How much will different sized intercooler piping flow?

[fergulus]

I am looking to find out the maximum airflow that you can push through 2.25", 2.5", and 3" piping. I see tons of intercooler setups with 2.5" pipes, but am trying to figure out at what lb/min each size will become a restriction.

I'm not looking for opinions, I am looking for the math to prove it as well.

 

[92AWDHX40]

Most use 2,5 im not sure if anyone has calculated flow rates, anything with 2.5 is larger than stock. 3 inch is a bit much i would think, also look at the room you have to work with.

 

[Steve93Talon]

We made 708 whp on 2.5" IC piping, I've seen no evidence that switching to 3" would gain any power at this level.

 

[92AWDHX40]

Thanks for that info steve, nice numbers also.

 

[fergulus]

I am fairly sure that most people will never go as high as 700 hp, which definately puts to rest the 3" piping. I am wondering at what point the 2.25" piping becomes a restriction.

I see most turbos with tiny turbine outlets, which is why I got to thinking about whether getting the 2.5" piping would even be beneficial to about 75% of tuners.

 

[kahl23]

Also something to consider is that a lot of 3" setups require the battery to either be dropped down to rest on the sub-frame (a huge pain in the ass, ask me how I know...) or relocated to the trunk. Some food for thought.

 

[fergulus]

I already have 2.5" pipes up top, and a SMIM. Doing that already required that I get rid of the large battery, but this thread is to find out airflow, to see at what point 2.25" piping becomes a restriction. This would also help people out with throttle body selection as well, knowing at what airflow their stock TB truly becomes restrictive.

 

[gstryyder]

JUST WANTED TO UPDATE THAT MORE ACCURATE NUMBERS ARE IN THE MAKING. =)

here ya go bud.

*.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

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


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>


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"

but it also depends on how smooth the piping is inside... and all the bends. this i would say is " perfect piping conditions" and if you would pick a number to upsize your piping at it would be when you hit about the .3 maximum .35 mach region.

 

[fergulus]

Thanks for the font of information! That was very informative.

My turbo (FP Green) is supposedly rated to 730cfm, but I doubt I will be close to maxing it out (only going to push ~26psi) so 2.25" pipes should still be fine, according to your math.

 

[gstryyder]

As long as you are running good hard intercooler pipes that are a full 2.25" all the way around or even 2.5" after the intercooler. I would not recommend running the stock intercooler, you need some form of an upgrade. Easiest is just a bigger side mount. Remember the smoother and shorter the pipes can flow the more accurate the chart is.

 

[viprez586]

Wow good info!
Glad I've got 2.25" all around, the velocity says it all!

 

[gstryyder]

Intercooler piping size is something I ALWAYS stress to people on when they are trying to get maximum performance and good spool and they just don't listen.

 

[gsxkid81]

someone should put this in the tech section

 

[fergulus]

I've got 2.25" lower intercooler piping, with 2.5" upper (blow thru) and a mid-sized front mount. I was trying to find out this information to see if there was a need for me to get 2.5" all the way around. I'm deployed, so I have nothing but time to second guess my work and scheme for when I get home.

 

[gstryyder]

Glad to help. I have learned from the wise people in the past and from all my research and studying due to my need to create the most efficient setups possible and maximize potential. And working in my shop it helps when you know more and know what you're talking about. Its something that defines why I have the job I do.. And its just good to know stuff. I would recommend if you ever decide to max your turbo's potential that you need to upgrade your size to 2.5".

for the plans you have now your setup will be fine.

Ran my 20g on the same setup you have and that thing spooled n flowed great. And i knew i was still efficient with the ~cfm's i was flowing.

One key is to have a good quality intercooler that won't create too much pressure drop and that flows and cools well. Just because it works... doesn't mean it is working effieciently.

 

[Budget90GST]

Is the CFM above in STP or ACFM (actual cubic feet per minute)?

How are you calculating your mach number?

Just curious.

 

[knochgoon24]

Is the CFM above in STP or ACFM (actual cubic feet per minute)?

How are you calculating your mach number?

Just curious.

And are those calculations assuming a parabolic flow through the pipes? With a no slip (zero velocity) condition along the walls.

I know I've learned the equations necessary in my fluid dynamics class, but they aren't pretty. Especially when you start to deal with the effects of the boost pressure, increased charge temperatures, and bends.

To get close estimates, you really need to consider a parabolic flow of some sort.

(I'm actually writing a program right now, due Tuesday, that calculates flow through a 2-D channel.)

