Dust collection related question. How many CFM?

[dbhost]

Okay dumb question here and it is sort of related to dust collection, well air movement anyway.

I am looking up answers to whether or not cold air intake systems would actually improve engine performance and I need to compare stock configuraitons to aftermarket. The known data is static pressure / vacuum (28" H2O) and duct size. (Stock 2", aftermarket say 4" for argument sake). I need to figure the CFM of both the stock and aftermarket configurations...

[Bill in Buena Park]

Dave - trying to understand your question. Some questions below, and some thoughts.

I am looking up answers to whether or not cold air intake systems would actually improve engine performance and I need to compare stock configuraitons to aftermarket.

What do you mean by "engine performance"? Is this an automobile engine? If so, are the cold air intakes like these?

The related sales material suggests:
"(Brand) cold air intake systems provide better acceleration and fuel economy for your truck or SUV. They are designed to replace your factory air filter and airbox assembly, getting rid of the restriction as they smooth and straighten airflow. The high-flow design of (Brand) cold air intake systems enables your engine to take in a larger volume of air, resulting in more usable power throughout the entire engine's rpm range."

The known data is static pressure / vacuum (28" H2O) and duct size. I need to figure the CFM of both the stock and aftermarket configurations...

Cubic Feet per Minute = (fpm * area). IIRC, area = (piR^2)/144 to adjust area to ft^2.

I think your area will depend on where you're measuring FPM in the system. For example, if I measure FPM at the inlet of my DC which is 4.75in diameter, it may be higher than if I have 8 inch ducting attached to the inlet and measure CFM at x feet away from the inlet, where the increased area would reduce windspeed. Wherever you pick to do the area measurement, you could probably use an anemometer to compute airspeed in MPH, and convert to FPM using a tool like this.

If your application is automotive, these concepts may apply there as well.

[dbhost]

Similar, but not all "Cold Air Intake" assemblies move the filter. The idea is to pull large volumes of outside air, not pre-heated in the engine compartment, thus denser air charge, into the engine.

In the case we are discussing it is the Air RAID Jr which utilizes the factory filter / airbox thus it keeps things like the Mass Airflow Sensor (MAF) etc... in place.



(Please forgive the dirty engine compartment, I have had other priorities... And have since cleaned it.)

Versus, and I hate to show this link as it is video, but a stock engine compartment with the OEM intake tube.

http://www.youtube.com/watch?v=wVPtqQtrSsk

At around the 9 or 10 second mark you can see how the stock / OEM snorkel narrows down to about 2" and passes through the inner fender. Yes it is technically a CAI as it pulls air from out of the engine compartment, but the one shown at top, has a MUCH larger intake area, and the duct necks down to fit into the stock airbox, about 1.75" tall x 5.25" ish wide...

I just can't believe some guys assertions that there is no performance improvement in adding a free breathing intake.

[unclecritic]

Different vehicle, i know, but i put a cold air intake on my 98 expedition and noticed a drop in performance, as well as a drop in mpg. I drove it for a few weeks with it on in both city and a 540mi highway trip and a steady
75 mph speed and mpg dropped from avg of 16 stock to 8. It had what seemed to be a little better low end grunt, but i think the open air sound was tricking me. I went back to stock and the check engine lights went away as well as the performancs drop.

I later found a mod using some 3" pvc to increase the the airflow at the point where the factory intake tied into the fender, getting rid of the factory connector which choked down to about 1.25" and ive noticed a little betterhighway economy, seems a little peppier, and sounds a little more throaty. Oh, and i also installed a better flowing filter inside the factory air cleaner box.

Fwiw

[dbhost]

Different vehicle, i know, but i put a cold air intake on my 98 expedition and noticed a drop in performance, as well as a drop in mpg. I drove it for a few weeks with it on in both city and a 540mi highway trip and a steady
75 mph speed and mpg dropped from avg of 16 stock to 8. It had what seemed to be a little better low end grunt, but i think the open air sound was tricking me. I went back to stock and the check engine lights went away as well as the performancs drop.

I later found a mod using some 3" pvc to increase the the airflow at the point where the factory intake tied into the fender, getting rid of the factory connector which choked down to about 1.25" and ive noticed a little betterhighway economy, seems a little peppier, and sounds a little more throaty. Oh, and i also installed a better flowing filter inside the factory air cleaner box.

Fwiw

The mod you are talking about is the Gotts mod. I had that on my truck. The PVC is very brittle and in my case cracked lengthwise. But my experience is the exception rather than the rule. I think I got some funky defective PVC...

Since you were throwing a CEL, I suspect you were using a full CAI, like the K&N FIPK, or even the AirForce One, not a cold air tube like my rig. Those relocate the MAF, and tend to give the computer funny readings, causing either a lean or rich condition. You need a custom tune to deal with the added air and to recalibrate to the new MAF location... If you had a CEL with a tube that kept the stock air box I would love to know though. That would be the first I have heard of that. (FYI... CEL= Check Engine Light).

