Perhaps the most common replacement go kart engine, the Predator 212 is an unbelievably good value. Couple the low initial cost with the super competitive and very reasonably priced aftermarket parts and you’ve got a recipe for the #1 engine for go karts. The Predator 212 is the engine I swapped onto my go kart and I’ve never looked back.
Because the aftermarket is so competitive, there are tons of options out there. The various parts tend to fall into as much of an industry standard as they can, in what’s called stages. Because this isn’t universal, I’ve done my best to keep the stages to the most commonly observed parts.
Stage 1 (Mild)
Intake – The most basic of upgrades, but possibly the most beneficial through the stages. The stock intake box has two filters and a non-direct design. The aftermarket intake kits come with an adaptor for your carb that will allow a straight or angled cone filter to be attached. Some nice upgrades here are filter covers that will keep water off the filter if you drive in rain or muddy areas.
Exhaust –As with the intake, very basic but not to be skipped. As the engine is now getting more air, you need to allow that extra air out efficiently. The stock exhaust is a mess of direction changes and baffling to reduce sound. Here you want a single 90 degree turn and a slightly bigger pipe size to let out the most air possible. You don’t want your exhaust to be bottlenecked, or it will limit the gains of every other part you could install.
Carb Jet –Lastly, the carb needs to keep up with all the extra air being pulled into the engine. By installing a new jet with a slightly bigger hole, you’re allowing more fuel to be pushed into the engine with the added air. The idea is to have the right size jet to allow enough fuel in to keep the same air to fuel ratio as the factory setup. Running your engine with too much fuel is called rich and running with not enough fuel is lean. Running rich is a waste of gas, and running lean can damage your engine and possibly blow it up. This is something you definitely want to get right.
Emulsion Tube –Some kits may include a different emulsion tube. This isn’t absolutely necessary at this point. You can use the stock one with the same results so don’t choose based on this. The purpose of an emulsion tube is to maintain the air/fuel ratio at all RPM’s. It’s where the jet connects to inside the carb.
Recommendation –For stage 1 your best bet is going to be an all in one kit. If you attempt to price each part individually you won’t be able to beat the price of a full stage 1 kit. Prices do change pretty frequently here since it’s the most competitive stage. GoPowerSports is almost always the best priced for this option though. Get their stage 1 kit here.
Stage 2 (Moderate)
Billet Flywheel –The flywheel connects onto the main shaft on the opposite side of the engine to the clutch, torque converter, or transmission. It is behind the pull cord. The stock flywheel is made of steel and is not overly strong. It was made to spin safely at the factory setting of 3,600 RPMs. If you remove your governor, which I highly recommend, you’ll be spinning the flywheel past it’s recommended rate. When you start doing this, it’s not a question of if, it’s a question of when the flywheel will break. When it does it’ll shoot pieces off in all directions and has been known to hurt people. A billet flywheel is made to withstand all RPM’s that the engine is capable of and will not break. It is also lighter and provides less rotational drag, essentially freeing up horsepower the engine already has. These are a pretty penny, but an absolute necessity.
Billet Connecting Rod –Like with the flywheel, the stock connecting rod tends to let go eventually when extra force is placed on it, as with an upgraded cam. Most kits that include an upgraded cam will include the connecting rod. The choices here are in length. The longer the connecting rod the further the piston is pushed up into the combustion chamber and the higher the compression ratio is. Generally the higher the compression the higher the horsepower. There are clearance issues though. Too long of a connecting rod and your piston will hit your spark plug or the side of your head. If you have not modified your spark plug, valves, valve springs, head gasket, or head at this point, a +.020 should give you a nice bump in compression.
Mild Cam –When it comes to cams, there seems like a million different choices. The two main things to look for are the lift and duration. To understand what’s happening here just think of how much and how long the valve is opened. The more the valve is pushed open, the more air and fuel will rush in. Valves are tapered so the further in they go, the more volume is available for air and fuel. Duration is how long the valve is held open. The more duration the longer the valve stays open. At this point, you have a decision to make. I don’t like spending money on the same parts twice, so you will need to choose your ultimate goal at this point. If stage 2 is where you’ll stop, look for something with a little less lift and more duration to get away with using the stock valve springs. The more lift you go the stiffer valve springs you’ll need, adding additional cost. Try to pick a cam that will complement your final goal.
Recommendation –For most this will be an easy decision. If you completed Stage 1 and you just want a little more power, a mild cam will get you there. If you got a taste with Stage 1 and want to keep going, spec out your cam based on the parts you plan to get from Stage 3 or 4. GoPowerSports just barely wins the price war here as well but BMIKarts offers more selection by selling the parts individually for roughly the same price.
