Rocketguy

I just found this on the web. Most of it is too much for me to understand but some of it makes sense.

Anyone think this guy is right or is this another LOL?

jeff in colorado

Sounds reasonable to me. But then I'm just some guy on the internet. lol.

MDchanic

I think this sentence sums it up:

"Below about... 228 MPH at sea level..., air is considered “incompressible”.
That is, even if the correct nozzle is selected, and the air is slowed down (the official term is “stagnated”) there will be zero trade [of kinetic energy (movement) into static energy (compression)].
No kinetic energy will be traded in as work capable of compressing the air. The reasons for this are not discussed here; the reader may consult any reputable fluid mechanics textbook for confirmation of this fact.
In plain English, a car is just too slow for ram air to work."

Remember, the science cited is not just speculation - look up in the sky the next time you hear a rumble and you'll see the same science holding a multi-thousand-pound jet plane over your head.

- Eric

RandyS

I vote for BS..........

bccan

I didn't read it as I would probably just glaze over but other than Pontiac's use of the term "Ram Air" didn't everyone else just pretty much reference air induction as far as production cars. Cold air induction, air grabber, OAI, etc. I always thought the main advantage was to feed the induction system outside, cooler than underhood ambient air.

If this makes no sense relating to the article I apologize, the topic just caught my eye.

1968_Post

I always thought the premise of Ram Air, Cowl Induction or O.A.I. was to provide cooler denser outside air rather than the hotter air encased in the engine compartment... not so?

1968_Post

bccan, you beat me to it... I was looking up the cowl induction used on the 1963 Chevrolet "Mystery Motor" engines. It was designed strictly for funtion, picking air up from the actual cowl vents at the base of the windshield.

Koda

I think that the answer is in the middle. Does ram air work as awesomely as advertised? Probably not. Does it help some? Sure. Most ram air intakes are cold air intakes, and outside air is more dense due to lower temps than underhood air.

This article misses a couple things. I have no idea who Dave Rodabaugh is. If he was an engineer, he'd say so. I've got a couple of mechanical engineering degrees, and I've taken fluid dynamics and aerodynamics classes, and my fluids book is holding my monitor stand up a little higher at home.

As Olds itself noted, the location of the scoops matter. Front of grille is optimal, with under bumper being close to just as good, and the top of hood is lesser. This has to do with the direction of air flow. Similar to how leaves won't blow out of your truck bed with the tailgate up (with the air flowing from top of cab to top of tailgate), most air will go over top the W-25 hood as opposed to in it.

He mentions in the article that there is no trade-off for ram air, thus no energy transfer. This is not true, any ram intake causes aerodynamic drag, and the energy the car puts in to overcome that extra drag is what is pushing the air.

Do I agree that ram air is less pressurized than supercharged? Sure. But, one simply has to look at an airspeed gauge on a plane to see that it does do some work.

I don't have the data to give good numbers. To test this, I'd hook an OAI setup to a wind tunnel, and put an engine on a dyno, and check power levels at various wind velocities. That would require a large wind tunnel next to an engine dyno, which I don't have available, so the best this engineer can say at the moment is that the cold air helps some, and the ram air effect certainly helps some, and it can't hurt.

Plus, it looks cool.

MDchanic

Or, to test whether ram air actually increased intake pressures (without confirming whether power was measurably higher, though there is a direct and calculable relation between the two), install pressure transducers in a couple of the intake ports, just before the heads, and maybe just before the carburetor for good measure, and then go out and drive the car at various speeds.

Probably cheaper.

- Eric

bccan

I know Koda is right - I have NEVER driven cars that get bugs on the windshield like a 70-72 OAI hooded car. I drive 20 miles in the suburbs of CT & you would think I traversed the Panama isthmus @ 100 mph. I usually scrub my windshield w/ 000 steel wool & glass cleaner to get the bugs off. Conclusion - more air goes dirtily over those scoops than in em.

Octania

The purpose of the OAI system is to let the sound OUT
so when you open them QJet secondaries, everyone knows.

