Actually can you red-line an engine these days…Most vehicles have limiters to prevent this…My Pathfinder would actually shut off the fuel if it red-lined…probably a good idea.
I know.
Truth is, most 4-pot engines will run out of poop before they go past redline anyway. Unless, of course, one creatively enhances their ability to breath. Perhaps I’ll fiddle with that ram air system next week on vacation.
My Scion has two openings at the sides of the lower grill that are plugged with cosmetic pop-in imitation “screens”, which while they look like screens are actually plugs (see attached photo). Such a wasted opportunity. I’m thinking of putting in a real screen with plumbing from the hole to the intake on the air cleaner box. It would provide some positive pressure on the air side of the air filter when rolling down the highway, theoretically reducing pumping losses through the filter. I might even supplement it with a high-flow filter (dry…I hate oiled filters). It should also provide a better cold air source than the current air supply cavity (inside the fender cavity). If the injectors can keep up with the added airflow it theoretically will give me a bit more HP at speed without any additional drain on the crank or backpressure of the exhaust.
I’ve just very recently been playing with this idea. Anyone have any thoughts?
Lots of current sports bikes are using some form of ‘ram air’ in their induction system, they’ll do just about anything for a few more hp at the top end. That said, your mods would seem to be a benefit at speed while at wide-open throttle. If that’s where you ‘live’, might be worth the effort. Otherwise, I don’t think you’d notice much change.
Ram air goes way back, but things are different now. In days of old, carbs put in more fuel than was used anyway, and had a capability to dump even more in. Simply adding more air was easily complemented by the addition of more fuel. More air in meant lower lateral wall pressure at the venturi which meant more fuel would be drawn in. The car could cruise with a little less throttle opening.
But today the ability to get more power will be limited by the injector capacity and the mapping in the ECU. The amount of fuel is indirectly affected by the increased airfllow via the MAF sensor, but it seems somehow different. Theoretically the car could cruise with a bit less throttle…I think. At WOT the injectors will probably have about as long a pulse width as the ECU will give them anyway. I’m basically just wondering if reducing the drag through the filter combined with the better source of cold air will make a difference.
Perhaps I’ll try it amd see what happens. If I do I’ll post. I’ll try to compensate for the placebo effect, which in my case is sometimes tremendous.
“Your butt dyno is full of crap” 
Why, thank you for noticing. Do you spend a lot of your day evaluating people’s butt dynos?
I just assume that theirs is calibrated similar to mine.
I see.
And what, exactly, in my posts is “crap”? I’ll be happy of you’ll correct me on any misconceptions I might have. I’m always open to new knowledge.
I think you misconstrued the intent of my post, which was not to insult you or imply that you’re wrong. The quotes were to indicate that it was a. . quote. A saying that’s fairly common in the tuner scene. It means that when you modify your car, you tend to think the mod gave you a lot more power than it actually does, because you think you’re feeling more acceleration than you really are. i.e. your butt dyno is full of crap and therefore you need a real dyno to measure the gains. I was under the impression that you were hinting at the difference between real performance measurement and the seat-of-the-pants-feeling measurement, based on your comments regarding the placebo effect.
You are 100% totally correct.
Please accept my apology. I did misconstrue the intent of your post. I’d never heard the saying before. I thought it odd, since you’ve always been a decent and knowledgable sort, but I’m afraid I got my shorts in a knot anyway.
And now if you’ll excuse me, I have a date to see “Grumpy Old Men”…
Have a truely beautiful evening.
About the effect of ram air at normal cruising speeds. Let’s say 60 mph. At 60 mph, the air entering the intake has enough kinetic energy to lift it about 120 ft into the air so when that kinetic energy is converted into potential energy (head in other words), the effect on the engine’s performance should be comparable to driving at a 120 ft lower elevation. I doubt you will notice the difference.
Doubling the speed quaduples the air’s kinetic energy and thus quadruples the head so going 120 mph is like driving at a 480 ft lower elevation. You may notice this.
Double it again at race car speeds and going 240 mph is like driving at a 1920 ft lower elevation, now we are talking a significant horsepower gain.
Ram air pressure is not “free” however, there is a significant gain in aerodynamic drag associated with putting a ram air opening on a moving vehicle.
It’s all good Mr. Thesame. 
Nada. Adding ram air is analogous to adding a mild supercharger without the crank drag. It minimally increases the air pressure going into the intake. What you’re forgetting by simply looking at the kinetic energy of the mass is that the engine has a mass airflow sensor that sends a signal to the ECU that when combined with other signals changes the squarewave the ECU sends to the injectors, changing the injector pulsewidth. Thus, there are secondary and tertiary effects.