 

[gstryyder]

To add a bit more info and maybe answer your questions and a few that people are probably thinking of typing...general equation and explanation for the calculations of finding mach for your setup are here. Mach number - Wikipedia, the free encyclopedia
mach is dependent on temperature directly. which is accounted for by the speed of sound in the equation. sound is a factor all in itself.
i would recommend readin up on this page. .. i know. im tired. maybe can explain a little better for ya tomorrow.
Speed of sound - Wikipedia, the free encyclopedia you need to adjust for this as far as temp goes also to be accurate enough. since there are such great variances. REASONING WHY A QUALITY INTERCOOLER IS A GOOD IDEA

another quick show of speed of sound... simple terms VERY GOOD TO READ THRU. ESPECIALLY THE LINKS ON THE RIGHT

http://www.ndt-ed.org/EducationResources/HighSchool/Sound/tempandspeed.htm


read this also.
Machmeter - Wikipedia, the free encyclopedia

as to answer the question:

And are those calculations assuming a parabolic flow through the pipes? With a no slip (zero velocity) condition along the walls.

Yes.
Also add to it that is in a straight pipe no bend situation. at a general given temperature ~60*F. which is also affecting the equation and accuracy. (have to throw that into your equation. there are so many variables that unless you feel like doing all the math. you go off a general bases.) these variables are why i adjusted the max mach value of the air/pipes. to account for imperfections, bends, and slight temp changes. but an accurate equation would require accurate numbers from the beginning based on your setup to be honest. this just gives you a general idea.

here is an explanation of the figures in the equation used above and Affecting variables.

1) The speed of sound is a function of the gas temperature. The numbers quoted above 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). Correct me if I am wrong. Or just guide/ link me to the info and I will learn myself. =).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 goes with 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. temperature also affects when your transition from hot to cold side of the intercooler. thus why i never understood why people will go with the same piping size all the way pre/post intercooler. or just run giant oversized interccolers with bad designs. such as the proven GReddy crap.

I really can't see lag with larger piping being a concern. Just the ability to run as effiecient as possible. yes lag is affected but it is other performance variables that matter more. 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. which is why i say to switch at a mach value (calculated) of 0.3 rather then 0.4

If you want help estimating conditions pre/post intercooler to get a better approximation or anything like that... just ask i will try to help or try to find the time to figure it all out. . i barely had the free time to gather all this together just found it a very important topic and set other things aside.

THERE ARE SO MANY VARIABLES THAT YOU MUST TAKE THE MOST ACCURATE (GENERAL EQUATION) ASSES YOUR SETUP AND GO FROM THERE. IT IS KIND OF HARD TO CALCULATE EVERY SINGLE LITTLE VARIABLE. SO WHAT YOU DO INSTEAD IS GET AS ACCURATE AS YOU CAN WITH GIVEN INFO AND THEN GO FOR A SLIGHTLY LOWER (THEN MAX) MACH NUMBER.


If I missed anything or if I need to answer any other questions I will try to do so tomorrow. IM TIRED.

HOPE THIS HELPS GUYS.

IN OTHER WORDS> YOU GET A BALLPARK FIGURE. TO GET AN ESTIMATE OF WHICH SIZE TO USE, AND TRY IT OUT. SEE HOW IT WORKS FOR YOU.

It is crazy how much thought you can actually put into building a car the right way.

now we see why just bolting up your favorite parts and cool looking shyt isn't always going to yield you better performance then the next guy.

IF I screwed anything up I will reread tomorrow when I am not falling asleep at the computer. so i am able to fix it. Please forgive my blotchy and jacked grammar. I will go through at fix it tomorrow. I am just so tired but wanted to throw this out there for you guys who will sit on here all night figuring this out.

APPROXIMATE CFM'S I WOULD RECOMMEND FOR EACH PIPING SIZE.

2" ~450-500 cfm
2.25" ~575-650 cfm
2.5" ~700-800 cfm
2.75" ~850-950 cfm
3" ~1000-1150 cfm

this is all depending on how much hot air you are pushing from that turbo...how much are you also maxing out your turbo? AND I AM NOT SAYING THAT GOING BEYOND THESE NUMBERS WILL NOT NET GOOD RESULTS EITHER. It is all still just a trial and error thing. Turbulance becomes a factor above .40 mach tho. so i would at least stay under that....not saying you have to but umm... ya know

 

[knochgoon24]

I didn't realize you put that much detail into the equations, since there really wasn't anything but final numbers posted.
I should have guessed that you factored that all in when you started talking about mach numbers. You probably lost a few people with that detailed explanation.

You've had a few classroom setting lessons in this, haven't you?

It's always interesting to see how my college courses tie into real life projects that aren't mundane.

