HPI Racing - Nitro RS4 MT Tech and Racing Tips

Since many of us here at HPI Racing compete on a regular basis, we come up with tuning, racing, maintenance and general technical tips constantly. This page will collect all the tips that we have gathered plus pull together the tips we get from our email bag.

The Tech and Racing Tips pages for all the cars will be updated as frequently as needed to keep pace with the new race hints and ideas we come up with. This page will have the newest tips listed first, with the date noted next to it.

Many of the tips will have thumbnail photos of what to do, where to put a part, etc. If you click on one of these thumbnails, you will download a larger (5 to 6 inches across, 40K to 80K) photo of the process involved with the tip.

Maintenance Tips - Find out how you can maintain your car in the best condition! Split between general maintenance and "serious" racing tips

Setup Sheets - Blank setup sheets for nearly all of our car kits, plus setups that have worked great for our team drivers!

How to Rebuild Your Engine!
Learn how to change your Nitro engine's piston and sleeve with seven pages of detailed pictures and rebuilding tips! Essential for all Nitro car and truck owners! Click here to start!

How to Make Your 15FE Engine Run Cooler!
If you run your HPI Nitro car or truck hard, your engine will benefit from better cooling. We'll show you how to install the #1703 or any option engine head. Useful for most HPI Nitro car and truck owners. Click here to start!

How to Upgrade the Carburetor on Your 15FE Engine!
For race-tuning your Nitro car or truck, a 2-needle carb is very useful - detailed pictures show you how to upgrade your 15FE stock carburetor to our #1634 2-needle carb! Useful for most HPI Nitro car and truck owners. Click here to start!

Don't modify the pipe
The plastic tuned pipe that is included with your kit is not meant to be modified - attempting to take it apart to "tune" it will result in poor pipe performance and other problems. Only our metal "can" muffler (currently included only with the Super Nitro RS4) can have a baffle removed for extra performance.

Neat Wiring!
A neat wiring job not only looks "professional", but it makes your Nitro MT easier to clean up and makes it easy to install the radio tray.

Fuel Tank Bushings
Use old shock o-rings to cushion the fuel tank and help prevent bubbles in the fuel line.

Slide Carb Linkage
Use our #A889 Slide Carb Throttle Linkage Set to attach engines with slide carbs to your Nitro MT! Use the servo arm, short Z-bend wire, brake wire and slide carb ball cup from your Nitro MT kit. From the #A889 set, use the two stoppers and setscrews and the spring (or use similar pieces that are available at any well-stocked hobby shop). Then assemble the pieces as shown below.


Our Nitro Star Pro 12R SC installed in the Nitro RS4 MT	The closed position of the slide carb	The open position

Speed Secret!
Our engineers purposely limited the amount the carb opens on the stock 15FE engine so that newcomers to R/C wouldn't drive an overpowered car. After you get used to the handling of your Nitro RS4 2 you can move the ball end on the carburetor arm to the lower hole, which will allow the carburetor to open all the way. This will get you increased top end speed and power!


The Nitro Star 15FE carburetor at the correct closed position	After moving the ball end on the carb arm to the lower hole, you can get the carb to open all the way for extra power.

Use Loctite!
For those of you who are trying to maintain your 2 speed transmissions: Try using a dab of Loctite on top of the Allen screw that holds the spring down, that should hold the screw in one spot so the shifting position doesn't change over time. You should take apart the two speed assembly every now and then, Clean everything with motor spray, and lube it with a high-quality grease (the grease that comes with our one-way diffs is lithium grease).

