KartFab
Active member
Engine Mods & Performance Parts
This guide will go over what it takes to modify a small industrial 4-stroke engine (Predator 212cc) to rev higher and have more torque (partially answering age old question -'How do I make my Go Kart Faster?' It goes over the basics. There are ALWAYS trade-offs to consider before purchasing and installing any performance part.
This guide will be for the average DIY person looking to get cheap/minor upgrades as well as some of the high end upgrades you see engine builders implementing on 'builder's prepared' engines. This guide will not show you how to install anything. It is only an introduction to performance upgrades. You have to do the research, and you are the decision maker. So let's start with the very basics. If you cut corners, you can ruin your engine so I have broken it down into suggested stages.
Stage 1: Intake, Exhaust, Jet -The best bang for your buck.
Cost: Under $100. Benefit: flow, significant horsepower gains
Out of the box, small engines are very restrictive to air flow. An engine needs to be able to breathe IN and OUT with less resistance. Adding a high flow air filter, and intake adaptor to fit the air filter will allow the engine to breathe IN easier. This is bolt on upgrade that requires no special tools. Half of the problem is taken care of, now the engine needs to breathe out.
A high flow exhaust header is what to get. Any header will modify your power band, but the 'best' one to get is an open '3 stage header' which keeps exhaust flow high for low end torque, and helps with flow on the top end of the RPM range. Headers are open (loud), but can have an aftermarket performance muffler clamped to them if you do not want to make your neighbors angry, of if you enjoy your ability to hear. When you do this type of upgrade, you will likely need to re-jet your carburetor so it will deliver more fuel with the added air coming into the engine. A nice upgrade to do when jetting is to get an emulsion tube for a stronger fuel signal at the carburetor.
Stage 2: Remove Governor - Unlock the RPM limit.
Cost: Free (governor removal) linkage kit $6-$30 Benefit: 3600 RPM threshold removed.
The governor has two main functions. 1) keep the engine's RPM limit around 3600. 2) opens throttle when starting for a hassle free start. Removing the governor will let the engine rev to a higher RPM, and sometimes prevents the engine from being cold started unless you manually open the throttle butterfly when pulling the starter cord. You need a socket set and basic hand tools to remove the governor. Some people also remove the governor arm and replace it with a bolt to seal the engine case. After removing the governor, you must either slightly modify the throttle linkage, or install a direct throttle linkage kit.
Warning: Once the governor is removed, you have eliminated a major safety mechanism that will keep your engine from wearing out prematurely, or throwing the connecting rod. There is still a debate about at what RPM this will happen, with real world experiences vs. safety factors coming into play. You can probably get away with staying in the 4K rpm range... but all bets are off, do it at your own risk. In spite of the debate, everyone agrees that the BEST practice is to get a billet connecting rod and flywheel so you don't have to experience catastrophic engine failure, or worse - serious injuries (don't freak out - usually the rod just punches a nice hole in the block, effectively ruining what you worked so hard to upgrade).
Stage 3: Billet Aluminum Connecting Rod & Flywheel - Safely run high RPM.
Cost: billet rod $70, billet flywheel $110 Benefit: engine doesn't blow up.
This is the insurance policy I HIGHLY RECOMMEND having against engine failure once you remove the governor. A quality billet aluminum connecting rod can safely operate even above 10K RPM's (not that you will ever reach this figure). Get a stock length billet aluminum connecting rod. For highly advanced builders, a slightly longer connecting rod, an d/or combination of performance piston and increased stroke crankshaft to build a 'stroker' engine is used. For the rest of us, just get a stock billet aluminum rod. Again, there is debate on whether you can rev to X RPM's safely with a rod, but the stock cast iron flywheel. Don't fall into the trap of thinking you will be 'safe'. Why would you risk your health, time, and money by cutting corners? In my mind, a connecting rod and billet aluminum flywheel upgrade need to happen at the same time. What is worse than a thrown rod punching a hole in your block? A shattering flywheel flinging high speed shrapnel everywhere with you being somewhere in the everywhere part. Alternatively, you can get a PVL flywheel for a little less $$, and have the protection from it shattering.
Stage 4: Camshaft & Springs- Help the flow, and target your peak power RPM band.
Cost: camshaft $40-$100 springs $6-$30 Benefit: power band shift and overall hp improvement
A) Cams One of the best ways to really boost your performance, and fully take advantage of all the other performance upgrades you have done so far. When you purchase a performance camshaft, the lobes on the cam alter lift and duration of the valves. In other words, they help with flow, and let the air/fuel mixture in/and exhaust out at certain times.
But which one? There are so many to choose from a.k.a. so many wrong ones to get. So which one? There is no magic bullet, and cams always have tradeoffs. A very relevant question is this: "Where do I want my peak performance?" You will have to decide if it is going to be low end torque, or high end torque, keeping in mind that low end torque cams cant rev high, and high revving cams can reduce your engines performance below stock at anything below the RPM range you will be driving your go kart in. So how would you like your 6.5 hp engine to have 4 hp when driving your go kart? Blindly buy the highest revving cam and you will find out the hard way.
