Staggered Intercooler Piping

[Cz.]

While looking at other builds, I’ve noticed that many people do a staggered piping setup for their intercooler piping. The logic being that the hotside air charge takes less space and that after going through the IC, the air will be cooler and denser meaning that the piping needs to be bigger to accommodate.
However, when I was looking at the “How much does your 7m breath under boost?” sticky and using the “mean gas flow” link I’m not sure how this staggered piping idea makes sense. Using the formula in the link, if you keep everything the same and only change temperature, the only # that is affected is the Reynolds #. If that’s the case, then is there any reason to have different piping size since temperature doesn’t affect the velocity characteristics?
I guess now that I think of it, a different reasoning for the staggered setup would be that by having smaller piping you could “fill” the IC faster (higher velocity air) and then you would have larger piping afterwards to slow the air down to the apparent ideal of 300 f/s at the TB.
Maybe I just answered my own question but I might be missing something here, so if someone wants to point out any mistakes in my reasoning feel free to do so.

 

[Doward]

From a Physics standpoint, the cooler, denser air would require LESS volume for the same velocity. So technically, you would want to stagger it the other way, unless like you mentioned - you want to keep velocity below ~300 fps

 

[Poodles]

The stock setup is staggered... (gets larger at the 3000 pipe)

Same as usual, the outlet on the turbo is usally smaller than the throttlebody, so it has to get larger somewhere...

 

[Cz.]

Yeah, I was thinking about this too, but I haven't seen any setups done this way, only the opposite.

From a Physics standpoint, the cooler, denser air would require LESS volume for the same velocity. So technically, you would want to stagger it the other way, unless like you mentioned - you want to keep velocity below ~300 fps

So no one has a clue as to how to do this in the optimal way?

 

[Doward]

Sure we do - but you'd need exact measurements of the temperature charge / pressure pre and post IC to determine the actual mass of airflow and optimize the system around that.

Then again, it would only be optimal at the exact flow/pressure you set it up for.

Unless anyone has any ideas for dynamically changing pipes?

 

[sthmstr]

It would seem to me that it's avery minimal improvement with any kind of leisure car. If you are doin F1 or LeMans then sure that kind of research would probably be worth it. You would also in that circle and income level be able to afford the precise meetering Doward talked about. Really If you want to increase velocity then you will want to reduce as you move away from the outlet. I believe the idea of running bigger piping closer to the TB is that you have collected a huge amount of air and every breath it takes is big lumps of air rather than the faster spit of a smaller shot. Kinda like intake manifold design-tech. Big plenum vs Small plenum and Big vs Small runners/ ports. Don't want too big though so you take forever to hit boost and your BOV does the stupid chuckle noise all the time.

Honestly dude spend your energy in making sure you have smooth and seemless transitions with straight shots. Keep the piping diameter simple as same in and out.

 

[supr88]

remember the faster the air is being forced down the pipe, the more friction which creates heat. makes sense to me.

 

[IJ.]

Keep it below .4 Mach.

2" piping
1.57 x 2 = 3.14 sq in
300 cfm = 156 mph = 0.20 mach
400 cfm = 208 mph = 0.27 mach
500 cfm = 261 mph = 0.34 mach
585 cfm max = 304 mph = 0.40 mach


2.25" piping
3.9740625 sq in = 1.98703125 x 2
300 cfm = 123 mph = 0.16 mach
400 cfm = 164 mph = 0.21 mach
500 cfm = 205 mph = 0.26 mach
600 cfm = 247 mph = 0.32 mach
700 cfm = 288 mph = 0.37 mach
740 cfm max = 304 mph = 0.40 mach


2.5" piping
4.90625 sq in = 2.453125 x 2
300 cfm = 100 mph = 0.13 mach
400 cfm = 133 mph = 0.17 mach
500 cfm = 166 mph = 0.21 mach
600 cfm = 200 mph = 0.26 mach
700 cfm = 233 mph = 0.30 mach
800 cfm = 266 mph = 0.34 mach
900 cfm = 300 mph = 0.39 mach
913 cfm max = 304 mph = 0.40 mach


2.75" piping
5.9365625 sq in = 2.96828125 x 2
300 cfm = 82 mph = 0.10 mach
400 cfm = 110 mph = 0.14 mach
500 cfm = 137 mph = 0.17 mach
600 cfm = 165 mph = 0.21 mach
700 cfm = 192 mph = 0.25 mach
800 cfm = 220 mph = 0.28 mach
900 cfm = 248 mph = 0.32 mach
1000 cfm = 275 mph = 0.36 mach
1100 cfm max = 303 mph = 0.40 mach


3.0" piping
7.065 sq in = 3.5325 x 2
300 cfm = 69 mph = 0.09 mach
400 cfm = 92 mph = 0.12 mach
500 cfm = 115 mph = 0.15 mach
600 cfm = 138 mph = 0.18 mach
700 cfm = 162 mph = 0.21 mach
800 cfm = 185 mph = 0.24 mach
900 cfm = 208 mph = 0.27 mach
1000 cfm = 231 mph = 0.30 mach
1100 cfm = 254 cfm = 0.33 mach
1200 cfm = 277 mph = 0.36 mach
1300 cfm max= 301 mph = 0.39 mach

 

[Doward]

Yep. It's been long established that around 300mph is as fast as you want the air velocity. Friction losses get big quick after around there.

 

[sthmstr]

That is some way cool info!! Airflow engineering is wicked BA.

 

[IJ.]

As long as you keep it below critical there's not a lot of difference to be felt in the real world, I did all the math built 2.5" pipes then upgraded to 3" for "future mods" and found that the bigger pipes let the 3540r spool earlier and while there was a drop in speed there was a gain in performance.

Moral of this is don't get too caught up with the theory

 

[sthmstr]

Moral of this is don't get too caught up with the theory

Cheers to that. I have spent days with Corky Bell's book (despite the advice of Bob Norwood) trying to build a theoretical setup. Mosty makes my brain hurt and turns out to be completely different when I built it.

 

[Big Rob]

Also note that the mass flow numbers IJ. posted are for a theoretical cross section, if you would like to be more accurate in your calculations you would need to include pressure drops across pipe length and bend radius's.