When do you need a bigger intake?
 

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On a turbocharged car, the intake is often sized according to the stock turbo from the factory. It will be designed to dampen noise, and fit with relative ease into a certain area of the engine bay. This comes before performance and this is why upgraded intakes are such a huge benefit to making power on a turbocharged car. Smoother tubing with a high flow filter will reduce restriction and make less work for your turbo. However, sometimes even these upgraded stock replacement intakes are not enough. Read More!

Nice article. I needed that info because I have the jrb 3.5 and wanted to go bigger. It looks like it wouldn't be much different unless I am pushing big power.

I thought the answer to the question was always :-)

For a street driven or daily driven car going larger than 3 is counter-productive. 3.5" may work though. Remember a 3" ID intake is good for well above 400whp. So adding a 3.5" intake (probably good for 600hp) on a car that doesn't have the supporting mods even for 350whp is not ideal because at low air flow (think idle, bumper to bumper traffic, and so on) the air speed is so small that may cause erroneous MAF readings. Still, a 3.5" intake may still be acceptable, but 4" is overkill for anything street driven.

Later edit: sadly, this is something that article is not mentioning about. "the bigger - the better" works well only when you're pushing for the maximum all the time (say, track). When still using the car for it original purpose the things became a bit more complicated.

I know a local here has a 4in intake on his daily.

And i have a 3.5in with no issues with driving (idle and everything) either.

sent from my Nexus 6P

Well since my hp goal is 600-650, I guess I am going.

I'm rockin a jbr 3.5 wide path full aluminum intake. Daily driven and no idle or driving issues after calibration. Plus the sound it makes is awesome [emoji1360]
I feel like 4in intake is better used for a huge turbo like a precision turbo. If you have a ko4 but plan on upgrading to a bnr , a Garrett or corksport turbo , 3in or 3.5 will do. Plus I heard of idle issues with the 4in intake.

I have a 4 in on my K04 DD and love it. Wouldn't do it any other way :-)

How's the fitment with the coolant line under the turbo inlet hole ?

Very tight with any larger than stock intake. But still doable...

I ran a 3.5" on my daily speed 3 back in the day. Ran perfect at idle and I didn't even run higher idle speeds. I think going up to 4" is where you might start to see some issues, but even then they are minimal.

The biggest issue I've seen from bigger intakes is popping the P0335 code. Since bigger intakes need to be scaled so high, when you turn the key on but the motor is still off, the ECU will see the higher voltage and think the car is running. It has a crank position sensor check that happens when g/s is over a certain amount and it looks to see the crank sensor pulse after a certain time frame. When that doesn't happen since the engine is off, it throws the code.

Most find it fairly easy to splice in some extra coolant line so you don't have to worry about it. I find it helps me to have extended it every time I have to remove the intake