On my rig I am using the stock air box, along with a K&N filter element, I know I should use a different filter, the oil in the filter media can foul the MAF, and has once already... The Gotts mod did improve my low end grunt a bit, and upped my mileage by about .5 mpg. Not much, but when you consider I was down to 12 (4x4 lifted with 35x12.5 rubber) I need all the help I can get... The AirRAID Jr. A.K.A. the AirRAID M.I.T. (Modular Intake Tube), keeps the stock airbox, sensors, filter element etc... but replaces the entire snorkel assembly, including the baffles and that stupid overly choked down part that goes through the fender...

[unclecritic]

100% correct on the gotts mod, odd that yours cracked. I love that you do the so much research. The COI I installed was a cheap one off of ebay that had horrible reviews i found out later but loml bough it for me as a gift so i tried it. It installed an "air box" of sorts in the engine bay and took its air in from the fender as well, but it didnt seal agaisnt the hood hardly at all so it was pulling engine bay air in more than anything, hence the poor performance.

My good friend is an porsche/audi tech, and for extra side money (he has 7 kids, needs all the money he can come across lol) he helps some of the younger kids in the area build up their german cars. He has seen drastic improvments just from a COI hardware install, but it takes getting into the computer and adjusting the tune for the performance hike. He starts talking about idle stuctures, fuel mapping, injector something or others, and my eyes start to glaze over. He has taken a monitoring program and driven the car stock and data logged, did just the coi install and data logged and in his words "not a whole lot has changed." He is convinced in order to use the available denser charged air a tune must be done.

He said we could do a bully dog tuner on my truck and it might do what is needed but thats more than i really want to get into. Im not trying to climb mountains or win races. Anymore anyway. But in my younger days...

[dbhost]

Totally agree that a CAI won't help without a tuner. I use an SCT XCal2 tuner with a VMP custom tune. Come sates for the big rubber and buys me some power... considering the added weight and rolling resistance the power added brings performance back to a stock truck. ..

[LCHIEN]

the quick answer is that air density is related to absolute temp. What would be the cold temp vs hot temps involved?

[dbhost]

the quick answer is that air density is related to absolute temp. What would be the cold temp vs hot temps involved?

In automotive terms, cold air is the air coming from outside of the engine compartment. Hot air is air sourced from within the heated confines of the engine compartment. There is a long history of varying attempts to get colder, thus denser air into the engine of automobiles, think about how functional hood scoops work. A cold Air intake by definition has to pull the intake air from outside of the heated air within the engine compartment. On the 1997 and up for modular V-8 trucks they pull the air from the drivers side front fender behind the headlight. The aftermarket cold air intakes separate a compartment within the engine compartment pulling air that is isolated from engine heat, through the headlight opening. My intake tube does the same thing, as it pulls from behind the headlight and is effectively out of / in front of the engine / radiator etc...

[LCHIEN]

thanks for the explanation but I was asking for the actual represntative temps involved...numbers in farenheit or centigrade. So cold air temps would be like 32F to 110F...? What are under the hood temps?

[mpc]

Anywhere from 20 to ~200+ degF above ambient depending on location under the hood and engine type/layout. A north-south mounted engine (i.e. the "old" way, driving the rear wheels usually) that is 4 or 6 cylinder and "cross flow" design (intake on one side of the cylinder head, exhaust on the other) will be hotter on the exhaust side. Non-cross-flow inline 4 or 6 cyl engines put the intake and exhaust on the same side of the head (like the 6 cylinder 4.0 & 4.2 liter engines used in many Jeeps) so the hot exhaust manifold would heat the intake manifold to prevent ice formation and/or gas condensation inside the pipes. The other side of such engines is often pretty bare... and that side of the engine bay will be heated mostly by radiator flow-through air so it won't be as hot. Cross-flow engines use engine coolant circulated through the intake manifold and carburetor base (if present) to keep those parts warm enough to prevent gasoline condensation; typical engine coolant temperatures are 160 to 195 degF so that side of the engine bay gets heat from the manifold, radiator flow-through, and from the engine block; it'll be around 100 degF above ambient I'd guess

North-south V-6 and V-8 engine compartments are more uniform in temperature, and will usually be in the higher temp ranges, since there are exhaust manifolds on both sides of the engine.

Transverse engines (like most cars today, typically FWD) used to be hotter up front (radiator and exhaust at the front, intake manifold in back and often buried under the windshield & part of the dashboard) though lately the exhaust is in back with cooler intake manifold up front. Temps in transverse engine bays is much harder to generalize as a result. It'll be cooler wherever the intake manifold side is, hotter on the exhaust side.

Typical exhaust manifold temperatures are around 800 degF with the engine warmed up but idling... and around 1000 to 1200 degF for medium horsepower cruising. Hard acceleration can get that as high as 1600 degF for a while; cars with turbochargers will more often reach the 1600 degF range. Cast iron exhaust manifolds (and turbocharger turbine wheel housings too) will have a bit of a glow visible at night at such temps. Radiator flow-through is higher than outside ambient temperature but below the engine coolant temp (radiators are not 100% efficient) so think anywhere from 20 degF above ambient up to 190ish max.