Fake Transponder Expert and experienced drivers who race at tracks that use transponders can benefit from using a practice transponder. Depending on where you place the transponder, it will affect the steering and handling of your car. Experienced drivers can feel the effect of an extra ounce of weight (about the weight of a transponder), so using a practice transponder can get you used to running with the extra weight on the car.
41 KB	These are the materials you will need to make a practice transponder: servo tape, hobby weights and a paper clip or something else you can make a loop out of. You can also use coins and servo tape them together. It may actually be cheaper!
32 KB	Attach servo tape to the hobby weights and put the paper clip in between them.
11 KB	This is the finished practice transponder. It weighs about 30 grams, and a real transponder weighs about 25 grams. You may want to cut off part of one block of weight to get a more exact weight.
50 KB	This is how most of the HPI factory racers attach the transponders to their car. You can also use a c-shaped piece of Lexan and screw it to the middle hole in the bumper, or mount it off the servo, although that may throw off your car's balance. Mounting it on the chassis also looks better than drilling a hole in the body, and it contributes to a lower center of gravity!

Cooling is key!
With all of the Nitro cars, you MUST cut a hole in the windshield and side window. To reduce drag, you can cut out part of the rear of the car also. If you do not provide ventilation to the car, you can easily overheat and destroy your engine!

Run the engine rich!
The Nitro Star engines are meant to run a little rich. You should have a nice plume of blue smoke when the car is at full throttle, and if you hold your hand at the exhaust outlet at full throttle, it should be coated with a light mist of oil. If you run the engine too lean, you run the risk of damaging the connecting rod, piston or sleeve.

Use the right percentage of nitro in your fuel
Call your hobby shop or talk to local racers to find out what percentage of nitro fuel they are using. We recommend and use almost exclusively 20% Nitro racing fuel. If you use a higher percentage of fuel at lower elevations or on hot days, you could damage your engine very badly. Racers at high elevations (7,500 ft and above) or in cold weather may want to try higher percentage nitro fuel.

Alkaline Batteries in glow igniter
If possible, use alkaline batteries in the glow plug igniter. They have more voltage than NiCads (rechargeable batteries) and don't discharge while in storage.

Solve your flooding problems
If you happen to flood the engine with glow fuel, here are two ways to clear out the fuel. The easiest is to close the needle valve all the way, and pull the starter cord a until the engine revs up. It will probably die very quickly, but that's okay, you can open it up two and a half turns (prime it one or two times) and it should start right up. The second method is to remove the glow plug with an 8mm socket and turn the car upside down and gently pull the starter cord so that the fuel falls out of the chamber. Make sure to face the glow plug opening away from anyone's eyes. Then replace the glow plug, re-prime and start the engine.

Mind your adjustments!
On any engine, the small black screw next to the air intake is the barrel stop screw. With the throttle servo at full brake, this screw should be adjusted so that the barrel opening does not change when going from neutral to full brake. This ensures that when you brake during a race your engine will not die or stall out.

Set the idle carb opening properly
On the .15 and .15SS Nitro Star engines, to set the low speed idle mix screw, move the barrel to the closed position. The carburetor opening should be no more than 1.5mm. To adjust, turn the mix screw all the way closed and back it out one and a half turns from closed. It should be no less than one and a quarter to one and a half turns out.

High speed needle setting
On the .15 and .15SS Nitro Star engines, the high speed idle mix screw should be no farther out than two and a half turns from closed.

Keep your truck clean!
To clean the chassis and engine, use Simple Green (lightly diluted or not at all) or Formula 409. They come in convenient spray bottles and will not attack the plastics on the car.

How to clean your truck's body
Use Windex or diluted Simple Green to clean the body inside and out. You may have to reapply permanent marker trim lines on the outside after cleaning.

Keep the air flowing
Be sure to cut air intake holes in the windshield. You can also cut out the right-side window to let more air in. If your motor runs too hot because of not enough air, you'll use up too much fuel and the engine could be damaged. Some HPI drivers leave enough of the window to make an air scoop that grabs a little bit more air and directs it over the engine head.

Basic engine tuning
The engine needs two things to run: air and fuel. If you give the car full throttle and it stalls, you are probably running too 'lean' - the engine is not getting enough fuel. Adjust the needle valve a couple of clicks to the left (open, or counterclockwise) to let more fuel into the carburetor.