe. It's all in the driving style, but the gains can be there. Before anyone says, if it works why didn't Subaru do it from factory: Factory cars target emissions first, then fuel economy. I'm sure all my aftermarket parts and tune wont pass the emission standards (even with cats).

 

In reality you will just about never earn back the money spent on mods in gas money, unless gas goes way up or you drive a TON of miles. I know that and I like a fun car those I buy those parts for fun first, and then if it improves MPG, even better. But I also love chasing numbers, so getting 35mpg is just as good as getting 300whp for me, if I can have both then even better.

 

Case in point about gas mileage and cost:

(Assuming gas at $2.80/gal, 15k yearly miles)

25MPG: $1,680

30MPG: $1,400

 

So if you do 100% highway you will save $280 a year, but in reality you will have lots of city miles and probably less miles a year, thus your savings would be even less. It would take years to pay for downpipe, header,turbo, and tune, that's why you have to have fun with them performance wise,

[Rhitter]

that's why you have to have fun with them performance wise,

 

Agreed completely with everything you wrote. My main point was chase fun

[Underdog]

Ah, you made it sound like there were bigger pipes in the STI version of the header then the measurements you posted.

 

If OEM header is 304SS then adding insulation and heat shields will actually reduce the header's life since they will contribute to overheating the 304. But heatshields to help prevent cold dipping the hot header (rain splash or snow), which also can lead to cracking.

 

It makes sense that the smoother bends wouldn't help too much with a stockish turbo, the back pressure is just too high to matter. With bigger turbos start requiring better engineering overall .

 

Oops - didn't mean to make it confusing. The pics I posted are from 2009 when I installed the JDM LGT twinscroll header/UP, which indeed uses smaller piping than the JDM STI twinscroll header/UP.

 

I absolutely agree that the design on the Tomei is superior particularly as the power requirements increase. My current iteration including the JDM OEM header/UP and '08+ STI TMIC is due to the limitations of 93 octane. That being said, if it looks like there is significant headroom, or if I decide to add meth or flex fuel capability, then those parts could be upgraded to the Tomei header/UP and GS TMIC.

 

As far as longevity on the JDM OEM header... there are very few reports of failures of any kind. I understand your point though and will be sure to check my header over after any dyno or other extreme usage situations.

[covertrussian]

Agreed completely with everything you wrote. My main point was chase fun

 

If it wasn't fun I wouldn't be here, I would be messing with something else non car related .

 

But I will say, even slight MPG gains in parts make it easier to justify go fast parts to the wife. Hey honey, this $700 header might give me 3mpg (claimed EL gains on lots of STI forums) and it should extend the life of the motor by keeping the detonation at bay.

[Gigs]

Ehhh I don't know if I really gained that much fuel economy. I got 25mpg driving back from the track at 70 one day with a 5w50 Redline oil.

[boxkita]

Ehhh I don't know if I really gained that much fuel economy. I got 25mpg driving back from the track at 70 one day with a 5w50 Redline oil.

 

I used to get 26 pre-mod. Post-mod, I got 19; and 23 if I tried really hard. Track mpg stayed about the same at 10mpg. When I took the mufflers off, mpg went to 14 (I only used 3rd & 4th and always in the 4k-6k range).

 

When I parked the wagon and got an econo-car, my daily mpg more than doubled. it was cheaper than a new engine.

[Gigs]

I used to get 26 pre-mod. Post-mod, I got 19; and 23 if I tried really hard. Track mpg stayed about the same at 10mpg. When I took the mufflers off, mpg went to 14 (I only used 3rd & 4th and always in the 4k-6k range).

 

When I parked the wagon and got an econo-car, my daily mpg more than doubled. it was cheaper than a new engine.

 

The close ratio jdm 6mt does not help either lol

[Rhitter]

@Covert, did you not look into the GTSpec headers because they don't come with an up-pipe?

[covertrussian]

I used to get 26 pre-mod. Post-mod, I got 19; and 23 if I tried really hard. Track mpg stayed about the same at 10mpg. When I took the mufflers off, mpg went to 14 (I only used 3rd & 4th and always in the 4k-6k range).

 

When I parked the wagon and got an econo-car, my daily mpg more than doubled. it was cheaper than a new engine.

 

Not a lot of power increasing mods will actually hurt your gas mileage, because power mods increase efficiency and efficiency increase applies to gas mileage too. I would say it's in your tune, efficiency mods do need a new tune (read less timing) otherwise you will loose gas mileage. Happened to me with my 16G install, I bet same will happen post header install header.

 

@Covert, did you not look into the GTSpec headers because they don't come with an up-pipe?

