Functional Ram Air Intake System

About Company

Design and development of ram air engine intake systems for Yamaha Vmax motorcycles. From drawing board  06/06 to prototype testing in 07. With first commercially available kit in 08.

Limited quantities



After waiting to see if someone would ever make a real ram air intake system for the Yamaha Vmax to replace the faux scoops I finally decided to do it myself. So I started with research on ram air intake systems, mainly already available on many street bikes. A good link on ram air systems for motorcycles is .


The first thing I wanted to know was what kind of air velocity and air flow was being created from the stock air box. By using formulas for finding cfm and how much air the engine consumes. Using 7.5 sq in, the inlet size of the stock air box opening the velocity of the air at the opening is about 100 mph. at 9000 rpm. The pressure created inside the stock air box is always negative, great for a vacuum cleaner not so good for an intake system. To test my numbers I made a pitot tube attached it to an airspeed indicator and went for a ride. Sure enough the numbers were close. Next I taped the Pitot tube along side the fake scoop to see how much air velocity there was at the outside end of the scoop, because the air close to the bike is being disturbed by the front end. The air at the edge of the scoop is not that disturbed and the velocity there was almost the same as the speed of the bike.


After determining how much of an opening at the front of the scoop and the amount of air the engine uses, speeds above 30 mph should start to create a positive air flow into the air box. So at least that part penciled out.


Even through the right side scoop would be restricted by the coolant manifold, I wanted to use both and thought that it would help equalize the air pressure. From the beginning I wanted to make a kit that would have the option to put the bike back to original. The first problem was to determine the best way to route the ducting to the air box. Unfortunately the original air box really left no options to route the ducting and increase the opening. The only other option that I could see would be to create a new air box with the ducting to come from just above the carburetors. Using a cad program I started by getting the measurements from the bike and drawing a design for a new air box. Maximizing the room to work with, I made three opening for a combined opening of about 11.4 sq in at the air box. The air filter stays in the same location only upside down so now the air flows up through the air box then down into the velocity stacks makes sense. A center dam in the lower section of the air box helps to direct the air upward.


I wanted to keep the look of the original scoop so that at first glance it looked like just another Vmax. The first step was to make a mold for the side scoops using the original shape. Made a design that is about ¾ inch wider at the opening and about ½ inch wider at the rear. This was to give more clearance for the ducting around the coolant manifold and the inlets to the air box. The other problem that I was concerned about was that the front of the air scoop opening would be too large. If there is more air going into the scoop then the engine can use, the air pressure will build at the front of the scoop. This could cause a condition where the air actually creates a bubble or dam and causes a lower pressure at the opening of the scoop. If you’ve ever noticed, that almost all of the street bikes with ram air systems on them, the intakes are relatively small.

The overall look makes scoops look a little wider when sitting on the bike. The other idea was to use the original scoops and just make the air intakes fit to them. That would require cutting and removing a support from the inside and grinding off the support for the fake intake grill.


After making the air scoop molds and a prototype that I could use for mockup, I went back to work designing the air box. I used templates from cad drawings to check for fit. Satisfied with my design I printed templates to use with foam board and poster paper to make a reverse engineered mold box that was poured with RTV silicone to make the air box mold. After making the first prototype air box middle portion that was fitted on the bike, the next part would be the lower section. Using cad drawings and block Styrofoam that was shaped and sanded to form the bottom of the air box. This piece was then used to make the molds for the lower section. The finished pieces are trimmed and fastened together using 1 inch fiberglass tape. Then the bottom section of the air box is fused to the middle section using an alignment template.


The middle air box section has a slot on the top for a 3mm x 3mm rubber seal. The lid has a ridge which makes the seal airtight. The lid also has a support for the v-boost controller and other electrical components that were originally on the inside of the left scoop. To allow for any movement between the connection between the air box and the scoops a D shaped rubber molding is used to make an airtight seal between the scoop intakes and inlets on the air box.


The air box has two tubes on the left front inlet for attaching the vent bowl tubes. This keeps the pressure in the float bowl equal with the air box pressure. This is why the original vents were placed by the inlets of the air box. There is also a tube above that which goes into the air box that was used for testing, but also could be used for a low pressure switch possibly connected to a led light or small gauge to show positive pressure.


The intake section from the air scoop to the air box could now be started. Using block Styrofoam, molding clay, and foam board, the pieces were shaped and sanded to fit around the coolant manifold, frame, carburetors, and cables. These parts were covered with fiberglass, then cut in half and used to make mold boxes that were filled with RTV silicone. The silicon makes a mold that does not stick to the resin and is easy to remove.


The various other pieces needed, the side trim support, the scoop attachment parts and the brackets for mounting the rubber carburetor seals from the original scoops are all made from silicone molds


The intake pieces are molded in two sections made out of carbon fiber and then fused together and attached to the side scoops with an alignment template. Some of the scoops are made from aluminized fiberglass, so has the look of chrome which seems to go nicely with the carbon fiber on the bike. They could also be painted any color. I sent a pair of scoops to, a company that does custom paint and graphics on helmets, motorcycles, personal watercraft, probably anything. They use a special system for applying an aluminum finish. That should make the scoops look like the original polished aluminum.


