Intake Questions

[cody994x4]

i have a few questions abt intakes...now that i have a programmer, will i see a 4-5hp gain out of a cai. i am considering a volant system because of the closed box design.it says expect 9hp so im guessing ill get 4-5. Also, will a CAI system reduce IAT's? or will it bring in more hot air???

at this point i want to know if a CAI system will still be beneficial since i have the gryphon installed, if i can get 5hp and cooler air i probably will invest in one, otherwise its a k&n filter.

oh and does a cai system come w a new MAF or no? because dont u need a maf that can read more air flow to really get the most out of an intake?

[shotgun]

Originally Posted by cody994x4

i have a few questions abt intakes...now that i have a programmer, will i see a 4-5hp gain out of a cai. i am considering a volant system because of the closed box design.it says expect 9hp so im guessing ill get 4-5. Also, will a CAI system reduce IAT's? or will it bring in more hot air???

at this point i want to know if a CAI system will still be beneficial since i have the gryphon installed, if i can get 5hp and cooler air i probably will invest in one, otherwise its a k&n filter.

oh and does a cai system come w a new MAF or no? because dont u need a maf that can read more air flow to really get the most out of an intake?

IMHO, you'd be better off if you did the Gotts mod and saved the money.

Regarding the IAT, check out this test from Banks. You can read the test parameters here: Banks Power | 04-08 Ford - F-150 V6 & V8>>Banks Ram-Air® Intake System

[Power Hungry]

I probably shouldn't say this because our business is technically based on marketing and advertising, but here goes...

What would you expect Banks to say about their products?

I'll give you that if you ran the Super Scoop Ram Air, you'd expect to at least see a noticeable decrease in ACT and I do agree that many "Cold Air Intake" system just suck hot air from under the hood making them not only misleading, but also rather useless. However, here's the thing about "Ram Air" systems... They don't work.

This is a post from the Corvette Forum the explains in detail why it doesn't work. It's really an interesting read and even without the Pitot-Static Tube calculations, it paints a pretty clear picture.

Originally Posted by 300bhp/ton

Originally posted at: http://forums.corvetteforum.com/c5-t...-or-truth.html

Marketers just can't resist it. Ram air! The words themselves summon up images of rushing wild beasts, or of secret military aircraft operating on futuristic principles.

Unfortunately, on most perofrmance cars, ram-air is as functional as tail fins were on cars of the ’60s.

What is it? Ram air just means using a forward-facing air intake to gain some extra intake pressure. We have all, as children, felt the pressure of moving air on our hands when we held them out the window of the family car. When moving air is brought smoothly to rest, the energy of its motion is converted into pressure. Motorcycles went through a "ram-air" period in the early 1990s, during which street bikes were equipped with the forward-facing "rocket-launcher" engine air intakes seen on many road-racing machines.

While it's appealing to imagine the forward velocity of a car being converted into free supercharge, the actual air pressure gain is extremely small at normal speeds. For example, at 150 mph, the pressure gain when air is efficiently brought to rest is 2.75 percent. Because this is a dynamic effect, it is proportional to the square of the air velocity. At a more realizable automobile speed of 75 mph, the effect (again with 100 percent efficient conversion of velocity into pressure) will be only one-quarter as great — that is, just under seven-tenths of one percent.

In fact, velocity energy is not converted into pressure at 100 percent efficiency. A figure of 75 percent efficiency is usual, which reduces our notional ram-air gain at 75 mph to one-half of one percent.

Therefore, at normal speeds, ram air is a myth. However, something much more interesting lies behind it, ignored by the advertiser's busy pen. That something is airbox resonance.

In order to implement ram air, the carburetors or throttle-bodies of our engine must seal to an airbox whose volume is large enough that the intake cycle of one cylinder cannot pull its internal pressure down significantly. Box volume is typically 10-20 times the engine's displacement. Then the forward-facing air intake is connected to the box. When this assembly is tested on the dyno — even without an external fan to simulate the high-speed rush of air past the intake — it is discovered that the engine's torque curve is greatly altered, with new peaks and hollows.

Why? The answer is airbox resonance. If you hold the mouth of an empty bottle near your open mouth as you loudly hum scales, you find that at certain “hum frequencies” the bottle reinforces your humming, which becomes louder. What is happening is that the springy compressibility of the air in the bottle is bouncing the slug of air in the bottle's neck back and forth at a particular frequency — higher if the bottle is small, lower if it is larger. Your humming is driving a rapid plus-and-minus variation of the air pressure inside the bottle.

The same thing happens inside a resonant airbox. The volume of air in the box is the “spring” in this kind of oscillator. The mass of air in the box's intake pipe is what oscillates. The “humming” that drives the oscillation is the rapid succession of suction pulses at the carb or throttle-body intakes. If the volume of the airbox and the dimensions of the intake pipe(s) are correctly chosen, the airbox can be made to resonate very strongly, in step with the engine's suction pulses. The result, when this is done correctly, is that the engine takes air from the box only during the high-pressure part of its cycle, while the box refills from atmosphere through its intake between engine suction pulses. This produces a useful gain in torque.

