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well i got a friend that has a mandrel bender and can make me the IC pipes, i want to daily drive about 300-350 but i also want to be able to push it more, hopefully reaching 450hp, what size pipes would be good for my hp limits?
 

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2.5
 

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2" ID is also good. May limit horesepower but that is 50% less pipe to fill therfore decreasing tubo lag significantly. I know lag doesn't affect peak dyno results but since you are looking for 300-400rwhp I assume you are aiming to build a well balanced car not a dyno queen......so keep lag in mind.
 
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Mostly Thumbs said:
2" ID is also good. May limit horesepower but that is 50% less pipe to fill therfore decreasing tubo lag significantly. I know lag doesn't affect peak dyno results but since you are looking for 300-400rwhp I assume you are aiming to build a well balanced car not a dyno queen......so keep lag in mind.
thanks for the advise bro.
 

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Hey Bryson......Area= pi x radius squared. Volume =area x pipe length. More volume means more lag.

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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good info here...however i think the question missed is...how the hell does your friend have a mandrel bender?

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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does anyone have any experience showing that changing to slightly larger diameter piping hurt lag?

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
 

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I agree with 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.
 

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so what size turbo would u need if you wanted to run 3" piping with a 80mm throttle body and custom 2jz style intake manifold around 25lbs ?
 
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IdealSupra said:
good info here...however i think the question missed is...how the hell does your friend have a mandrel bender?

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...
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.
 

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MKIIIpowered said:
Well I run 2 3/4 quarter piping but what do I know. ;)

Will
see will? if you had 2.25" pipes your monster a/r would spool at 2200 rpm ;)

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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