And, feeding the engine air from BEFORE the radiator, not after.

Octania

"The amount of air which is inducted into a cylinder is a function of the air’s density. As the air flows through the intake tract, it loses pressure, and as the pressure decreases, so does the air’s density. (Denisty is mass divided by volume. Since cylinders are a fixed volume, increasing the density will also increase the mass of the air in the cylinder.) There are two ways to increase the pressure and density of the air inducted into the cylinders:
- Decrease the pressure drop from the throttle plate to the cylinders
- Increase the starting pressure at the throttle plate.
Ram air is an attempt to do the second. Under normal circumstances, the air at the throttle plate is at atmospheric pressure, and this pressure drops until the air reaches the cylinders. Ram air would start the process at some pressure higher than atmospheric, and even though the drop is the same, the cylinder pressure is higher because of the increase at the start."
=====================
This is where the deviation from sense begins.
The author is assuming that pressure and ONLY pressure is the method by which OAI is effective- perhaps because he chose to pick on "RAM AIR" named systems. Another method of increasing the density of air, which the author notes is a way of cramming more air molecules into the engine, is by using air at a lower temperature.

Where does your 1968 98 get its air from? Underhood, after the radiator. Hot.
Where does your 1968 W30 get its air from? Under the bumper. Cooler.

Notice how nowadays ALL vehicles use cold air induction. It does matter.

"Ram" effect or not.


"Select one of the two types of intakes, warm air, or cold air. Beyond that its just about looks."

That's OK, I'll take the LOOKS of the OAI system, then.
I'll put the scoops on backwards so that I have a divergent scoop too.


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MDchanic

The author is specifically addressing the concept of "ram-air," which involves using some sort of a scoop to try to increase the pressure of incoming air by harnessing the velocity of the air stream moving past the vehicle.

He is not discussing OAI or the far less "sexy" post-late-'70s induction systems which you mentioned, that involve a modified snorkel and a length of dryer hose into the fender.

You're arguing with nobody.

- Eric

66-3X2 442

I read a story a while back about cold air induction and the Chevy style of drawing air @ the base of the windshield was hands down the best way. It had something to do with that area being a low pressure area instead of forced air. I do know if you take the plastic top from a 70-72 OAI cleaner,the car is faster.

allyolds68

I could never figure out why they didn't make the 68 cowl hood functional instead of putting those worthless under bumper puddle catchers down there.

Professur

Given the choice between a ram air scoop or a shop vac supercharger ... Go with the one that looks coolest.

Redog

So I guess the time slips I have showing a faster ET using different kinds of intakes are incorrect also. I guess the ET is faster for the Ram Air time because when I drove it down the track I must have torn a hole in reality and the 1/4 mile finsih line in that alternate world was set at the 1000 foot mark. Luckly I broke back into our reality before turning off the track.

garys 68&72

The corvette L88 style hoods were actually used in racing because the base of the windshield was a high pressure area with no drag disadvantage. That's where they draw their air from.
Although I'm not sure if seals were even engineered to withstand any measurable pressure differential into the carb.

Fun71

It's a high pressure area, not low pressure. The "cowl induction" setup on the Chevelle and Corvette and the Trans Am shaker scoop, amongst others, were based on the same principle.

allyolds68

Daveh once said in an old ROP thread that they never had time to correctly test the 68 hood to see if the cowl vent would work so they just threw those scoops under the bumper

Koda

I really think they should have given the 67 parking light scoops to the 68.

Octania

what a great idea.....
'68 parking light OAI

66-3X2 442

Like I said,it was a while ago and I'm glad you got me corrected.

Lonestar

Oh boy, this is one of those threads! However, NHRA's (and others) Competition Department would personally come rescind my Pro racing license if I didn't respond to this.

The article quoted seems to be referencing only OEM setups and are mostly accurate. However, some of the statements are very general in nature and could be interpreted as applying to all hoodscoops or air induction systems. This is simply not true. Read on for a non OEM viewpoint from a racer &, team owner...

