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Keep the GT Spec Headers on my Classic or not?

Old 11 May 2016, 02:02 PM
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HonestIago
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Default Keep the GT Spec Headers on my Classic or not?

Hello all, first post here and hoping for a bit of input if you'd be so kind!

I recently bought an STI Version 6 Wagon which has GT spec headers fitted along with a fully de-catted 3" Apexi Exhaust. It was mapped by Andy Forrest to c.340bhp apparently and whilst I love how it goes, the noise is dreadfully loud!

My previous Impreza is an MOT failure MY00 UK Turbo which I am looking to break in the next month or so (and then swap some good bits onto to the STI).

I am planning to swap a 2.5" system with a 200 cell sports cat downpipe and Ninja II backbox onto the STI but cannot decide whether to also swap the headers at the same time before getting it mapped again. I would still be hoping for 330+bhp if I keep the GT spec headers and suspect approx 310ish(?) would be the result if I change back to OE.

Any thoughts on what I should do?! Do GT spec headers improve spool much? I am hoping the exhaust change will make the sound a bit nicer but can't help but hanker for the burble of the original headers...BUT I know I'd notice a loss of 20-30bhp! Dilemma!
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Old 11 May 2016, 02:54 PM
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Keep the gt spec on, it will be your muffler that's loud.
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Old 11 May 2016, 03:02 PM
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I was sure below 350 that you were better off with ported stock headers,

would spool quicker with stock.

the uppipe that comes with gt spec isnt great either

Best set up for you would be ported stock headers and a harvey uppipe

also i doubt theres anything like 20-30 bhp difference, maybey a little torque if anything

Last edited by SmurfyBhoy; 11 May 2016 at 03:03 PM.
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Old 11 May 2016, 03:12 PM
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as above a ported stock manifold with ported up-pipe will work better on a standardish setup. The cast material of the standard manifold also accentuates the burble where as the stainless steel gt spec make it a little more raspy, if you're gt specs are in good nick you could get 250 for them and put the money towards the ported setup from AS Performance
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Old 11 May 2016, 03:17 PM
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I'm getting good

Year ago was me asking these questions.

Learned loads a stuff off this forum
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Old 11 May 2016, 09:53 PM
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I really appreciate the replies!

That said, getting a ported set of headers isn't really an option just now unless I can get them fairly cheaply! I may look into getting a set down the line For now it's a straight choice between what's on the car and the OE headers off my UK turbo. Unless of course anyone knows of someone in Aberdeenshire (or the Scottish Borders!) that can port my OE headers for me!

Do the GT spec have better spool than stock unported would you say? Apologies, I have just read so much conflicting info! Car is essentially standard besides the headers/exhaust, Turbosmart FPR, Walbro Fuel pump and an Alcatek.
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Old 11 May 2016, 09:56 PM
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Get a 3 bolt Harvey uppipe for the gt spec headers, will help spool.
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Old 12 May 2016, 08:57 AM
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In order of best spool,

1. Ported stock
2. Stock
3. GT Spec

Harvey upipe will help on all of them,

If it is spool your after I'd reccommend a 2 bolt harvey uppipe from as performance,

This with your stock headers would be best for your power levels,
and if you wish to get them ported try a guy John Goulding from Spool Motorsport outside Edinburgh, if he can't do them he will know who can

AS-Performance sell ported headers on an exchange basis too.
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Old 12 May 2016, 01:34 PM
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Thanks for the input, will research the Harvey up-pipe as combining that with OE headers could be a good all round solution.

Hoping the exhaust change isn't going to rob me of too much power but I want it fully legal and would rather keep my hearing!
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Old 17 May 2016, 12:33 PM
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What gains can you expect to get with the uppipe on standard headers? (Over both standard headers and standard uppipe)
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Old 17 May 2016, 12:58 PM
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Where in Aberdeenshire are you? we might be able to do a deal if real GT Spec I have ported headers but want to go GT Spec as i'm running over 400.
PM me if interested.
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Old 17 May 2016, 01:09 PM
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Originally Posted by SmurfyBhoy View Post
In order of best spool,

1. Ported stock
2. Stock
3. GT Spec

Harvey upipe will help on all of them,

If it is spool your after I'd reccommend a 2 bolt harvey uppipe from as performance,

This with your stock headers would be best for your power levels,
and if you wish to get them ported try a guy John Goulding from Spool Motorsport outside Edinburgh, if he can't do them he will know who can

AS-Performance sell ported headers on an exchange basis too.
If he has GT spec he'll need 3 bolt
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Old 17 May 2016, 01:42 PM
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Originally Posted by Power Junkie View Post
Where in Aberdeenshire are you? we might be able to do a deal if real GT Spec I have ported headers but want to go GT Spec as i'm running over 400.
PM me if interested.
PM sent
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