Hi,

Is there any downside to using a 2" pipe from my bnr stage 2 turbo to the intercooler? I was gonna use 2.25 from turbo to cooler and 2.75 from cooler to engine but a 3" to 2.25" reducing elbow is pretty hard to find. I have the ebay intercooler with the 3" inlet/outlets. It's much easier to find a 3" to 2" reducing elbow so now I'm thinking of using a 2" pipe from the turbo to the intercooler. Then I'm gonna use a 2.75" pipe from the intercooler to the tb. The greddy tb piece is 2.75 so that is why I decided on this size for the piping after the intercooler.

I have a series 4 13bt in a first gen so the piping on the hotside isn't that long, maybe 18 inches max.

BTW, I'm using the 90 degree elbows on the intercooler because it will greatly simplify my piping.


thanks

 

2.5"

*shrug*

 

do you have a FMIC? the least I would run is 2.5", best is 3"

 

3"....

 

http://www.amazonhose.com/ call these people they can find you anything. plus they dont sell crap couplers. only 4ply silicone the hard stuff.

the way mine is setup is a bnr stage 4, hot side 2" to 3" pipe from turbo, reduced down to 2.5 for the inter cooler and then back to 3 on cold side and then reduced down to 2.75" for the greddy adapter.

 

3.0" pipe it too big.
Hell, 2.75" pipe is still too big.
2.5" is okay.
2.25" is still okay.
2.0" is fine.
You get better response with the 2.0" IC pipes.


-Ted

 

Ok, thanks for all of the info guys. From all of the research I have done, I think the smaller piping is better for my setup (BNR stage 2). I've decided to stick with 2" from the turbo to the intercooler. Cheap ebay intercooler has 3" in and out so I'm using the 90 degree reducers on both sides. I'm gonna run 2.75 from the intercooler to the engine. I have that greddy tb piece and that's 2.75.

2" plus 2.75" divided by 2 is and average of 2.375" piping. I think it's perfect. My average piping size might actually be just a little larger because the piping on the drivers side is about 1/3 longer than the pass side.

This turbo engine is in my 85 so the total piping distance is alot shorter than a fmic second gen so that should help lessen the lag.

Thanks again!
John

 

Keep in mind that the flow difference between 2" and 2.5" pipe is huge. A 2.5" pipe will flow ~90% more air than a 2" pipe at the same pressure, and will have ~70% less pressure drop at the same airflow. I wouldn't run 2"...

And just because the TB connector is 2.75" doesn't mean you have to run a pipe that big. 2.5" will be fine.

Lastly, flow depends (mostly) on cross-sectional area, not diameter. A pipe halfway between the CSA of 2" and 2.75" pipe would be ~2.4". Might as well use 2.5"

 

I'd recommend staying with the 2" on the hot side, since thats the size of the turbo discharge anyway. I'll be putting a Garrett GT35R on my s5 13bt soon that's in my 85, and it's discharge is still 2", so that's what I'm staying with.

For the cold side, I'm running 2.5", for the better flow. But I wouldn't go any larger than 3", simply because lag from having to pressurize all the extra volume would outweigh the benefits, unless you're just going for peak hp and running some pretty high boost that is.

 

I used the old school greddy intercooler, witch is 2.25, on my bnr stage III and stage IV and it worked very well. don't have any comparisons with the 2.0 pipe but seriously the diameter of the stage III and 4 is 2.25 the stage II should be that same size but maybe not.

 

All I can say is I went with 3 inch and it is way to big. It almost covers the stock turbo!

 

Why do you think you need to match the size of the compressor discharge?

So why not do the same on the hot side for better flow? Why restrict one side?

 

^ ^ ^
You don't really need to match the size of the compressor discharge. It just helps limit total volume that the turbo has to pressurize. By running piping on the hot side the same size or just slightly larger than the discharge, acts as if you just extended the dischargerto reach the inlet of the intercooler.

The reason not to then use the same size piping after intercooler, is that when exiting the core, the larger the piping is the easier the air will flow. The limiting factor here though, is that you still have to consider the total volume that then must be pressurized in turn. Otherwise, if say for instance, running plumbing for intercooler was the same as for exhaust systems (on turbo cars), you could then just go with bigger is better mode of thinking, and only have to worry about using the largest piping possible.

Hope this clears things up a bit

 

Wow, it took a little time for this thread but we got some very good opinions on here. This was my line of thinking as well. The o/d on my turbo is 2", the i/d slightly less than 2" so I shouldn't need to go much bigger on the hot side. Also, it's in an fb so that pipe on the hot side is only going to be fairly short, approx 18" long. Then after the intercooler I'm going to reduce it from the 3" outlet on the intercooler to 2.75 (for simplicity sake so I don't need another reducer at the tb). Pipes don't need to be the same size on both sides. Alot of the newer kits I see coming out keep the pipes smaller on the hotside than the cold side. The nissan silvia's are a great example where you see this used. And I tend to think on the same lines as flyasshooptie that it is the total volume of air that matters. I also believe that keeping the hotside about the same size as the outlet on the turbo will keep the velocity up as the air moves into the intercooler.

 

Absolute bollocks. The longer a pipe is the more restriction it causes. The smaller a pipe is the more restriction is causes. Simple as that.

That's not a reason to use different-sized pipes, that's a reason to size them both based on how much they need to flow, not what they're connected to.

Note that I never said anything like "make it as big as possible", only that 2" piping is an unnecessary restriction. I wouldn't go over 2.5" unless I was planning on making a lot of power.

I don't get why people are so hung up on the size of the turbo discharge. You're connecting to an intercooler with a 3" connection so why not use that instead? It makes just as much sense (i.e. not much). Like I just said, it should be clear that the restriction caused by the intercooler pipes depends as much on their length as their diameter, and the turbo dischage is only that size for a very short distance, only a small fraction of the length of the pipes.

This is a big misunderstanding that seems common around here. Keeping the velocity high in intercooler piping has no advantages. It simply adds restriction.