Intercooler pipe size

[gtx510]

What's the OD of the throttle body? The part where the hose goes on? I wouldn't going bigger than that. That'd also avoid funky transitions right before the t/b.
Sizing your piping ID to your throttle plate size sounds sensible, or to the size of the t/b inlet ID if it tapers to the plate.
Just like a larger intercooler core or longer piping, larger diameter tubing increases turbo lag. CorkyBell's book actually gives formula's to calculate the (lag) time with different ID tubing and airflow rates.

[Jho]

The TB is 2.5" diameter, that is why 2.5" piping is optimal IMO.

[Turpro]

when i boost next spring im going with a 2.5.

[gtx510]

BP t/b plate is 55mm? 55mm = 2.17", a little more than 2.125" (2-1/8")
16g tubing is ~1/16" (0.0625") thick, 2x = 1/8"
with a 55mm t/b 2.25" or 2-3/8" seems like it'd be enough.

Are you sure the t/b OD is 2.5"? b/c than would be 63.5mm, I'm not saying it's not possible, it's just an odd number vs. 60mm, 65mm, 70mm, etc.
there should be enough room for a 55mm plate and 60mm (2-3/8") OD?

[popsicle]

run 2.5" charge pipes. that's the way to go. and it will save you much trouble when you do upgrade to a larger turbo. the vj20 gets boring pretty quick. or at least it did for me. even with the vj20 however 2.5" charge pipes aren't too bad at all. and trust me i've used and tried a bunch of different BPT setups.
Des.

[92_2_fast]

I'm running 2.25 w/ a 30X12X3 IC and wish I'd gone bigger with the pipes. Go 2.5 and be happy

[FE3-323]

be smart & go small to big I run 2" into a 2.5" IC & 2.5" out to the TB.... this gives you quicker response, less PSI drop & more air velocity.

I had been told from a shop that you should run 2-2.25 from the turbo to the IC, then 2.5 from the IC to the TB.

I figured it out with asking... My common sense told me to do it this way

[FE3-323]

2.5" is over kill for the VF12 pre IC if you ask me.

[bgdriver]

I'm not sure of the exact formula but it does exist somewhere in Corky Bell's Maximum Boost where you figure out, using the CFM of the engine, the size of the piping, and the pressure ratio of the turbo, the velocity of the air in the intercooler piping, it needs to be around 250 ft/sec. I'll try to post it in a minute if I can find the book.

[bgdriver]

CorkyBell's book actually gives formula's to calculate the (lag) time with different ID tubing and airflow rates.

time = V/flow rate X 2

and here's his section on tube sizes:

There is probably a magic number that airflow velocity in a tube should not exceed, for reasons of rapidly increasing drag and consequent flow losses. I suspect this number is around mach .4 or about 450 ft/sec (bgdriver: whoops off by about 85%!), since drag, and therefore flow loss, increases significantly after this. Tube size can be easily checked by calculating the maximum airflow attainable, dividing by the area of the tube in square feet, and dividing again by 60 to convert to feet/sec. An approximate value for maximum airflow can be obtained by multiplying the desired bhp by 1.5.
Example:
Let power = 400 bhp, for which maximum airflow is approximately 600 cfm, and air tube diameter= 2.5 in.
Then
Velocity = airflow/area=

600 ft^3 per minute multiplied by 1/60 minutes per second
pi(2.5/2)^2 in^2 (Ignore this111) 1/144 square feet/ square inches

= 293 ft/sec

(sorry this is really hard to type out but pi(2.5/2)^2 square inches belongs under 600 ft^3 per minute and 1/144 square feet/ square inches belongs under 1/60 minutes per second, /= divide, and ^=to the power of)

The speed of sound is approximately 1100 feet per second. Therefore,
Mach = 293/1100 = 293 ft/sec
Thus, the 2.5-inch-diameter tube will be enough to flow 600 cfm without unreasonable drag. (my emphasis)
resist the temptation to use larger diameter tubes than necessary, as little drag is created in smooth with gentle bends. Larger tubes will only add to the volume of the IC system (read: more lag), and that is not a good thing to do.
RULE: A large tube is not necessarily better than a small tube.

/quote
Anything within the quote in parenthesis is me writing not Corky Bell
My fingers hurt.

[laruei]

you know when you posted that at first i didnt read it becuase it didnt make sense. i just did and it does...yay!

no but seriosuly. if anyones cars on here need 600cfm...then i will give them a pat on the back thats a lot, consider a big block 440, 454, 460 areas...almost all at some point came with a 600cfm quadrajet or a holley...so i think a 4 cyl..needing 600cfm is kinda silly. but cool if it does...lol

[Limegreen MX-3]

2.5 in on my setup