when does 2.5" intercooler piping start to become a restriction

[bart simpson]

i have 2.5" piping all around, just wondering since im going with a big port head and a bigger tb/intake mani. its an 80mm tb. pte 750core aswell set up now... 2.5" coldside. stock like 60mm tb. pte 750core.

This ad is not displayed to registered or logged-in members. Register your free account today and become a member on Honda-Tech!

[Schister66]

Directly from the FI FAQ

...by the way, .4 Mach is the point at which air becomes turbulent and losses in efficiency start to occur exponentially. The key is to stay under that speed. You want to use the smallest piping possible that still flows enough to meet your needs. Larger than necessary piping increases lag time with no measurable gain

Originally Posted by BlueShadow

The velocities are in miles per hour and mach, and the flow rates are in cfm. Measurements for the piping are in inches.

<FONT COLOR="blue"><FONT SIZE="5">0.4 mach = 304 MPH</FONT></FONT>

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
<FONT COLOR="blue">585 cfm max = 304 mph = 0.40 mach</FONT>


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
<FONT COLOR="blue">740 cfm max = 304 mph = 0.40 mach</FONT>


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
<FONT COLOR="blue">913 cfm max = 304 mph = 0.40 mach</FONT>


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
<FONT COLOR="blue">1100 cfm max = 303 mph = 0.40 mach</FONT>


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
<FONT COLOR="blue">1300 cfm max= 301 mph = 0.39 mach</FONT>

Modified by Schister66 at 9:52 AM 10/15/2008


Modified by Schister66 at 9:53 AM 10/15/2008

[turboteg2nv]

Originally Posted by Schister66

The key is to stay under that speed. You want to use the smallest piping possible that still flows enough to meet your needs.

So I understand all that, but how do you calculate how much CFM's you'll be flowing in order to know what size piping to use? I'm guessing it can be found with whatever turbo specs you are using?

&lt;----I'm an accountant, not an engineer

[ExVtec]

Originally Posted by turboteg2nv

So I understand all that, but how do you calculate how much CFM's you'll be flowing in order to know what size piping to use? I'm guessing it can be found with whatever turbo specs you are using?

&lt;----I'm an accountant, not an engineer

+1.

[Schister66]

In order to convert from Lb/Min to CFM for the equation above, you take the flow rate in Lb/Min for your turbo (generally an educated guess based on the pressure ratio and power created) and multiply it by 14.27. That will yield the CFM flow for your setup.

For Example:
T3/T04e 57trim .63ar @ 21psi makes 452 whp
This turbo is known to have a 50lb/min compressor wheel which will make ~500bhp. Since we're using whp above, we can assume this turbo is pretty close to its max of 50lb/min.

Now to convert that to CFM, you take 50lb/min x 14.27 = 713.5 CFM. When you refer to the table above, you can see that we're starting to max 2.25" piping, but we're still in the "good" range for 2.5"

You're an accountant...not an engineer. I'm a Pre-med student...not an engineer

[LastGenEK]

^ good info here^





Modified by Schister66 at 11:31 AM 10/15/2008

[twkdCD595]

Very good information ^^



Thats how it was explained to me as well, well I was trying to ballpark what size I needed.

[irishflame27]

awesome read!

[Tony the Tiger]

I think a good practice is to go a little larger, knowing our pipes has tight bends, etc.. which hinders flow and velocity. On the list above, I would up-size the piping if you are higher than 0.30 mach.

In my case, I originally had 2.25" piping on my old turbo setup. I went with larger 2.5"/3.0" charge pipes after surpassing 380WHP, the car felt quite more response when hitting full boost with larger piping. Although the data above indicated that I was still below 0.4 mach with my old smaller 2.25" piping, my butt dyno indicated otherwise.

This was done with identical turbo (GT2871R), with nothing else changed except for charge piping. Old piping was 2.25" from turbo to intercooler, and about 2-3 feet after the intercooler then it expands to 2.5" in the engine bay. I changed out the piping mainly because my old pipes were steel and I wanted aluminum for a change (and to practice my aluminum TIG welding) and wanted a beefy-looking 3" upper pipe. After looking at my Supra with 4" upper charge piping and 100mm throttlebody, my Integra's 2.5" upper charge pipe was so lame

After increasing charge pipes to 2.5", and a little of 3.0" just before the intake manifold,, boost was getting full hit noticeable sooner. Although on the dyno, it only registered 50-100RPM better spool which was negligable and wasn't consistent, it felt great on the streets especially at lower gears as the turbo felt like it had more "hit" as the boost fully builds.

This is different than your current situation of course, but going 3" now wouldn't hurt if you intend to run over 700 CFM anyway.

[Schister66]

^^That is a good point and its hard to argue with a real-life comparison.

The equation and numbers above i believe are only for the flow rates of straight piping and doesn't take into account bends which, as Tony mentioned, are another restriction. Thanks again for the great input

[turboteg2nv]

*Book marked this for later reference. Good stuff guys

[peakaboost]

great info

so let me get this straight. i have 2.5" piping with a s362.

I think max,the turbo is good for 65lbs/min/680+whp or around there....

lets say i was around 650whp...61lbs/min...870cfm

63lbs/min=899cfm

So from this info...im getting that my set up and 2.5" piping would be good for around 650 to say 665ish.

if i did 65lbs/min i get 927.55cfm....just over the limit. so with this turbo,and my set up,im pretty good with my 2.5" piping.


Modified by peakaboost at 7:39 AM 10/16/2008

[Schister66]

Originally Posted by turboteg2nv

*Book marked this for later reference. Good stuff guys

Its also linked in the Forced Induction FAQ...

