Does anyone here use a ram air intake? How much "boost" does this setup provide (at say 80 mph)? Advantages/disadvantages?

 

The only pro to this system would be the effect of cold(er) air into the intake. However, you have to keep the air inlet off of the ground, as temperatures near the surface of the pavement can be pretty hot. Also, make sure wherever you're racing (legally, right?) allows this kind of modification.

Cons of the system are probably cutting up the hood, and it does not provided any "boost". There will not be a pressure differential with a system like this at speeds that most street cars can attain - unless you had some really trick aerodynamics for that purpose, but that would probably increase drag and slow the vehicle more than the air system would gain.

A system like this could be rigged up with pretty good results i'd imagine (1-2 tenths in the 1/4 mile maybe)

 

You need to talk to an aeronautical engineer before you think about "Ram Air", better yet look on the internet. From what I have been told, "Ram Air" is not beneficial unless you are moving at around 186 mph. After that point, the "ram air" effect begins. Why Trans Am made a "Ram Air" intake remains to be seen. Guess it would be "Hype" or some other Marketing scheme. Let us know what you find out...

 

Yeah, its around 200mph where this sort of system will actually start forcing the air at pressures above atmosphereic.

The 'ram air' system works... but not becuase of any ramming effect, the real gains are from sucking ambient temp air rather than hot underhood air into the intake system.

 

Looking at Type-RJ's picture (is that endyn's SC car?) is a little misleading. I don't think you can "ram air" through that filter.

 

In regard to Ram Air: "The scoop helps, but not because of any appreciable ram pressure effect. At the end of a quarter mile drag race, a '98 Firebird Trans Am with a WS6 Ram Air option is traveling about 100 miles per hour. This relatively modest speed (by aircraft standards) provides an apparent increase in pressure of only one percent. Further, automobiles spend relatively little time at 100 miles per hour. More importantly, however, the hood scoop delivers cooler, denser, outside air to the engine with much less friction loss than a conventional intake for a significant performance improvement. Answer your question?"

 

you cant ram air through there... it was a description of what a good cold air system *could* be like....

And yes thats endyn's SC car...

 

While there might not be any "boost" in the system, wouldn't forcing air in through the hood have the effect of decreasing the intake vacuum? ie, making it easier for the engine to breathe since it doesn't have to work "as" hard to pull air in. Not saying it'd be a big benefit... but wouldn't a gigantic scoop eventually have the effect of allowing the engine to be more efficient, provided you're going fast enough, and it's large enough?

 

The engines ability to suck air in will still be dependent on the largest restriction in the system, which is probably the intake valves and intake runners in the head. So you can sitck that cone filter out of the hood, and it wont make much of a difference. The idea is to balance the entire system as a whole... intake tube diameters come into play as well.

The exception to this is a phenomenon called resonance supercharging, where you can acheive a resonance effect (due to pressure waves) in the intake plenum depending on the intake runners size, plenum size, air intake diameter/length which will create a small pressure delta from ambient that can help power output at a narrow rpm range. This is the reson for systems like BMW's new continuously variable intake length manifold on the new 7 series V8, or dual runner intake manifold systems. However we've now eceeded the scope of the original question....

RJ

 

I was thinking something like this:

(Stupid tripod won't let me link to an image.)

http://nikiloco.tripod.com/crx/coldair.html

I've heard of "boost" levels as high as 6psi at 80 mph, but I was skeptical.


[Modified by manveer, 3:16 AM 2/24/2002]

 

Somebody call?

K, let's look at this logically. Let's assume that you have a turbo that can pressurize the intake manifold at 6 psi. Let's also assume it's 85% efficient (optimistic but doable).

Therefore, in order to maintain a 6 psi boost, said turbo would have be pushing air into the intake manifold at a rate of 536 mph... hmm...

So if we replace the turbo with a "ram air system" capable of producing 6 psi...
536 mph - 80 mph = 456 mph increase due to the inlet design alone!! I want to meet this intake designer!! I have a job for him/her!

But wait, it gets worse!! Due to compression, that 6 psi air is now at a temperature of 161°F!! So, any ram air system that could produce 6 psi also increases the temperature by about a hundred degrees!! Hence, it's not exactly a cold air system anymore!!

Supporting math:

Given a pressure ratio of 1.4, this gives an increase in dynamic pressure (*cough*screenname*cough*) of 863.6 psf.

Such a pressure increase also gives a density ratio of 1.18 (I can show you the equation for that, if you like).

dynamic pressure of 863.6 = 1/2*density of air*V^2

Backsolve for V using rho = 1.18*.002378 (density at sea level) and you get 536 mph!!

Andy - who should be doing something else...





[Modified by maxQ, 6:59 PM 2/24/2002]

 

If it takes that much air intake speed to generate any theoretical boost... why was it such a power reduction for F1 cars back in the mid '90s when the FIA mandated holes in the back of the air scoops to slow the cars down? Ferrari cut the holes in the side of the scoop during a practice session and were 9mph faster on every long straight than every other car there because of it. Yes those cars are going ~200mph, but wouldn't they need to be going much faster to make a difference in power?

 

I made a "ram air" system for my '94 GS-R which I drive at HPDE. I modified the passenger side turn signal lense by removing the lense from the front bulb and I removed the bulb socket from the back of the lense. I also made my own "Icebox" CAI ( http://www.geocities.com/bretq/DIY_Icebox_CAI.html ) (nearly identical to the Comptech Icebox) which has the intake opening right behind the turn signal lense. I have a "connector" which connects the modified turn signal lense to my "Icebox" CAI. This setup feeds cold air "directly" into the stock airbox. This is comparable to the setup used on the Realtime Racing Type-R Integras. The only difference is that Realtime removes the passenger side low-beam headlight and then routes cold air into a NSX airbox.

Here are some pictures.

Modified "ram air" turn signal lense:




"Ram air" turn signal lense with "connector":




"Icebox" CAI with turn signal removed:

 

Know a guy who has a Camaro SS with ram air hood. He actually blocked it off and routed the intake through the lower chin openings on the grille. Ram Air was actually hurting performance, he claimed another 6 or so HP from taking the system out and setting it up how the non-ram air hoods are set up..
Hearsay, but those cars have so much damn power, who is going to miss 6hp?