Flow bench test would be more than enough to come to a conclusion. Dyno testing would require hundreds of runs to get any sort of conclusive result, given the variation between runs, and the minimal gains if any that an aftermarket intake provides.

TK

 

I don't have a K&N filter but would more than happy to flow the stock intake if I can find time. If someone wants to send a K&N filter, or donate one that would be fine too.

 

it wouldn't require hundreds of runs. if you stay on the same dyno after a good couple runs with the car there's not reason you couldn't mark gains or losses with 2 or 3 different products.

 

I agree.

Hundreds of runs would definably mean that the Dyno is not a stable and capable tool for measuring accurate HP values.

There should be some tolerance standard on the Dyno. Does anybody know what this is in HP?

 

are you asking does anybody know what the tolerance is, in HP? that's something you have to check with the manufacturer. differentials in weather (i.e. temperature, humidity, air quality, etc.) with affect your results. SAE standards "correct" for given air characteristics, however, may still be off.

 

Well, I found this document which somewhat corresponds to the SAE standard J2264.

http://www.autoalliance.org/archives/dynoreport.pdf

Apparently there is 0.2% tolerance on the base inertia. That does not say much as there are other tolerances involved as well.

From what I can read on the net, it seems that you can safely say a +/- 3HP tolerance. Obviously there are assumptions like weather, humidity etc....

This is quite interesting as when aftermarket products are marketed with numbers within this range, you will probably not be able to see the gain when using two different Dynos (the tolerance will just eat it up).

So perhaps that could be a good rule of thumb. Any aftermarket product that claims to have less then (or equal) to 3HP gain could just be in fact the Dyno tolerance.

 

ok i see where you were looking for. i agree about the +/- 3 hp. you might want to see it's tolerance for torque too, since hp numbers are derived from torque.

 

No need to do that.

(Torque x Engine speed) / 5,252 = Horsepower

Assume that Engine Speed is accurate and the tolerance is negligible. Therefore the only contributor (to the tolerance) in the equation is the Torque. They are directly proportional.

Therefore, tolerance in Torque = tolerance in HP

 

HA! here i am, an ME at my desk and i didn't even have that go through my head. thanks for the heads up.

....so....new topic? haha

 

My head hurts from reading this. What is looks like is Nissan might have gotten it right this time in the stock form. Is that where this is going? I need another Whiskey! Great job on the equations.

 

Well, before we can finally determine if any after market intake (including Nismo) will produce any noticeable gains outside the above specified tolerance range; a study needs to be done.

Perhaps the first step is to determine the capability of the Dyno with a specified tolerance range. Running the same car a few times should be good enough for all intent and purposes.

Stock air box should be the baseline and the other 2 intakes types (hot and cold) could be tested thereafter.

Anybody interested in running this test?

Fun fun, the wonderful world MENG!!!

 

Some information already available from other people's dynos indicate that the stock airbox, produces better low-mid range torque than any of the aftermarket intakes. All intakes including stock use the same diameter piping AT the MAF. Aftermarket intakes tend to go slightly larger before and after. We could hypothesize that the stock intake tube diameter doesn't flow any less in the low to mid range, while providing better velocity. If any aftermarket intake is going to show gains, its going to be at the very peak of the rpm range, probably around 6500rpm and above. Even at redline, the flow rate is fairly low for each bank of the engine, between 180-230CFM based on VE range of 80-100%. The aftermarket intakes are capable of outflowing the stock intake at larger CFM ranges, but at a range of 180-230CFM, it might be a very small difference, maybe enough to produce 2-3hp peak. 2-3hp gain falls within dyno tolerances. Even then the dyno doesn't replicate the affect of the air ducts on the stock airboxes. Once the car starts moving, any flow benefit of the aftermarket intake, can become negligible.

TK

 

I see some are confused about so called ram air why engineers ALWAYS start with the natural [supercharging] effect from Earth's atmosphere 14.7 psi [sealevel] and work towards the intake valve subtracting restrictions to pressure along the way to find the real PSI trying to flow thru the valve curtain area [the imaginary doughnut of space].