 

[gstryyder]

JUST AN FYI!!!

i will be updating with more accurate real time factors involved and get more accurate numbers especially factoring in some variable automatically. so it is more accurate for you guys. yet, i am very busy and it will take some time. HOPEFULLY ONLY A FEW DAYS. but it all depends on how busy i am. please bear with me. I am doing my best to get this as accurate as possible for out applications so i can elminate most variables. rather then making you do some of the math. ...

Jst keep that in mind. these numbers are not perfect. but they will get more accurate and eliminate variables as time goes on. i am working on just a general equation to throw it all together. but it takes alot of time. if somebody wants to pitch in or knows there stuff and wants to help. ### do or pm me. those of you who understand all this stuff. know the variables ad such i am referring to that are not currently accounting for. i am in the process of an update. but this is it for now. stay tuned for morew folks. The revise version. FYI. this is fairly close just no cigar to being right. my numbers are not wrong as they stand. they could just be more accurate for the given application and eliminate variables and make it easier for you guys

I will let you know when I have more updated information.

SORRY, I AM JUST A VERY BUSY INDIVIDUAL LATELY! =) Still trying to do my part to help out.

 

[pboglio]

Here is the calculator for pressure losses in a typical throttlebody:

Throttle Body Sizing Calculator | REVTRONIX

Take it for what its worth.

I'll make this quick. Off my spreadsheet, given an airflow of 45 lb/min, turbo outlet temp of 375*F, turbo outlet pressure of 25 psig the following pipes will drop the listed psi:

2.25" O.D. straight tubing: 0.17 psi per foot
2.5" O.D. straight tubing: 0.10 psi per foot
3" O.D. straight tubing: .04 psi per foot

Using a (bend radius/pipe diameter) ratio of 1 which is a pretty tight bend and the worst you will see or the tightest you can bend a tube without rupturing it, the K factor (loss coefficient for a 90* bend) is roughly .25-.4. Using K = .35 I get for the following:

2.25" O.D. 90* bend: 0.27 psi per bend
2.5" O.D. 90* bend: 0.17 psi per bend
3" O.D. 90* bend: .08 psi per bend

Various pipe step ups or step downs will yield various additional K loss factors and you'd need to consult a Fluids text for the appropriate charts.

I use the rule of thumb that every 1 psi drop is roughly 10-11 h.p. lost at the 450 h.p. level. So if I have a 2.25" lower I.C. pipe that has 2 90* bends with 4 feet of straights, I get a psi loss of about 1.22 psi loss. If I upgrade to a 2.5" pipe with the same configuration I get about .74 psi loss. For 3" I get about 0.32 psi total pressure loss. At best, the switch to the 3" pipe on the lower I.C. pipe is worth about 0.9 psi gained back in the intake manifold, or about +9.0 h.p.

Also keep in mind when you switch to bigger I.C. pipes the transition off the turbo outlet has to be taken into consideration, which the psi loss actually increases as the pipe size increases, so the gains going to a bigger lower I.C. pipe are not as great as the case I just illustrated. Which is why you need to sketch out exactly the pipe configuration you have now and what you will have when you uprgrade for an accurate loss analysis.

You can play with the numbers all day long but you get the idea. There are gains to be had optimizing the piping size IF your turbo compressor is already dropping off boost at high rpms. Otherwise the turbo will simply command itself to spin up a little faster to compensate. When the turbo is pinned wide open at high rpms and your already seeing boost drop off due to the engine outflowing the turbo, THIS is where reducing pressure losses in the intake system pays off.

In my case, I saw a +1 lb/min increase and 10 h.p. gain swapping out my lower 1.675" j-pipe to a 2" j-pipe because I was already maxxing out my turbo compressor. Otherwise you won't see gains.

 

[dsm-onster]

I've been under the impression that most of us operate at over .5mach at 7500rpms. So the sub .5mach flow numbers would mean nothing WRT max effort. That means that 2.5" piping would be good for quite a bit more than 900cfm or 63lb/min. . . I could be very wrong. I can be somewhat impressionable .

 

[romeen]

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

I completely agree.

IMO, even more important than the effect on lag time is engine response. Just as the smaller ports with the resulting increase in air velocity of a 2G head make for a more responsive engine, I would think the IC piping is also part of that equation. In other words, the entire intake tract is part of the whole system and shouldn't be thought of as separate parts.

A family friend has his PhD in fluid dynamics. I asked him if 2" piping would be a restriction if flowing 36lbs/min of air. I don't recall the exact math that he used but his conclusion was that it didn't even come close. I do remember that he used Mach 1 (not Mach .4) as the point of restriction. He did not take into account the variables which you factored in but the basic principle is the same.

