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flat v hemi
flat v hemi
Predator 212 Hemi Number: 60363
Predator 212 Non-Hemi Number: 69730
predator 212
predator 212
The cheap engine used for stock class at many go-kart circuits, including that at LeTu
Combustion Chamber Non-Hemi Hemi
Output 6.5 hp 6.5 - 6.8 hp
Displacement 212cc
Torque 8.1 ft-lb (@ 2,500 rpm)
Max RPM 4800
Mounting Pattern (LxW) 6.40" x (2.95" to 3.17")
Dimensions (LxWxH) 15.4" x 12.6" x 13.6"
Weight 37.5 lbs (17 kg)
Stroke Length 55 mm (2.12")
Bore 70 mm (2.76")
PTO Shaft Rotation Counter Clockwise
PTO Shaft Size 3/4"Dia x 2.43"L
PTO Shaft End Tapped 5/16-24 with 3/16" key
Disclaimer, all of the below measurements are not exact and may not be the same for every engine, only because every predator engine is slightly different because they are so cheaply made.
CYLINDER HEAD
Throughout the entire 4-stroke procedure, ensuring that the valve and piston never come into contact under any circumstances is crucial. Failure to prevent such contact will result in engine destruction.
Maintaining a consistent gap between the valve and the piston is imperative at all times. A minimum clearance of 0.030 inches between the piston and the valve is required in the predator due to thermal expansion and the connecting rod stretching.
The Hemi piston sits roughly .020" at TDC below the top of the cylinder, and the non-hemi is roughly .010" to.015" in the hole.
As a very generalized rule of thumb, for every .010 shaved off the block, head, or head gasket, it is a 1cc reduction.
Hemi head cc is about 24cc stock, with a flat top piston. The non-hemi has a 3cc dished piston with a 22cc head.
The stock head gasket is a .045" on the non-hemi and .040" in the Hemi but can be replaced with a .010" gasket for a .3 Hp gain.
SPRINGS
The stock spring tension is ≈ 10.8 lbs. Max Wire Diameter Of .071”. Valve Spring Installed min height of .815", max height of .850". The stock springs limit the engine to 4800 RPM due to valve float (when the springs are too weak to seat the valves before the cam pushes the valves down again), but 12 lb springs would allow the engine to go to around 5500 RPM.
The valve lash should always be checked on a stock predator before running. Intake 0.004" - 0.006" Exhaust 0.006" - 0.008". For both of these, I would lean towards the smaller distance.
VALVES
The valves for the predator engines are solid low-carbon steel with a 45-degree seat angle. Their dimensions are: HEMI: .216" stems, 1.06" intake, and .984" exhaust.
Non-Hemi: .196" Intake Dia, .218 Exhaust Dia stem tips, 2.513"‐2.520" valve length, .982"‐1.064" Dia intake, .946"‐.982" Dia exhaust.
Seat size for Intake side is .880", Exhaust is .850".
When prepping an engine for races, I recommend putting on higher flow intake and exhaust in order to allow the engine to flow and "breathe" better. This includes a large filter with an adapter and an exhaust pipe with a screw-on muffler. This kit can be bought, including carburetor jets, online.
If you put these on, however without jetting the carb or vice versa, the engine will run lean or rich, respectively.
TORQUE
Values for the head components (all should be put back in with a drop of thread locker)
Head bolts: 17 foot lbs or 204 inch lbs
Rocker studs: 17 foot lbs or 204 inch lbs (non-hemi)
Rocker adjuster nuts: 7.8 foot lbs or 94 inch lbs
Exhaust nuts 17 foot lbs or 204 inch lbs
Intake nuts: 5 foot lbs or 60 inch lbs
AIRFLOW IN THE HEAD
A stock Hemi head flows around 50 cfm, and a stock non-hemi head flows about 52 cfm. After porting the head (cleaning up any rough edges from the casting process and rounding out sharp corners), a 22% gain in flow is expected, equating to ≈ 1hp on a predator.
Here are some tips for porting a head:
Ensure a smooth transition from the casting port to the bowl cut for the intake. Make the short side radius as even and smooth as possible. Bringing the port floor closer to the valve is beneficial, as well as smoothing the area around the valve guide and reconnecting the port roof to the valve guide. However, working on the port-floor to valve-seat transition is the most significant improvement.
Regarding the exhaust, round off the short side radius, but not as extensively as in the intake. Focus more attention on the area around the valve guide and on both sides of it. The most crucial flow area in the exhaust lies in the two shallow grooves on either side of the exhaust valve guide. Maintaining a straight area beneath the valve before the turn for the exhaust ports is important. The outer part of the turn is more critical for exhaust flow compared to the short side radius, as the flow is being pushed out rather than drawn in like the intake. This is a key consideration for optimizing the exhaust system. While scavenging can be improved, it's worth noting that in a single-cylinder engine, there are no additional pulses in the exhaust to aid in drawing out the burned fuel.
