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Also struggling to get my head around this. I think the bold below is the most accurate/best statement from the top thread, I'm unsure about his filling calc but I suspect the extra difference in time to fill from 2" to 2.75" over the short length of hot side IC piping would be barely noticeable. I think basically we are trying to get the air from the turbo to the intake with as little pressure drop as possible. Pressure loss is generally a factor of velocity and roughness/restrictions (with the same flow - smaller pipe means higher velocity, higher velocity means higher friction losses) When talking about restrictions other than friction on IC pipe walls, the smaller the diameter pipe has a bigger the restriction (i.e 2" 90 degree bend causes more pressure drop than a 2.75" 90 even at the same velocity, when you take into account the higher velocity from smaller pipe it compounds) Imo you want to be at the point where it’s not causing a significant pressure drop, but also not overkill. But I don't know where that is I think you are right on cold side, I'd probably go 2.75" hot side just to know it's not causing any pressure drop/restriction.

Read all that and got this as well. tight bends are bad intercooler core design is the biggest factor for real world. Which makes sense as there are some terrible designs with nasty bends at the entry and tiny passages through them. pipe size makes little difference compared to those two if like @A_J_T said you stay about the outlet size. other than that's is complex physics interactions wizardry no one really can explain well that makes little difference.

I've read many threads on this before, these two are good value. https://forums.nasioc.com/forums/showthread.php?t=2399163 https://forums.nasioc.com/forums/showthread.php?t=2648685 My 2c, I think at lower power levels like we are all dealing with 400kw- then its not a massive contestant in the game. As long as you are not going smaller than your turbo outlet things should be good. Smaller pipe is easier to work with and route through the engine bay. I went 2 hotside and 2.5 cold into a 2.75TB

Yep, big phenolic spacers help things out. Raise the turbo by 1cm and add 8mm spacers and you're almost back to where you started. But then obviously the downpipe doesn't fit, and suddenly you're like "why didn't I just go twisted?"

well we all want power in different places also don't we. their cars being rwd i imagine they (for the most part) don't want turbos which are quite as peaky low down as ours from stock, think the original configurations with engine/turbo/drivetrain setups were to prioritise top speed on nissan vs pure acceleration on subaru

Been thinking about this recently while planning for my FMIC setup. Why are cold side pipes larger than hot side pipes? Let's use my build as an example: - Turbo compressor outlet: 2" - Intake manifold inlet: 2.75" - FMIC inlet / outlet: 2.75" Sizing of the above is obviously a big influencing factor, but why would cold side pipes be bigger? Isn't the science that hot air is less dense and takes up more space? Therefore after being chilled through the intercooler, the space required for that same volume of air should be less, because it's more dense? I.e larger cold side pipes could cause lag because air velocity is now slower due to the bigger pipe diameter. Smaller hot side pipes make sense. Lastly what would you do in my application? 2" pipe from turbo to core, or have a transition somewhere in between or at the turbo even. Seen 2.25" on many intercooler kits. Likewise with the cold side, 2.75" from core to inlet or step it down?

I'm sure there has been much more advanced study/calc's done on this, would be good to find and have a read. But i'm sure for the majority pretty much what @Gripless said above, bends are bads, pipe sizes should be in between the turbo outlet and the TB inlet size. Mines not quite what you're describing, but the hot side does have about 450 degrees of bends in it. After having reading through this and getting my head around it, I think i'll have another attempt.

@Saleti what area u in? if in auckland or can travel here, we just did a 260kw on a v7 with very minimal mods and still on 98 pump gas...

KM’s are getting up there but no reason to need anything thicker yet. You get much tapping from the heads? Dunno at what point it exactly becomes an issue but thicker oils can have detrimental effects on the AVCS operation. Castrol Edge 5w30 would be my choice. I always wait for a decent sale a super cheap and buy 2 so i’ve always got one ready to go

5w40 or 10w40 with those kms.

I would imagine it started life with 5w30.

Mmm I'd keep driving to a minimum if that's the case. Springs are something you don't want to get wrong.

Sorry bud Saturday.

