TPI Intake Valves

Thunder Products, makers of the innovative TPI Valves, now offers their adjustable intake valves in two forms; round and flat, making them suited for most any kind of installation.
The premise is simple; a leaner fuel-air mixture makes more horsepower. Many intake systems are somewhat restrictive, and modifications to reduce these restrictions are often rewarded with gains in power.
Many times you don’t know for sure where and how much you should open up the intake, and this is the beauty of the TPI Valves. Since they’re adjustable, you can install them and leave them closed and still have a bone-stock intake. Open them up slightly and you only let in a bit more air. Open them up more and you allow even more air. TPI calls this “air jetting”, allowing the intake of more air in contrast to adjusting the amount of fuel. More air and more fuel generally results in more power, as your engine is simply an air pump.
TPI valves are especially helpful on engines that have exhaust modifications. Thinking of the engine as an air pump, if you let it breathe on the exhaust side you can also let it breathe more on the intake side. Instead of drilling holes and experimenting by gosh and by golly, the TPI Valves give you that precious adjustability.
We’ve installed TPI Valves into a number of sleds and dirt bikes, usually on machines that clearly had an intake restriction or ones that were over-fueled and could benefit from more air. Our latest subject was our 2004 Yamaha SXViper that we had installed a Bender single pipe and silencer exhaust system into. This engine also featured the DCS detonation control system, so we could monitor the difference our TPI Valves made to the air-fuel mixture.
The DCS monitors the engine for detonation (too lean) and flashes a light on the dash, so we installed our TPI Valves with confidence. Thunder Products suggests one valve per 200 cc of engine size, so we installed four of them (round ones) on the top of the airbox under the foam. We started out running them closed, then gradually increased the amount of opening and took notes as to the performance gains and spark plug indicators. Basically, the more we opened them the better it ran. We opened them all the way and still didn’t get the DCS to flash, so we felt safe.
Then one day it was pretty cold out and we were running hard through deep snow up in the U.P. of Michigan. After a few miles of hard pulling the DCS light started to flash, so we stopped and closed two of the valves part way. DCS light went off, and once the temps came up slightly we opened them back up all the way and away we went.
Several speed shops have learned the best placement for TPI Valves on specific models, and again the beauty is they’re adjustable and you can always close them to get back to stock. You can use them to open up a restrictive intake, compensate for changing air temperatures or elevation, or just to experiment and explore “what if” scenarios.
The (Low Boy) flat ones sell for $19.95 each, and the (Knobby) round ones go for $16.95 each, with colored Low Boys available at $21.95 each. Install at least one per 200cc of engine displacement, and have some fun. Contact Thunder Products at 320-597-2700 or order from many performance shops worldwide.