WAI vs Ram Air Intake --- at speed...

[theunchosen]

The issue with WAI. . .is it just forces you to drive more economically.

A Prius can be driven and get mid teen mpg. With its limiter hardware it also tips the driver's habits towards eco friendly driving(fuel economy data, atkinson engine, and so forth).

If you put a rather strong spring on the back of your gas pedal. . .you would get alot better FE too. Not because the spring is magic. . .but because you subconsciously aren't going to push it down as far. . .because its hard and we're lazy(or at least I am ^_^).

Yes the throttle plate is obviously the biggest restriction to most cars most of the time. . . but its alot like running two pumps in series. The first pump is a bit more powerful(the ram scoop) and the second one still turns(because you are still powering it) but its under much lower load. So it requires less effort to turn over the second pump(the cylinders on the intake stroke) if you are pushing the fluid right up to it.

Yes you are likely to lose FE with a ram air intake because you have more available power so at any given depression of the accelerator(gas pedal, right pedal whatever) you are going to use a little more fuel. If you just now got into the car and are very ecominded and self-conscious about it. . .you can get better FE. If you've been driving it. . .well you are used to pushing the pedal down to X to achieve Y speed. Now you push the pedal down X and you achieve Y+Z speed where Z is the extra power to acquired from the slightly larger amount of fuel and air at pedal position X.

Its rather obviously true. If we consider the simplest available system(sort of ^_^) Diesels. . .what do diesels do to get awesome FE. Cram a ton of cold air into the cylinder. . .but they don't usually have throttles. The effect of adding a scoop to a gasser would probably be dwarfed by the effect of adding a scoop to a diesel(if it didn't have a turbo. . .lol).

[Frank Lee]

"The first pump is a bit more powerful(the ram scoop) and the second one still turns(because you are still powering it) but its under much lower load."

nope

[theunchosen]

alright fine,

[edit] with the throttle plate restricting the flow rates of the what I called "smaller" pump(which is more powerful compared side by side without throttle to the scoop) the ram scoop produces a greater flow[/edit]

That better?

The Ram scoop is flowing more air(at speed) than the engine does after being restricted by the throttle.

?

[Frank Lee]

nope.

ok now i'm repeating myself, but i'll re-phrase to see if that helps:

say you have a 100hp engine. to go at x steady speed requires 14hp. to go at that steady speed we need to suffocate that 100hp down to 14hp.

agreed???

so the psi or lack of it matters not. if you have more psi ahead of the throttle SOMETHING must be done so that no more than 14hp is produced and that something is throttling back until all the conditions in the intake after the throttle are AS THEY WERE BEFORE.

now if you are at or very near WOT and are accelerating or going top speed, if the ram works you may see something. but we are talking fe driving.

[theunchosen]

I agree Frank, Totally agree.

Point is instead of choking out some of the torque as pumping losses we use it to propel so we go x+1 speed. So we get there slightly faster(we didn't use anymore fuel just used less fuel to rotate the pistons around and therefore more fuel went to the road) which means the engine doesn't run quite as long.

[volvompg]

This is really interesting because I have somewhat of a "ram air" set up taking in air from directly behind the grill. I think that FrankLee and Unchosen both have their points here. To maintain a given speed with a ram air set up you would just let up on the throttle slightly; however, if we added in the variable "traffic conditions," which sometimes require more acceleration than we'd like for FE, a ram air set up would allow you to open the throttle less for a given acceleration.

[Frank Lee]

Originally Posted by theunchosen

I agree Frank, Totally agree.

Point is instead of choking out some of the torque as pumping losses we use it to propel so we go x+1 speed. So we get there slightly faster(we didn't use anymore fuel just used less fuel to rotate the pistons around and therefore more fuel went to the road) which means the engine doesn't run quite as long.

ok i see where you are coming from.

but when the o2 sensor fixes the ratio are you sure we didn't use more fuel?

[theunchosen]

Its hard to say Frank,

The problem with getting a little boost in speed out of the same amount of fuel(less pumping energy) you create a little more air in the intake(ram scoop) and then burn a little more fuel.

In Turbine engines you get runaway caused by the increased intake speed increases combustion energy increases compression, increases combustion. . .and so on and it. In a turbine driven engine its a big deal. . .reciprocating. . .not so much because there is only so much pumping loss to overcome.

Its going to be a small improvement with a ram scoop, but there theoretically is an advantage so long as you don't lay into the throttle too hard with the added power. That said. . .it is a real improvement opposed to a "restricter plate" WAI.

And no the air density influencing the engine has nothing to do with why the run at altitude. Its a calculus maximization problem. The higher you go the crappier your turbojet engines work, but you get ALOT less air density. They go to 30+ thousand feet because at that altitude the radial compressor at the front of the turbojets can still supply enough compressed air(If theoretically they could run the engines at sea level and the aircraft at 30K feet they would) to make the turbines push enough.

If you think I'm wrong. . .ramjets are turbojets which let the compressor "runaway" and compress the air to the limits of the housing. Then it has a giant scoop to force feed air into the engine. They are actually more efficient than regular jets.

The only problem is. . .you have to piggyback them up to mach 1.5 or so and then drop and engage them. It costs a ton of fuel to launch and so its not viable but a WAI and less air in the engine blah blah blah. . .its a restricter plate, look it up under NASCAR.

[greasemonkee]

Originally Posted by theunchosen

If you think I'm wrong. . .ramjets are turbojets which let the compressor "runaway" and compress the air to the limits of the housing. Then it has a giant scoop to force feed air into the engine. They are actually more efficient than regular jets.

Interesting, operating principal. Seems like there would be a centrifugal stress issue with these.


For the sake of staying on track, I haven't picked though this entire thread but, we do know that open loop engages at X throttle position on MOST management systems, regardless of manifold pressure. With that, it is possible to achieve a higher MAP at <X throttle position. Due to the choked gas flow (among other working factors); the mass air flow of the intake manifold is higher with the slightly pressurized environment pre-throttle plate at <X tps in turn producing more hp in closed loop than the manufacturer intended for it to.

Obviously, this would eventually get dangerous or inefficient if the engine were to see these higher pre throttle plate pressures as it would be too lean to produce power efficiently and safely.

[theunchosen]

If you are force inducing air into the engine the MAP vacuum will be less at any given throttle position. I think thats what you are saying. . .?

Also the 02 would throw a CEL and kick out the MAP readings if it got too lean. the EGT would probably also chime in. That situation it would go limp and run rich.

Although. . .the MAP is going to try and run around 14.7 in open or closed. . .you just won't be getting feedback from the O2 and the EGT won't factor in as much to the fuel injection. Open or closed the MAP is going to keep it from getting too lean unless you tamper with the wiring or the ECU(insert resistors or change the fuel-air map.)