Kinugawa make nice actuators for VF turbos. Lots of spring, arm and mounting plate options. Not too expensive and can be bought locally or direct.

@awd.club my engine builder has a brand new forged short block assembled ready for deliver for $2800. If you're interested pm me please.

Oooh haaaaai! We have a gravex that we'd like to throw round the track! Sent from my TA-1012 using Tapatalk

Anyone happen to be coming down from AKL with a random empty car trailer? I have another Avenger to pickup....

on a high level, doesn't it just increase the area to pressurize, which directly affects your throttle response? in theory allows you to reserve a higher volume of pressurized air for a larger turbocharger application? why would better velocity in the pipe matter when your throttle body / intake manifold would take care of all that where it's really important? is that a bottle neck anyway?

That is the theory, I did write that poorly, meant area to expand into to drop the speed. But to have increased velocity won't you have more pressure and therefore heat since it is a confined space? Also wouldn't it be ideal to have matched to throttle size for when the throttle opens then the pressure wouldn't drop from the expansion of going through the larger throttle area. Like using it as a storage tank for the already pressurized and cooled air. it may be a balance between less ideal in the pipe and more ideal in the cylinder. maybe that also gets balanced with throttle response. Ok at this point it does my head in as too many factors. Need someone with flow modeling software to try it. Someone must have somewhere on the Internet.

Remember about turns are a big issue with fluid dynamics

My guess is air speed and expansion as it cools could be a factor. the velocity out or the turbo and heat are both high, at the throttle cooler and slower.

Hmmm. Pressure, density & velocity. Higher pressure would increase response (thought test this using extremes of density). Velocity is where we lack understanding, right? From Murch's old post, thin headers are the win. Was this due to velocity or pressure, and as you state @Not_Sean, due to the interaction with another part of the system in regards to either temperature or a bottleneck/step change? Almost need a napkin and a mech engineer who understands fluid dynamics 101

@Batbaruman yeah exactly and also how you drive or race and the road conditions. Linear power is pretty nice when it's wet and rainy or slow traffic compared to everything else it's all a trade off. rally is all gears and most of the rev range race is mid to high rpm range once started some engine braking and mid corner throttle drag is all redline and only enough rpm for gear rpm drop But there is also the newer cars with si drive so you can have all 3 if you wanted. Or on an after market ecu or boost controller you can have the same.

Indeed I did, pretty much straight bolt in for me, I think I had to slightly cut the heat shield to fit, but basically bolt in. One thing to note is that my car drove very differently after, I would get some silly boost spikes (not sure if turbo related or tune related?) But I have now since done a couple other things (front mount, ebc etc.) and been tuned and run 223kwatw, but prior to front mount was doing something like 178kw

This car uses stock equal length headers at 800hp... the only headers that they could find that wouldn't crack. http://www.driven.co.nz/news/lifestyle/alister-mcrae-wins-second-straight-leadfoot-title/

Yea will start a build thread soon

would people be interested in some Twin Scroll (GDB and GRB) upgrades that does not cost the earth... been looking at some packages and they seem a lot of money we have a few test cars with better top end pull than the packaged ones but still in testing at this stage before finalizing

its fully possible on stock ecu from v7-v11 and done multiple setups like that.. works rather well actually can also adjust for either more noise or more flames on decel ( depending what ppl like) for launch controll we can usually get 24psi at round 6500 rpm for the agressive launches (stock ecu ) can be dialed in lower obviously depending on what all the driver needs (or depends what level of show off they wana do ) @Batbaruman a little retard and turn off the fuel cut on decel and u will start getting it also for launch controller - use a spark cut setup not the fuel cut builds a lot of boost if thats what u need and raise the limit a bit more could meet up one day and try a few things out if u want

Now I'm been a couch scientist here but maybe its bigger so the engine through the throttle body can take in more and create a vacuum from the size change, so it helps "pull" the air from the turbo through the system. But at the same time, this could just be because most cars the throttle body is pretty large, on my ST 2.5" and the intercooler piping is all 2" but all the modded cars get the best out of all pipes going 2.5"

1000cc fuel injectors will usually get 300wkw on 45psi base and good fuel pump capacity but that's usually there limit