I am a bit confused when I measured the outlet size of a GT30 I got. The outlet size is ~2". If the outlet size of this GT30 is 2" (as as I understand it the GT35 outlet is the same size), why do people need to upgrade the thickness of their piping (post turbo)? I think OEM piping is ~2.2". I can understand getting rid of kinks and shaping parts to flow best, but I do not understand why people go to 2.5" more or less 3" intake piping (post turbo)?

Any explanations are appreciated. Thank you!

 

Love how nobody has a good answer here. There isn't one.

 

cause - if it's bigger it must be better, if it's better you can sell it. duhhhh...

 

In my case it's because my intercoolers don't have stock hose clamps, etc.. Plus I have TiAL BOV's on my Y-Pipe. So when building a new Y-Pipe why not go a little bit bigger?

 

Probably because in the aftermarket segment, companies would have a much harder time selling people stuff that is the same size as Oem. Bigger must be better, of course......

 

Well....thats just it! Most people expect that bigger is better. and it is a good sales pitch. however you are messing with velocity of air flow which at a certain point is important. not to mention the constant upsize and downsize creates eddies and turbulence which further disrupts air flow and velocity. i agree sometimes bigger is better just cuz it looks or sounds cool.

however the fact is that uniformity and smooth transitions and turns are the goal.

Flow=Pressure/Resistance

 

It is based in cfm. you need to move X amount of air and burn X amount of fuel to make X amount of HP. Its that easy. The hard part is to know how much the bends effect the cfm and the temp too. bends are restrictions and cause heat build up plus stall the air flow. To big and you are just filling big void with air. Is bigger better?? The strippers say so! not the dyno.

 

I look at it as "volume". Kind of like a "waiting room" for compessed air. The more air you can have backed up, ready to be shoved into the chamber, the better. Plus it has more time to cool off...wired logic, but....seat of the pants you notice it, so it's not BS...

 

a waiting room that takes time to fill up first rather then moving to the TB quicker. also the larger the diameter the more surface the air comes in contact, surface = resistance

 

....but the bigger piping on my car got me 80whp sooner with 600 rpm of quicker spool...defies logic...

 

i believe you had bigger piping to the turbo inlet. this thread is about turbo outlet.

on the inlet yes. you want the leas amount of vacuum possible in those pipes during spool. if you have vac in the turbo inlet pipes - you can improve. nothing logic defying here.

 

As far as I know, on ttboost's last upgrade he was using our 2.5" x 75MM Y-Pipe and our intercoolers with 2.5" inlets/outlets along with the fresh air inlet pipes.

 

I believe they go hand in hand BUT I believe and go by that velocity is more important then volume, if it doesnt create friction and heat build on the inner surface from being too small of a dia./path,, velocity will make a better fill and stronger flow stream...IMO..

 

John, We have always been told of power increases on dynos when modified cars with larger turbos and higher boost have been upgraded with our intercoolers with larger end tank openings combined with our Y-Pipe/75mm plenum set-up. IMO, this only stands to reason as the OEM piping was designed for K16 turbos running .7-.8 bar of boost.

Modified cars with larger turbos such as GT28's, K24/18G, GT30, etc., then pushed to 1.4 - 1.5 bar of boost are flowing significantly more air than the OEM piping was designed for, so the question is "are the OEM post turbo pipes and intercooler openings sufficient in size to accomodate all this extra air without restricting it or is larger plumbing required post turbo to match the increased volume of air being pushed to the motor with the significantly larger turbos at double the OEM boost level?" I am not a flow dynamics expert, but from what we have seen and heard from customers dynos, it seems the larger piping is making more power than the OEM piping in these applications in back to back tests. Personally, I'll stick with my fully upgraded intake path with my full supporting modded K24/18G car and be very comfortable with this choice.

 

Hi John,Thanks for your info..I was just mentioning it as a general statement as far as air flow basics,which applies more so to non turbo's..I agree some what with your above statement....Yes,if everything is bigger and at a higher boost level it will make use of more volume but going too big in certain areas may also hurt the velocity of the charge....