General Engine Tuning Tips

Maintenance/Tips
Fuels
Setting the high speed needle
Setting the low-speed needle
Performance Engine Tuning 101
2-Stroke Engines 101

Engine Power Secrets

Force 12 Modifications

 

 

TRX-15Modifications

More Engine Mods.

The Basics

Before you even think of messing with the engine make sure you READ and UNDERSTAND every thing in the engine booklet that came with your car. The booklet has all the necessary info to understand the way the engine works and how to adjust the carburetor. The book also tells you how to set the needles back to the factory default in case you deviate too much from the factory settings. Primarily most engines are set with an engine break-in mixture setting, rich on the low end and rich on the high. If you only tune your top end. You wont have the acceleration that you could be getting and if you lean out the top end to compensate for the rich low-end then you will notice the engine will run hot and may even flame out if let wide open too long. Flameout = When engine is so hot that it will shut down by it's self. An overheated engine typically wants to die when brought to an idle speed. Note: The Traxxas Web Page has a great deal of information for the Nitro beginner.

Basic Engine Tuning Tips : Acceleration is controlled primarily with the low-end needle. Overall engine temperature is controlled by the high-speed needle. The rule of thumb is get the bottom end lean enough so that when you idle for 10 seconds and blip the throttle there should be a slight hesitation by the engine while it's getting rid of the excess fuel and then accelerate rapidly from there. If you let the engine idle for 10 seconds -gun the throttle and the engine revs up like it would do while exiting a corner then the low mixture is too lean. Low Mixture adjustment should be made a little at a time, until the engine responds as required. When setting the needles in an engine always check temperature after every two laps to make sure the engine is not overheating. Usually the spit test is a good indicator for getting a ball park idea if you think it's running too hot or lean. After the last lap on the qualifying run, let the engine idle a bit. If it dies it's probably too hot.

Okay, I know this is easier said than done. Adjust the high speed so you don't bog down when accelerating and you see blue-smoke coming out the exhaust. You'll have to re-adjust both the low and high speed needles until A) You can idle well B) Accelerate well C) Not overheat.

Maintenance

TRX-15:

1: After a day of racing empty your tank, suck the line dry and add half a dozen drops of Marvel Mystery Oil inside the carb. and on the piston head. Crank engine over a couple times and close it back up.

2: This engine likes Hotter Plugs. Like Mc-Coy MC-59, and the O.S. #8. The engine might not perform it's best with other heavy-duty (cold) plugs.

3: Take the one-way bearing out of the pull starter/easy start mechanism and clean it well. I ran a gallon of fuel and mine died because of lack of maintenance. I still have not found what is best to increase the life of the one-way bearing, If the bearing starts slipping blast it with motor cleaner and reinstall. According to Traxxas technical service, the oil leakage from the starter shaft is enough to lubricate the one-way. Having cleaned that area of the engine many a time - there is enough oil back there to kill a horse. That's funny because on O.S. engines the Starter remains quite dry and oil free when compared to the TRX15. But, then again that could explain why the O.S. bearing has a plenty of wheel bearing grease.

4: Whenever the thermometer start reaching for 80 don't be surprised if your finely tuned engine starts to sound like crap. Most of the engine tuning skill I have developed involve working with engines in tropical weather conditions. Think of it like an eternal summer. Anyway, I found that when tuning near 90 deg my low-speed needle was very close to factory settings and the top end was fairly rich. You might need to re-set the carb min position, to help get more fuel on idle and keep those temps down. It was unfortunate that I had to burn up a couple of good plugs to realize that I was running a little on the lean side. Well, I'm glad that I'm almost out of 10% nitro. Switching to 20% will allow the carb to move more lubricants through the engine without affecting the throttle response. Remember that when you change fuels you need to do another short breaking-in session.

Warm weather starting techniques

5: You will find that in warmer weather the engine will be difficult to start if your bottom end is too lean. Loosening the glow plug helps to get fuel in the engine, so does covering the carb opening with your finger, and turning the engine over as you alternate between covering and uncovering your carb. The priming pump works best when throttle is left fully open. If you feel the engine is getting harder to turn over tighten your plug - it should fire right up. If it doesn't back up the plug and burn some of the excess fuel. Tighten up your plug and it should fire. Always check your plug and your glow-igniter. If you use your E-Z Starter, getting a clip-on glow igniter can help you get a cranky engine started by burning excess fuel between start to avoid hydro-lock (when the engine has too much fuel and will not turn over). A glow ignitor will also help the engine rev-up when it's really loaded up with fuel, as happens when the engine takes a while to start. With the E-Z start many times you get the engine started and seconds later it dies when you try to rev up the engine -because of excess fuel.