Another thing that can make a difference in auto engine power, besides lowering the intake air temperature, is to find a source of higher pressure air. Think back to some of the old muscle cars with hood scoops. Remember those that had the scoop pointed backwards? Those designs captured the higher pressure air bubble at the base of the windshield... basically like a 1 to 2 psi supercharging effect at higher MPH speeds. Otto cycle engines (i.e. 4-stroke gas engines) make power based on the number of air molecules in the cylinders. Lower temperatures raise the density of air ==> more molecules for a given volume. Pressure packs the molecules more closely ==> more molecules for a given volume again. Air from inside the fender area is rather cool and, depending on the front-end styling and design of the vehicle, may get some ram-air supercharging effect as well. The other primary reason for taking air from the fender area is that it's a big plenum - i.e. the air inside the fender moves fairly slowly compared to the air in the actual engine intake piping. Thus any water splashed into the "plenum" area will naturally drain downwards and away from the engine intake. Cars with a nose-mounted air inlet (like many Fords of the late 1980s that had two openings surrounding the "Ford" emblem in the nose) would sometimes swallow a gulp of water in heavy rainstorms or when another vehicle splashed through a big puddle... if the piping doesn't have a water separator in it then that gulped water ends up inside the cylinders. Water does not compress well... when the piston comes up and tries to compress the water something else has to give: connecting rod bends/breaks, piston shatters, head gets pushed off the engine, etc. Happened to a co-worker of mine; Ford did a big recall to add water separators to many cars after a particular rainstorm in SoCal lead to many such engine failures.

Look at the shape and size of the intake pipes too. Just like dust collector piping, the size of the pipe, the shape, and the radius of bends plays a big role. Tight curves are BAD. Though tight curves make good water separators, especially when they go down and back up (like a sink's P-trap). Think of air as lots of itty-bitty marbles zipping along the piping. Any place that makes the marbles change direction will also cause them to pile up on the far wall of that curve - the weight (actually mass) of the moving molecules/marbles makes them resistant to changing direction. Piled-up marbles a) aren't going into the engine so they don't contribute to power and b) reduce the effective pipe area that IS flowing, choking the airflow a bit. Tight bends lead to more pile-ups. Horizontal vs. vertically oriented oval piping changes the size of pile-ups too. Just like in dust collector piping.

mpc

[LCHIEN]

Air is of course oxygen and nitrogen and the ratio remains essentially unchanged at different pressure and temperature points so basically the Oxygen is a direct functinof the density.

Thus the relative density of air gives the ratio of oxygen between the two points, more oxygen rate combined with more fuel rate therefore increases the combustion rate and hence the power of the IC engine.

The density is essentially goverened by Boyles law and CHarles law
At the same pressure and a fixed mass of air the volume is inversely proportional tot he temperature. THe temperature is related to absolute zero (Rankin and Kelvin), not the zero we normally use in F and C which adds a bias of 460 or 273 repsectively.

Assuming outside cold air temperature is 70F (530R) and the hot intake air is 150F (610R) then the increase in density is 610/530 or a 9% increase...
THis helps only is you can get more fuel as well.

I'm just using wild guesse at numbers here, you haven't told me what the cold air and normal intake temperatures are.

[LCHIEN]

...
I just can't believe some guys assertions that there is no performance improvement in adding a free breathing intake.

The total power is limited by availability of both fuel and oxidizer.
If there is not enough fuel flow rate then no matter how much more oxygen you put in the combustion chamber, there will be no more power...

[mpc]

Auto engines are generally limited by air quantity, not fuel quantity. If the engine were ever fuel limited, the engine would be running lean. Lean burns hotter and, if not corrected, leads to piston melting/damage, knocking/detonation which is a violent "bang" of the air+fuel mix vs. a more controlled combustion rate; this bang is what bends/brakes rods in engines and shatters pistons. No engine design should ever run lean. Fuel injectors typically have to operate within a 20% to 80% duty cycle range (duty cycle=ON time divided by total ON+OFF time) to reliably open or close... otherwise fuel flow isn't what the computer commanded and the engine ends up running rich or lean --> bad performance, bad emissions.

Fuel systems (pumps, piping, injectors, etc.) are designed with a fair bit of excess capacity (margin) to allow for manufacturing tolerances in fuel pump performance, normal reductions in fuel flow as the pump wears and/or the fuel filter gets dirty, etc. This sizing considers factors like operating the engine at low altitudes (Death Valley) on a high barometric pressure day (even lower effective altitude) when it's cold outside, the engine is running at full throttle (accelerating the vehicle, climbing a hill, etc), etc. Most fuel systems have at least a 20% reserve capacity and many approach 50%. Smaller engines often have more reserve fuel pump/fuel system capacity simply because manufacturers often use one fuel pump for several engine/vehicle designs with small or medium sized engines. As long as the injector duty cycle stays below the 80% limit (or whatever spec exists for a particular model injector) there is excess fuel capacity.

mpc

[LCHIEN]

OK, I Guess i'm not an engine expert. THat makes sense.
So if engines are typically limited by air volume then decreased air intake restriction would improve the performance.

of course, an engine could also be limited by exhaust restriction and backpressure... the other end of intake restriction.