HPI Racing - RTR Super Nitro RS4 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 in the future 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!

Install MIP CVDs
MIP doesn't make their famous CVDs for the Super Nitro at this time, but you can put them together from these parts:

MIP CVD Bone for Associated RC10 B2/B3 #1010 or Team Associated #9278
MIP MT Axle (Front) - #1071 or HPI #80817
MIP MT Axle (Rear) - #1072 or HPI #80818
MIP Coupling Kit - #1012

NOTE: The ends of the CVD Bones will sit right on the edge of the diff outdrive cups, so if you are using a powerful engine (1 hp or more) you may have trouble with the CVD getting damaged.

Add a belt roller guide
Nitro racers can add a bearing-equipped roller guide onto the front pulley mount. Our #72060 Aluminum Pulley Mount and recent runs of the plastic mounts have an extra hole that allow the installation of a pilot shaft or screw that can hold bearings against the front belt. This is not an essential feature, but some racers like the option to do this modification. Parts used for the pictures below: one 3 x 15mm metric cap head screw (#Z545), one 3 x 5mm metric binder head screw (#Z515), one servo saver shaft 4 x 10mm (#A168), two 4 x 8 x 3mm ball bearings (#B017) and a few 4 x 6 x .3mm washers (#Z695). You can use different screws and parts that those listed, but these are the exact parts shown.

Click here for the larger image

Vibration-proof your fuel tank
Use machine screws, locknuts and old shock o-rings to make bushings for your fuel tank. This will help prevent the formation of bubbles in the fuel lines as you run the car. See the arrows in the picture below for the location of the o-rings.

Click here for the larger image

Lower Your CG!
Racers are always looking for a way to lower their Center of Gravity (CG). HPI Factory Team Drivers mount their Nitro car throttle servo below the graphite upper deck, as well as removing the thick aluminum washers that space the graphite battery tray above the upper deck. This lowers the center of gravity quite a bit on the Nitro car kits.


Use the same screws and nuts, just move the throttle servo mounting ears under the graphite upper deck.	You can use Shoe Goo to attach rechargeable batteries to the graphite battery tray.

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.

If you are hearing a strange squeaking sound as your Super Nitro RS4 drives by, use the remainder of the kit's grease tube to lubricate the ends of the dogbones. Just a light coat will get rid of the squeak!

"HPI Racing Friend" Rowe Patton of Tennessee is an HPI Nitro freak! He owns one of the first Super Nitro RS4 kits shipped out, with his Super Nitro almost completely paid off before he even went to pick it up! Rowe (or Metalhead, as he likes to be known) sent us these pictures of his innovative setup on his Super Nitro. He used a remote glow plug normally used on R/C planes and helicopters and mounted it on the front fuel tank mount. Rowe used a model from Model Products Corp. that cost about $11, and says it took about ten minutes to install the unit. These remote glow plugs can be found in the R/C plane section of your local hobby shop. The main advantage of doing this is that you don't have to drill a hole in the top of your body to attach the glow plug igniter! Thanks, Metalhead!

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Experienced builders may have noticed the second antenna mount on the removable radio tray - this is meant for racers who want to be able to take out all the radio gear and not have to worry about the antenna mount in the standard position. The Super Nitro RS4 bodies have a second antenna hole dimple on the body if you wish to use the optional antenna mount.

For those of you who are trying to maintain your 2 speed transmissions: Try using a dab of Locktite 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).

Make a 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!

Tip for super-performance types: The lightweight flywheel (#A925 for pullstart engines, #A926 for non-pullstart engines) is best for big tracks with long straights, like those at many permanent race facilities where 1/10 and 1/8 gas pan cars race. The stock flywheel (available with the Nitro RS4 and Nitro RS4 Racer kits) is best for smaller tracks, like typical parking lot tracks where gas sedans run on the same tracks as electric touring cars. The reason is because the lightweight flywheel lets the engine reach higher RPM, so it is best for tracks where speed is important. The stock flywheel, because of its slightly heavier weight, is best for tracks where low-end acceleration is more important.

You can use part A050 (Black On-Road Front Spring) to get a smoother feel to your braking. This is the part number of the spring that many of you have noticed on the brake rod of our full-option Nitro RS4 (featured in the Option Parts pictures), and it comes stock on the Nitro RS4 Racer kit.

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 window of the car also. If you do not provide ventilation to the car, you can easily overheat and destroy your engine!

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.

Call your hobby shop or talk to local racers to find out what percentage of nitro fuel they are using. We recommend and use 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.

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.

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.

On the .15FE 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.

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.

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.

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.

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.

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.

The optional clutch bells (14 tooth, part number A814 and 15 tooth, part number A815) are meant to increase top-end speed. They won't improve acceleration (bottom end), but will make the car faster at the top of its power band.

Use the stock external antenna mast, not a 'stealth' antenna that is hidden underneath the body. A little wind resistance is better than risking radio interference that could cause a huge crash. Also, if another racer is running on a frequency that is close to yours, your car may glitch and get twitchy at the opposite end of the track. The extra range may mean the difference between you hitting a wall and getting around that hairpin!

Many racers like the large front bumper that is included in all HPI 1/10 touring car kits. Most of us here at HPI use our optional Foam Bumper (# 6231) to make our bodies last a bit longer. Foam bumpers also support the nose of the body, so the front spoiler doesn't hit the ground as the wind goes over the car.