Testing the effects of Ram Air

If you remember one thing from high school chemistry class, it might just be that gasses, such as air, become denser when cooled. When it comes to engines, cold air means more molecules of oxygen available for combustion. This boils down to more power.

Supplying an engine with fresh cold air is a benefit most auto makers have exploited since the '60s. Unfortunately the better air quality usually comes at the expense of air quantity, as the factory air cleaners are restrictive and designed to minimize sound rather than maximize flow. Most of us try to solve the quantity problem by installing the "muscle car" standard, a 14-inch open element air cleaner. Though it does breath well, it sucks in hot air from the engine compartment.

The ideal situation is a ram-air setup, which not only provides the engine with cold air, but also large quantities of pressurized air. Air pressure at the front of a car can be as high as 3" of Hg at 80 mph. Directing this to the carb is essentially a free, albeit very small, supercharger!

Until recently making an effective ram air induction for your carbed engine meant either installing a big and conspicuous scoop on the hood, or fabricating an sealed air-cleaner and running ducts to the front of the car. In other words, it wasn't a simple task, and the end result often didn't look too great.

Fortunately a company called Air Inlet Systems has made installing a ram air system on your carbed Ford a very simple project. AIS makes the "Ram Air Box" a high-capacity, air filter housing with twin snorkels. The hand-laid fiberglass housing has been designed to optimize air flow and pressurization. Flow comparisons between the stock 1985 Mustang HO dual-snorkel (14"x3") air-cleaner and an AIS 14"x3"with 80 deg. snorkers, show an increase of over 350 cfm (Superflow 1020 pro-bench with pressure set at 10 inches of water.)

The beauty of the Ram Air Box, besides its exceptional flow, is that is utilizes a standard 14" diameter base, lid, and air filter. Depending on hood and engine accesory clearance the box itself can be ordered in a 3", 4", or 5" tall configurations, with either 80 or 110 degree separations between the snorkels.

AIS claims most users see a 2 to 4 tenths improvement in ET, and as much as 10% increase in power and long range fuel economy.
We decided to see if we could confirm these claims for ourselves. Our 1967 Mustang had been running consistent 13.0 - 13.10 for the past five months, with seemingly no hope for a 12 second time slip. No matter what we tried we could not gain that extra tenth. So needless to say, we weren't too convinced that the Ram Air Box would do it. Fortunately we were proved wrong! Very wrong! Quarter mile results confirmed over 2 tenths improvement and a gain of 3 mph over our previous bests without ram-air. To top it off, we noticed an increase of about 2 mpg on our 100 mile roundtrip drive to and from the racetrack.

We track tested the Ram Air Box on Project '67. We made no changes to the engine or car other than installing the Ram Air Box. The 289 powered Mustang had run a previous best of 13.03 @ 104. Just to show its no fluke, we made six passes on the same day with the Ram Air Box, and all six were in the 12's! The top three are listed here:

Ram Air Box w/ air filter
(Best Run)

12.80 107.32 1.76
(2nd best)
12.83 107.12 1.75
(3rd best)
12.83 106.60 1.77
Ram Air Box
w/o air filter
12.95 106.12 1.78
No Ram Air Box
(Previous Best ET)
13.03 104.16 1.78

There is absolutely no doubt that the design of the Ram Air Box yields convincing results. This may in fact be the cheapest horsepower you can buy for your carbed Ford! We were also curious if the Ram Air Box worked better without an air filter, but we actually lost a tenth and 1 mph without it. We figure the air filter reduces turbulence in the box and straightens the air flow to the carb. As mentioned before, we used a cheap paper filter, but a good cotton gauze will flow better. Who knows, we may still be able to squeeze another tenth out of the 289!



In This Article...
FordMuscle tests the Ram Air Box on Project '67 Mustang.


1 There is not much to it... Shown here are the 14"x3"@80 deg. Ram Air Box, 14" drop-base and lid, aluminum duct, and 14"x3" aircleaner. AIS can also supply you the ducting and air cleaner base/lid if needed.

2 Assemble the Ram Air Box: Slip the provided horseshoe seal over the edge of the base. We had to cut a small notch in the base to clear the plug wire on our large diameter distributor cap (see next photo.)

3 Set the base on the carb. Note that we are using a "drop" base which was necessary to have proper hood clearance due to the taller Victor Jr. intake. Depending on your hood and vehicle, you may be able to use a standard flat base.

4 Set the box on top of the base and drop in the air-filter. Use the same size air filter as the box, in this case a 14" x 3". (Although we are using a paper filter here, a high quality cotton gauze filter will flow better.)

5 Finally set the lid down and secure the wing nut. Note that the lid is NOT meant to rest on the box, but rather in the box on top of the air-filter.

6 A true ram-air effect requires the openings to face directly into the path of air flowing towards the car. On most cars the grill area an ideal high pressure zone.On our Mustang we chose to cut holes directly beside the radiator. Keep in mind you may have to move things around to get the ducts to fit. Having relocated our battery to the trunk made things much easier. Other areas to consider are headlight buckets, if your car has dual sets.
duct adapter
7 Insert the duct adapters into the radiator support. We secured them with a few pop-rivets. AIS sells a variety of adapters and inlet scoops to look trick as well as improve flow.

8 Finally hook up the aluminum ducts. Use 4" hose clamps to secure the ducts to the snorkels. The completed installation functions as great as it looks.


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