The air box is made of vinyl ester resin because it has a higher heat and chemical resistance. It has four layers of 6oz woven fiberglass with two layers on either side of 5 mm flange nuts for securing the lid. Then there is a layer of 19 oz sq/yd knytex x-mat on the lid and sides. I haven’t tested it but is probably built proof. The first prototype air box is still on the bike and is holding up nicely.


The kit would include vinyl Yamaha emblems sticker that can be either black or white. The sticker on the scoop intake is optional, it is also a vinyl sticker, was made to copy the (Danger Intake) type on fighter jet engine intakes. I wanted to have something that would offset the dark opening that warn of the impending danger. So as not to suck up any small animals or children.


Working part time from the start of the initial concept to the first prototype, spanned about 14 months. The average time to make one complete set is approximately 100 hours. With a job that keeps me away from home most of the time, it is harder to plan lay-up so usually try, to make an air box or a set of scoops and intakes at a time.  The goal is to have several complete sets by summer. It will include instructions and all the necessary parts except the bigger main jets.


Not knowing if the whole thing would fly apart or something I put round foam air cleaners over the rubber velocity stacks to keep anything from getting sucked into the engine. Initially I did not change any jetting on the carburetor so the bike ran fairly decent (did start to miss around 7000 rpm’s). Confident that the air box would stay together I removed the foam air cleaners from the velocity stacks. That’s when the real problems started. The first time I rode the bike it would not even go faster then 65 MPH so I knew that some serious re-jetting was in order.


I started talking with various mechanics, some of whose philosophy seemed was “just put in a bigger main jet”. So I went down that road, having to pull the carburetors each time, went up to the biggest I could find #220. The bike would run a little better each time but was still seriously missing at higher rpms. I reduced the #1 main pilot air jet on the top opening of the carburetor down to a #50 which made the idle and low power setting normal.


Even after reading the mikuni carb tuning handbook was still not able to figure out what was going on. Not wanting to burn up an engine trying to figure this out I installed a fuel air ratio gauge. Found one at Innovate Motorsports that I mounted by the speedometer and put the wide band oxygen sensor onto the header just past the collector. Now at least I knew what was going on. Really didn’t know what the problem was until doing research found out that the dyna-jet stage 7 jet kit had air restrictors that where installed into the main air jet. Not really knowing what size to start with decided to thread the opening of the main air corrector on the top of the carburetor out with a 5mm tap so that I could install different size small round jets.


I started with a #90 small round jet in the main air jet opening and then reduced the main jet to a size #185 went for a test ride. Now it was running a little rich, but it was the first time since I started testing that the bike ran good (got my V-max grin Back : ). I am still fine tuning with a #175 main fuel jet and a #70 for the main air corrector jet. The bike runs hard all the way to redline with the air fuel ratio gauge showing about between 12 and 14 to 1 this is very close to stoichiometric mixture of 14.7 to 1. There was a little hesitation when moving the throttle from about a third to three quarters open. The bike has a dyna-jet stage 1 so moving the clip on jet the needle down one notch that took care of that. A main jet size of #170 or #175 gives the best results.


 So where am I going with this? I have a domain name right now it is a website under construction that will have more pictures and information. It will also be used to order custom sets with different options like carbon fiber or just paint grade parts. The paint grade parts are easier to make so they will be offered for less then the ones with a fiberglass finish. I took the air box cad drawing and made a solidworks file that can be used to make molds for rapid prototyping. They would make air boxes out of the plastic like the ones used on the bike. The only problem here is that the air box could be made very cheap but the initial cost to make the molds is about $50,000. Ouch! A bit over my budget which is already a little stretched on this. So I will probably just be making a limited number of custom orders. Eventually I would like to have someone to help with manufacturing or even who might want to take over the whole project.


Now to answer the big question does the whole thing work? What I do know is that by hooking a tube from the air box to a manometer the air pressure in the air box starts showing a positive pressure once the bike starts accelerating above 35 MPH. Using a set up to mount a video camera on the faux tank I made some recording of some runs, (seriously I wasn’t going to try and read and remember a bunch of numbers while going fast). The results of the manometer show that the pressure kept rising with speed up to about 8 inh2o at around 125 MPH and the bike was still accelerating. I’m speed restricted by girlfriend to 125 MPH also there was a curve in the road. Converting 8 inh2o to psi equals about 0.3 psi boost. Another good article found online at involves testing a bike with ram air on a dynamometer at static and by forcing air into the air box. Then, comparing the results from out on the track to conclude the amount of extra hp from a ram air system.


 After reading the ram air article that even the best design will only give about 0.5 psi increase in pressure. The real test would be to run a bike on a dyno before and after with the kit on. The only problem would be to simulate the effect of ram air into the engine. The pressure of air at sea level is approximately 14.7 psi. Boosting air pressure from turbo charging or supercharging by another 14 psi would theoretically double hp  assuming 100% volumetric efficiency. Using math, the hp increase from a 0.3 psi boost would yield a 3 to 4 % increase in hp. Considering that the pressure created in the stock air box is always negative the kit definitely allows the engine to breath better. I would have to say it does work.


The real kick for me is every time I look at the front of the bike and see intake openings instead of plastic grills and I know they’re real.