Ram Air Question

[Guest EDBS0]

Got the bug to do a Ram Air Induction for the Reatta. Got it mostly figured out just don't know how big the opening should be.

There are and have been a number of cars with Ram Air and Cowl Induction and in my opinion I think that they all use rather small induction openings.

What would the optimum size be for a Ram Air opening for a 231 cubic inch Reatta. Are there any calculations that can be performed or is there a web page that you can point me to?

I know it is a tough question and so far I have found nothing.

Perhaps it is a simple as "bigger is better"?

[Guest spongebob]

i have ram air on my bike, and it dosent come into play until something like 100mph. the bike is a 750cc engine, and the air ducts are the size of a base ball ( one on each side of the bike). i have a artical on the subject, but its on motorcycles, not sure ive ever read anything on this with cars..

the reatta is taking air in front, isnt that about as good as it gets??

i had a corvette that had this as well, a flap opened up and air was taken in at the windshield area when the secondaries opened up, but again, you had to be really up to speed to get the air pressure to work..speeds that the reatta will never see <img src="http://www.aaca.org/ubbthreads/images/graemlins/frown.gif" alt="" />

[padgett]

Most "Ram Air" on production cars was cosmetic only, scoop on early 70's Trans Am faced backwards to maximise sound to passengers and to avoid any real effect.

True Ram Air required special/different carb jetting and the mfrs did not want to certify anything like that). Real "Cowl Induction" required replacing the vent opening at the base of the windshield with ducting - '67 Z-28 (before it became popular) had that as part of the Z-284 package.

Most were placed at least 6 inches in front of the windshield just to avoid that effect. Others faced forward but were low and in the boundary layer of the hood flow.

'67-68 Olds 443 had real ones below the bumper and were two (one each side) about 1"x 3" each. Thunderbolt Fords were special built and replaced the high beam headlights which was a common place and size for real ones.

For a street car the major benefit is cool air and the Reatta already draws from in front of the radiator support.

Forward facing ones need to have doglegs to prevent heavy rain and puddle splash from reaching the engine. On the Reatta, this is built into the air cleaner box.

If you really want to do something, a duct replacing the driver's side fog lamp would be as effective as anything, keep in mind that the entire intake systen is designed for 1.75" and there are numerous choke points, some as low as 1.5" diameter but the biggest on is the stock air filter (I keep looking for the filter box from a late Alero V-6 that uses the considerably larger A1279C. Have had a few rentals and the airbox looks like it would fit.

Mice thing about MAF controlled feedback FI is that it can adjust automagically.

[2seater]

Got the bug to answer a question no one asked, eh? <img src="http://www.aaca.org/ubbthreads/images/graemlins/laugh.gif" alt="" /> It would be interesting to see if there is any positive pressure near the stock air inlet when at speed. Maybe a manometer or low pressure gauge calibrated in inches of water column? Part of the problem is the additional plumbing required may cancel any potential gain. It looks pretty tight to run down behind the headlight with a duct of any size.

I got interupted and forgot one other thing. The GM Ross suggested location of the filter where the charcoal canister is will also provide a clear path to get down forward of the left wheel with a duct up to 3.5"-4" in diameter and you can go almost anywhere from there. The stock air box and charcoal canister must go of course. Water ingestion would have to be dealt with too.

[Guest EDBS0]

2Seater;

At the open end of the stock air horn there is a 2 inch in diameter opening: with an opening of 3.1 square inches. This appears to be the bottleneck in the intake system. <img src="http://www.aaca.org/ubbthreads/images/graemlins/mad.gif" alt="" />

I have been able to take some clear acrylic pipe 3" ID in diameter: with an opening of 7.1 square inches (229% larger) from the end of the stock black air tube off the throttle body. I have turned it 75 or so degrees and inserted the air temperature sensor in the elbow.

Obviously the stock air horn and air box have been removed.

To the open end I have attached a Kool Blue air filter MKU6001 that is rated for 270HP. Dimensions are 3 and 15/16ths and 1 and 15/16th by 7 inches long. I would describe it as a long narrow, tapered, oblong cone. It is enclosed in a 3L pop bottle. At the other end there is 4 inch aluminum dryer hose for a couple of inches. Under the fuses/relays and under the windshield washer tank I used 3 inch aluminum dryer pipe. That is all that could fit. Through the bulkhead the 3 inch pipe has to be slightly crimped to fit through the existing opening. It is probably 2 and 3/4 inches in diameter with an area of 5.9 square inches or 190% of the size.. Used lots of that Red Green magic Duct Tape. Once I know that it all fits I would like to fibreglass it.

Presently I have a CAI taking cold air through the stock opening in the bulkhead through the filter, past the air temperature sensor to the throtttle body.

Yet to come: Make the 90 degree turn down and then to the Ram Air opening. I have an opening of 70 square inches in mind. Taking off next week to NY and the Hudson Valley and then to Stowe for the British Invasion the following weekend so not too much time to play with it.

[2seater]

Good old Red-Green. If it can't be done with duct tape it isn't worth doing, eh? It sounds like you have a pretty good system already. I do suspect there may be a little pressure available at that location already. There is a small slit opening below the headlight and some air is probably pushed upwards by the little chin flap into that relatively sealed are behind the headlight. If you could figure out how to run a clear plastic tube filled with water from the area behind the headlight into the cab and watch what happens to the water level under steady state cruise conditions. Both ends of the tube need to be open, and watch out for that vicious acceleration <img src="http://www.aaca.org/ubbthreads/images/graemlins/grin.gif" alt="" /> You would have to limit pressure inside the cabin too or it will mess up the results. I had considered a variation on what you have done and that is to place the filter directly on the MAF, inside an enclosure of some sort and feed air, from wherever you can get it, into the enclosure. Multiple smaller ducts would be possible in that application.

[padgett]

Keep in mind that the "C" engine throttle plate is only 1.75" diameter and is the limiting factor. Anyone know if you can bolt up a "L" (snakes: 91-on) throttle body to a "C" plenium ? (Have one but lost the spare manifold somewhere...)

[Guest Greg Ross]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> (Have one but lost the spare manifold somewhere...)

</div></div>

<span style="font-weight: bold">Pardon!</span>

[padgett]

My spare "C" manifold. I really need to get the garage cleaned out and now that the summer is moderating (been a week since it went over 90) am running out of excuses.