Question: Ram air and water

[Thebrek]

I am currently installing a stingray hood scoop on my 81. I am wanting to make it ram air. I have a 15" K&N air filter and the standard chrome cover on top and bottom. My worrie is about rain it's a daily driver and I do not want to cut a hole in my hood until I research more would appreciate the suggestions. Also the actual scoop is already open in the front and back.

 

[Mac]

Sorry to be the bearer of bad news but when it comes to most cars, the 'ram air' effect is more perceived than actual.

In order to achieve an improvement in the volumetric efficiency, you need to increase the atmospheric pressure at the intake the same way as superchargers and turbochargers increase the pressure at the intake. By having the scoop open in the front and the back, the likelihood of gaining an increase in atmospheric pressure is nil.

Ram-air intake - Wikipedia, the free encyclopedia

If you're driving daily, you will have rain, dust and other crud lining up to fill your air filter.

My 73 has the factory set up which has openings at the rear of the hood scoop that open at wide-open throttle. The marketing of the day suggested the ram air effect would ensure cooler outside air would be available. Practical result: louder engine noise transmitted to the driver. Performance change? Not so much.

-Mac

 

[Tom Bryant]

Your '81s factory air inlet ducting already draws in cool outside air for the engine. Cooler air is denser and makes more power. It's also more noticeable with a modified engine. If you removed the flexible ducts so you were drawing in hot under hood air you might notice a slight negative difference in the way the thing runs but it wouldn't be much. If you are going to seal the air cleaner to the hood scoop you will basically end up with exactly what you now have except for the water, leaves and debris that will make it's way into your air filter.

I assume you are talking about the '67 style scoop. There is a reason Chevrolet never opened up the front of that scoop. Even the L88 had the air intake openings on the rear of that scoop to take advantage of higher pressure at the base of the windshield and a cleaner air source.

Tom

 

[JohnZ]

I am currently installing a stingray hood scoop on my 81. I am wanting to make it ram air.

There is no "ram air" effect with a forward-facing scoop on the hood surface; the inlet is in the slow-moving boundary layer airflow. That's why Pro Stockers have their Harwood scoop inlet 18" above the hood surface, and even with that there's no ram-air effect until well over 100 mph.

 

[Tuna]

I'm with JohnZ on this as to the "ram-air" effect. I had a "ram-air" system on my old Grand National and it didn't make any difference until I was well into 3rd gear.

Now for rain issues. If you have a hole in the hood that allows rain water on to the air cleaner, there definitely needs to be drain holes somewhere to take the water away from the air cleaner. Baffles between the "scoop" and the air cleaner would be good to redirect any water to keep it from getting to the air cleaner and engine.

My old '69 Runner had the vertically facing holes in the hood that were supposed to allow fresh air to the engine. The hood was sealed to the bottom air cleaner housing but it had drain holes in the hood ducting to keep the water from the engine.

With my GN, the "scoop" was below the bumper with a 3" flex hose to the K&N filter that was a foot or more higher than the scoop. It was hard for the rain to get up hill that far and cause any problem but I did have to pay attention to driving into deep water - if the scoop was under water, it sucked up water instead of air. Not good.

 

[i10fwy]

I agree with all the above, An engine is a air pump, they do not make a very good water pump. :ugh

i10fwy

 

[lars]

In researching articles I've written on the development of the GTO, I had access to quite a bit of test data from Pontiac Engineering. Pontiac offered "Ram Air" systems for several years on the top-end engine options, but test data showed, as John states above, that the hood scoop has to be located a minimum of 6" above the hood in order to get out of the "boundary layer effect" and produce actual "Ram Effect" above 90 mph. For styling reasons, marketing nixed any scoop that tall, resulting in open "Ram Air" hood scoops that had no ram effect whatsoever - the "Ram Air" systems on GM cars, including the Vette, were marketing gimmicks with limited, if any, actual performance gain. They did allow the engine to draw in cool outside air that had not been heated up in the engine compartment, but there was no ram effect at all: The forward-facing scoops simply don't have any ram effect unless they are located significantly above the surface of the hood, and you're moving at a high rate of speed.

If you're going to spend a ton of time and effort to create a "ram air system," you're better off spending that time and money on other areas, unless you simply want to create an illusion of ram air, as GM marketing was doing.

Lars