GUARANTEED FIT FOR Coolster Reaction 200-S 175CC ATV: New GY6 175cc Internal Reverse ATV Engine.New GY6 150cc, 175cc, or 184cc Internal Reverse Engine.  This is a guaranteed direct fit for your vehicle and everything bolts up identical to your original stock engine including the shifting controls. ADD A UNI-FILTER TO YOUR ORDER AND GET A ONE YEAR WARRANTY. YOU HAVE THREE ENGINE OPTIONS Engine 1: 150cc Standard stock GY6 Engine with stock transmission--GUARANTEED DIRECT FIT.  Engine 2: 175cc GY6 Racing Engine with stock transmission--GUARANTEED DIRECT FIT.  This engine comes with the 62mm big bore cylinder and piston kit pictured below installed in a bored out case.  We strongly recommend the BDX performance transmission for performance engines--Click here to see why.  Engine 3: 184cc GY6 Racing Engine with stock transmission--GUARANTEED DIRECT FIT.   This engine comes with the 62mm big bore cylinder and piston kit pictured below installed in a bored out case and a 3.0mm high performance stroker crank.  Call regarding this option. We strongly recommend the BDX performance transmission for performance engines--Click here to see why.  YOU HAVE FIVE POWER PERFORMANCE OPTIONSOption 1: American made high performance Uni-Filter air filter ensures clean air to your engine and long life.  See why a NEW Uni-Filter is MANDATORY for ALL new engines and purchase at this link.   Your one year new engine warranty applies only if a new uni-filter is purchased with this engine.  If you don't get a Uni-Filter you are guaranteed to be putting dirt into your clean NEW engine.  See DetailsOption 2:  BDX High Performance Racing Transmission and Gates Powerlink Belt:  Click here to see detail or add to your order..  If you add this option the parts will installed into your new engine. A Performance Transmission is the difference between a sluggish, slow and inefficient go-kart and a peppy, speedy and powerful go-kart that utilizes the full power of the engine.  See details.  Regular price $249 - Now FREE when you send us your old core engine.  See shipping prices for you to send us your old engine.Option 3: The BDX A12 Cam Shaft changes the power profile of your GY6 engine  to provide the optimal balance for both low end grunt and top end speed.  If you purchase the A12 Cam Shaft it will be installed and tested in your new engine.Option 4: 11 Pole Stator, rectifier and harness adapter.  With this option you get more power to run your lights and other accessories.  If you get this option it will be installed and tested in your engine--Click Here.  The engine comes stock with an 8 pole stator.  Option 5: Performance Exhaust:  You can get the BDX performance exhaust for any of the engines above for an estimated 10% to 15% increase in raw power--see video!.  Your stock exhaust is restricting your power because the exhaust gases are being squeezed out through a tiny hole.  The BDX Performance Exhaust fixes that.  If you get a performance engine without the performance exhaust you will be restricting some of that NEW power. To see details or add the exhaust to your order click here.  Or see our video to see what this increased horsepower looks like in a race click here..Read article on how displacement relates to more power.How big bore kits & strokers workTAKE A LOOK AT THIS COMPARISONStock GY6 Engine BDX Performance Racing Engine We build and test our 175cc racing engine in our facility in Virginia.  We disassemble your 150cc engine, bore the case to make it larger so that we can install a 62mm big bore piston and cylinder.  Then we re-assemble and test your engine.Boring the Case for the 62mm Cylinder and Piston62mm 175cc Big Bore KitBe sure to read the article on how displacement affects your power.Click here to see additional important information regarding this engine.Visit our Facebook Group and share your experience and show some pictures and videos of your vehicle.Visit our Facebook Page and see the latest things that we are doing.