# 2.5" intercooler piping ok for 700 horses?



## 98rzvr6 (Nov 12, 2005)

Hey guys Im gonna be running a precision 750 intercooler and a gt4088r so im hoping to make around 700 horses this year so my question is, is it alright to run 2.5 inch intercooler piping or should i step up to 3 inch? The reason why i ask is because i already have 2.5 already fabbed up and tig welded and its fit great so i kinda wanna stick with it but will it really make a difference? The gt40 is a 2.5 outlet so i dont see why i couldnt but just making sure. thanks


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## 5mall5nail5 (Mar 13, 2002)

Should be fine - it may take more careful design in bends and transitions but it should work.


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## marat_g60 (Mar 5, 2003)

Im in the same boat but shooting for 600whp, Im probably gonna stick to 2.5". For your setup you can just step up to 3" on the coldside if you're concerned about it. It'll just be more efficient, but you can try out the 3" I know its been done countless times before.


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## TIGninja (Mar 21, 2010)

Turbo outlet size to intercooler and TB size from cooler to TB


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## 98rzvr6 (Nov 12, 2005)

Im assuming your asking me sizes? 2.5 from turbo to 3 inch on intercooler to 3inch from ic to 3 ich throttle body


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## marat_g60 (Mar 5, 2003)

What he means is you should run 2.5" from turbo to intercooler, and 3" piping from intercooler to TB.


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## GTijoejoe (Oct 6, 2001)

Most vehicles over the 700hp club generally use 3" piping after the IC in my experience. 
But its not like it can't be done w/ 2.5"


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## procket2_8 (Feb 19, 2004)

Heres a little engineering to blow your mind because I actually just figured this out mathematically the other night, because I too was having doubts on my 2.5" setup. 

Mass flow = density x velocity x area (pipe) 

Pressure is relative to velocity, usually higher pressure lower velocity and vice versa, so 

With a smaller pipe, you will run a higher velocity making up for a lower area. There is a point where you can "choke" the flow and actually become less efficient but for a 700 hp car, with a 2.5" pipe the velocity difference is about 30% higher than a 3" pipe. I think when I figured it out it was 400 ft/s for the 2.5" and 330 ft/s for the 3". But when you go to 3" at the throttle body you actually lose some velocity and increase pressure again. Until you are truly going for a world stunner turbo car the differences are minimal mathematically. 

Thank you Engineering college.


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## dub_slug (May 12, 2008)

Good post procket :thumbup:


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## EugeneDubbin (Aug 31, 2008)

procket2_8 said:


> Heres a little engineering to blow your mind because I actually just figured this out mathematically the other night, because I too was having doubts on my 2.5" setup.
> 
> Mass flow = density x velocity x area (pipe)
> 
> ...


Sweet info. Thanks for contributing some technical data. Don't see a lot of that around here lately!

I'm going to couple this info with this idea:



TIGninja said:


> Turbo outlet size to intercooler and TB size from cooler to TB


and do a little math for my setup, but that sounds pretty ideal overall.


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## procket2_8 (Feb 19, 2004)

No problem. That question was in the back of my mind for a little while and I finally had time and brains to figure it out. Glad I could shed some light on the subject and contribute some "hard" evidence.


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## GTijoejoe (Oct 6, 2001)

procket2_8 said:


> No problem. That question was in the back of my mind for a little while and I finally had time and brains to figure it out. Glad I could shed some light on the subject and contribute some "hard" evidence.


I dont mean to offend you :heart: but there's no 'hard evidence', you posted theory. Flow vs. piping size has been around the block many many many times around here. Simple engineering calc's rarely uphold in the real world, the system it self is more complicated given the fact the piping is not always straight and it goes through a cooler. 

Don't get me wrong, I'm not knocking you at all, just shedding some light not to take it as gospel :thumbup:

The logic behind Tig's advice is as simple as understanding that the turbo outlet and the TB are the choke points of the piping system before and aft IC, the IC should be sized and efficient enough not to be the choke point.


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## procket2_8 (Feb 19, 2004)

GTijoejoe - you are absolutely right! But until someone shows me some flow bench data on piping size theory is all I have and can present.

I am a proof is in the pudding person, and after going through engineering school, doing thermal fluid sciences labs and studies and creating one hell of a turbo spreadsheet to determine the compressor and piping size I need I have a good understanding of things. After crunching the numbers my mk4 vrt was almost dead nuts on power and boost compared to my calculations, so either I have a coincidence, luck, built a great car or all three...

There is also function, fit and budget and there aren't many people who can have a 700 whp car and have all three.

Also bends do not affect the velocity so much they create pressure loss which creates an increase in velocity of the air. 

I am not saying I am guru but I would like to see some flow bench work on this subject before I can come to any "stone" conclusions.
:thumbup:


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## GTijoejoe (Oct 6, 2001)

oh sir we understand. There are many of us that have multiple engineering degrees and experience :thumbup:

I was only concerned with 'hard evidence', the truth is you won't find it on the vortex. Compared to other communities the information isn't there, there is no flow bench data, the only proof in your pudding your going to find is by the dyno and that type of info is there, just not here. There isn't alot of 600+hp builds going on here, they are rare by quantity.

Either way, I'm not entirely convienced that flowbench data would give you what your utlimately looking for anyways. Sure it will give you the flow and understand the efficiency of your system, but intake velocity is very important for an engine in producing power, that coupled with the intake manifold etc. will change from setup to setup... the flow bench will not give you power output.


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## huichox4 (Nov 8, 2004)

GTijoejoe said:


> oh sir we understand. There are many of us that have multiple engineering degrees and experience :thumbup:
> 
> I was only concerned with 'hard evidence', the truth is you won't find it on the vortex. Compared to other communities the information isn't there, there is no flow bench data, the only proof in your pudding your going to find is by the dyno and that type of info is there, just not here. There isn't alot of 600+hp builds going on here, they are rare by quantity.
> 
> Either way, I'm not entirely convienced that flowbench data would give you what your utlimately looking for anyways. Sure it will give you the flow and understand the efficiency of your system, but intake velocity is very important for an engine in producing power, that coupled with the intake manifold etc. will change from setup to setup... the flow bench will not give you power output.


as long as the flow numbers are not specific to one component only you are correct, but if you design and build each component to flow the same from one transition to the other you can definitelly correlate CFM to HP. 

if you put your setup on the flow bench it should be from the intake to the turbo, then from the turbo outlet until the IM runner flange


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## procket2_8 (Feb 19, 2004)

I forgot to mention before that convection cooling uses velocity in the equation, so the faster air will help with cooling. 

Also bigger turbos flow more air at a lower pressure..ie velocity is greater....just a thought.


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## killa (Nov 26, 2000)

yes, it's fine.


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## Romerid3r (Jan 3, 2009)

bends and turns will be ur nightmare 2.5in is fine


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