intercooler install / modifying plenum

[Spook's_Skyline]

been all over the shop getting quotes for fitting my intercooler (gtr on gts-t)

The mob ive just talked to said, the gtr cooler will work awesomely, but he wants to mod the plenum and move the throttle body to reduce piping

is this a good idea? the guy said he would use a curved section up to the front of the plenum

i like the sound of reduce piping, but have heard stories about custom plenums being dodgy and not flowing air to all cylinders

whats the go with that?

is there anyway we can test that all cylinders do get a propper air flow with the custom plenum?

is this the best way to install an intercooler?

[GeeTR]

Need a little more information on the "curved section up to the front of the plenum" bit. I know a few guys who have seen good numbers from fabricating a custom can on top of the standard RB25 bottom runners. G-Reddy of course make a plenum, plus a heap of major places here in Oz.

Do they flow evenly to all cylinders? A flow bench is used to check this often when being thought about, but I could imagine a lot of ones wouldn’t ... otherwise I guess the detonation threshold of the lowest common dominator, would be the point where the "limit" is reached.

If you were going to hang onto the car and start making serious power, the custom top half would be a good start for me I reckon!

... but just ma pinion.. =)

[JCMarshall_Law]

Think had about how much pipe length you will save, is it really woth it. There is a pressure loss of about 25 Pa (N/m2) (0.0036 Psi OR 0.00025 Bar) in 1m length of 65mm (2.5inch pipe) really, is it worth all the effort. The maths to work out that pressure loss is at the bottom of the post.

Also,

The factory plenum and inet runners were designed that way for a reason, very close to symmetrical flow with equal length runners, ie equal air flow to all cylinders so fuel trimming is not required.

Personally, I do not like the design of most aftermarket inlet manifolds, sure some flow better but pressure drop between cylinders can be significantly different resulting in different air flow and screwed up fuel trimming (some cylinders running rich, some lean - makes it very hard to tune). If you want to do it properly your are going to need a management system that allows fuel trimming, eg, Motec, (can't comment on PFC, Wolf etc.. never had experience).

My advice, leave the factory manifold unless you want really big power numbers, save the money,

Here is the maths to work that pressure loss;

Air at 60 oC flowing in a 1 m galvanized duct - 65 mm diameter - with velocity 15 m/s. (All guesses at a typical operating condition)

Reynolds number Re = dh v ρ / μ

where

v = velocity

ρ = density

μ = dynamic or absolute viscosity

Re = ( 1 kg/m3 15 m/s 0.065 m ) / 2 x 10-5 Ns/m2 = 48750 (kgm/s2)/N ~ Turbulent flow

Using Moody Diagram - the friction coefficient - λ - is:

λ = 0,015

The major loss - Darcy-Weisbach Equation

hloss = λ ( l / dh ) ( ρ v^2 / 2 )

= 0,015 (1 m / 0,065 m) ( 1 kg/m3 (15 m/s)^2 / 2 )

= 25 Pa (N/m2)

= 0.0036 Psi

= 0.00025 Bar

So with a whole extra meter of intercooler piping you would see 6.9964 Psi instead of 7 Psi at the manifold.

[R32Big_boy]

[GTR-80Y]

Damn, u should be at MIT or sumthin!

[R31 POWER]

Thats good to know JCMarshall_law,I'll keep my cooler pipes how they are!

[Parag0n]

JCMarshall_Law just made my brain explode

[krzysiu]

i take it its not worth playing around with the plenum then thx to Marshall_Law's theory lol

[Dash]

That formula is for a "straight" piece of pipe yeah?

Not taking into account the extra bends involved or the fact your still running over

the top of the motor(heatsoak).

What about how long it takes to fill that extra volume.

Not knocking you just asking a question.

[KamikazeR33]

the plenum i have on mine is a custom top half.

i leaned out the a/f ratio on my rb25 and held it flat and finally blew at 260km/hr

interestingly enough the cylinders that went were 3 and 4 not the end ones like everyone thinks

[JCMarshall_Law]

"Just" is right the calc is for straight pipe, I was more just pointing out that there is dick all pressure loss in uniform pipe with that diameter at that velocity. You can work out the minor losses (ie losses from bends, valves (throttle) etc..) with the eqn below.

All just an excuse to use those old uni books.

ploss = ξ 1/2 ρ v^2

where

ξ = minor loss coefficient

ploss = pressure loss (Pa (N/m^2)

ρ = density (kg/m^3)

v = flow velocity (m/s)

hloss = head loss (m)

g = acceleration of gravity (m/s^2)

Typical values of minor loss coefficient

Flanged Regular 90 deg Elbows ξ = 0.3

Threaded Regular 90 deg Elbows ξ = 1.5

Threaded Regular 45 deg Elbows ξ = 0.4

Flanged Long Radius 90 deg Elbows ξ = 0.2

Threaded Long Radius 90 deg Elbows ξ = 0.7

Flanged Long Radius 45 deg Elbows ξ = 0.2

I pulled most of this stuff off http://www.engineeringtoolbox.com - really usefull sight.

[Sydneykid]

If you want to do it properly your are going to need a management system that allows fuel trimming, eg, Motec, (can't comment on PFC, Wolf etc.. never had experience).

Power FC's have individual cylinder trim for the injectors.