This one will be aerodynamically “free”. The hole is currently plugged. Opening a plugged hole and allowing air passage in a spot that already is part of the aerodynamics should, if anything, reduce resistance. Rather than the spot being a plugged recession, as it currently is, the air going in there will now be passed into the engine, used, and blown out the exhaust. In short, this one would be analogouse to creating a hole for air to pass where a flat verticle panel now exists.
Were I adding a scoop that were not there, I’d agree with you. But I ain’t.
In truth, I suppose I could estimate the gain. I could look up the output curves of the
mass airflow sensor,
throttle position sensor,
add a variable for the engine demand (I know the displacement and with that can figure how much it needs to suck in over the RPM range up to its redline),
add a variable for the increase in pressure at different speeds at, say, 29.92 in. Hg.,
even look up the output curve for the temp sensor to see what it’ll do when cold,
and build a mathematical “model”…
but there’s a problem: even though I can determine all that I don’t know that I can find out what, as the variables vary, the sqauarewave will be to the injectors, how big the bandwidth will be, using the stock program. If I could, I could calculate the fuel delivery 'cause I know the injector orafice and fuel line pressure. I could then determine the air/fuel ratio and even determine if at WOT near redline with the expected intake pressure at 75mph, the injectors will be capable of providing sufficient fuel.
Ah, but what fun would that be. Best case, I’ll notice a difference in passing power on the highway. Worst case, it’ll go lean and I’ll have holes in the pistons big enough to pass a cigarette through.
Thank you Shadow.
The thing with ram air is that it has to be properly designed for the airflow and the intake of the particular car it’s on. Yanking a headlight and sticking a PVC pipe in the hole does not effective ram air make. A real, effective ram air intake requires math and thoughtful design, else you end up canceling any gains due to airflow buffeting, or you don’t get any air at all because the ram air isn’t in the right place, and so airflow means it’s not getting as much air rammed in it as it should. Those homebrew ram air setups you see usually do jack for ram air. They help out off the line because they function as a cold air intake, and so you don’t have engine bay heatsoak slowing you down, but at high speeds they’re usually ineffective, and sometimes detrimental.
You’re right, of course Shadow. And if it actually does increase intake pressure, I don’t know at what point the injectors and the programming would need changes to take advantage of the added air.
But hey, I’ve got some time off coming, nothing better to do, and I’m curious to see if it’ll make a difference. It is as much an assumption that it won’t help as it is an assumption that it will help. I try stuff like this all the time. Sometimes it works, sometimes it doesn’t. Either way, I always learn something, usually something useful.
I see it as comparble to sound proofing my car. It was long my belief that since road noise (I thought) mostly propogated up through the suspension adding soundproofing would have only a small effect on a car with high road noise. Then, a few months ago, I had to remove the interior panels in the rear to access the upper shock mounts anyway, so I figured I’d throw in some structural sould deadener before reinstalling them just to see what would happen. It made such a huge difference that I was reluctant to admit it to myself, attributing it to the placebo effect. When I finally admitted how much quieter the car was I did even more. And that too made a difference.
I even discovered that much of the whooshing sound from cars passing on the other direction apparently largely comes through the body sheetmetal. Adding structural damer to the sheetmetal behind the B pillars suddenly cause the whooshing to virtually disappear. It too me a few days to realize what the sound was that had disappeared.
Maybe I’ll have the same luck again. Maybe not. I learned a great deal from the sound deadening experiment. I’m sure I’ll learn something from this one too.
I’d wager you’ll pull it off, based on your engineering and aviation background.
I figure I gots a 50/50 shot. I’ll post and let evryone know.
Without RPM, you can have no horsepower…Horsepower will increase with RPM until the engines efficiency, (it ability to produce torque) falls off greatly…That’s why racing engines do everything they can to reduce that drop in torque at high RPM.
Honda’s 250cc, 6 cylinder 4-stroke motorcycle racing engine demonstrated this principle to a very high degree…That engine reved to 17,500 RPM for a REASON…
Actually, you can have horsepower without RPM. The formula for drawbar horsepower is pounds of force times feet per second / 550
For example, the wind blows on a sail with a force of 55 pounds and this results in the sailboat moving away from the wind with a speed of 10 ft per second, the wind is delivering one horsepower to the sail.