DIY Intake

Bulletz4break

I could see some young kid driving a civic doing something like this but come on guys don't do this to a 370z... Not to mention that the tubing isn't even smooth inside and is going to cause turbulence. If you can't afford an intake just leave it stock.

SuperDave

I'm sorry, I've got to comment again. That so many people are under the misunderstanding that any intake pipe which is not smooth must create air turbulence, which must be bad for your engine...


Without getting into aerodynamics, venturi effect, and optimal velocity equations, is a golf ball perfectly smooth? Are an airplane's wings perfectly straight? Do the factory rippled intake tubes on billions of cars create turbulence which would reduce the efficiency of said car? Is some / any air turbulence always bad? Think about why...

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wanker

Sorry can't agree. Surface drag has many factors including the air temperature (i.e., density), velocity, compressibility etc. Hence, given the relatively low velocity of the air in an CAI, and the many turns of an engines CAI system, I'd still say that smooth is better.

SuperDave

Correct, and if it's reduced surface drag and a smoother air flow you are trying to accomplish then congratulations. However, if it's horsepower you are trying to accomplish (as with an intake), then you want more air as opposed to smooth air, as well as some turbulence (see: volumetric efficiency) to aid in mixing with fuel, which is heavier than air.

What do you think a turbo does? Makes the air really smooth going into the engine, or crams a crap ton of air into it without worrying about how "turbulent" it is.

This is where most people go wrong. Yes, usually when trying to reduce drag, smoother = better. But you're not trying to reduce drag here, you're trying to increase volume. More air = more power, smoother air !=(necessarily) more power.

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Bulletz4break

Why is intercooler piping smooth then? So your saying it would be better if it was ribbed? Your logic is way off. You don't want turbulence.

Jordo!

It depends on where and how much tho'. Many OEM MAF's have airflow sraighteners to reduce tumble effects and thus take more stable readings as air passes over the hotwire. Ours doesn't and is thus very sensitive to misreads when pre-MAF turbulence is introduced.

Also, we're talking air ingestion into a system ("suck") not the mixing and compression of air and fuel ("squish"). At that point, turbulence is not really an issue again until we get to its expulsion ("blow") to facilitate optimally timed post combustion (bang) events to re-create vacuum inside the cylinders (ready to "suck" again). However, internal turbulence can work against effective mixing, its just less of an issue as the aim is compression at a fixed point (timed spark event).

VE is another issue entirely -- effective cylinder filling, usage of the mixture, and ultimate emptying of post-combustion gasses. With a turbo, some of that is re-routed, to be used to spin the turbine, but, yes, restrictions or poor flow characteristics matter there too.

On the intake side of things, its a balance between smooth flow and speed vs. volume (faster in a narrower tube, slower in a wider tube, all things being equal), provided the engine can optimally accommodate the volume of air being drawn in.

As to the flex-tubing on the Z, that's strictly convenience (and maybe a bit of extra outer cooling) for Nissan -- "smooth tubes" definitely make a bit more power than the OEM ones as verified on several before and after dynos -- same diameter, smoother transitions, less flex, less internal turbulence, more airspeed, improved flow, better power.

Straitened vs greater turbulence is also a factor even in filtering incoming air. Straightened air simply flows faster, all else being held equal.

On a somewhat related note, you will have greater filling with hot over cold air, as the gasses expand, but you have less oxygen (reduced efficiency) taking up the same volume, thus, less power to be made during combustion events... same is true at higher altitudes as well.

BTW, compressors work by functionally improving VE by cramming more oxygen into the same space (available volume of each cylinder), not by simply creating a greater volume of gas. It's the number of oxygen molecules (and, well, a concordant volume of fuel) that matters.

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