I personally would suggest getting a 'mild' cam that will rob limited performance from the low end, and provide peak performance mid range, and still be able to rev to 6000 or 7000 RPM. If you don't anticipate revving to high rpm, it might be a great idea to get a winch cam, or torque cam for riding a go kart around. Watch out for cams that may require 'clearancing' as these are for advanced builders.
B) Valve Springs You must decide which set of valve springs to use based on your target power band, AND the camshaft. Camshaft's typically have a 'cam card' that recommends what to set your timing to, among other things. You can use your cam card's specs to find out which springs to get.
Valve springs are two faced. They work for you, and against you. Although springs are simple, the combinations available are numerous, just like camshaft choices. A rule for springs is that the heavier the spring (compression resistance), the more horsepower they will rob. That's right, choose the wrong spring set and you actually lose performance with zero gains anywhere. Valve springs are designed to keep the valve train from the cam to the valve seats in sync. The cam(through the valve train) opens the valves, and the springs close the valves through their compression resistance. When you rev above a certain RPM (about 5500 for most stock 4 stroke engines), the springs cannot close the valves in time and/or the valves actually bounce on the valve seats -this is what is called valve float. To prevent valve float, a spring with more compression resistance is installed, which prevents floating until a higher RPM is reached. The higher spring resistance internally reduces the power output at the crankshaft.
You need to select a spring set that will experience valve float just above your maximum RPM. You do this to mitigate parasitic drag. The nice benefit of choosing a lower lb rating valve spring, is that leading up to valve float, the spring's energy has the least amount of parasitic drag, which translates into more power at the crank. So the moral of the story is don't get dual valve springs for a 8K revving engine, and put them on an engine that can only rev to 6k rpm with the cam and other performance mods, it just ruins engine performance, the irony.
Conclusion
There are always limits. There are always trade-offs. Understanding why parts do what they do, and what you want out of your engine, as well as the limitations they all have will help you answer your own questions. This guide will probably give you more questions than answers, so please, if you are serious about performance mods and want to upgrade your engine, call a go kart race shop and talk to their engine builder for expert advice for your situation.
If you want to get parts, just google "your engine+insert name of part" then hit enter, crazy i know. Here are a few places to get the parts for a 212cc predator though
GoPowerSports - high flow intake/exhaust kit
Arc Racing - billet flywheel and connecting rods
DynoCams - camshafts/springs
or any other place that sells this stuff, google really is your friend, and you can probably find tons of places selling the same stuff.
This guide will go over what it takes to modify a small industrial 4-stroke engine (Predator 212cc) to rev higher and have more torque (partially answering age old question -'How do I make my Go Kart Faster?' It goes over the basics. There are ALWAYS trade-offs to consider before purchasing and installing any performance part.
This guide will be for the average DIY person looking to get cheap/minor upgrades as well as some of the high end upgrades you see engine builders implementing on 'builder's prepared' engines. This guide will not show you how to install anything. It is only an introduction to performance upgrades. You have to do the research, and you are the decision maker. So let's start with the very basics. If you cut corners, you can ruin your engine so I have broken it down into suggested stages.
Stage 1: Intake, Exhaust, Jet -The best bang for your buck.
Cost: Under $100. Benefit: flow, significant horsepower gains
Out of the box, small engines are very restrictive to air flow. An engine needs to be able to breathe IN and OUT with less resistance. Adding a high flow air filter, and intake adaptor to fit the air filter will allow the engine to breathe IN easier. This is bolt on upgrade that requires no special tools. Half of the problem is taken care of, now the engine needs to breathe out.
A high flow exhaust header is what to get. Any header will modify your power band, but the 'best' one to get is an open '3 stage header' which keeps exhaust flow high for low end torque, and helps with flow on the top end of the RPM range. Headers are open (loud), but can have an aftermarket performance muffler clamped to them if you do not want to make your neighbors angry, of if you enjoy your ability to hear. When you do this type of upgrade, you will likely need to re-jet your carburetor so it will deliver more fuel with the added air coming into the engine. A nice upgrade to do when jetting is to get an emulsion tube for a stronger fuel signal at the carburetor.
Stage 2: Remove Governor - Unlock the RPM limit.
Cost: Free (governor removal) linkage kit $6-$30 Benefit: 3600 RPM threshold removed.
The governor has two main functions. 1) keep the engine's RPM limit around 3600. 2) opens throttle when starting for a hassle free start. Removing the governor will let the engine rev to a higher RPM, and sometimes prevents the engine from being cold started unless you manually open the throttle butterfly when pulling the starter cord. You need a socket set and basic hand tools to remove the governor. Some people also remove the governor arm and replace it with a bolt to seal the engine case. After removing the governor, you must either slightly modify the throttle linkage, or install a direct throttle linkage kit.
