Guest tom sixbey Posted February 28, 2001 Share Posted February 28, 2001 hey guys, i am planning out a ram air system and i've come up with some ideas i need support or correction on.. I'm no aerodynamic expert, but here's what i think the system should consist of: 1. A SMALL airbox/filter system that fits directly ontop of the carb with inlets for ram air, an inlet for underhood bypass air, and a cable operated selection system that lets the driver choose between bypass and ram air. 2. Very large intake scoops on the front of the car that are connected to the airbox through air tubes that DECREASE in diameter as they go towards the airbox. 3. EGT gauges and a lean/rich adjustment control for the fuel injection system. I'm guessing that the venturi effect in the air ducts (decreasing diameter) will force the air to accelerate as it moves towards the airbox. When a car is traveling at high speeds, a TON of air is stacking up infront of it. Instead of trying to push that air out of the way, why not take it and force it down the car's throat? This would necessitate VERY large induction scoops in the airdam/ grille, but i believe it would work out.. - what do you guys think? Quote Link to comment Share on other sites More sharing options...
Guest kc6wfs Posted February 28, 2001 Share Posted February 28, 2001 Hi Tom, It should work. Might go lean if the input was way to large, but it would take track time and playing with jets to fine the highest mph. I was going to play with the same idea in the upcomming weeks. What I was going to do is this. I'm running a holley 750 vac sec and going to get a volicty stack from holley and get one of the 10" air cleaners, cut out the top same size as the stack, braize same size flex tubing onto top and run it to the front of the grill with a wide mouth type inlet and see how that does at the 1/4 mile track. I've seen pics of turbo forced induction type of inlets for carbs but have no idea on where to buy them. Banks has a bunch of pics in a holley book. Looks real neat!!!! What do you think? Dave ------------------ www.geocities.com/kc6wfs/240z.html www.NitroPhotos.com Quote Link to comment Share on other sites More sharing options...
blueovalz Posted February 28, 2001 Share Posted February 28, 2001 I've got a 240sx with a home made ram air on it that works very well. I made a fiberglass canister that completely enclose the K&N filter. This sealed canister then was ducted to the front of the car with 4" ducting to a fake (now turned operational) air scoop. Initially I ran a 3" line, but testing indicated very little pressure rise. After enlarging it to 4", the pressure in the canister became measureable (was greater than the normal outside air pressure). This is a fixed system with no doors (completely air tight). Performance increase: Acceleration at highway speeds (i.e passing power)is now as quick in 5th gear as it used to be in 4th, but not much help at any speed less than 40mph. Disadvantages: More trouble to clean the filter, and the filter gets REAL dirty after about 20K miles. I never had to adjust the EFI system for it because the ram effect is just not that much, and ventury operated devices (carbs) are self metering so no jet changes will be needed for them. Terry Quote Link to comment Share on other sites More sharing options...
Guest tom sixbey Posted February 28, 2001 Share Posted February 28, 2001 this is something i'm definately gonna play around with... - I've looked at those ram air boxes that claim to give you .2-.4 difference in the quater mile, but maybe that system could be improved upon... Quote Link to comment Share on other sites More sharing options...
johnc Posted February 28, 2001 Share Posted February 28, 2001 What's important in any kind of ducting is to build a way to get the air in and not let it back up. What you need to build is a large area behind the initial opening and then duct air from that. Bad diagram: < front of car _|----|___________|-------| /-|____|-----------|_______| If you just build straight tubes or a decreasing funnel shape as you mention you'll get air packing up in front and the flow will reduce significantly. Look at ProStock, F1, and any number of other hood scoops. Also look at the brake cooling ducting systems on closed body sprots cars. They all have a large plenum area behind the opening. ------------------ John Coffey johnc@betamotorsports.com Quote Link to comment Share on other sites More sharing options...
