Porsche-O-Phile

Without the full system (including 3" downpipe) what's the point?

sweanders

Stock configuration without a cat is with a muffler in it's place, on 1991 models there is a third muffler between the cat and rear muffler.

I don't see what you mean about "only free flowing" since a free flowing muffler is basicly a perforated pipe with a resonance chamber around it and there are several of those on the market.

An exhaust is not only about the size of the tubing, the way it bends and changes shape when needed is also important to keep up velocity. I am pretty sure that installing a crappy 3" downpipe consisting of just two bends and a piece of tubing can rob power since a bend that is to sharp slows down and compress the gas and since there is extra room in the there will be added turbulence.

WesM951

Jim, Yes Borla does, they even make a 4" to 4" if your that crazy

Missin2

hmm.. Interesting question..

IMHO best bang for the buck exahust wise would be taking the stock exhaust,

remove the cat
and tack on a better rear section (muffler only) like a magnaflow strait through, the XR1, or the likes..

The tricky part in many areas is finding someone underhanded enough to take out the cat where its illegal :rofl:

Bigger is not allways better.. however Less resistance is good

With the plan above you can probably get that all done for under $150, for the muffler 2-feet of strait pipe and an hour of labor at an exhaust shop..

Exhausts for these cars are WAY too enspensive IMHO so i will be going with the plan above.. i can live without the extra 5 hp..

Missin2

hmm, anyone have a stock cat/down pipe around MD that they are willing to part with?

I may get to work on this in a week or two once i am done with emissions..

I allready have the pipe.. and for the non stainless magnaflow its only gunna run $60.. and I can weld..

jerome951

Check with Mike Buck (that's his user name). I think he's trying to get rid of a stock system and he's in MD.

From what I remember, conventional wisdom says removing the cat and muffler and going to a good, full 3" system is worth 10-20 hp plus faster spool up.

Duke

Well, just remove the cat back and do some test runs without it. Power gains!

Mike1982

Yea, you have to remember that when you remove the cat, like I did, you have to re-adjust your boost unless you have a EBC. I went from a 15psi car with a clogged cat to ~18psi car with a 3" cat-bypass from fabspeed. I had to get home and turn it down, THEN go out and get on it. All I can say is postive things about Fabspeed, very nice to work with. Great product. Now, with this pipe, the sound is just awesome at full power. Add that in with a wall, like on the highway, and you find yourself just slowing down and speeding up to hear it!! Oh yea, the spool up is much quicker!! It was about 3k before I got full boost, now I can go full boost at about 2,750 or so.

NZ951

Jeff, I will be making a downpipe as well, maybe might buy the SFR downpipe if I get lazy as that will require some more effrot, and they are the most cost effective option by far. I am surprised no one has noted before and after HP gains by going to a 3" apart from Vitesse (its good to have a very experienced vendor contribute here!). I guess I will test back pressure and see if the exhaust is being restrictive! I want to get to 400HP in the smartest way possible on pump and 18psi Only 60HP to go!

Porschefile

NZ951, I see you said "full" in the title. Are you referring to a full 3" as in the gains between the stock 2.5" turbo "elbow" (pipe connected to turbo, some call it a downpipe) and a full 3" elbow? This is what I was assuming. If you just mean an entire 3" exhaust (catback, downpipe, etc) compared to the stock 2.5", it can only make more power. It seems that some on here think there is no real performance improvement in a 3" exhaust, but that's just ridiculous. Look at ANY dyno of any other turbocharged vehicle of similar displacement (even smaller displacement) and you'll only see gains. Now does that mean that larger is always better? No. A 4" or larger exhaust for a 2.5L would be completely ridiculous for anything under 600+hp. A 3" exhaust is decently sized for anything ~2.0-3.0L IMO.

I'd like to counter the question by asking, does anyone on here have any dyno charts showing a loss in power or no gain in power from a 3" exhaust?

NZ951

Yes I am referring to a full 3" system inc the downpipe. It depends on the back pressure whether there will be gains or not. Yeah a 4" system is a stupid idea I agree.

RolexNJ

Then why did Porsche have a 4 inch system on their 944T Cup Car Series as stated in the December 2004 issue of Excellence? You know something they didn't?

NZ951

Yeah Porsche never made any mistakes or produced anything that was not optimal. Infact, lord knows why they didnt put is on the 944 turbo off the shelf. So Rolex, how much was backpressure reduced by going form the stock format to the 4" in those cars with their turbo config? Also, do you have any idea of the flows capabilities of 2.5 inches? You want real world examples? Special Tools 2.5 monster producing well over 400WHP on a couple of grand in Vitesse products, stock exhaust.

Duke

Please you two...it would be nice to see a thread without you fighting.
Regarding exhaust piping size like 3" versus 4" there are different theories. Corky Bell for instance mean it's plenty enough with 3" for most high HP applications whereas other books states otherwise.

IMHO for max HP I'd go for a 3" with the WG dumping free.

NZ951

Thanks for your post Duke, some guys just cant keep it technical and on topic!

Yup, Corky says exactly that, I plan on a 3" system with a ATM WG pipe...