Q: what’s the appropriate size intake pipe from filter to turbo
 

Context: I’m in the process of assembling a turbo NB from scratch, built around a Trackspeed cast manifold and EFR6758.

Already in place:

• 2” hot side pipework
• 2.5” cold side in 2.75” TB
• 3” exhaust

The EFR compressor inlet is 2.5”.

Is there any reason to use any larger than that to feed the turbo from the filter? Or put another way, is 3” piping going to make any difference to how the turbo responds.

Without any science to back this, I think 2.5” pipe will be no meaningful restriction compared to the air filter which will be essentially the same regardless of whether it has 3” or 2.5” pipe sucking on it.

My plan is to house the filter behind the fog light with a pipe that passes behind the headlight.

What do you think?

If for some reason 2.5" is all that'll fit, do that, but if you can I would use 3.0" with a stepped coupler or taper it to 2.5". Probably not going to net any big power, but a 3" tube shouldn't cost more than a 2.5" tube.

I used a Silicone reducing Elbow that went from the turbo inlet diameter, to, IIRC 3" for the filter assembly. Since I, as many do, needed the elbow to get the filter over to the side, this was the minimum restriction for the total set-up; as it allows for a gentle change in diameter.

DNM

Isn't adding a 3:2.5 reducer just gonna add more head loss than a straight 2.5 pipe?

No. On the outlet going from 3 -> 2.5 it would but on the suction side going fun 3 -> 2 it won't. The two greatest restrictions on the suction side are the air filter and compressor wheel. As long as the step from compressor wheel inducer to tube diameter is around 30% bigger, you're good to go. That size is pre-engineered by the compressor housing inlet (unless you stay modifying housings for bigger wheels). But the largest filter you can fit, the better off you are.

The end result - 2.5" to 3" elbow + 3" pipe and filter
 

https://live.staticflickr.com/65535/...4f2e20c2_k.jpg
https://live.staticflickr.com/65535/...fb4125b2_k.jpg

Thats gotta be just about the best intake possible imho. Good work!

Sorry to dredge up an old thread, but pleased to see I'm not the only one to go 3" into wheel well.

I went with a 2 45" turns though to try and lessen the restriction; meant I had to cut a lot of the wing out.

Note the difference between a car that's lived in the UK to Australia lol.

https://lh3.googleusercontent.com/MA...-no?authuser=1

Heh! I also like to clean. What’s black on mine used to be more more dusky!