legacycentral bbs

I haven't decided on what to get yet. i had in mind hks 3in downpipe plus a 2.5in custom catback. or maybe hks dp and prodrive muffler with a custom midpipe.
what do you think?
also, what springs fit my car and work the best. anyone know the factory spring rates for a 92 legacy turbo sedan?
thanks

I would go with a full custom exhaust, so that you won't have any non-fitting issues. Plus, it would be a lot cheaper then getting HKS pieces and such. A nice full turbo back exhaust is exactly what your car needs.

Oh, I forgot...go 3" all the way. This has been disscussed to great lengths, and I really don't see the benifit of any less then 3".

i heard the hks downpipe was a direct bolt on. also, could we possibly meet up sometime. i would love to look at your car. i am interested in how you mounted your vdo boost gauge. i bought one but am unsure on where ot put it. oh, and more info please on you air/water intercooler setup.

so is it better to go with the 3" cat back exhaust than the 2.5"?

-Ryan

Aaron: Sure we can meet up sometime, would be fun! We could also see if any other washington members want in too. I am in Seattle right now. I installed my boost guage exactly how the write up on Dave's website says too. I will also get around to do a write up soon on my air-water intercooler, I have some pics I am going to try and send to Dave to get up on this site around friday or so.

georryan: If you were *just* doing a catback on a legacy turbo, I am not sure what size is better. ANybody else? Are you going to be upping your boost at all?

eventualy yes i will up my boost to around 13, but it may be a little while
I'm currently looking for a good intercooler, probably gong with an air to air for ease of installation (no water pump). But I also got to wait for money on that one. I just got hte car this year and have a lot of mods in my plans, but working it out may take a little bit.
-Ryan

hey zak, that's great! currently i am not driving it cause i am going to replace the cv boots next week and some tune up stuff is going on it. but when i get her rollin', i will let you know. i was thinking about going 3in turbo back, cause i want to raise the boost to about 12 psi. i would like to have an intercooler though when i raise the boost. later on down the road, i would like to get a fuel cut defenser, a better turbo, rebuild and build up the motor and run about 15psi.

ps, i saw how dave mounted his gauge, but i want something different. my friend is going to make me a single a-pillar pod and a double gauge pod to go under my ashtray in that little cubby-hole.
-aaron

I would highly recommend getting an intercooler before boost is raised past 10 psi or so. It might not be too bad for the engine, but its nice to have it there so that you really dont have to worry about detonation. A nice simple 93-96 WRX air-air intercooler should fit relatively easy (at least compared to a air-water intercooler).

Yeah that's what I've been reading.

What do you know of as far as the installation for a 2000+ intercooler, similar to ones going up for sale on ebay these days? Will they fit ok? Would it work better if I welded shut the y and opened it up on the side?

-Ryan

Sorry this isn't really an exhaust question, I'll repost it under the right forum.

-Ryan

georryan wrote:so is it better to go with the 3" cat back exhaust than the 2.5"?

-Ryan

honestly.....it really depends on a couple things. How much boost you're running, type of turbo, intake mods, and what type of power you are looking for.

Typically if you don't mind lag, a 3" exhaust will flow more at higher end, hence give you a little more power.

But a slightly smaller exhaust will have less lag and little less power. I'm not exactly sure as to how much lag and how much power you will gain or loose, but it's something you really need to look into a little more closely.

Also, you can do intermidiate sizes.....like 2.75" and such.

Having had an entire system installed myself, i can comment on not only how well any upgraded system works, but how well it fits.

I had my downpipe and midsection installed by a guy who's done exhausts for years, and it was his honest opinion that without some fabrication, it's pretty much impossible to get the stock plate to accept a 3" pipe. 2.75" is what we went with all the way back to the middle, where it joined the 2.5" portion that i've had installed since last fall.

2.5" was as large as the shop felt comfortable installing, given that there's not very much room, and it was an on-the-spot job without a lot of time for tweaking. 3" Dynomax muffler is stuck on the end, with an 8" Magnaflow tip to get the end pas the edge of the bumper.

Any upgrade will make you more power here, so whether you go for a 2.5", 2.75" or 3", you're better off than the stock setup. With the original RHB52, i get incredibly quick spooling, even when i barely slip the clutch at a stop light. I don't ever plan on making more than 230hp anyway, and i've got plenty of flow for that.

Dave

thanks zak and dlc.
i personally have not decided whether to run a full 3in turbo back. i feel i would benefit from a 3in downpipe, but would rather run a 2.5inch catback to keep the exhaust velocity up. for example, look at the Turboxs turboback for the wrx. it uses the same theory and setup. they have 4inch bellmouth dp that blends to 3inch and 3in to a 2.5inch catback.

actually i think i have decided. i think want a full catless turboback. i want it to have a 3in downpipe. 2.75in midpipe and a 2.5inch axle back. this will be custom of course and have blended pipes for both reductions in size. i just have to decide on what tip. single or dual like stock?

-aaron

but would rather run a 2.5inch catback to keep the exhaust velocity up.

Correct me if I am wrong, but wouldn't running a 3" the whole way back keep velocity the highest instead of going into a bottleneck? Turbo XS does use a 4"-3" conversion, but ends at 3, which is pretty big. If they went 4" all the way back, it would no doubt hurt them. ( I assume They would need to be running a very large turbo to make use of that.....)

