which one would you keep!? lets talk!

[archaeic_bloke]

k, so tonight i bought a set of turbo outlet pipes to go with my 2860's... they're RS*R divded outlet pipes.. suuuupper nice and im real keen on them!

heres the question... do i use the RS*R downpipe that i got with the outlet pipes? or do i use my Trust MX downpipe?

heres the pros and cons i can think of... please tell me what u think is better:


Trust MX downpipe:
PRO - has equal length runners (heard this was super important)
CON - has 1mm smaller diameter inlets than the RS*R pipe
CON - has a stupid wideband bung welded in a retarded position (ill never use it.. but its still there)
CON - made of steel and is now coated in high temp silver POR-15 paint (will never come off) and a high temp clear coat.


RS*R downpipe:
PRO - looks SUPER nice and is a super rare and baller item
PRO - came as a kit to match the turbo outlet pipes
PRO - inlets are +1mm bigger than the trust unit
PRO - appears to be made from a VERY high grade stainless steel that would look un-real with a polish and clean.
CON - runners are not equal length


so basically what it comes down to for me is how important is the equal length runners thing? which would u guys choose to use?

[GTRADDICT]

would use the Trust (= length +++). If the RSR are as rare as you say, they will add value. Just like oldschool ram horns for old V8's. Having rare stuff on a car is fun ( and fun to brag about) but is that what you really want...

Whatever you choose, you won't regret

Good luck

[archaeic_bloke]

here i found this:

http://www.rs-r.com/store/pc/viewCategories.asp?idCategory=21

thats showing Sti downpipe and evo down pipe going for around the $300 USD mark... so i would assume since its more material and more welding the GTR pipe would go for maybe more like $400 USD? what do u guys think?

[malibusst]

equal length means nothing.............

[Daryl @ RightDrive]

I'd stick with the RSR myself...especially if it matches the outlets better.

[frankiman]

ok, i'm nearing the end of my fluid mechanics class, and this is all about fluid mechanics

from what i've learned, heres what i think;


let me shoot you a couple of formulas


Q = volumetric flow rate
A = area of pipe section
V = flow speed

Re = Reynold's number for turbulence
p (rho) = fluid density
u (mu) = fluid dynamic viscosity

E (epsilon) = pipe material rugosity
f = coefficient of friction of pipe

KL = sum of minor loss values based on pipe design and system elements
g = gravity

hL = head loss of system
this is the most important part, the head loss is the lost energy (or flow), the smaller the head loss, the less restrictive your system is

in this case, a parallel system, the total head loss is the average head loss of all pathways
and total volumetric flow rate is the sum of flow rate from all pathways



lets do a little analysis;

have equal length runners would only make it so both head loss would be the same, lets say (1+1)/2=1

but with runners as short as possible, the head loss in the shorter runner is less, so total is less; (1+0.9)/2=0.95

also, with all those formulas you can clearly see that the section diameter has an enormous impact on the whole system, and head loss
(don't forget A (area) is also a fonction of D (diameter)

so as diameter inscreases, head loss decreases exponentially
up to a point where the value of Reynold's number is below ~3000, which means the flow isn't turbulent but laminar, which uses another set of formulas, which in term means even less head loss


also, the MX pipe is made of steel
and the RSR is made from stainless steel which has a much lower rugosity, so less friction


go with the RSR

baller status enabled

[evilgtr]

your not going to notice a performance diff. in either one so go for the looks

[frankiman]

your not going to notice a performance diff. in either one so go for the looks

theoratically, the RSR gives 30+ hp more, errrrr, +30% bragging rights

[archaeic_bloke]

valid points.. but you all neglected one thing that mcfly pointed out on GTRPWR....

look at the Y-section.. where the 2 pipes meet... the trust merge is WAAAYY less turbulant of a merge than the RS*R merge...

thoughts on that?

[frankiman]

that is what the KL factor determines,



the difference in KL factor isn't significant overall

remember this isn't the twin turbo pipe, the merge will be turbulent for sure, wether its a little less turblent doesn't change a whole lot considering its just expelled gazes

[Daryl @ RightDrive]

I prefer the simpler line of thinking....they are both fine.
In reality, if you throw both of them on a dyno, you will probably not see any power difference at all, and if there is a difference it will be very slight at the most. No need to over analyze this to death. Both are from reputable makers, so both are great choices!

[frankiman]

No need to over analyze this to death

heh, i'm an engineer, its in my blood

[BlackAura]

Wow....I knew I should have gone into mechanical.... I did software engineering....we did a little bit of that stuff, but never did get into crazy fluid dynamics like that.

[archaeic_bloke]

ok one last point to raise then,

the fact that the trust has equal length runners means something... its not negligble... equal length runners means both turbos spool at the same rate... where as non equal length means one could potentially spool quicker than the other....

anyone disagree with that?

this would cause turbo shuffle... right? (yes i have already modded the twin turbo pipe)

[Skym]

But exhaust gas leaves engine in pulses of exhaust gas (firing order of engine), not one long stream from all cylinders at same time.

That's where timing of exhaust gasses, equal length comes into equation, as you need to time the pulse to miss another pulse at collector. Listen to tip of exhaust to see what I mean, as you can hear the pulses.

The shorter vs long pipe is probably due to pulse timing between turbo 1 and turbo 2. So basically they might have worked out the pulses miss each other and result's in exhaust flowing better at higher rpm's.

The fact that the RSR has a straight pipe off dumppipes means less restriction at higher rpm's, which is more important when it comes to producing hp.

The merge of both pipes is not that much different and doesn't effect flow or hp, as the pulses would be timed to miss due to short, long pipes on RSR pipe.

This dyno graph of SR20DET with dual equal length front pipe with same merge on front pipe as RSR front pipe -

http://www.kts-web.com/kouza/intake_ex/frontpipe/index3.html

My opinion is RSR front pipe, RSR dumppipes, as they are designed to work together in diameter, etc. Also stainless doesn't rust, as even when exhaust is painted with high temp paint, the paint can come off in places when exhaust touches the road and exhaust rust's on outside.

The shuffling could be caused by internal wastegates having the wrong psi spring hence the shuffle. This could be tuned out via individual cylinder fuel trim on some highend aftermarket ECU's or playing with ignition timing. Connecting intake, exhaust pipes probably shares the extra intake or exhaust gas, so intake, exhaust pressure equals out in both pipes.