A carbureted, naturally aspirated drag racing engine, with a forward facing hoodscoop of the proper design is quicker and faster on the drag strip than either no scoop, cowl induction, or rear facing design of any height. Major sanctioning bodies determine which classes will prohibit the use of a scoop, and they regulate the type, size, and design of said scoop where permitted. This explains why Stock Eliminator, and others, utilize a stock appearing hood. Also, some X275 classes and independent orgs or classes that strive to retain a "stock" look either prohibit scoops or they allow only a specific size "cowl" scoop. That said, in the premier N/A doorslammer class in any organization, PRO STOCK, hoodscoops are not required by rule but are present on EVERY entry and indeed are regulated to size, height, and design to ensure a level playing field. Ambient temp probes, velocity pitot tubes, density meters, etc. are not legal on raceday but are often utilized when testing.

Now for the interesting part. Does a PRO STOCK hood scoop "force" air into the carbs or are there different forces at play? The players spend hundreds of hours in the wind tunnel measuring all things related to C/D and downforce to plot areas of low and high pressure. The hood scoop area is a major focus of these sessions. The information gleaned is guarded like the recipe for Kentucky Fried Chicken but there are performance gains to be had. A quick note regarding the "bug line" on the windshield mentioned above... there is NO bugline on a Pro Stock car. Their body packages, while regulated, are very sophisticated and extremely aero efficient.

MDchanic

I observe that the scoop in the photo looks like a jet engine cowling.



Coincidence? I think not.

- Eric

Run to Rund

Legend has it that Olds used the Lockheed wind tunnel to help determine the placement of the 1966 OAI ducts and bezels. My empirical observation is that at cooler temperatures, the car runs quicker. At high speeds, such as when I put it into neutral at the end of the quarter mile, the engine will stall unless I give it some throttle.

Lonestar

Good eye... it's amazing to review the progression of the simple hood scoop since the mid '70's. Performance has improved as a result.


I would be surprised if all of the manufacturers didn't take advantage of the technology of the time and the resources they had available.

Cold air and proper tuning = quick. What's your trap speed? Clicking the car into neutral at the end of a hit will certainly kill the engine in some cases and nearly all high hp (over 1000) applications. The jetting, float level, needle & seat settings all come into play as well as the effect that deceleration has on the carb(s). We normally click 'em, neutral with the automatics, clutch on the 5 speed EFI car, kill the ignition simultaneously, and hit the chutes at the finish line to obtain the best possible data from the recorders. Other than the EFI car ours will die too if we simply lifted and particularly when the chutes hit.

TripDeuces

We've had this discussion before on here. Maybe even several times. Although it's called 'Ram Air' I don't think a 'ram effect' was any part of the equation but rather a tag line to promote sales.
I think we all can agree that any performance increase is due mainly to the cooler denser air rather then any ramming effect forcing the air in. I also believe that although the Olds W30 hoods have the low scoops that are in the boundary layer of stagnant air they are also far enough forward that they pick up a considerable amount of cool air.

Diego

I always had the belief the A12 Plymouth and Dodge cars had the most efficient system. Chrysler did wind tunnel tests to come up with the design.

It's also my understanding that the OAI was a great design but not necessarily efficient because the air going from the tubes to the air cleaner could gain in temperature, but can't say for sure. Overall it's probably one of the better designs out of the bunch.

rustyroger

I wonder what the air speeds in the ports of inlet manifolds are. I understood that having inlets of the correct length would time a pulse of dense air to coincide with the inlet valve opening at certain engine speeds, part of the reason why small displacement, high output engines have a narrow power band, particularly two stroke engines. If it is less than 230mph then there would be nothing to gain, I think Yamaha motorbike racing development might know a dead end when they meet one.
This is very much a laymans view, what I know about ram air principles and port tuning can be written in large print on a small piece of paper.
But I am always willing to learn more, separating fact from myth is the difficult part.


Roger.