Warning: Once the governor is removed, you have eliminated a major safety mechanism that will keep your engine from wearing out prematurely, or throwing the connecting rod. There is still a debate about at what RPM this will happen, with real world experiences vs. safety factors coming into play. You can probably get away with staying in the 4K rpm range... but all bets are off, do it at your own risk. In spite of the debate, everyone agrees that the BEST practice is to get a billet connecting rod and flywheel so you don't have to experience catastrophic engine failure, or worse - serious injuries (don't freak out - usually the rod just punches a nice hole in the block, effectively ruining what you worked so hard to upgrade).
Stage 3: Billet Aluminum Connecting Rod & Flywheel - Safely run high RPM.
Cost: billet rod $70, billet flywheel $110 Benefit: engine doesn't blow up.
This is the insurance policy I HIGHLY RECOMMEND having against engine failure once you remove the governor. A quality billet aluminum connecting rod can safely operate even above 10K RPM's (not that you will ever reach this figure). Get a stock length billet aluminum connecting rod. For highly advanced builders, a slightly longer connecting rod, an d/or combination of performance piston and increased stroke crankshaft to build a 'stroker' engine is used. For the rest of us, just get a stock billet aluminum rod. Again, there is debate on whether you can rev to X RPM's safely with a rod, but the stock cast iron flywheel. Don't fall into the trap of thinking you will be 'safe'. Why would you risk your health, time, and money by cutting corners? In my mind, a connecting rod and billet aluminum flywheel upgrade need to happen at the same time. What is worse than a thrown rod punching a hole in your block? A shattering flywheel flinging high speed shrapnel everywhere with you being somewhere in the everywhere part. Alternatively, you can get a PVL flywheel for a little less $$, and have the protection from it shattering.
Stage 4: Camshaft & Springs- Help the flow, and target your peak power RPM band.
Cost: camshaft $40-$100 springs $6-$30 Benefit: power band shift and overall hp improvement
A) Cams One of the best ways to really boost your performance, and fully take advantage of all the other performance upgrades you have done so far. When you purchase a performance camshaft, the lobes on the cam alter lift and duration of the valves. In other words, they help with flow, and let the air/fuel mixture in/and exhaust out at certain times.
But which one? There are so many to choose from a.k.a. so many wrong ones to get. So which one? There is no magic bullet, and cams always have tradeoffs. A very relevant question is this: "Where do I want my peak performance?" You will have to decide if it is going to be low end torque, or high end torque, keeping in mind that low end torque cams cant rev high, and high revving cams can reduce your engines performance below stock at anything below the RPM range you will be driving your go kart in. So how would you like your 6.5 hp engine to have 4 hp when driving your go kart? Blindly buy the highest revving cam and you will find out the hard way.
I personally would suggest getting a 'mild' cam that will rob limited performance from the low end, and provide peak performance mid range, and still be able to rev to 6000 or 7000 RPM. If you don't anticipate revving to high rpm, it might be a great idea to get a winch cam, or torque cam for riding a go kart around. Watch out for cams that may require 'clearancing' as these are for advanced builders.
B) Valve Springs You must decide which set of valve springs to use based on your target power band, AND the camshaft. Camshaft's typically have a 'cam card' that recommends what to set your timing to, among other things. You can use your cam card's specs to find out which springs to get.
Valve springs are two faced. They work for you, and against you. Although springs are simple, the combinations available are numerous, just like camshaft choices. A rule for springs is that the heavier the spring (compression resistance), the more horsepower they will rob. That's right, choose the wrong spring set and you actually lose performance with zero gains anywhere. Valve springs are designed to keep the valve train from the cam to the valve seats in sync. The cam(through the valve train) opens the valves, and the springs close the valves through their compression resistance. When you rev above a certain RPM (about 5500 for most stock 4 stroke engines), the springs cannot close the valves in time and/or the valves actually bounce on the valve seats -this is what is called valve float. To prevent valve float, a spring with more compression resistance is installed, which prevents floating until a higher RPM is reached. The higher spring resistance internally reduces the power output at the crankshaft.
You need to select a spring set that will experience valve float just above your maximum RPM. You do this to mitigate parasitic drag. The nice benefit of choosing a lower lb rating valve spring, is that leading up to valve float, the spring's energy has the least amount of parasitic drag, which translates into more power at the crank. So the moral of the story is don't get dual valve springs for a 8K revving engine, and put them on an engine that can only rev to 6k rpm with the cam and other performance mods, it just ruins engine performance, the irony.
Conclusion
There are always limits. There are always trade-offs. Understanding why parts do what they do, and what you want out of your engine, as well as the limitations they all have will help you answer your own questions. This guide will probably give you more questions than answers, so please, if you are serious about performance mods and want to upgrade your engine, call a go kart race shop and talk to their engine builder for expert advice for your situation.
If you want to get parts, just google "your engine+insert name of part" then hit enter, crazy i know. Here are a few places to get the parts for a 212cc predator though
GoPowerSports - high flow intake/exhaust kit
Arc Racing - billet flywheel and connecting rods
DynoCams - camshafts/springs
or any other place that sells this stuff, google really is your friend, and you can probably find tons of places selling the same stuff.
