2.5" vs 3" NA/Turbo

[Keymaster666]

As the title suggest...

I'm NA now, but planning to go Turbo next year...

So should I get a 2.5" exhaust and stick to it even with turbo setup later or should just go 3" now and prep it for Turbo?


How much of a difference does a 2.5" to a 3" really make?

Especially for NA cars? is 3" bad for the car? too little back pressure? Too loud?

For 2.5" on a Turbo, is it restrictive? Not free flow enough?

[DarkPira7e]

What are your power goals? 2.5 won't really be a restriction. I had 330whp on stock exhaust. Would it have been more with a larger exhaust diameter? Yeah, but it's not like you need it. If you have an external wastegate that is recirculated, you'll notice more of a restriction. Go with the 2.5, you'll be fine

[Keymaster666]

Originally Posted by DarkPira7e

What are your power goals? 2.5 won't really be a restriction. I had 330whp on stock exhaust. Would it have been more with a larger exhaust diameter? Yeah, but it's not like you need it. If you have an external wastegate that is recirculated, you'll notice more of a restriction. Go with the 2.5, you'll be fine

Oh wow, yes, I wasn't even planning to upgrade the exhaust as I like to have a sleeper feel of a car.

Goal is around 300hp daily...and most likely with a vented wastegate.

So going 3" is fairly pointless if one isn't pushing for 400hp or more hey.

[DarkPira7e]

Originally Posted by Keymaster666

Oh wow, yes, I wasn't even planning to upgrade the exhaust as I like to have a sleeper feel of a car.

Goal is around 300hp daily...and most likely with a vented wastegate.

So going 3" is fairly pointless if one isn't pushing for 400hp or more hey.

Oh, since you asked about upgrading the exhaust, I assumed you planned on it. Stock exhaust is not 2.5"..

You'll be fine with stock exhaust. I liked mine, but honestly just wanted a little more noise, the turbo quiets it down even more than stock, nobody could hear my car until the wastegate opened, then the entire town knows where I am. If you follow the right of the two gauges, you'll see how the sound correlates with boost pressure- 9 o'clock on the gauges is 0 PSI, 12 o'clock is 15 PSI

Here's my car, it's barely audible unless the wastegate is open.

[Keymaster666]

Originally Posted by DarkPira7e

Oh, since you asked about upgrading the exhaust, I assumed you planned on it. Stock exhaust is not 2.5"..

You'll be fine with stock exhaust. I liked mine, but honestly just wanted a little more noise, the turbo quiets it down even more than stock, nobody could hear my car until the wastegate opened, then the entire town knows where I am. If you follow the right of the two gauges, you'll see how the sound correlates with boost pressure- 9 o'clock on the gauges is 0 PSI, 12 o'clock is 15 PSI

Here's my car, it's barely audible unless the wastegate is open.

Oh wow, that is stock exhaust? I know stock is around 2.1", and quite a lot of bends restirctions, but to know that you can get that much power cramped in with the stock zorst is a good start to me...then I guess 2.5" will just be enough.

So is it true that turbo will quieten down the zorst noise?

[DarkPira7e]

Originally Posted by Keymaster666

Oh wow, that is stock exhaust? I know stock is around 2.1", and quite a lot of bends restirctions, but to know that you can get that much power cramped in with the stock zorst is a good start to me...then I guess 2.5" will just be enough.

So is it true that turbo will quieten down the zorst noise?

The turbo does quiet it down, it's like adding a fat muffler at the beginning

[Keymaster666]

Originally Posted by DarkPira7e

The turbo does quiet it down, it's like adding a fat muffler at the beginning

What kit are you running and I hear turbo flutter

[Breadman]

i asked mike this question a while ago but it was for SC. he said for my goal of 3-350 wheel it didnt matter

[Keymaster666]

Originally Posted by Breadman

i asked mike this question a while ago but it was for SC. he said for my goal of 3-350 wheel it didnt matter

So the size of exhaust doesn't really matter for these power level...mostly will just be sound

[DarkPira7e]

Originally Posted by Keymaster666

What kit are you running and I hear turbo flutter

It started as a CXracing kit but is modified a bit. You hear the turbo flutter because I blocked off the blow-off valve to see how long it would last like that. Didn't seem to hurt performance or the turbo. Maybe after years it would wear the bearings out fast? I don't know.

