STi M'8

Hi everyone,

After I replaced my (light & powerful) decatted MY98 for a (heavy & stk) STi8 two weeks ago, exhaust upgrade soon became a concern



I was very familiar with 97-00 classic systems, starting from manifold to the tip, same with new age up pipes... but putting my brand new STi8 2m above the ground, with a MY00 3' Blitz center and muffler was a great disapointment.

After an hour or so, I had to accept the fact that it definetly won't fit to the 2 pieces/2 cats first section.
I mesured the center around 126cm (more or less 5 minus a classic).

So I'm back to zero again, with few options in front of me (and few pieces of various lines also).

I won't go for a decat... as it seems to risky, even with an adjusted restrictor. I am running Std ECU (at least for a few months).

I am wondering about the following options, and so looking for the corresponding figures:
-std downpipe cat, 2nd de-cat (where can I found a tube ?), specific STi7&8 center + Blitz rear...
-fitting a WRX 01 downpipe cat (identical to MY00 plus 2nd probe port), 3' tube center + Blitz rear...
-fitting a 2.5' sport cat, 3' tube center + Blitz rear...
-fitting a 3' sport cat, and same as above. APS 3' would be an option then...

Are those 2 lasts invests worth the money?
Advice needed !!!

Cheers m8's

Callum Ferguson

iTrader: (1)

Noticed that you had no replies so here's one for a start
I know it was not one of your chosen options but the Milltek system is worth considering. I have one on my STi 7, 70mm / 2.75" inc sports cat in the downpipe. Nice increase in noise, not tiring. According to Milltek they have been proven up to 340 bhp unless anyone else knows of more...just about to try & find out if a little more is possible
Have fun with your car and rest assured it has a lot more hiding under the bonnet }

callum

hades

Have got the APS 3" cat and centre on my 02 WRX (but with the APS 2.5" backbox). In conjunction with a decat up-pipe, an ECUTEK and a few other little bits it gave 284bhp/272lbft (remember this is just a WRX). I'm totally happy, and imho the APS is a lot better quality than most exhausts, so will match the Blitz nicely. Would highly recommend it.

Only "problem" is that the APS with a cat and a central resonator might be a little quiet if you are used to full 3" system with the blitz. It is designed to work with the STi as the downpipe splitter actually needs grinding down slightly to match with the WRX's smaller turbo.

Even if you put a milltek/APS or other sports cat system on, I'd suggest monitoring the boost spiking/detonation (you may still need to adjust restrictor size), and also give serious consideration to uprating the fuel pump. Prodrive have now come to the decision a better pump is necessary with a 300bhp PPP.

FWIW, a mate with an STi7, full decat and restrictor mod is getting less boost spiking (hence lower peak boost = safer) than he had as standard, and yet also ~310bhp.

In an ideal world, I'd recomment uprated fuel pump, APS exhaust and an ecutek remap (this will control the boost nicely), but that wouldn't give you much change from £2k. I know of one STi7 with over 330bhp from a full decat and ecutek.

aus73

You will have to get the ecu re-mapped if you fit a de-cat 3" exhaust. Have a look at this:

http://www.g-force-motorsport.co.uk/dyno/aps_exhaust_compare.htm

This is an STi 7 with APS 3" into 2.5" rear box - compared to standard STi. You MUST have an up-rated fuel pump and sort out the boost spiking!! If you run to the redline in 5th and 6th gear your engine will run lean on the standard system. You can re-map these cars with just an exhaust/standard airbox and standard filter to push 330bhp - but you may be getting close to maxing out the injectors aswell.

APS have a full 3" system which is available in 3-4 weeks. We're going to run some comparison tests and see what the benefits are - apart from more noise

Chris Davies
___________________________________
1800bhp - NO Wheelspin - NO Excuses

Lemmy

I would recommend Power Engineerings sports cat exhaust system which is gas flow rated upto 400 hp. PE recommend an Ecutek remap as well which includes an uprated fuel pump. With this setup there is no need to change the restrictor to eliminate boost spikes. You should see 320-330 hp and a very flat and broad torque curve.

The exhaust system is of very high quality, one Subaru dealer has commented that it is the best he had seen, and not excessively loud. It makes a nice burble at idle, is fairly loud on WOT, quiet when cruising on the motorway and does not boom.

Hope this helps

Alan

STi M'8

Thanks for your replies, I even considered modifying my location in profile to get an answer

>Callum,
Ain't no doubt it has a lot more hiding under bonnet, it would not have replaced my 98 otherwise.
I heard about the Milltek system in here, but I thought it was a 2.5'... I'm going to have a close look at it.
Just for my info, are you running an uprated fuel pump?

I've got a Walbro 190L ref.GSS250 on his way from Texas, but not fitted yet. I'm still doubting it is a mandatory mod. on every single v.7 or 8 with modified exhaust... but just in case of, and anticipating a future Ecutek remap I'll replace the stk one.

I might be wrong, but my understanding of the situation with reference to the actual european STi fleet running sportcats and mislaneous exhauts without any pb, is that the pump flow can be overtaken in certain conditions (typically overboosting) or some cars may have some less efficient pumps... anyway, it is fixed: I'll get one.

Back to exhaust, I'm not going to thank Hades for his comments
Arrrgh... I see the APS 3' sportcat system in most of my dreams, but it's damn expensive to get one into France.
About your mate with a full decat STi7 and modified restrictor, do you know some more about it? Peak and hold boost figures for instance... one of my mates in Paris made a similar mod, using a 1.2mm restrictor in the line and seem pretty with it also. I'm still not really comfortable about the de-cat system since I saw an STi7 open block (nothing related to deck, but rods ).

Thanks to Chris and Alan as well for your infos.

Just to keep you posted, waiting for a final 2,5 or 3' sport cat, I found an interesting option by modifying a 00' std classic front cat to replace the 2 cats original STi system. The idea is (still) to fit my Blitz centre and aft.
It is quite a deal as the M6 gearbox is much bigger than the M5, but after removing all protections, shortening the vertical fitting and welding an other 18X150 probe port on the aft section, it seems to play...
Gearbox clearance is about 10mm on its side, so I will wrap it into thermal shield. I let you know some more tomorrow, preparing some various restrictors to anticipate spiking

Bye for now.

Callum Ferguson

iTrader: (1)

Yes, I am running a Walbro 342 pump, 255lt I think, kindly supplied by Mark at Lateral Performance. I have also ported the headers and fitted a Roger Clark Motorsport K&N induction kit to help it breathe a little better. It has been to John for a conservative Ecutek remap so I have no spiking issues. IMHO it now runs like it should have done out of the box. I am gathering a few bits for the next phase
If Chris at G-Force can supply a full 3" APS system soon then this is well worth a close look as is Pat's new H&S system.

callum

hades

IIRC, he has somewhere around 16-17psi peak and held. I do remember that his boost curve had no overshoot - it got to peak and stayed there, and it was quite a low peak for an STi. 1.25mm restrictor rings a bell, but I may be wrong.

I don't know the guys from g-force, but it may be worth speaking to Jamie Whitfield (JW racing) about possibly getting you an APS exhaust into France if you want one. He's always been very helpful whenever I've dealt with him.