GoPowerSports Stage 2 BMIKarts Stage 2 Parts
Stage 3 (Wild)
Valve Springs – Valve springs are typically needed based on your cam or RPMs. Either your cam tries to push the valve open too far and your spring can’t efficiently pull the valve back shut, or the RPMs put too much demand on the spring that the valve stays open too long. This is commonly called floating the valves or valve float. This just means the valve is not closing when it should and starts to cause issues with combustion. The stiffer spring rates will allow for more aggressive cam’s and still allow the valves to close in the correct amount of time. Upgrade your springs based on your cam recommendation and target RPMs.
Aggressive Cam –Your aggressive cam will have a higher lift and more duration. The higher the lift the more horsepower you will get in the upper RPMs and the less torque you’ll feel in the lower RPMs. The more duration you have the more horsepower you get in the RPM’s just like lift. Predators have a single piston so there are no benefits of overlapping lobes like in vehicles. There are typically no limits to lift and duration other than the clearance to your spark plug and whether or not your engine is able to idle. You won’t really fall into either category if you stick with the supplied cams on the market. Also keep in mind the higher lift you go with, the higher RPM you need to be at to get the most out of the horsepower. For instance, a common high lift cam is .356 and the target RPM range is 8,500 to 9,000. For another common cam of .308 the target RPM range is 8,200 to 8,400. My recommendation here is to stick around .285 as that gives you a lot of lift still but within a lower RPM range. Basically more usable horsepower through the engine RPM range.
Spark Plug –Spark plugs are a hotly debated topic when it comes to which spark plug makes the most amount of horsepower. The thing you need to keep in mind here is that as you up compression, or increase RPM’s you need a spark plug of higher quality to increase the life. AR3910x spark plugs are commonly recommended however they are a non-resistor type. They emit a radio frequency that causes interference with other electronics so look for a resistor type spark plug if you have other electronics on your go kart. A good resistor type spark plug is the NGK BPR6ES.
Rockers –When you upgrade your valve springs, there’s no better time to replace anything else in the head. Rockers can be upgraded to ones with less weight and higher strength materials. There won’t be much or any horsepower gains here, but there will be a little more peace of mind in a more quality part. Rockers aren’t typically a component that fails so my recommendation would be to leave the stock ones unless your cam suggests new rockers.
Head Gasket –While you have the head off it’s also a good time to replace the head gasket. When you do this there are many different thicknesses available. This will allow you to raise or lower the compression ratio just by choosing another thickness. Generally, you want a higher compression ratio if you can clearance wise. Ideally, you would measure the distance between the spark plug and top of the piston, and pick a gasket that would make the clearance very little, something like .003. This would allow the highest compression without any chance of breaking anything. Also, keep in mind that certain cams will require a minimum or maximum compression ratio that you’ll need to stick with to get the correct performance from the cam.
Stage 4 (Extreme)
Carburetor –Once you get a more aggressive cam you’ll really benefit from a better carburetor. A bigger jet will only take you so far before your fuel delivery becomes your limiting factor. An upgraded carb like a Tillotson or Mikuni will allow greater control of fuel to your engine and ramp up as your cam desires more fuel.
Race Head –At this point, you are going all out. Once you maximize the cam you’re able to run the next thing you want to upgrade is your weakest point. You’ll probably be maximizing the physical space inside the head that allows in air and fuel. A race head will have bigger ports and allow more air and fuel in. It will also come polished on the exhaust side to aid in better exit of the exhaust. It might also allow for different valve sizes to step up on the size of open the valve covers. Really a race head should only help a very select few people who are just trying to squeeze out every last ounce of power.
Fuel Pump –Fuel delivery to small engines is gravity fed but that can become unreliable if you run low on gas and are taking corners fast or sloshing your gas around. A fuel pump can be added to maintain consistent fuel delivery and protect your investment a little more. You really need a consistent reliable fuel delivery otherwise if you run lean for too long your engine will blow up on you much quicker. Upgrading to a fuel pump is more about insurance for your engine than gains from performance.
Turbo –In the spirit of attempting to cover as many options as possible, you can custom build a turbo onto your engine. The general setup is similar to a car but requires some custom welding and manufacturing. If you’ve made it to this point you’ll want to do quite a bit more research than we have time for here.
Nitrous –As with a turbo, nitrous is an extreme option but something you can implement on a small engine as well. The theory is the same with a vehicle and implemented the same way. As with a turbo, more research will be required here. I can say though, a little nitrous will go a really long way on a small engine, and you really have to watch RPMs otherwise you’ll just be maxing out the hardware and risking the engine.
Modifying and upgrading the Predator 212 is a very easy and rewarding process. One thing to keep in mind is to make sure you know if your 212 is a Hemi or non-Hemi. This is determined by looking at the valve cover. A Hemi is a rough looking square cover, while the non-Hemi is a polish cover that is smaller at the top and larger at the bottom. If you have the option to pick, go with the Hemi. It’s got a better, revised version of the head. Also, note though, the non-Hemi is required in California for emission reasons. You’ll have to buy online most likely if you want the Hemi in California.