[ITR-EKcoupe]

hey tony did you notice anymore lag at all when you changed to the bigger piping?

[Tony the Tiger]

Originally Posted by ITR-EKcoupe

hey tony did you notice anymore lag at all when you changed to the bigger piping?

In my case, not at all and the dyno didn't report any later spool. However, I felt a slight flat spot on my powerband at partial boost regions, such as slowly rolling into the throttle off the lights. I am pretty sure the smaller piping improved low boost regions (there would never be enough flow to max out 2.25" piping at a measly 5-8 PSI), so it would benefit quicker spool at lower boost regions. The larger piping really felt nice as I wind up from 15-full boost, and would give a much snappier response from gear to gear. There is really no one-size-fits-all, even for piping unless our pipes are made out of expandable latex

[Leebro61]

Originally Posted by Schister66

You're an accountant...not an engineer. I'm a Pre-med student...not an engineer

In that case, it is understandable that you missed a few things. Here are the main ones:

1) The speed of sound is a function of the gas temperature. The numbers quoted above in the FAQ are using the speed of sound at ~60*F. The speed of sound is higher pre and post intercooler (unless you have an ideal intercooler) and needs to be considered.

2) You cannot convert directly from Lb/min to CFM. One is a mass flow rate and one is a volume flow rate (different units). To get from one to the other, you need to know the density of the flow. My guess is that if you found a conversion factor online somewhere, they are using the density of air at ambient conditions (temp/pressure). Obviously if you are in a compressed environment, the density increases and your volume flow would decrease for a given mass flow.

Another consideration that I never see mentioned when this topic comes up:

1) Pressure Drop: Pdrop = 4UuLR^2 (&lt;-- Centerline Laminar flow solution)
*U: Velocity
*u: viscosity
*L: Length
*R: radius

To sustain a high velocity flow you need a large pressure drop. Losses associated with bends and area transitions are also a function of 1/2*Velocity^2... so smaller piping results in higher pressure drop and higher flow losses.

I really can't see lag with larger piping being a concern. The turbos people are using respond fast, flow lots, and the piping is never fully evacuated. I would always err on the side of too big vs. too small.

If you want help estimating conditions pre/post intercooler to get a better approximation or anything like that... just ask

[Schister66]

^^Well...you take the cake sir. I wont pretend to have that kind of knowledge behind me . I take it you're something other than an accountant or Pre-med student/ professional

I guess i'll have to jack my roommate's Fluid Dynamics book and have a look. Thanks for the great input

[blinx9900]

interesting info...

[Tony the Tiger]

It's a lot of guesswork until we put it to the test... The biggest variables of all charge piping setups are still the amount of bends, the radius of the bends, length, and probablydown to how sloppy the welds are inside the piping with backpurged vs non-backpurged...lol That's just piping too, and we haven't even considered the turbo's compressor efficiency. Such cases, like some turbos benefit from a steep elbow right after the compressor outlet because it bumps up the pressure ratios up to hit a nicer the sweetspot on the comp map. Some compressors that dislike high pressure ratios will love larger piping and high flowing FMIC cores, etc.. and it completely depends on the turbo it is running, and where the engine/airflow lands on the comp map. You can almost estimate the efficiency of the FMIC core, and the inlet and outlet temps because they have to work within a useable range. If a turbo setup is seeing 60+ deg air temps, it has problems, so the rest can be guessed pretty close to the spot.

I'd go bigger, no higher than 0.30 mach on the list provided by Schister66's post. That list helped me put most of the guesswork out of the choosing a piping size You are absolutely correct, lag from oversized piping is nothing to be concerned about, but it is still detectable and the car will drive differently like what I've experienced Only for those nitty picky people like myself who jumps from a useless 800WHP+ street car, to a nice responsive 350 WHP roadracing setup, and then to a laggy 1.8L that I feel such miniscule changes to the car.

[Schister66]

^^Tony is exactly right. There are too many variables to calculate the exact piping size with good accuracy; however, it does provide a good starting point. Also, not many people are as picky about small details like a 200rpm increase in spool time. Use the numbers above (using something more towards 0.30 Mach) as a reference when deciding on your needs.

[crazy_d]

what are, if any, the benefits of having smaller hot side pipe going into a larger cold side pipe? example, 2.5 to 2.75

[TopEndTuner]

I don't want to resurrect the thread but I have a delima. I'm running a Holset HX35W and by these conversions Its 60.85lb/min X 14.27=868.3CFM. I thought my piping setup was pretty good but I don't know now. I'm running 2" from the charger to the intercooler and 2.25" from the intercooler to the TB which is a OEM Type R. Do you guys think this setup will hinder me from getting to 400 WHP or do I need to increase the sizes on both ends? And before you ask I thought the smaller piping might help rid me of some boost lag from the larger charger.

Originally Posted by crazy_d

what are, if any, the benefits of having smaller hot side pipe going into a larger cold side pipe? example, 2.5 to 2.75

X2

[champLSinteg]

For 400whp you will be fine with that size. The CFM rate you calculated for your turbo is the max it can flow but you are obviously not going to max it at 400whp. I would say it would be flowing let say 45lb/min to get that power. So 45lb/min X 14.27=642.15cfm and that is still under .4 mach when using 2.25in piping.

[TopEndTuner]

Okay I was thinking that the CFM I calculated was the Max output and I figured that would vary by the amount of boost. Glad to know I'm good. Does anybody know an equation to calculate the cfm of say any charger at only a percentage of its max?

[scamp91ex]

man i love these "nerd" threads where i actually learn stuff! this is exactly why i am a ht-member. thanks guys!