Don't get the CXracing kit. It requires a lot of effort to get rid of all the warped flanges

[Keymaster666]

Originally Posted by DarkPira7e

It started as a CXracing kit but is modified a bit. You hear the turbo flutter because I blocked off the blow-off valve to see how long it would last like that. Didn't seem to hurt performance or the turbo. Maybe after years it would wear the bearings out fast? I don't know.

Don't get the CXracing kit. It requires a lot of effort to get rid of all the warped flanges

Haha yeah I thought you might have blocked off the BOV, thought the kit came like that.

Heard that it hurts the turbo, but i guess with casual driving and daily wouldn't really kill it...as long as you don't beat the crap out of it, or track it daily.

I got a Custon Kit made, and already a few that was fitted on a few 86 in the country...so I guess it should be ok.

But aren't you worried the turbo will break one day and the shrapnel will get into the engine?


I want the flutter, not worried of the turbo itself just the motor

[DarkPira7e]

Originally Posted by Keymaster666

But aren't you worried the turbo will break one day and the shrapnel will get into the engine?

I want the flutter, not worried of the turbo itself just the motor

There's no way the turbo would come apart just from the pressure in the charge pipe pushing back on the compressor wheel. I have a friend who had done this exercise on his WRX from about 2011 to 2018 when he sold it with no issues on the VF34 in all that time.

Financially I'm not worried about my engine which is why I wanted to try it with a $200 turbo VS a high quality Garrett unit or something similar. I don't think going turbo if you have worries about the engine or are in a tight spot with finances ever works out in anyone's favor anyway.

If you want the noise, get a blow off valve and just tighten it all the way; it'll do the same thing. I just didn't want to worry about a leaking flange with the CXracing intercooler

[Keymaster666]

Originally Posted by DarkPira7e

There's no way the turbo would come apart just from the pressure in the charge pipe pushing back on the compressor wheel. I have a friend who had done this exercise on his WRX from about 2011 to 2018 when he sold it with no issues on the VF34 in all that time.

Financially I'm not worried about my engine which is why I wanted to try it with a $200 turbo VS a high quality Garrett unit or something similar. I don't think going turbo if you have worries about the engine or are in a tight spot with finances ever works out in anyone's favor anyway.

If you want the noise, get a blow off valve and just tighten it all the way; it'll do the same thing. I just didn't want to worry about a leaking flange with the CXracing intercooler

Yeah, makes sense, stick with NA if you can't afford to go turbo and worry about the impact that it might cause.

Thats why I bought a kit but haven't installed it, and slowly but surely prepping for it and a lot of supporting mods slowly gathering up.


Didn't think that CXracing is that problematic...

But after your mods, i'm sure its running nicely with no leaks?

[DarkPira7e]

Originally Posted by Keymaster666

Thats why I bought a kit but haven't installed it, and slowly but surely prepping for it and a lot of supporting mods slowly gathering up.
Didn't think that CXracing is that problematic...
But after your mods, i'm sure its running nicely with no leaks?

Slow and steady is the way to go!

On my CXracing manifold, every single flange needed heavy belt sanding to get them flat, it took several hours to get the exhaust leaks to stop, especially the wastegate flange.

The downpipe provided did not fit at all, so I had to custom fab something that fit.

The issues were limited strictly to the flanges and fitment, all the welds are decent and nothing has cracked. The intercooler worked great and I had no other complaints- made great power and I love the equal length setup.
I also ran my own wastegate, a Turbosmart Ultragate 38mm. I wouldn't ever trust the wastegate provided by CXracing to manage something as important as diverting exhaust gas accurately.

The car doesn't run right now since i'm putting a built block in ( my timing chain guides let go somehow, thanks Toyota) so I'm going to build the car a bit differently; using the JDL intercooler, different turbo, re-doing the downpipe again, but I will keep the CXracing manifold, since it worked well and I put the work in to get it that way.

If i had to do it over again, I would have bought a JDL kit out of the gate with the GTX2867R and been done