can U get even less restriction or 3" piping is pretty much the best U can get?
I say this cause there are silencers widder than 3" right?

 

for an engine this size I can't imagine ever needing anything over 3" unless the hp numbers were getting huge. Unless you're makign a good deal of power, I doubt even 3" pipe would be necessary.
Patrick

 

I know that a 3" pipe is one of the best for these cars but I'd agree I don't think you'll need anything bigger than that.

 

Yes! Bigger is better on turbo- period.

I had the 3 1/2" JIC turbo back on a stock hybrid turbo. I had to restrict my exhaust down to the 3" Racing Bear Turbo back because I could not fix my boost creep.

The 3 1/2" exhaust spooled the turbo MUCH earlier. Boost off idle, and it felt like a larger engine. I could cruise at 1,000rpm in 4th and pull smoothly up the revs from their.

RB 3" couldn't drive below ~1,500rpm smoothly since that is where boost was commng on now and full boost was 500-1,000rpm later.

Although, I could drive the car at the higher rpms around town now since it was SOOO quiet.

Turbo= bigger exhaust is better.

 

can U guys explain in simple english what boost creep is ?

 

Boost creep is the condition when the wastegate is open all the way to bypass exhaust gasses from powering the turbo exhaust wheel, but not enough exhaust can be bypassed through the wastegate so boost continues to rise since the exhaust wheel keeps accelerating.


-edot- I just saw in my last post I typed Racing Bear. Fat finger typing, naturally I meant Racing Beat.

 

You realize that larger pipes decrease backpressure, and less backpressure will not allow your turbo to spool as quick. The less backpressure you have, the more air will want to bypass the wastegate and exit through your 3.5" pipe.

Your torque curve will suffer as a result, hut you should see slighhtly higher HP numbers...

Not to mention your another 1/2 inch closer to the ground.

 

Do you need bigger than 3 inch?
Is the outlet on your turbo bigger than three inches? There are other factors that come into play, but quite frankly unless you have a hugemoungeous turbo 3 really should be plenty, and like was said above, there is such a thing as too big you start to sacrifice low end when dropping restriction that much. The 3.5 being better than 3 post was probably a coincidence, besides thats based on his butt dyno, not fact.

 

THX !!
allways nice to see helpfull ppl here instead of the usual "go die somewhere else U noob" lol (joking,. or not ;p )
thx again
to the favorites this post goes

 

at stock or near stock levels then 3 inch is fine. but once get get outta that range and are wanting 400 or more then u need to get bigger than 3 inch. yes 3 inch will work but bigger will release more power/spool in those higher hp applications.

 

Do you have an N/A or TII?

 

You realize that larger pipes decrease backpressure, and less backpressure will not allow your turbo to spool as quick. The less backpressure you have, the more air will want to bypass the wastegate and exit through your 3.5" pipe.

This is incorrect. The lower backpressure causes more of a pressure differential between the sides of the turbo exhaust wheel and therefore faster boost response and total turbo shaft speed therefore, more gas will have to flow through wastegate to keep the turbo shaft speed (boost) the same.

Your torque curve will suffer as a result, hut you should see slighhtly higher HP numbers...

Since boost comes on faster you get torque earlier.

Not to mention your another 1/2 inch closer to the ground.

Actually, my JIC sytem had more ground clearance everywhre except where it had to cross the rear axle and the muffler.

 

good thread!

 

Since the TII question has been answered, what about N/A. What's the best size? Ignoring the 5/6th port backpressure necessity.

 

U bet it !! really great

I believe that bigger = better since the objective on N/A is allways less restriction, then wider piping = less resistance (right? )


about what car I have.. I still don't have. but its a S5 TII

 

I would think bigger is better, but I'm also assuming there's a point where going bigger is not worth it / not a smart idea. That's what I'm looking for.

 

wow, someone has absolutly no clue as to how a turbocharger functions....

 

I'm in that boat, thus I keep my mouth shut . Oh, someone answer my question please!!!

 

instead of makin comments like that drago, why dont ya give some info to correct his confusion. Everybodys gota learn take a step up and share your knowledge.

 

Not true.. you need an exhaust that'll keep the amount of air coming out of your engine moving and creating scavaning..

In a nutshell... if the exhaust is too big then the air stalls and each slug of air coming out of your exhaust port hits a wall of stopped air in your exhaust, if the piping is too small then you get backpressure

Frank

 

I'll second everything IAN said. I run a custon 4" DP into dual 3" pipes on my car and have been very pleased. People run 3" all the time, and make good power with it. Really, the benefits of larger piping are seen in better spool etc... not an increase in top end. There are plenty of people making 400, 500 and possibly more HP with 3" exhausts. Generally speaking, the turbocharger itself is all the back pressure a turbo system needs.

As for ground clearance... my 4" pipe still sits above the frame rails... so I'd say I dind't sacrifice any clearance

NA's on the other hand, as was previously mentioned, do have an optimum diamter etc... but since I drive turbo, I have no idea what it is

Also on the turbo, the manifold design is very inportant to the performance of the system. Again, the cheap generic manifolds (HKS cast, OBX etc) will work.... but they are not ideal.

 

GOt it !
any idea about the ideal size ?

 

I'm not positive but i have been told that on a N/a car that you should need no larger then maybe 2 and 1/2 piping unless your making killer power. just my .02 cents, comeone correct me if i'm wrong

 

2.5" is still too big..

mazdatrix uses 2" straigh dual and i've found that to be very good.. helps out from low and all the way to about redline in S4's.... unfortunatly for it to work really well i'm guessing your gonna have to make your actuators work off the airpump on S4's and if you don't have the air pump your gonna have to use electric actuators or do a search for many different ways of making it work..

but if you don't wanna do that you can always use the small line mazdatrix uses on there. it comes out from the header from the front rotor and goes into the small pipe going to the actuators.. unfortunatly i don't think it'll supply enough backpressure to open the ports till very late..

 

BLUE TII and carx7 are correct. When it comes to turbo, bigger is better, resulting in faster spool up, more torque and top end. Is there a point that the dia is too big? Not really, you may reach a point were your not gaining anything other then noise, but you wouldn't be able to fit that drainage pipe under the car!

N/A wise, 3" is way too big unless your running a full bridge or peri port. key in N/A applications is maximum velocity with minimum back pressure. Anyone saying "you need some back pressure for torque" is full of ****. Its not the back pressure thats maintining torque, its the fact theres a bottle neck somewere thats maintaining higher velocity. For street cars be it stock port, street port, or mild 1/2 bridged, 2" primaries collected to a 2 1/4" ~ 2 1/2" merge and 2 1/2" pipe out or 2 2" if running a dual muffler. you could run dual 2.5" after the collector, but you probly wouldn't see gains or looses unless your heavy on the nitrous. the after market systems available for the 2nd gen all fall into these pipe diameters for a reason.

~Mike...............