Remember not to remove material from both ports excessively. Creating a large bowl below the valve is detrimental. Also, avoid modifying the backside of the bowls as they are already oversized by the factory. Only adjust the ports where they align with the manifold, ensuring a proper match.
SPARK PLUG
The recommended Predator 212 spark plug gap is 0.027" -0.031". This is the space between the ground wire and the center electrode.
Ensure the spark plug threads and the female (cylinder) side are clean and dry. Finger-tighten the spark plug, then use a plug wrench to tighten it 1/2-2/3 turns on plugs with a copper gasket.
The predator uses a BP6ES-type spark plug. We use the E3.111 racing spark plug.
Lean condition engine: The Spark Plug head will look light tan. There will be some minor carbon buildup. The engine will run hot.
Rich condition engine: The Spark Plug head will look black but dry There will be a good amount of carbon buildup. Carbon deposits will build up around the piston rings causing the engine to lose compression. This will increase the chance of fouling the spark plug and causing engine miss-fires.
Cylinder head temperature is good to monitor, and generally, once the engine is warmed up, at full throttle, the temperature of the head around the park plug should be about 470°F after the engine has been messed with. A box stock predator will run rich and cold at about 400°F. Exhaust gas temp at full throttle will be around 1000°F.
IGNITION
Rotate the flywheel forward (right) to advance timing.
A stock coil gap of 0.016 ± 0.008 (This is the gap between the ignition coil and the flywheel magnet.)
The spark occurs at 24 degrees BTDC on the stock engine. Advanced timing of 30 degrees is perfect for a stock racing Predator 212. Every .006" filed off the stock key allows for 1° of advance.
If you advance timing more than 6°, you will lose power in the lower RPM range
Typically a spark advance of 1 to 1.5 degrees increase per 1,000 RPM is characteristic of engine demand.
Stock Flywheel weighs 5.25 to 5.4 lbs. Torque flywheel to 54-foot lbs. Do not use Loctite on the flywheel spindle.
OIL
Takes .5 quarts of 10-W30 oil. Use conventional oil for a 1-hour 3400-RPM break-in period, and for better engine health, run this break-in oil with a zinc additive like "Lucas Oil 10063". After the break-in period, replace with full synthetic oil.
If the weather is very hot and the engine is running for a long time at full tilt, 10-W40 may be a better option as it operates better at higher temperatures.
There are two parts to each oil code. For instance, 10W30 has two parts, 10W and 30. These are the viscosity indices for the oil at low and high temperatures, respectively. The lower the number, the thinner the oil.
"Conventional" means that the oil comes from an organic source, whereas "synthetic" is made in a lab.
Where Synthetic Oil Wins
Synthetic oil provides better protection than conventional oil
It flows better in cold temperatures and withstands higher temperatures better
It helps fuel mileage
Where Conventional Oil Wins
It is cheaper
It helps the engine handle the initial friction better
It helps the mating engine parts to wear properly during the first few hours of usage
GAS
8.3: 1 Compression Ratio with a PSI ≈ 100, stock, but this changes engine to engine as they are made cheaply.
Holds .9 gallons of gas in a stock tank.
If the engine runs constantly, like at a race, 87 octane, ethanol 10 gas is fine with fuel stabilizers added, such as "seafoam." But if the gas is allowed to sit for extended periods, the tank and carburetor should be emptied or filled with ethanol-free gas.
Octane rating, sometimes known as an octane number, is a measurement of a fuel's capacity to sustain compression in an internal combustion engine without detonating. The more compression the gasoline can sustain before detonating, the higher the octane number.
Ethanol is a grain alcohol derived from distilled maize that may be combined with gasoline and used as a renewable component in automobiles. Ethanol contains intrinsic qualities that cause metal parts, especially carburetors, to corrode, as well as the deterioration of plastic and rubber components, difficult starting, and shortened engine life.
CARBURATOR
The stock main fuel jet is .028" ID. Length is .340(+‐.005).
Emulsifier tube ID is .066", and OD is .154". The minimum length is 1.092".
The carb bore depends on the brand of carb but is generally:
.945" on the inlet and .748" in the venturi
If your carburetor comes with a Fuel-air ratio adjustment screw, it will control the amount of gas that enters the engine. Tightening the screw will make the mixture rich, and if you loosen the screw, the mixture will be lean.
For use in an engine with less restricting intake and exhaust, it is prudent to upgrade the emulsifier tube to a #140 and the jet size to a .037" ID or even up to a .038". This will let the engine get enough fuel for the air being let in and will help it run cooler. Stock the carb runs lean (to meet EPA requirements). Note: ALWAYS store the engine with the fuel shutoff valve found on the carburetor in the "OFF" position.
