2" or 2.5" tubing for DIY FMIC setup??

[hotrodf1]

Hey guys,

I have been thinking about doing a DIY style FMIC sometime in the near future. It seems like most of the piping kits are in the 2.5" alum tubing. But when I look at the pics of most of the branded kits, the piping looks like it might just be 2.0". Can anyone suggest whether 2 or 2.5" tubing would be best for no more than 10psi on stock internals motor??

It seems the 2.0" would offer less turbo lag for sure, since the volume to fill would be quite a bit smaller I think.

From my meager math skills it looks as if sizing up from 2.0 to 2.5 increasing the volume inside the piping by a whopping 56%.

what do you guys think??

 

[505zoom]

Air expands and gets denser as it goes through the IC. So, if you want to keep the pressure and velocity exactly the same throughout the whole IC system, you need to use larger piping for the cold side than you use on the hot side.

As for the actual diameter, that depends greatly on how much power you are going to run.

 

[Dpwhitehead1]

well i've got 2.5" cold and 2"hotside...

 

[hotrodf1]

well i've got 2.5" cold and 2"hotside...

Hmmm. Never thought about that.
I think maybe 505zoom meant to say they other way around? Since the air after the intercooler will be cooler and more dense, the pipe would be smaller to keep the velocity the same.

But does it matter anyway??

I suppose using the smaller pipe on the cold side would be one way to reduce the overall volume of the system without sacrificing the flow from the hot air direct from the turbo.

 

[505zoom]

Hmmm. Never thought about that.
I think maybe 505zoom meant to say they other way around? Since the air after the intercooler will be cooler and more dense, the pipe would be smaller to keep the velocity the same.

Nope... you need a larger volume pipe to deal with denser air.
Hot, thinner, less dense air = small diameter
Cold, thicker, denser air = larger diameter

But does it matter anyway??

If you want to half-ass it, no. If you want to do it right, yes.

I suppose using the smaller pipe on the cold side would be one way to reduce the overall volume of the system without sacrificing the flow from the hot air direct from the turbo.

(uhm)

 

[Dpwhitehead1]

Hmmm. Never thought about that.
I think maybe 505zoom meant to say they other way around? Since the air after the intercooler will be cooler and more dense, the pipe would be smaller to keep the velocity the same.

But does it matter anyway??

I suppose using the smaller pipe on the cold side would be one way to reduce the overall volume of the system without sacrificing the flow from the hot air direct from the turbo.

no dude, he meant what i said. exactly how i have it. go get it done

 

[hotrodf1]

Hmmm.

I'm still having trouble getting my brain around this one.

2" pipe for hot air
2.5" for cold air.

Wouldn't that mean that there would be a lot more velocity in the small tube, considering that the same weight of air is traveling through the system. So then the air would be moving slower while in the intercooler (large x-sect area), and then would remain moving at the slower rate while it travels to the TB through the bigger 2.5" pipe?

Perhaps there's not as much velocity change as the air goes from the IC to the cold pipe, thus less turbulence??

maybe I'm trying too hard?

 

[Dpwhitehead1]

Hmmm.

I'm still having trouble getting my brain around this one.

2" pipe for hot air
2.5" for cold air.

Wouldn't that mean that there would be a lot more velocity in the small tube, considering that the same weight of air is traveling through the system. So then the air would be moving slower while in the intercooler (large x-sect area), and then would remain moving at the slower rate while it travels to the TB through the bigger 2.5" pipe?

Perhaps there's not as much velocity change as the air goes from the IC to the cold pipe, thus less turbulence??

maybe I'm trying too hard?

trying to hard. ...that's what most people run.

 

[hotrodf1]

trying to hard. ...that's what most people run.

thought I might be. Are most of the professional kits done the same way as well?

I'm an engineer by trade so I'm usually drawn to the "why" side of things u know.

Hell,, it would be easier to snake the 2" tubing to the intercooler anyway, since the A/C compressor is in the way. . .
Maybe that's why???

sorry, couldn't resist. . . .

 

[Dpwhitehead1]

thought I might be. Are most of the professional kits done the same way as well?

I'm an engineer by trade so I'm usually drawn to the "why" side of things u know.