 

They look identical to Tomei's, but thinner at 14gauge, and they do come with up pipe. But it looks like they have been discontinued: https://www.rallysportdirect.com/part/exhaust-headers-and-manifolds/gts-per-1258-gtspec-equal-length-exhaust-manifold

[bhazard]

So if I want a header I should go for the $800 Tomei and not the $100 eBay special? ^_^

[covertrussian]

So if I want a header I should go for the $800 Tomei and not the $100 eBay special? ^_^

 

Yes! Ebay ones are really thin, poorly welded, fit poorly, and will crack in no time. Even $500 ebay ones are not worth wasting your money on.

 

Tomei's are actually $711 shipped. I got mine cheaper over black Friday though.

[bhazard]

Yes! Ebay ones are really thin, poorly welded, fit poorly, and will crack in no time. Even $500 ebay ones are not worth wasting your money on.

 

Tomei's are actually $711 shipped. I got mine cheaper over black Friday though.

It was sarcasm [emoji14]

 

Last winter my buddy and I found a clean Impreza for his girl. Fixed the bent valve and he insisted on getting the cams ground and putting a cheap header on it. Sounds tinny and the thing has cracked more than once. He didn't even bother with a flex pipe.

 

His girl isn't even a car girl. It's an appliance to her. He's a "bolt on" kind of car guy.

[covertrussian]

Sorry missed the sarcasm over text

[Rhitter]

Are you going to do any DIY header coating? Or just wrap it? also, with an OEM catless uppipe any reason to use an after market one?

[covertrussian]

No plans yet, I'm against wrapping 304 stainless, so that's out of question. I wish I could get it properly coated, but that's outside of my price range.

 

I think I'll just run them as is, I've been running the invidia up pipe which is half thin and 304ss for 3 years now and it's been fine, so these should be fine.

[rang0]

Well, while on the subject, I actually just bought some used el tomei header/uppipe off another member with about 10k miles on them. Both the headers and uppipe were wrapped by the previous owner. Uppipe wrap held up real well but the header wrap is starting to fray/come undone.

 

Would it be a good idea to try and salvage whats left and perhaps use more wrap to bandaid the areas of concern, or should I just remove all the wrap off the header? I'm not really familiar if that's damaging in any way to the header to remove the wrap (adhesive?).

 

Loved the write up by the way. Great research and I read it right before I pulled the trigger on the el tomei headers and it was the final positive point for picking them up!

[covertrussian]

One thing that you can do is wrap the header as is with some metal tape that is used for duct work. The adhesive will burn off the first time you run the car, but it should mold together into a protective layer.

 

A lot of people suggest this even on brand new wraps, since oil spillage on exhaust wrap can be a fire hazard.

[0h5LGT]

No plans yet, I'm against wrapping 304 stainless, so that's out of question. I wish I could get it properly coated, but that's outside of my price range.

 

I think I'll just run them as is, I've been running the invidia up pipe which is half thin and 304ss for 3 years now and it's been fine, so these should be fine.

 

I'm planning on going with an invidia up pipe for the meantime to get rid of the stock up pipe converter and egt. I have to spend money on an ap and a turbo back so I wont have cash for the header right now. It's good to know invidia will work reliably.

 

Thanks for the wealth of information.

[covertrussian]

Before buying the Invidia, I would suggest maybe going with an STI/oem catless one, they are much cheaper, especially if you get a header with an up pipe.

 

If your planning on getting a 2 bolt header (without up pipe), I would suggest getting a better quality up pipe from the get go, like a GrimmSpeed or Perrin one, both of those seem to be thicker then the standard 1.5mm that Invidia and others are.

[0h5LGT]

I was worried about the cat and egt sensor after reading how they can be an issue.

 

If my flanges weren't rotted and hanging on by a thread i'd just be going stage one and driving the car, but I need to do the turbo back. Might as well go as far as I can, it's one less worry.

 

If the perrin or grimspeed will bolt up to the tomei no problem then i'll go that route.

[covertrussian]

They will not, they are 2 bolt while tomei is 3 bolt. This is why I'm saying get the cheaper OEM one interim, they go for $70ish shipped used. Invidia will run you up $150ish and GS and Perrin will run you up over $200.

[0h5LGT]

Thank you. I haven't looked into it until tonight, I haven't had the car a month. I'll be ordering a used up pipe gaskets and stud kit.

 

Last question, i'm curious who you'd suggest for a catted turbo back.

[covertrussian]

Sorry can't help there, running OEM myself (I like it quiet). I would ask in the 4th gen section .

[0h5LGT]

I hear ya. I didn't check for used pieces in good shape until now. They're out there and reasonably priced. I'll make up my mind soon, but in the meantime i'm going to get rid of the up pipe cat, egt and do the resistor mod until I can buy the ap.