Zak,

Velocity decreases with an increase of volume.

So...for example, a 3" exhaust would be able to flow more then a 2.5".....however the exhaust gas speed would be lower for the 3" compared to a 2.5".

If you wanted to get real technical, you could run a 2.5" downpipe, and mid-pipe, and then go to a larger muffler/rear section to help the exhaust gasses flow better.

hey zak, i was wrong. the turboxs exhaust does taper from 4inch to 3inc and stays 3in all the way back. Although, i personally do not see it as being a bottleneck. the farther away exhaust gases get from the engine, the cooler they get, which slows it down. ceramic coating helps keep heat in and velocity up.

legacy777,

If you wanted to get real technical, you could run a 2.5" downpipe, and mid-pipe, and then go to a larger muffler/rear section to help the exhaust gasses flow better.

that is not exactly true according to what you just said before it. if you run a smaller pipe and dump it to a big 3in from the axle back, that would slow it down at the end (velocity).

i still am unsure of what i want to do with the exhaust.

You want to keep your exhaust gas velocities up before the turbo and right after.

Here are the reasons.....and if anyone has anything else to add or correct, please do.

The before turbo exhaust gasses are what powers the turbo....velocity and heat are the two driving factors. So you don't want to go too large there.

After the turbo.....you have a situation that is somewhat similar to a n/a engine in which you need backpressure to help with exhaust gas scavenging and keeping good low/mid power.

With a turbo, you don't want too much backpressure.....but the principles mentioned above still apply. But more so in how quickly the turbo spools and lag. With the exhaust gasses higher after the turbo you are helping it spool by a pulling affect....as well as pushing from the engine.

I said what I said about goin to a 3" later back because at that point you're going to have lost some of that initial velocity. It will have dropped to a point where it's not going to really make much difference for the axle back & muffler section.

There is definitely a science to exhaust sizing.

I'll post some info I snagged from a yota forum.....

Hope that makes sense what I said

It really comes down to making everythign work as a system together. On my GVR4, I am pushing a bit over 400 hp at present (runs mid 12's at 119 ish), and still hvaea 2.5 inch turbo back exhaust....easily flows the air, and spool is nic and quick. I drove in another GVR4 this weekend with a custom Garrett setup..easily a low 12 second car, and also runs a 2.5 inch.

On my Legacy, I did the HKS downpipe intended for a WRX (we retail them at under $200, so it a great value), which fits perfectly, with the exception that the O2 sensor wire needs to be extended a bit. From there, I had a 2.5 cat back section fabbed up and used a Tanabe muffler with a 2.5 inch inlet...good spool with my TDO5 turbo, and nice enoguh top end considering the lack of boost I am running (10 psi). The HKS downpipe does eliminate all cats though, so something to consider there.

You can easily go too big ith the exhaust, and can hurt more than help, not to mention get very loud very quicky on a flat motor.

Well i am pretty sure i dont' 3inch all the way back. i am still debating on whether to taper from 3-2.75-2.5 turboback. or just do a 2.5 inch catless turboback. i dont' want a high revving beast or high end freeway racer. i want a well rounded setup that will allow good spoolup with awesome midrange and good topend with enough flow to accomadate like 12psi and a turbo upgrade down the road. thanks guys, this site is great.

Aaron.

Aaron - make your downpipe selection first, then go from there. Don't get hung up on the bellmouth (ours, TurboXS) vs twin dump (BPM, Vishnu) vs factory style (HKS), as it makes little to no difference on a sub 350-375 HP car. From there, this should make it easier: there is a minimal price difference between 2.5 and 2.75...2.5 is certainly more common though. Also, 2.5 is more than large enough to handle 12 psi on any bolt on turbo available...I would venture to say it is sufficient to handle closer to 20 psi, and certainly can flow 400 HP's worth (as evidenced by man a DSM, including mine).

good luck!

well adam, down the road (1.5 yrs) I plan on rebuilding the motor and building it up. i want to get forged pistons, port/polish heads & throttle body and extrude hone the intake manifold. plus, get stonger valve spirngs and the pistons would be overbore. upgrade the turbo and run about 15psi with a new clutch , flywheel and some good engine management. btw, do the pink wrx STI injectors fit the legacy turbo?

btw, thank you for your input on this.
- Aaron.

The pink injetcors do not fit, though there are heaps of larger injectors out there that will.

The pink STi injetcors for the new age car are top fed, our cars need side fed...no bother though, as GReddy and many others offer suitable injectors, and there are some used cars injectors you can use too (red top Silvia motors foir example come with 550cc side fed, high impedance that would work, as do JZA80 Supras ('94-'97 twin turbo). You can also go to STi units from the older WRX's, though these are only marginally bigger than what we already have (they are 440cc, ours are 380cc IIRC)

In short, you need side fed, high impedance, Denso plug.

Adam

Ok, first the best thing you can do is get rid of the cat and get a straight through muffler. Back pressure on a turbo is crap. My experience is that turbos run best on just a downpipe and no other exaust. The turbo itself is all the back pressure (and more) that is needed. I don't care about the velocity out the tailpipe because that is for scavenging and I don't see how much of an exaust pulse makes it through the impeller. Velocity doesn't have too much to do with the turbo, heat it what drives the turbo. So if you have never run just a downpipe and felt the difference... I'd say 3in DP 2.5 back with a straight through muffler and high flow cat if you have to is the way to go.