Hell,, it would be easier to snake the 2" tubing to the intercooler anyway, since the A/C compressor is in the way. . .
Maybe that's why???

sorry, couldn't resist. . . .

could be man.. there's perf info on those. most guys go this way. like i said, i am too.

 

[hotrodf1]

could be man.. there's perf info on those. most guys go this way. like i said, i am too.

alright, will be filed under "things I learned today"

 

[Dpwhitehead1]

alright, will be filed under "things I learned today"

hahah. i learn something new every day.especially working on cars.

like, o-rings on injectors are made an easy install w/ petroleum jelly.

 

[mryellermp5]

i have alot of misc 2.75" bends and lengths if interested and couplers w/ t-clamps i was gonna use for the coldside but i have alot exrtra...lmk

 

[505zoom]

Hmmm.

I'm still having trouble getting my brain around this one.

2" pipe for hot air
2.5" for cold air.

Wouldn't that mean that there would be a lot more velocity in the small tube, considering that the same weight of air is traveling through the system. So then the air would be moving slower while in the intercooler (large x-sect area), and then would remain moving at the slower rate while it travels to the TB through the bigger 2.5" pipe?

Perhaps there's not as much velocity change as the air goes from the IC to the cold pipe, thus less turbulence??

maybe I'm trying too hard?

Nope... here lemme try one more time on this one for ya.

Think of the system with a 2" diameter pipe going from the turbo to the IC. The air in this pipe is very hot after going through the compressor, so it is going to be thinner than it will be after it is cooled.

The hot air inside this pipe will have a given velocity/pressure for a given RPM/gear. Now that air gets cooled down in the IC, which makes it expand and be more dense.

If you then used a 2" diameter pipe from the IC to the motor, you would be basically cramming the cool, dense, expanded air into a pipe that is too small.

If you do it properly, and make the IC to TB pipe a larger diameter, then the colder denser air can move along at the same velocity and pressure as it was before it was cooled.

Hope this helps.

 

[Dpwhitehead1]

Nope... here lemme try one more time on this one for ya.

Think of the system with a 2" diameter pipe going from the turbo to the IC. The air in this pipe is very hot after going through the compressor, so it is going to be thinner than it will be after it is cooled.

The hot air inside this pipe will have a given velocity/pressure for a given RPM/gear. Now that air gets cooled down in the IC, which makes it expand and be more dense.

If you then used a 2" diameter pipe from the IC to the motor, you would be basically cramming the cool, dense, expanded air into a pipe that is too small.

If you do it properly, and make the IC to TB pipe a larger diameter, then the colder denser air can move along at the same velocity and pressure as it was before it was cooled.

Hope this helps.

that should work wonders.

 

[BradC]

The hot air inside this pipe will have a given velocity/pressure for a given RPM/gear. Now that air gets cooled down in the IC, which makes it expand and be more dense.

Wouldn't air (a gas) contract when cooled?

 

[505zoom]

Wouldn't air (a gas) contract when cooled?

If cool air was lighter and thinner than hot air, then we would use cold air in "hot-air baloons", no?

 

[hotrodf1]

Wouldn't air (a gas) contract when cooled?

He's right . . .
remember from physics . . .

PV = nRT (IIRC, its been 8 or 9 years for my old ass)
Pressure * volume = n *r * T(temp)

So, if the temp goes down (after the IC) the equation shows that either the 1) pressure must fall, or 2) the volume must decrease.
We know the pressure should be close to the same before the IC as it as after the IC (maybe within a 1psi or so??), so with the same mass of air in the system, that only leaves the volume, which will be smaller.

This is why I thought the bigger pipe should carry the hotter air, which would be a larger volume (by weight) than the cold, dense air.

 

[awsmp5]

thats mind boggling... dense means more mass no? as in a dense rock has more mass in the same volume as a less dense rock so if the mass is going to be the same since there's no more air being added...
shouldn't the hot side be bigger than the small because hot air and hot hting in general expands?

 

[hotrodf1]

thats mind boggling... dense means more mass no? as in a dense rock has more mass in the same volume as a less dense rock so if the mass is going to be the same since there's no more air being added...
shouldn't the hot side be bigger than the small because hot air and hot hting in general expands?

More dense means more mass, as long as the volume is not changed.

yes sir, thats what I'm takling about if I read the post correctly

Mass is the product of volume and density

Mass = vol * density