The BLOK engines are based on the OS Engines XZ-B Spec II. Carburetor and carb inserts are the only differences. The 22C carburetor is used on the 21aM and comes with 6.0 and 6.5mm venturi. The 21J is used on the 21aP and comes with 6.5 and 7.0mm venturi.

More info can be found here
BLOK 21aM
BLOK 21aP

Final Break-in

All Blok engines sold after March 4th, 2019 are now oil bath broken-in using our proprietary system. All that remains is a short process to complete the break-in before it is ready to race. More info on our break-in process can be found here and here.

1. Fully install the engine.
2. Start the engine on the box.
3. Make sure the engine idles by itself.
4. Idle a half of a tank.
5. Let the engine return to ambient temp.
6. Repeat steps 2 through 5 three more times.
7. Run the engine on the ground or track under low power.
8. The engine can now be raced.
We recommend always preheating your engine before starting, even after it has been run for several gallons. Preheating reduces stress from starting, helping to prolong the life of your engine.



Replacement Parts

All OS Engines .21 XZ-B Spec II parts will fit the BLOK 21aP and 21aM engines. The only difference being the 21aM uses the 22C carburetor.
A good selection of replacement parts can be found here.

How to set endpoints for maximum fuel economy and drivability.

These engines are very powerful, which IMO is a good thing as it's challenging to modify an engine to produce additional power from what it was designed to without sacrificing durability or longevity. With a little tuning, you get the best of everything, great power, long runtime and a long lasting engine.

We chose our new engines because they're extremely reliable, easy to tune and make incredible power... but wasted power is wasted fuel! What most people don't realize is that with these engines the power can easily be turned down to increase mileage and drivability. Also, engine temps are reduced, and your engine will last longer. When tuned correctly and with correct EPA/clutch settings you should be able to get 10-minute pits easily.

First and foremost, the key to extended run time is to reduce wheel spin. Reducing wheel spin is paramount because if you are increasing throttle and the vehicle is not accelerating, fuel is wasted. Think about it like this, run time is roughly equivalent to mileage and if you're using more fuel to go the same distance, mileage goes down. Run time can be maximized by reducing the throttle end point and/or by adjusting clutch settings or using a different clutch.

Let's work with endpoints first. I recommend starting with the 6mm venturi in a buggy and the 6.5 in a truck unless you are on a very high grip track or need additional power. Set the throttle pull on the bench by using a set of calipers and measuring the distance from the mid needle to the low needle. Wide open throttle (WOT) with a 6.5 mm venturi should be about 61.7 mm or 62.2 mm with a 7.0 venturi. You can also adjust WOT by removing the air filter tube and verifying the slide pulls one point past the venturi at full throttle.

In a truck, we generally keep the EPA at 62.2 mm as trucks generally weigh more and have additional traction due to the larger tires but in a buggy, our engines generate quite a bit of power and can be a little difficult to drive.

For this reason, we recommend turning down the EPA on buggies and we've found the optimal setting when measured from the mid to low needles to be roughly 59.6 mm. Turning down the EPA does two things; it makes the vehicle much easier to drive without sacrificing top end and significantly reduces wheel spin which improves runtime. If you feel that you need additional power, increase the throttle EPA and retune the engine. Typically we only increase the EPA on high traction surfaces or tracks where we need a little more power out of the corner to clear jumps.

Next is the clutch. With the clutch, you can adjust the power delivery and 'feel' of the engine. If you have very good throttle control changing the clutch might not be as important, but with me, this helps a lot. Like I mentioned before, a truck can typically use all the power our engines generate and we recommend an aluminum flywheel, but in a buggy, we usually recommend a steel or heavier flywheel.

A steel flywheel can help provide a more linear feel to the throttle especially on low to medium grip conditions. IMO a steel flywheel is very important and should be used almost everywhere with the 21aM engine in a buggy. If traction is low or you feel that the buggy still has too much power, carbon shoes can also be used to help smooth power delivery.