Why the 3 inch downpipe

[Otto Man]

Would someone PLEASE explain the need for the 3-inch down pipe, and it's merits.
There is a tremendous amount of talk about this and there are some of us (me) who haven't any idea what it means (sorry for being dumb). In other words, why does opening up a "flow" AHEAD of the CAT have any benefit?
I am not in a hurry to do this upgrade but just as curious as to know why it is FIRST on an upgrade list.
Maybe it's not for everyone?
Thanks
Chris

[svony]

3" downpie: obviously it's larger than stock which means less air restriction and therefore more power and faster turbo spool-up.

Usually when someone adds a 3' downpipe they also replace/remove the cat so it is never an issue.

After you do this mod you will realize why everyone makes such a big deal about it. Also do the K&N conical filter if you haven't already.

Good luck
Wes.

[GAboySVO]

Chris,

The internal combustion engine is essentially an air pump. The more air it pumps, the more power it can produce.

Ideally, all intake and exhaust components are matched to allow the maiximum amount of air to flow through the the engine. For a production car, compromises are made for pricing, regulation, safety, insurance, etc. The exhaust on a stock SVO is a restriction to more air flow through the egine. Back pressure in the downpipe slows the turbo spool up speed and also restricts the air flow through the engine.

It is first on the list because it is one of the cheapest upgrades you can do, bolts right in, and is needed for any future mods. If you put on a ported head and didn't open up the exhaust, you would not get the full benefit of the expensive head job.

My Sac Mustang downpipe is like a megaphone for the turbo whistle and it can add 6 - 10 HP.

[Otto Man]

Thanks for the lessons!
If I really wasn't interested in doing any major upgrades, just interested in a nice stock 85.5 setup, would this still be a no-brainer? (I mean, I'm all for a couple more HP if its a cinch to do.) If so, is there a Sac Mustang Model 123 (with O2 sensor hole), a Sac Mustang model XYZ cat, and a Model ABC Y-pipe that are all compatible with my 2-1/2 inch exhaust? Keep in mind I need to pass emissions every 2 years!
I have read quite a bit of posts about down pipes that don't quite fit, no O2 sensor hole, etc, etc. So I just assumed this was kind of a headache upgrade that has never been perfected, but for 6-10 HP was worth the busted up knuckles and a weekend.
Thanks again
Chris

[richsvo]

Chris,
For those who want to stay mostly stock with the added benefit of this upgrade, then the Sac. type pipe is the best way to go. They make two versions...a short one and a long one. The long one is intended to bolt up stock (including CAT), and the short one is intended for those who want to modify their exhaust. I SERIOUSLY doubt that any of these mods are going to affect the ability to pass a sniffer test...There are many others out there making downpipes similiar to Sacramento Mustang. Check over on turboford.org...there are at least three I know of...Cheaper too, I think.
Rich

[Otto Man]

Then here begins my questions:
Sacramento Mustang lists a down pipe model: SVO-7250 as being:
"3" diameter pipe immediately following turbo allows faster spool-up" and "By-pass Catalytic converters".
I can't do that!
This are my questions:
1. Does the Sac down pipe accept a cat? It appears not
2. If not is there another Sac model or brand not on their site?
3. Will I then need a different cat? No prob, just let me know.
Don't get me wrong, money aint a problem. I just want to buy THE parts that work.
I don't get to look under THAT part of my SVO that often so I am a little "green" in this area.
And I am a little curious, this 3 inch down pipe (which ever one works) bolts right up to our stock turbo "elbow"?
Sorry to beat this horse but I think this is all usefull info for me and the other rookies.
Chris

[Otto Man]

Thanks Mike, but....
This seems to buttress my original thought that there is NO model number for the upgrade for this "down-pipe". It is a buy and modify type deal. Don't get me wrong, but I ain't gonna"buy a pipe" just to have some one fudge the install. I need a cat and I need to pass emissons. I'd like the improved breath in my engine, but I ain't gonna sacrifice my emissions.
Maybe a new air cleaner? (just kidding)
Thanks, I'll stay stock!
Chris

[Stinger]

Chris, I can build you whatever kind of DP you want, whatever kind of Cat you want, etc....all you'll have to do is have it welded onto your stock "catback". This should help solve the "problems" you are finding with the ready-made units available.

Stinger

[Otto Man]

You Guys Win

I've decided this is worth doing so I have a couple quick questions. My friendly local Midas will do the install. They may even make the down pipe, I'll get back to you on this!
1. Sacramento vs ATR down pipe? I just want a 3" tube that goes down to the CAT from the elbow and doesn't hit anything. I'll have a CAT welded to it. What's the cleanest and best pipe design?
2. 3" I/O Cat: Which one? I notice this internet site called MagnaFlow has a 3 inch "mirror" (wow). Any suggestions on another source here or is this as good as it gets? Remember I flunked emissions and I'm burning precious "fix" dollars here.
3. Is the FlowMaster Y-Pipe something I need to order before I go to Midas?

This has been a fun thread. Thanks for all of your input and suggestions. (and I sure hope I ain't becoming a PIA)

Thanks again,
Chris

[richsvo]

What's the cleanest and best pipe design?

My suggestion...Give Stinger an email and have him make one for you. From what I've seen and read, he does excellent work. I'm sure that together you could work out a game-plan to fit your needs.
HTH,
Rich