NZ951

Well, empty space is a volume (dynamic volume to some extent possibly as the valves open and close, hmm in fact maybe its constant) that the turbo must compress... thats why i think that. Maybe if i asked why you think that larger diameter pipes or larger IC may increase lag?

You are describing compressor surge in your second sentence.

NZ951

Forgot to add also have 3 angle cut valves with the ported head...

evil 944t

[QUOTE=NZ951]Maybe if i asked why you think that larger diameter pipes or larger IC may increase lag? QUOTE]
They increase lag because of yes, the extra volume not because the turbo has to work harder to fill it. The extra lag is measured in hundreths of a secound not more than one. The turbo is always spinning so the IC and pipes fill way quicker than you think.

333pg333

Well we wound up putting the new inlet and t-body on anyway adapted to the stock i/c and pipes for the moment so at least we'll see what the difference is like when we go up to the custom i/c and approx. 3" pipes.

NZ951

[QUOTE=evil 944t]Ok so you accept that the extra volume influences the turbo's ability to produce the boost at certain RPM, why isnt it therfore harder for it to maintain it? I agree I am probably being niggly and the imapct wont be huge...

NZ951

PS I love you evil, not at all trying to be an ***... I am still very much a novice, just trying to learn.

Geneqco

[QUOTE=NZ951]I think because it has already filled?

NZ951

[QUOTE=Geneqco]The fill is dynamic, that volume of air is constantly being consumed through the head...

evil 944t

Thanks! lol..

Well, I'm out of analogies and ideas for answering your question. Porschefile hit it dead on with the straw analogy.

The reason why the turbo isn't working hard rather than just working is because the big IC tubes "empty" out and the turbo has an easy time filling it quickly. If the turbo is big, not only does it fill the smaller tubes fast, it over fills and causes heat through friction. Over size the IC tube and the the walls get lined with turbulant air and create a path for the clean flowing air.

Keep in mind, I'm talking about a larger turbo on stock equipment. Not a over boosting k26/6

NZ951

So you are saying you get MORE friction from a smaller surface area with smaller IC pipes? I would have thought the opposite...

As for the turbulent air with larger pipes... actually its the opposite isnt it, the boundary layer is greater with diameter and length. This air is not turbulent, unless the surface of the pipe is rough enough to break the surface tension of the air.

Not sure porschefiles analogy was spot on as it assumes no more restrictions in the system, but the head is at the end of the straw

evil 944t

No., thats not what I'm saying! How can you get more friction with less surface area? That obviously doesn't work. I'm saying with a larger turbo, you are getting the same friction but with much more air passing through creating more heat faster than air going through at a slower rate.

It would be like dragging a piece of metal on the street. If you go slow, it would get warm and eventually hot. Now if you start out fast, it would get hot faster.. Same amount of surface area on the metal but Its just covering more area faster. Make sense? If not, I have to throw in the towel..

oh, to answer your last paragraph, your right. Thats where proper tube sizing comes in handy. I'm not talking about 10" pipes.

NZ951

Ah I think I have found where we are going wrong... the air doesnt go through faster, firstly the velocity is initially less because of the larger IC pipe size, secondly and most importantly, the head is determining the amount of air consumed Your discussion all makes sense to me if the straw has zero restriction at the end, but... there is that pesky head at the end.

evil 944t

Yes, I am talking about a pipe with an extremely modded head. I would not go over 2.50" on a stock cleaned up head. There are to many other restrictions before the pipes become the problem...

The head/cam determines all! BUT, you can force it through and if you have to do that then reduce all your other retrictions. Do anything to reduce heat and back pressure.

Driftomagnifico

Theres really only two considerations.

1. Thermal loss: The intercooler pipes act as very low efficiency heat exchangers. Increasing the size of the pipes will increase the surface area and the amount of heat capacitance. This is one reason why the majority of pipes out there are aluminum. The pipes on a 951 however, are too short to account for this.

The 951's intercooler is a decent OEM design, but when you get into running the car on a track only the leading face of the intercooler is going to cool the air. As the air travels further back it's ability to shed heat is significantly reduced (on the order of about 50 - 60% less effective) because of the thick core. Like any heat exhanger you want surface area and the 951 just doesn't provide that.

The basic intercooler kit for a 240SX is 600mm x 300mm x 65mm give or take on the brand.



To give you an idea on size. Blitz rates this intercooler at 400 HP... lol.

2. Flow ability: Pipe size is relative to the flow volume as is the core sizing. You only want to reduce pumping losses before it reaches the throttle plate. The only downside to oversizing is volume increase. These aren't issues for the 951 as you have 2' of intercooler piping. My 240SX has about 8' of intercooler pipework to fill before it gets to the throttle plate.

333pg333

So Dave this is obviously dependent on the system working as a whole. No point enlarging the pipes if the rest is stock or near enough?

Drifto, there are many people who think that by having much longer i/c pipes than the 944's it will introduce big lag time. There are others who refute this. What's your opinion based on experience. ps I'm in the 2nd camp.