Using this idea, motorcycle engines have been able to realize torque increases, in particular speed ranges, of 10-15 percent. In race engines, it is usual to tune the airbox to resonate at peak-power rpm to increase top speed. For production engines, it is often more useful to tune the box resonance to fill in what would otherwise be a flat-spot in the torque curve, resulting in smoother power and improved acceleration.

Early resonant airbox systems used long intake pipes that terminated in forward-facing intakes. More recent designs do not connect the ram-air pipe to the box at all, but terminate it near the airbox entry. The actual entry pipe is a short piece of tubing with bellmouths on both ends. This is done because (a) the potential gain from actual ram air is too small to worry about, and (b) it's easier to tune the airbox with a short tube.

Where vehicle speeds are very high, gains from ram air are significant. This was discovered by Rolls-Royce in the late 1920s as the company developed its R Schneider Trophy air racing engine. At speeds above 300 mph, it was noticed that the R’s fuel mixture leaned out enough to cause backfiring. When the mixture was corrected for ram-air pressure gain, the engineers realized they had a "free" source of power. At 350 mph the gain from ram air is almost 15 percent. Similar mixture correction is necessary when ram air is used on drag-race and Bonneville cars and bikes.

Intuition suggests that a forward-facing intake made in the form of a funnel, large end foremost, should somehow multiply the pressure of the air, resulting in a much larger pressure gain at the small end. Sadly, intuition is wrong. In order to convert velocity energy into pressure, the air has to be slowed down, and this requires a duct that widens rather than narrows. Next time you fly on a commercial airliner, note that its engine intakes widen as the airflow approaches the compressor face. Such widening passages are called diffusers, and they are universally used in the conversion of velocity into pressure.

Language often plays tricks on us — especially when language is used by product advertisers. "Ram air" sounds much more appealing than "resonant airbox." Nevertheless, it is airbox resonance that actually generates a significant power gain.

------------------------------------------------------------------
Cliffnotes:

-Ram Air a myth? = NO
-Does it work on a road car = NO
-At 150mhp there is next to no gain.
-Significant gains arn't seen until 300mph+
-The air box is the key, not the ducting.
-When buying a CAI/induction kit look for the one that uses air box resonance


Edit: Additional Reading

Intake temperature is a whole different ball game.

The simple rule is:

'Cool for power (maximum charge density), hot for economy (minimum charge density to reduce losses due to throttling).'

Although in many cars the under bonnent temperatures are no where near as bad as many people beleive. This refers to a 5.3 liter Jguar XJS V12. So a big engine in a small engine bay.

The under-bonnet air temperature at idle can easily get up around 70 C but the faster the car goes the lower the air temperature falls - simply because the radiator is passing its heat to a much larger quantity of air per second - so at 80 mph. the engine is breathing air at around 45 C. That's still a bit higher than the ideal but not nearly so bad as many people think. Obviously the standard arrangement helps to maximise economy in moderate speed urban cruise without compromising top end power too much.

In setups that duct cool air from outside. The power gains from such a system are almost certainly attributed to the filter, and less restritive intake (meaning quite simply a bigger opening), and a form of air box resonance coupled with a 'cool air intake' from outside the engine bay. Sadly even at very high speeds (well over 100mph) I doubt that it has any form of 'Ram Air' effect. If you reconfigured the system to take air from the inside of a wheel arch it would produce the same results as having the intake ducts at the front of the car. The source of the air, not the location of the ducts is the important factor.

Remember the only way to get a greater volume of air into the engine is to compress it. This is what turbo and superchargers do. An air intake scoop either on the front of a car or on the bonnet will not compress the air at any speed most people are likely to travel at.

Taking the airbox resonance theory futher with the intake manifold itself by optimising the length and entry profile into each of the tracts to better exploit induced harmonic resonances in the air as it flows towards the cylinder. Any tube containing air can be made to resonate at certain critical frequencies in the manner of an organ pipe. Such is the case with the inlet tracts of an engine and if the natural resonance frequencies can be matched to the engine speed then a mild supercharging effect can be induced. Get it wrong and the reverse will apply, resulting in a loss of performance.

I'd keep my money in my pocket and stick with the Gott's type modification.

[shotgun]

Bill,
Thanks for that great post. I couldn't have said it better if I knew all the details (or how).

My point was not to promote Banks (I've always known Ram Air is basically a marketing term). My college thermofluid dynamics class taught me that.

My point was to debunk the COLD air intake marketing hype. Hence, like you, I suggested the Gotts mod and pocket the $250-350 an intake will cost.

Unfortunately Truckin', Two Guys Garage, Power Block, etc. keep promoting how much we need to let our trucks breathe better. And we have just the product for you...

[cody994x4]

bill has just provided a plethora of helpful info. looks like ill b spending sometime researching and educating myself on this subject.

but thanks for the cut & dry answer shotgun...looks like ill be dng the gotts afterall.
thanks guys

[Longshot270]

That was a great article!

I also did the math not too long ago (Bill probably remembers me asking him what g/s means, I knew that info would be handy ) and for a custom ram air on my truck to actually do more than fill the small amount of vacuum I would have to be travelling at least 95 mph with practically no engine load and low rpms, a feat that simply isn't possible in our trucks. Plus it would only be about 1% increase under the before mentioned conditions and at 100% efficiency from outside to the cylinder.