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Old 12-13-2005, 04:04 PM   #1
TurbojonLS
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Default HKS Replica Header

I purchased an HKS Replica Header from Subietuning a few months ago. After taking my time getting the EGT bung welded, I finally installed it.

I didn't take pictures, but it looks similar to this (w/ the exception of the crossovers being next to each other vs. above & below):

Just a basic replacement header for the stock exhaust manifold. Fully polished, the joints in the crossover pipes allow for some flex. All flanges were nice and beefy. No shavings were evident in the header or on the flanges.

Other Engine Components:
Drop in Filter
Helix Uppipe
Daddy's SCP Maddad shorty downpipe
Prodrive Oval-Tip Axle-Back
UTEC (Rev 6 UTEC running Version 5.0 Firmware and a Stage II Map. Some timing and fuel changes have been made, but no major tuning. Wastegate is set to be closed below 10 psi, & the "gain" (forgot the actual term) is set at 47)
Stock 3rd cat and resonator section remain

Install Notes:
2 nights before installation the header was wrapped with Thermo-Tec exhaust wrap, and I decided I was going to wrap the uppipe with the same wrap as the header, so I pulled it off at the same time. My first attempt at installation involved trying to get the header & uppipe installed while connected - it just didn't quite fit. So i seperated and reinstalled each individually. The subframe U-brace had to be removed in order to install this header - had I tried this the first time I think I could have installed the header/uppipe combo as one piece. Because of this step, install was a little more involved than a basic R&R of the stock manifolds, but nothing too complex.

Install/Fitment Issues:
1 - The header collector is further out than the stock collector (closer to the tire) - so much so that I couldn't use an O2 socket to reinstall the sensor (it just wouldn't position correctly). I used a 7/8 wrench from underneath.
2 - The header was about 1/2" from the U-Brace on the passenger side. I figured this would be enough, but after a week of hearing occasional rattles I realized I was wrong. So I took it off & beat the "lip" of the U-Brace so it was facing down instead of horizontal. I did this in the front of the brace also, just to make sure. No rattles in the Month since I did this, and it appears to be giving it plenty of clearance.

Impressions:
Power: There is a definite change in the power curve. The power in the upper end of the RPMs has increased dramatically, while it has shifted to the right a little. The turbo spools a little later, but not so much that I really notice when driving the car. It may spool later, but by 3000 RPM it feels like its making more power - both part- and full-throttle. Its actually a lot more fun! No dyno numbers yet.
Sound: It sounds great. I hung onto my stock axle-back muffler to put on in case I hated the way it sounded, but no need. It doesn't appear to be much louder than it was previously, but it does sound more "edgy" or "sharp". It is definitely quieter than when I was running a regular Borla Cat-Back w/ a stock downpipe. The normal Subaru exhaust note is still there, but it has been changed a bit. Wife said she couldn't tell it was in, so that's a good thing!

Before/After Measurements:
I took before/after sound measurements with my RadioShack dB Meter. I didn't attempt to follow the SAE standards for measuring exhaust dB, but I followed the same process each time. I was about 6" from the exhaust tip at about a 30* angle. The car was in the garage at the time, so there is some resonance, but again - I did this to get before/after numbers on my car w/my setup.

Before:
In-Car Idle: 61 dB
Out-of-Car Idle: 89 dB
Out-of-Car 3000 RPM: 98 dB

After:
In-Car Idle: 62 dB
Out-of-Car Idle: 89.5 dB
Out-of-Car 3000 RPM: 97 dB

Before/After EGT comparisons were made off my Omori EGT Gauge. On the stock manifold the probe was tapped at the 2/4 casting button. On the HKS Replica Header, the probe is in the #4 cylinder, about 1 1/2" from the head flange. The probe is on the outside of the runner, just as when it was installed in the stock manifold. EGT measurements were taken on the same day on the same stretch of road, under mostly the same conditions. Values are at 7000 RPM in 2nd Gear, on a run that started at 2000 RPM.

EGT Before: 1375

EGT After: 1250

I have UTEC logs I made during these runs and during some before/after 3rd gear runs that I'll post up comparing spool. When analyzing these runs I realized I needed to go and revise my boost map, as I was running higher boost in the upper RPMs than I was previously. More Efficient header design?


Other Search Terms:
Header, Headers, ExhaustManifold, Manifolds, Exhaust Wrap
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Last edited by TurbojonLS; 12-13-2005 at 05:36 PM.
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Old 12-18-2005, 02:05 PM   #2
Lotta b00st
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Default

thats an awsome review. iam thinking of getting headers with the attachable up-pipe, some say your bottom end power vanishes but thats very hard to believe.
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Old 12-19-2005, 06:08 PM   #3
TurbojonLS
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Quote:
Originally Posted by Lotta b00st
thats an awsome review. iam thinking of getting headers with the attachable up-pipe, some say your bottom end power vanishes but thats very hard to believe.
I definitely wouldn't say it vanishes. It drops, especially below 2000 RPMs, but it doesn't vanish. And the changes in mid- & top-end power are well worth it!

Just an FYI, if the header you're talking about is one of those w/ a 3-bolt flange & a specific uppipe, they can be problematic to install. One of the bolts is really hard to get to, and almost worth installing outside of the car and then installing as one piece.
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Old 12-19-2005, 08:38 PM   #4
BigClunke
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Default

You could definitely improve spool and low end power by leaning out your a/f to create higher egt, thus improving spool. Your egt seem rather low based on what I recall others have reported. That could be a good thing; as long as there is nothing wrong with your gauge. You have a lot of room to improve the low end with tuning. Headers shouldn’t be analyzed with a fine-tooth comb until a tune has compensated for the drop in egt.
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Old 12-20-2005, 05:52 PM   #5
TurbojonLS
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Quote:
Originally Posted by BigClunke
You could definitely improve spool and low end power by leaning out your a/f to create higher egt, thus improving spool. Your egt seem rather low based on what I recall others have reported. That could be a good thing; as long as there is nothing wrong with your gauge. You have a lot of room to improve the low end with tuning. Headers shouldn’t be analyzed with a fine-tooth comb until a tune has compensated for the drop in egt.
Oh, believe me, I have a huge amount of tuning to do. On the one dyno run I made (pre-headers) I was off-the-scale rich from 3500 rpms up. Since I wasn't very tuned before, its still a fair comparison. However, my A/F below 8psi is pretty good now - between 14:1 & 13:1.
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