TheColonel

This may be a stupid question, but why are they called short ram air intake? I know what ram air is, and the SRI I had on my Integra certainly wasn't using the motion of my car to cram in more mixture per stroke. Does it just sound cool?

wakeech

marketing bullshit.

ram air doesn't exist, so what's the harm in calling something that isn't "cold air" "ram air"??

RXE16T

It's like advertising a titanium exhaust as being "20% lighter than stock!"
As wakeech said, it's purely a marketing ploy to get you excited and make it sound like it has some sort of realworld benefit to the average driver.

Mr M

The VDI (Variable Dynamic Intake) uses the pulses caused by intake air hitting the rotor that has its intake ports closed, to help charge more air into the rotor housing with its intake port open. Whether this can be classified as ram or not is academic. It uses dynamic pressure waves to help 'pull' the intake mixture into the rotor housing. I don't know why someone is calling it ram, when everyone else in Mazda is calling it VDI...

shelleys_man_06

That's exactly what I was thinking.

wakeech

mmmmmmm... that's not quite it.

the reasons that 'short ram air intake' is bs are:

1. people have this impression that driving into air helps the motor suck it down when in reality the motor is sucking air in far far faster than the car is moving, unless you're cruising in overdrive in the city... at speeds that low there is very very little positive pressure increase, and with the scoops and funnels and whatever it would cost you a lot in drag at the high speeds where it's "suppost" to help.

2. tuning something resonantly for length or volume is a bit of a tricky thing. never are these things tuned at all. they are " 3" IN DIAMETER!! FOR EXTRA POWER AT THE STOPLIGHT!!" or something stupid, and molded just so you can SEE it in the engine bay (intakes are little more than underhood jewelry, just like a stupid billet oil cap, for god's sakes) and it fits. those're the two main criteria when designing an intake.

VDI has the intake runners, the intake plenum, and the "snorkels" (the inlet lengths themselves) all working together in concert. the pressure waves are the fluctuations in flow (lowest pressure at highest velocity, highest pressure when the port closes and flow backs up), and this can be utilised to create a higher pressure difference across the intake system when you have the peak of your high pressure wave (which you can think of exactly like a sound wave, 'cause it kinda is) reaching the transition from the runner back into the plenum while the flow at the port is the highest (lowest pressure), and then again in the plenum as the waves travel outward with the high to low difference, and out again for the length of the intakes into the plenum.

on top of that there's the multi port system which does well to maintain velocity into the combustion chamber (the faster the air is moving in the lower its static pressure, eh) and allow for a large cross section of area for relatively low velocity and low pressure air (compared to a mechanically compressed charge) to fill the combustion chamber quickly.

Mr M

By "thats not quite it" do you mean "that is not correct"?

I based my explanation on information I got from the engineer who designed the system, so I'm pretty sure it is correct (unless he is having mental lapses).

I just though it might be possible the person referring to RAM was confused with meant the VDI, which is why I explained VDI.

I know VDI is not really RAM. RAM is more to do with the intake of air, from the air-intake, and using the whole intake system like I think you are trying to explain.

NavyDood

That actually can be a big deal depending on the weight of the exhaust. Crude Examp: On my 94 ZX-7 the stock exhaust weighed 38 lbs. The Muzzy Ti exhasut weighed a total of 6 lbs.

Ram Air:

You also need to remember on a true ram air, it is not going to benefit you until you reach higher speeds. Ram air effect does not come into play generally until you get above 70mph. And then it's minimal. After about 100mph, that is when ram air will be beneficial. The inlet of the ram air and/or the air box need to be engineered properly to allow the proper pressure build up in the air box for the given engine needs.

The largest benefit of a ram air would be nothing more than always breathing the coolest air possible unless your constatly cruising above 100mph. You would never be sucking warm or hot air from under the hood. If you throw a K&N or similar filter on, and it's not sealed off in a box under the hood breathing fresh air, it's just sucking warm or hot air.

wakeech

yeah, word Mr. M. not that it's incorrect, just the whole "ram is bullshit" kinda vibe i'm trying to promote.

merlin00gt

The biggest marketing ploy for "Ram Air" came from the late Trans Am's, whos hoods had scoops designed to "force" the air into the engine. This didn't work too well, as there was a high-pressure spot on that part of the hood, thus not ramming anything. The race C5 Corvettes have the intake where the licence plate is; This does work, as there is a low-pressure there, thus cramming air into the intake/engine. Wheather this actually produces any positive pressure is subject to debate. I remember something being published by GM saying that at 120mph, the race C5 produces +1psi of "boost" by the ramming effect of their intake. Then, we're back to the marketing BS again.

wakeech

i think you've got your high's and low's confused there, but no biggie.

it's not really debate, 'cause you can actually measure the "phenomenon", or even just with a little simple theory it's not hard to see that the "ram air" effect is garbage.

your regular chevy 350 at 4500 rpm (not even at redline) is drawing in 12 825L of air per minute, which is 213.75 l/s (wow). with a scoop that has an area of, oh, say 50si, which would be 0.338msq you'd have at 60 mph (which is 92 kph which is um... 25.6 m/s) a maximum of 8.65 L/s. for the scoop to be delivering the amount of air the engine needs by having it "rammed" in would be 632.37 m/s, which is goddamned fast (2276.63 kph, 1422 mph ish).

uh, is my calculator broken??
in any case, the motor is sucking air in lots faster than the car is moving through it, so there is no such thing as a ram air effect.

merlin00gt

D'oh! Yeah, high/low...whatever :P
As much BS as it may be, it sure does sell. Plus, scoops look kewl :|

As for the MPH (1422) I'm sure there's some folks out there that swear their car can do that, if only they had enough road.