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2.5

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coo thanksCkanderson said:

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Going from 2.5'' to 2.0'' is a 50% drop? Hmm, I must be taking the wrong math courses.

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Keep in mind, a 2" pipe will only have 64% of the area that a 2.5" pipe has.

G

thanks for the advise bro.Mostly Thumbs said:

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2"

3.14 x 1x1 =3.14

2.5"

3.14 x 1.25 x 1.25=4.9

4.9 divided by 3.14 = 1.56 ....thusly 2.5" pipe has 1.56 times the volume of 2" for a given length. (56% increase....)

The math course I took to figure this out was grade 9 math....then on to a mech eng degree....what math are you using ?

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im not an expert but i know here in the entire state of FL there are only two mandrel benders and both are huge commercial companies who dont bend pipe for the public....like directly....

jsut curious... and i too say 2.5 in a good balance for not to bad lag and the hp range.

from the numbers he wants..he probably wont have to upgrade the turbo much if at all......if done properly...

it theoretically shouldn't hurt lag in terms of how quickly the turbo spools up unless you have a situation where the increased volume is _very_ large, like, in compared to the flow rate. the volume increase between 2.5 and 2" piping would certainly be significant in relative terms, but how much volume does like 5 feet of 2.5" and 2" piping take up?

the difference in volume between that much piping would be on the order of like a tenth of a cubic foot. that doesn't seem so significant when flow rates are on the order of hundreds of cubic feet per minute.

maybe the effect is more one of throttle response, or the 'lag' is because of poorer off-boost performance because of low velocity through the pipe?

but at high flow rates, smaller diameter piping and the turbulent flow that would undoubtedly result from it might offset some of those considerations. i have no idea really, i'm just guessing

i always thought it was strange that toyota used such small piping with such a big motor. many other OEM turbo set ups use much larger piping after the intercooler. volvos use ~2.5" piping, saabs, audis, ~2.375", all with much smaller engines (though they are running higher boost).

anyway, the same argument about lag has been made about using larger intercoolers. mk4 owners say they don't notice any increase in lag when they install those huge ass FMICs. *shrug*

i personally would go for something larger than 2", but worry a bit less about diameter, and more about using as few transitions as possible and making them smooth.

shiva

At one time I ran the *theoretical* calculations in terms of displacing the volume of intercooler pipe with various crank HP. At 400 HP, we're talking hundreths of a second difference. At 100 HP, its only a couple of tenths.

In reality, I did notice a difference in lag by a change from stock to 2 1/2 hard pipes. It DECREASED. I'm assuming this was because the turbo wasn't fighting the poor stock piping design or wasting time expanding the stock rubber hoses.

50% is not equal to 56%.Mostly Thumbs said:

4.9 divided by 3.14 = 1.56 ....thusly 2.5" pipe has 1.56 times the volume of 2" for a given length. (56% increase....)

I win!

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he is the head service tech and installer at vacuum pump systems, inc. and friend bobby is the owner and yes they don't bend pipes for the public, but i been working with them for a while now.IdealSupra said:

im not an expert but i know here in the entire state of FL there are only two mandrel benders and both are huge commercial companies who dont bend pipe for the public....like directly....

jsut curious... and i too say 2.5 in a good balance for not to bad lag and the hp range.

from the numbers he wants..he probably wont have to upgrade the turbo much if at all......if done properly...

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916 Posts

Well I run 2 3/4 quarter piping but what do I know.

Will

Will

see will? if you had 2.25" pipes your monster a/r would spool at 2200 rpmMKIIIpowered said:Well I run 2 3/4 quarter piping but what do I know.

Will

2.5" here. have a short length of 2" right off the turbo but after that its all 2.5". i went to an ic quite a bit bigger than stock and its cross flow. at the same time did the pipes. and mine spooled quicker as well. maybe if i ran 2" it would have been quicker still but i dunno.

dave

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How would 2.5" crush bent pipes do?

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