So how would one go about making a NA legacy a bit quicker?

[ODB]

love my parents' BF GTB.

Full leather version with a few STi bits and bobs came like that outta japan.

if they dont root it too much ill buy it off them sometime!

[Guest boostin]

 ODB said:

love my parents' BF GTB.

Full leather version with a few STi bits and bobs came like that outta japan.

if they dont root it too much ill buy it off them sometime!

BF GTB?? You mean BF GT or BG GTB??

[ODB]

apologies its a BH wagon.

[Shale]

Was gonna say. I want a BF GTB if it comes with a mystical aura ;D

[cpt kernow]

So serviced today and snorkelectomy.

Lets hope the plugs make a difference. My feelers got 1.8mm gap!

And take a look at the exhaust system for those who haven't seen an NA's before. It's soo weedy when compared to the stock one on single turbs like my forester. I think I'm gonna save a few hundy and get a system made from the heads back. Nice and tuned to increase the torque.

And after doing the foz's plugs last year, the legacy's are a breeze.

[BC5RA]

They are supposed to be smaller.

NA do not react the same way to increases in the exhaust system diameter as a with a compressor. It will reduce back pressure and make for a more doughy drive.

If any sort of size increase is desired then think in small increases of 1/8's and 1/4's also mandrel bent turns.

[Guest boostin]

And you want equal length for NA. Tuned won't cut it.

[cpt kernow]

Yup they are meant to be smaller, but when comparing to the oil filter it's a pretty tiny system, I think it's done so tight to maximise scavenging at low revs for the highway.

I think a nicer formed shape, bit larger in diameter, then openning up after they join into 1 will do the trick. This setup only increases 10% in CSA after the join. And anything afer the 4-1 joint won't make FA difference except on noise. If the regs and your ears could cope, it could all be ditched from under the gearbox back.

But I'm just hoping to find the nice bolt-on-premade fix, lol.

[Guest boostin]

Look at one of the later model equal length systems maybe, from a BP Legacy or GH Impreza. You will need a sump to match though.

[Shale]

I dunno about going any bigger/gruntier than what's on there. It's very different to my N/A headers - which go 4-2 pretty much straight off the exhaust ports into a single Y-pipe. Quite restrictive, but N/As need a wee bit of backpressure to maintain any sort of torque. Given just HOW restrictive my exhaust was in comparison, I can see why I got good gains in going to a 2.5" catback.

What sort of difference would EJ25 N/A headers do? The equal length puppies.

[nzkaosnz]

I have a set of aftermarket tuned/equal length NA EJ20 Headers available....

Made a fair difference

(suit stock sump, bolts up to std mid pipe)

Mt wellington, akl.

[ReubenH]

Put turbo headers on. You won't go any faster, but you'll sound faster.

[ODB]

I say its all just pissing into the wind.

Quick, N/A and Subaru do not mix well.

Clint is trying hard with his monster but thats the exception, not the norm.

Just buy a turbo BH wagon!

[Shale]

 ODB said:

I say its all just pissing into the wind.

Quick, N/A and Subaru do not mix well.

Clint is trying hard with his monster but thats the exception, not the norm.

Just buy a turbo BH wagon!

Again. Why would he when he already has a turbo forester? Lurk moar.

[Guest keltik]

 Shale said:

but N/As need a wee bit of backpressure to maintain any sort of torque

Sorry but i disagree. Get a correctly sized set of headers made by a pro. Thats your best bet. Anything else is a waste of steel.

[Shale]

Hmm... most of what I've heard people experimenting with and discussing seems to go in reverse, but what you said is what I originally wanted to do. Bump up the flow and go to town.

So the theory goes, backpressure and scavenging is more important in N/As to maintain torque (particularly low end), but a lot of this seems to come from old school and turbo-based experts.

My own intention is to get properly designed headers from a pro, not throw a bolt-on at the car, but this is a long way down the track.

As for bolt-ons, it'll be interesting to see what's out there if anyone's going down that path. Borla and its replicas seem to have a lot of 'turbo-sound' headers for N/As, but those aren't conducive to power gains

[Guest keltik]

I mean backpressure seems to be a load of s*** from what im reading.

Edit: Or more accurately, backpressure is a load of shit and calculating the correct exhaust pipe diameter and length of runners to maintain gas velocity is well outside the scope of the average clubsubber.

[Shale]

If it is, then that would mean happy times for real exhaust mods. ;D Hope you're right.

[aim]

Does anyone know the theory behind maintaining a bit of back pressure in order keep torque up down in the low end? I have my own ideas as to why, but I would've counted them negligible in the grand scheme of things.

[Guest boostcut]

 aim said:

Does anyone know the theory behind maintaining a bit of back pressure in order keep torque up down in the low end? I have my own ideas as to why, but I would've counted them negligible in the grand scheme of things.

thats the idea of the supertrapp muffler

[Guest boostcut]

http://www.supertrapp.com/product_sections/cat.asp?CatID=31

[Guest keltik]

As far as i was aware. Backpressure is bad, however...at lower revs - smaller diameter piping keeps the exhaust gas velocity high. The higher velocity equals higher inertia and therefore aids scavenging and reduces turbulence from the transition from cylinder head port to exhaust pipe.

At higher revs, the narrow pipe becomes inefficient and therefore you get some element of backpressure.

[cpt kernow]

 keltik said:

As far as i was aware. Backpressure is bad, however...at lower revs - smaller diameter piping keeps the exhaust gas velocity high. The higher velocity equals higher inertia and therefore aids scavenging and reduces turbulence from the transition from cylinder head port to exhaust pipe.

At higher revs, the narrow pipe becomes inefficient and therefore you get some element of backpressure.

At last some real theory.

Back-pressure is a mis-nomer. You don't actually want any back pressure at all. It's other name is restriction.

What people usually refer to is the inertial flow of gasses in the pipe. The idea is to have the gasses flowing along a pipe, that when the exhaust valve closes the gas continues to flow creating a really low pressure zone in the heads after the valve. Then when the valve next opens the exhaust can whip into the the pipe real quick and even suck some out the cylinder.

If the pipe's too big then the gasses effectively just dissapate into fresh air. There's no inertial suction to create the low pressure zone.

The opposite is true on the intakes. That's why some V8's have long tuned intakes for low revs, to gain inertial flow then the higher revs when it's irrelevant the butterfly whips into short mode.

But bear inmind my actual theory knowledge falls over when it comes to some cars, as there's always someone who's done it before so you can learn from them and not bark up the wrong tree.

[subieboy]

 Shale']

[quote name='ODB said:

I say its all just pissing into the wind.

Quick, N/A and Subaru do not mix well.

Clint is trying hard with his monster but thats the exception, not the norm.

Just buy a turbo BH wagon!

/quote]

Again. Why would he when he already has a turbo forester? Lurk moar.

:

[cpt kernow]

if Someone could find me a mint BH 2002 turbo wagon with 80,000 on it for $7500 that gets over 600km on a tank then I'd snap it up.

the service had gone a long way to making it move quicker, but the snorkelectomy makes it sound hoonish so's going back in on the weekend