The carburetor, which comes stock on the Predator engine, is a basic float style, generally only having an adjustment for idle speed. There are three brands found on these engines: HUAYI, RUI*ING, or SP.
It works by allowing fuel to fill the bowl until it lifts an air-filled float which rises and pushes a small needle into a hole, disallowing any more fuel from entering the bowl. This fuel is then pulled upwards by vacuum from the carb venturi through a main fuel jet and then an emulsifier tube (labeled "air jet" in the exploded view). The gas is then "atomized" or split into tiny droplets mixed with the air before the air-fuel mixture enters the engine.
HARDWARE
No matter the system used, the higher number means, the stronger the bolt. Common steel bolts purchased from a hardware store are made of low-carbon steel with low tensile strength, usually in the neighborhood of 50,000 to 60,000 psi. They also bend easily and have little corrosion protection. In contrast, aircraft bolts are made from corrosion-resistant steel and heat-treated to strength over 125,000 psi. Use aircraft-grade bolts in high-stress areas.
One tip I have is to remove this shaped plate found under the cylinder. Its there to protect the engine from debris but in the case of racing, it only reduces airflow over the fins and thus cooling.
Another tip for racing predator engines is to remove the "low oil sensor". Because these engines are intended to be used as generators, and the oil is often forgotten, they have a low oil sensor that will cut off spark if it does not read the resistance expected from oil. This is a problem when racing because when going around a corner, oil will slosh in the crankcase, tripping the sensor and killing the engine.
Cut the wire that goes to the crankcase, and simply unplug the other. Then unbolt the sensor and toss it.
It may be necessary to add a kill-switch to an engine or kart to meet requirements.
The 'kill wire' is an important part of the engine. Its job is to stop the engine from running when certain conditions are met. It does this by stopping the spark plug from producing a spark.
The 'kill wire' connects the ignition coil inside the engine to a green plug or connector. From this plug, there are two more black wires. One goes to a kill switch, and the other goes to an oil sensor.
When the kill switch is turned off or the oil sensor detects low oil, the 'kill wire' completes a circuit. This means that the electric current can flow from the ignition coil through the kill switch wires and out to the engine's body. As a result, the spark production is stopped, and the engine no longer runs.
A spring can be added at the blue circle, pulling in the direction of the arrow, in order to help the throttle return to idle and aid in a snappier throttle response.
The throttle linkage is necessary to understand. The throttle arm (outlined in red) moves left (as shown by the orange arrow) in order to accelerate. This pulls on the governor spring, which pulls on the elbow-shaped governor arm. This arm then pulls on the throttle rod in order to accelerate.
The governor is acting on the elbow-shaped governor arm and attempting to pull it back towards the right any time the engine exceeds around 3600 RPM. The governor (yellow) overpowers the governor spring, and thus no matter how much you pull the throttle arm, you will not accelerate anymore. If the governor spring is made shorter or stretched further by putting it in a further hole, a higher RPM can be reached before the governor overpowers the governor spring. It should be in the farthest hole from the shaft.
TIP: Loosen the green nut in order to let the throttle move easier.
The governor itself is important to understand. It connects via a gear to the crankshaft and has an arm that attaches to the throttle linkage.
The best possible explanation of the governor is in this youtube video.
https://www.youtube.com/watch?v=3jUpb71D3is
you can skip to time 2:07
A term used to describe all the work done in the above material is "Stage 1", meaning you have a large air filter, exhaust, jetted carb, and ported head, and have checked all clearances.
Some questions I had are "Which is better, a muffler or no muffler" and "At what RPM do I make my peak torque and horsepower". Here are the dyno results which answer all of those questions
"Stage 1" Muffler
Peak torque at 4200 RPM (10.86), Peak Hp at 4700 RPM (9.07)
"Stage 1" No muffler
Worse torque and Hp
Run the engine with a muffler.
An engine is designed for a specific flow of gas through the piston chamber, valves, and exhaust system. The engine tune relies on some degree of back pressure to push against in order to balance the gas pressure in the engine and maximize power and torque. This is called back pressure.
In addition to using a muffler, we have learned that running the engine at or a little above 4700 RPM is ideal and will yield the best speed with a stage 1 kit. With all above modifications, this engine should push 5400 RPM and make 10.2 HP.
Torque Converters
If you put the spring in hole number 3, the spring will be the tightest, meaning it will require more force to compress the spring. Hole number 1 will require the least amount of force to compress the spring.
More force required will mean better low-end torque and better acceleration but will take longer to get to top speed.
For best results with the above modifications, put a green spring in hole 3.
Here is a quick guide to the springs and holes for the CVT
So, you removed the cover of the slave pulley to move the spring around? You’ll now need to preload the torque converter. This is done by turning the fixed cam that you are holding against the torque converter in a counterclockwise direction until it hits a stop. You’ll have to do all this while pressing the fixed cam against the torque converter. Next, put the snap ring back on and re-install the pulley.
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