DavyZ Posted March 1, 2001 Share Posted March 1, 2001 CarCraft or Hot Rod magazine had a how to make a ram air induction article that was pretty good. It used tin stack boots from the hardware store (look like funnels for ducting). The only thing is, I looked at what was available and it was ugly. I have too much pride to use those. Fiberglass or carbon fiber seems like the best alternative. I want to find out more about what John Coffey just mentioned about the air plenums needing to be there. Seems rather odd... Quote Link to comment Share on other sites More sharing options...
johnc Posted March 1, 2001 Share Posted March 1, 2001 What we want to achieve with an intake system is to provide a larger VOLUME of air than is needed by whatever device we are supplying the intake air to. By containing this larger volume in a plenum we achieve some small level of pressurization. Often there is a mis-understanding concering air intakes and the marketing term "Ram Air" that Pontiac trademarked. In no case are these intake systems ramming air into the carburator. What they are really trying to do is get a large volume of air into the plenum right above the carburator. The larger the volume in the confined plenum the greater the pressurization. The speed that the air enters that plenum is only relevant as it relates to the volume of air that gets into the plenum. For an intake system with relatively long ducts, placing a plenum right behind the intake opening, the amount of air that piles up in front gets reduced thus increasing the volume of air that actually gets into the intake and eventually to the plenum over the carb. Remember, the longer the intake tube, the greater the restriciton and volume reduction. This sounds counter intuitive, but I read some original research on this subject on the NASA report server. I tried to dig this up to post here but I'm getting a 603 timeout when I try to access one of the documents. Here's a list of possibly relelvant documents and a link to the server. I'll try tomorrow to see if I can get through. http://techreports.larc.nasa.gov/cgi-bin/NTRS 572 -1 An experimental investigation at large scale of several configurations of an NACA submerged air intake, NACA-RM-A8F21, Oct 19, 1948 498 -1 Internal-flow systems for aircraft, NACA-TR-713, Jan 01, 1941 484 -1 An experimental investigation of the air-flow of a scoop-type normal-shock inlet, NACA-RM-A55A13, Apr 28, 1955 479 -1 Investigation of air flow in right-angle elbows in a rectangular duct, NACA-WR-L-328, Oct 01, 1941 407 -1 The structure of turbulence in fully developed pipe flow, NACA-TR-1174, Jan 01, 1954 ------------------ John Coffey johnc@betamotorsports.com Quote Link to comment Share on other sites More sharing options...
DavyZ Posted March 2, 2001 Share Posted March 2, 2001 John, it's good to have people like you in this forum! Quote Link to comment Share on other sites More sharing options...
Guest kc6wfs Posted March 2, 2001 Share Posted March 2, 2001 Hi all, Here is another good one. http://naca.larc.nasa.gov/reports/1938/naca-tn-631/ "Wind-tunnel tests of carburetor-intake rams" Thanks for the links John!!!!!!! Dave ------------------ www.geocities.com/kc6wfs/240z.html www.NitroPhotos.com Quote Link to comment Share on other sites More sharing options...
johnc Posted March 2, 2001 Share Posted March 2, 2001 Perfect link! From page 2 and 3: "If the effect of the propeller is neglected, it is apparent that the maximum pressure obtainable from the air stream is the dynamic pressure due to the forward velocity of the airplane. Not all of this dynamic pressure is available for increasing the carburator-intake pressure, however, since losses occur int he carburator intake ram. Friction losses are present in every ram and cannot be eliminated. Anothe rloss exists int he form of an entrance loss, part of which is due to entrance shape and location and part tot he fact that the velocity of the air entering the ram must be reduced from that of the air stream to the velocity required at the carburator." "As this reduction in velocity occurs without expansion in the case of the external constant-area type, it is reasonable to expect losses due to spillage and turbulence to exist. If it were possible to take the air into the ram at the velocity of the air stream and expand it until its velocity were reduced to that required at the carburator, it should be possible to eliminate the losses due to spillage and turbulance." The document goes on to discuss the construction of two type of constant-area rams with five different types of entrances. It looks like I understated the importance of the speed of the air entering the ram. Synchronizing the air entry speed with the needs of the carbutor appears to by importnat and the plenmum right behind the ram intake appears to achieve this sync to some degree. ------------------ John Coffey johnc@betamotorsports.com Quote Link to comment Share on other sites More sharing options...
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