Intercooler piping size is something I ALWAYS stress to people on when they are trying to get maximum performance and good spool and they just don't listen.

Agreed. A lot of guys just don't put much thought into this.

 

[gstryyder]

I've been under the impression that most of us operate at over .5mach at 7500rpms. So the sub .5mach flow numbers would mean nothing WRT max effort. That means that 2.5" piping would be good for quite a bit more than 900cfm or 63lb/min. . . I could be very wrong. I can be somewhat impressionable .

not trying to be argumentative... i am asking as a question to further help the situation. i was stating that because .4 mach is where the air will start to create turbulance without any (help from factors). thus being less efficient. unless the efficiency lost is minimal to the gain achieved by continuing with the same size piping and creating more turbulence while increasing air speed just because it is not MAXED out and completely inefficient... not even factoring that an intercooler and piping "imperfections" will create more turbulance. how much turbulence would you want to create in your setup that is unnecessary.

since i find you to be a person who's knowledge i can trust ... i want to ask you. if you can help me out in figuring this out a bit. i would like your input and a bit of help in the situation since you bring up a good point. how is it that you determined most dsmers by 7500 rpm's are hitting .5mach.. is it due to the fact that is what our motors create or is that just a general statemen and seeing where most fall under?) because like i said, the chart is not accurate for our real time instance with compressed air, the extra heat, and all that.. in my opinion when i eliminate some of the variable it will show that the intercooler piping can flow more air at the same mach number based on the fact the air is denser (under boost/ being compressed) and more air well in turn require less actual space. thus more air can flow.

i personally know that these piping sizes can flow more than listed.... that is why i want to fix the math. since i know they can. ... just need to get more input and do the math. thans for throwing that out there. man.

OR has it been noted that going up to even .5 mach would still be efficient enough to see more gain then loss? trying to figure out exactly what you are trying to get at. i know that the mach number can be changed... per what people find to still be a true gain which is why i ask the question. my only statement by putting up the above chart is that once you hit .4 mach you are creating a less than "perfect" flowing environment. not saying it would not be safe or possible to go past that. it was just a general starting ground to determine where we can go from with the numbers.

if it is true that with our application that we could stretch the mach number then i would be more for it. as long as it is know to still work well.

as far as pboglio... i would have to say i appreciate the input... good info in there.

romeen- thankls for your response also but, as far as the mach number you referenced... i am not sure i would even go near 1.0 mach... but hey to each his own. i guess you could as him why he threw that one out there maybe? just so i know. =) in my true opinion that is a little bit off the charts as far as pushing your efficiency and self induced turbulence... but hey, what do i know. and as far as the whole piping size change.. this is a very good point. you will obviously loose some pressure and flow ( nt in are but with speed and adding turbulence when you suddenly jump in size. thus why when i build my setup i am going to shoot for the smoothest transition possible. this is also part of the reason why i shake my head when i see people with a 3" or more gm maf... getting thrown in the middle of 2.5 inch intercooler piping. its like wtf? but most people don't care.. expansion of piping size has its pluses, but i don't see any when it comes to expanding and then reducing. seems like things are going backwards to me.

but i am glad there are some people that pitched in with ideas, questions and just input or "impressions" . and thanks dsm-onster you bring up a good point but, would like to be able to take that info and ponder and adjust the numbers based on it. if you could throw out more info or respond to what i said above that would be great.

i want to go a little bit further with this and actually chug thru the math but i am tired. sooooper tired. my bro had a baby last night, i am tired ### i was at the hospital. and work was intense once again. but another day. its not like we have to save the intercooler piping world all in one day. . peace out guys. i am going to bed. yes, it is 7 and i am passing out.

dammit have to really fix that grammar. sorry mods. i will do it when i am not half asleep. =)

 

[knochgoon24]

In the fluid dynamics class I had this semester, here's the numbers we talked about:
Up to Mach .3 - Flow can be modeled as incompressible using ideal fluid type equations.
Mach .6 - Peak air speed reached in the cylinder heads of some performance engines (so even higher isn't hard to imagine)
Mach 1 - Causes lots of design problems.

We never messed with calculations of anything with a mach > .3 because I guess we'll deal with that next semester.

Here's a site that mentions the mach .6
http://www.rbracing-rsr.com/machcalc.html
And if their calculator is correct, at 8000rpm, with a stock piston and intake valve, our intake flow only hits mach .409 in the head with the .490 value in the calculation, and mach .597 with the .336 value. Different cams affect that mean flow coefficient.