intercooler pipe size question

[polobai]

quick question for you guys-for my setup with a gt4082, FFI short runner intake with a Q45 throttle body, which size intercooler pipes options would you go with:
1. Hot side: 2.5 inch pipes, cold side 3 inch pipes.
2. Hot side: 3 inch pipes, cold side 3.5 inch pipes.

My dilemma is that the Q45 is about 88mm in size, or about 3.5 inches, but my entanks on my Greddy intercooler are only 75 mm, or about 3 inches. The compressor outlet on the GT4082 is 2.5 inches also. Im inching toward option #2, but i want to make sure that throttle response will still be decent. Is anyone running any similar setups, and what pipe sizes are you guys using?

 

[rakkasan]

I'm going with 2.5 inch/3 inch pipes. I know that I won't flow more than that set up can handle, but I dunno, you might be able to. I'm trying to keep lag as low as possible.

Regardless of which one you use, let me know please.

 

[polobai]

i think im going with the 2.5 and 3 inch setup-should be fun! we will have to cruise when we get our beasts' running again!

 

[IJ.]

I'm a little confused to the reasoning behind the mismatch in pipe size?

The Hot air is less dense therefore Larger in volume and once it goes through the IC it'll be cooler/denser/smaller so if you were going to run Odd size pipes wouldn't you go hot=3.5" and cold=3"?

Having said that grab a Comp map work out what pressure ratio you'll run convert that to CFM then base your pipe size on that to keep it below Mach 0.4/304mph and this will give you the most throttle response V's flow.

Bigger isn't always better in this case.

 

[forcefedsupra]

Smaller pipes make you spool faster. It takes less time to fill less space.

 

[MKIIINA]

/\ while this is true you need to look at flow also. you dont want to pick pipes that are going to be a restriction down the road.

that said i agree with IJ as im thinking you have the piping backwards for your measurements. you are going to waste time (lag) letting those larger pipes fill up on the cold side while the hot side is creating a bottle neck. i realize you are running the q45 tb and want the best flow but it might be overkill.

 

[IJ.]

Smaller pipes make you spool faster. It takes less time to fill less space.

As long as you're NOT going past mach 0.4 in velocity.......

It's one of those times where a bit of Math will yield great results!

Too large a pipe and you end up with "Perceived Lag" while the Turbo may spool quickly it takes time to fill the pipe due to slow gas speed.