The reason FlowBenches use 25" or 28" WC is because actual measurements in running engines show this to be the case. That the actual pressure in front of head at end of runner is 25-28" or 14.7 minus 1.0 psi or 13.7 PSI.

13.7 is 6.8% restriction from Earth's atmospheric pressure so they divide up the intake into sections and allow each [runners, plenum, TB, air duct, MAF, filter and housing , intake duct] to attack the restriction problem by optimizing each section.........then of course making sure they all work together well.

 

The idea of a tuned intake port (for those not following) is similar to a pipe organ, or a trombone. If you make the pipe longer, the resonant frequency will be lower. If you make the pipe shorter, the resonant frequency will be higher.

So in a truck where you need gobs of torque at 1000 RPM's there are generally VERY long intake runners, on a sports car, generally there will be shorter intake runners.

What you are tuning is the "peak torque" location of the engine. I put it in quotes because you're tuning one aspect of the engine, and not anything else, so its the point that the intake manifold flows the best, not necessarily the entire engine.

 

The tuned part is so the wave [reflected] arrives just before the intake valve closes to give one last puff of air into cylinder at a slightly higher pressure than the bulk of the filling.

This only works at one narrow rpm range and varies with air temperature and humidity.
http://www.sengpielaudio.com/calculator-speedsound.htm

The speed of sound [helmholtz] increases with temperature and can easily change 7% across the 32F> 120F.

So this means that the peak torque RPM may change with air temperature.
If the rpm doesn't change the reinforcement AMOUNT will change.

Actually there are multiple harmonics which can supplement rpms higher than torque peak rpms and subharmonics from [plenum, TB, and air ducts] that are used to boost efficiency [mpg] at 55-60 mph cruise.

 

wow. thanks for the technical info. looks like i've gained a little more knowledge in the explanation of tuning.

 

Hey guy's,

I think you are forgetting some calculations in your equations.
Mach Index

When the flow velocity through a orifice reaches the local speed of sound, a change in the pressure downstream of the orifice can no longer be communicated to the flow upstream of the orifice. The flow is then called "Choked"

When the air is halted and the valve opens it does not mean anything happens at all. At least from what I am trying to understand of this theory "I am still learning." For example when the valve starts to open and has a gap the engine might be spinning to fast for any air to start flowing at all, however once the valve reaches a certain lift than air will start to flow into the cylinder. If the air speed reaches the speed of sound then there is no flow.

Also, as a outsider looking in, you have two throttle bodies which has much more flow potential than most cars on the road. Most have one control valve like on my SHO. You have essentially cut the work in half with two intake tubes. There is a good chance the factory system is great from the factory. Not the case with most cars, however improvements can be. Maybe everybody is going in the wrong direction. The aftermarket tubes might be too large. If they are larger than stock then velocity has been change. Too confiscate for this you can make the intake length longer to increase velocity, or try a smaller tube like the factory with a better flowing filter. I would even try smaller diameter tubes for S@%T and Grin...

 

I've been toying with that idea as well. Improving the stock intake design without changing diameter of any of the piping. The connection points of the "tubes" looks like they could potentially cause some minor turbulence and by trying to give the air an even more straight shot into the TB. Added to that some sort of box that connects to the ducts so the car can draw in air directly from the top of the front grill, where pressure should presumably be the highest once the car is moving at high enough speed.

TK

 

look at the air intake venturis. they already are about as straight as possible. unless you modify an intake manifold to face the throttle bodies toward the front of the car it's not getting much straighter.

plus you're not really thinking of the air pressure correctly. atmospheric air is all around you, and it's sitting at the same pressure. if you technically want higher pressure air, then heat it up - which your engine compartment does for you. you might be wanting a higher pressure differential, which a tuned intake setup may do for you - but still the gains wouldn't be very high.

 

Pressure differential is what I was meaning. It might be a small gain overall, but the idea just retains everything that makes the stock intake work so well. Basically I was just brainstorming ideas to add to the existing setup, things the factory wouldn't do because of complexity. One would have to measure the pressure differences at different points of the car while its in motion to find the ideal location to plumb the scoops. It's mostly just thinking out loud.

TK