-7/9s Or -5s Garretts

[Ants]

That's the reason why some tuners are against 4in zorst with low mounts because you may loose torque and hence loose response as well.

[Piggaz]

???

Because pressure BEHIND the turbine wheel and not allowing the exhaust gasses to exit the pipe, HELPS the turbine flow?

If that's the case, I better get one of my twin 3 inch pipes, chuck it in the bin and just run a single 3!

[Ants]

Keep ur pants on Paullie... u run a 2.8ltr engine and the thread above is specifically relates to 26's not stroked engines.

[scotty nm35]

lol.

I made an extra 30kw going from 3 inch to 3.5, less exhaust back pressure the better. The turbo is enough restriction already.

[Ants]

lol. I made an extra 30kw going from 3 inch to 3.5, less exhaust back pressure the better. The turbo is enough restriction already.

Acknowledged, that the bigger the zorst the more power you will make.

HOWEVER....torque numbers can drop due to exhaust being too free flowing and not having enough back pressure to produce torque at lower gears and rpms.

Usually the torque is reallocated to another part of the curve (at a higher end) giving you lower response but higher HP.

[scotty nm35]

Back pressure is created by the turbo, once it is through the turbo you just want it gone.

Anyone running a Varex muffler will tell you when closed the lag is severe, and torque drops right off.

[Ants]

Look if your xzorst is too small it will be too restrictive, but if its too big you will loose torque in the lower revs but gain bigger HP.

Its about reaching that performance balance for 26's (non stroked engines) with low mounts. Otherwise you would see every man and their dog dropping 5in xorst in there car.

Edited May 29, 2013 by Ants

[hazjaz]

Running a 3' with -9s, cams etc would be more responsive/higher torque then running with 3.5'? But the 3.5' would be a higher power figure.. Is this correct?

[Mick_o]

LOL!

[Ants]

Running a 3' with -9s, cams etc would be more responsive/higher torque then running with 3.5'? But the 3.5' would be a higher power figure.. Is this correct?

No mate. You would most likely see an increase in both torque and HP with 3.5in zorst depending on your setup.

Please read carefully what I wrote in my previous last two posts.

3in or 3.5 inch is perfect.

Are there any significant performance benefits to be gained of a 4in zorst on a 2.6ltr (with low mounts) compared to a 3.5in? - I'm inclined to say no, and as do other members who run 3.5inc and make 400kw+ atw.

Edited May 29, 2013 by Ants

[XGTRX]

You want NO exhaust back pressure in forced induction..... period, end of story. Small NA engines different story. Large NA engines the average Jo wouldn't be able to tell the difference because the is so much torque to begin with.

Secondly if you are rebuilding your engine put performance cams in it and run -5s. Best all round setup for response and HP in a 26.

[Roy]

if u got to big it will be to laggy and not responsive, some backpressure is good! 3.5" is perfect!

Definitely can be the case on NA cars.

On turbo cars its not the point that too large an exhaust causes loss of back pressure. Its how you do the larger diam exhaust can increase back pressure.

Off the turbo a small step change in diameter can be good at straightening the airflow for better flow in the exhaust. But generally sudden changes in diameter can add to back pressure. So if you go from a little 55mm opening in the turbone housing to a 3" pipe then the turbulence caused by the dramatic change can add to back pressure and poor cylinder evacuation.

If I was doing a twin setup I would plann on doing twin 65mm off turbos and then nice pipe merges into 3.5-4.0" cat back and mufflers. (or twin 3" with 2.5" final mufflers)

[Ants]

You want NO exhaust back pressure in forced induction..... period, end of story. Small NA engines different story. Large NA engines the average Jo wouldn't be able to tell the difference because the is so much torque to begin with.
Secondly if you are rebuilding your engine put performance cams in it and run -5s. Best all round setup for response and HP in a 26.

Yeah....and what exhaust system would you run?

Edited May 29, 2013 by Ants

[Roy]

Me? Somethintg custom that I built that probably wouldnt work anythign like I hoped or an off the shelf exhaust

I have a twin setup planned for my car and just need to find the right price turbos so I can click "checkout" on my shopping cart of goodies for a twin setup. 4 mufflers and twin cats should hopefully mean I dont get booted off at track days

[Ants]

Not you Roy......I have no doubt you know what setup you want to run.

[XGTRX]

3.5 like everyone else uses because it's obviously proven to work. Most important part of the Setup that really effects response is the manifold design the change the exhaust gas velocities, volumes and pressures BEFORE the turbo. Once the gasses have done their job you need to get them out as fast as you can so not to interfere with the incoming gasses. That the theory anyway.

[Mick_o]

XGTRX just won the internet! NO BACK PRESSURE IN FORCED INDUCTION! Think about it? How do turbocharged engines produce torque? Yep you guessed it! A turbocharger! The sooner you get it spooling the sooner you start producing more torque! If you create "back pressure" either side of the turbine you introduce lag and lose down low torque. Back pressure in turbocharger talk is something we call "a restriction"

[Ants]

3.5 like everyone else uses because it's obviously proven to work. Most important part of the Setup that really effects response is the manifold design the change the exhaust gas velocities, volumes and pressures BEFORE the turbo. Once the gasses have done their job you need to get them out as fast as you can so not to interfere with the incoming gasses. That the theory anyway.

agree, but also having a tuned exhaust system AFTER the turbo will also contribute to responsiveness and performance just like Roy mentioned.

Edited May 29, 2013 by Ants

[XGTRX]

Did I really win!!! Do I get an Elvis Presley badge. :-).

With the theory about tuned exhaust, I think front pipe diameter is more critical than anything else to get those gases out.

[scotty nm35]

agree, but also having a tuned exhaust system AFTER the turbo will also contribute to responsiveness and performance just like Roy mentioned.

I highly doubt it, or the Gibson 32 would have run a nice aftermarket 3.5 inch system instead of sidepipes.