Staring a hot engine

6: When your engine dies on the track and you need to get the thing started open up the throttle all the way. Leave the throttle fully opened and either attack your pull start with your good arm (hehe) or use your E-z starter. You will have better and faster results with the E-Z starter. Borrowing a starter box also helps tremendously. Once the engine fires it will probably die quick, next time it starts ease up on the throttle and you'll be back in the game. If you have a pull starter it will take longer... be patient and alternate between left and right arm, to rest your shoulder! If you have the time (practice) just be patient, let the engine cool for a few minutes and resume starting.

Fuels

If you ask 20 people about which is the "best" fuel you will probably get close to 20 different answers all supported by some type of claim. Either in the performance arena or on the longevity or how "cool" the engine ran. I'm not too shy about giving you my opinion on fuels -and I wont hold any of it back.

Rule #1, there are no rules...

Everyone has had good and bad results with brand X fuel, many times there was something else wrong with the engine, bad plug, contaminated fuel, bad clutch... plugged fuel filter, or other reason, that made your engine act weird, you attribute it to bad fuel, and move on. Then come the testimonials...

Here is my testimonial -It's littered with my own opinion, but if you read between the lines, you can actually get something good about it.

I have tried Blue Thunder and the TRX-15 engine would overheat (Not enough lubricants) -anyway lack of lubrication is what I attributed the constant flameouts and the inability to get temperatures back down to reasonable levels without hurting performance. I've had excellent result with Traxxas Fuel 10% and 20% Nitro fuel, even the guys that are wining use this stuff (20% Nitro). Tuning was good and starting was superb. It's important that you understand that a TRX15-PRO is not an OS CZ-R or CV, from past experience O.S. engines are very fuel tolerant and will run with most fuels just fine. Buy fuel in quarts until you find one that works, then instead of going for the cheap stuff. Buy a gallon of the good fuel, it will save you money and will make your engine run better. It takes time before fuel goes bad, even if the gallon last you a long time in the long run it will save you money!

More on fuels and clearing up the general confusion...

Today I use Wildcat Premium Plus 15% w/ 18% Oil for all my small block engines and have had nothing but excellent results. I run tank after tank...after tank with no flame-outs or overheating problems. The fact that it cost less than Blue Thunder means nothing, except that the serious airplane flyers wont accept to be taken advantage of when it comes to the cost of fuel. Us "car" guys are a lot smarter and wealthier than our plane flying brethren. That why we pay almost double for fuel that is supposed to have the same ingredients as the airplane fuels.

Next time you have some free-time pull out the documentation on your engine and read the fuel specs. You're not supposed to run an engine with fuel that's only got 12% of oil in it. I know the fuel manufacturers want to influence you into thinking otherwise, but that's not the case. Remember that "oil" is more expensive than methanol. So 12% fuel is cheaper to make than fuel with 16-18% oil. To think that car fuel manufacturers have the nerve to charge more for fuel that's cheaper to manufacture is just incredible. If you use low oil content fuel you are just reducing the life of the engine and making it harder to tune. Some engines will tolerate low-oil fuels better than others, but the fact is that most engines operate better with a higher oil content.

If you doubt about what I'm saying here, look up the shinny Blue Thunder "race" fuel. "Race" what is that supposed to be, well on the label it says something about having more castor oil in it... They might as well just put a plane on the label, because the fuel is starting to look a lot like airplane fuel.

To sum it all up when it comes to oil percentage in fuels, more is definitely better. 16-18% oil content will do the following for you:

Note: Anything higher than 18% and performance loss begins to be an issue, but for the back yard basher even 25% oil can be used with no problems. Remember don't use no-brand name fuel. Most "quality" airplane fuels will work very well for car engines. Don't use fuel that's uses 100% synthetic or 100% castor oil as lubricants you want to use a mixture of the two. Typically 80% synthetic 20% castor blend is ideal. If you have access to methanol and nitro methane buy a quart of Klotz Tecniplate (with benol) and mix your own fuel. You will probably only save a couple of bucks a gallon but you will always know that your using high quality components and that your fuel is fresh. 8 years ago I blended my own fuel and never had to rebuild my engines even after 4+ gallons of fuel. If you use 12% oil fuel you might get to the second gallon without a rebuild...you might get less.

Will engine performance increase with 10% oil fuels running 25% Nitro, YES. Will the engine life be sacrificed, YES. Is it worth it...to Me -NO. Keep in mind, that some people will sacrifice their engine to go a little faster in the straight-a-way. I'm not saying this is a bad thing, we all have different goals when we go racing; re-building engines every weekend -Is just not MY goal.

For more information on lubricants and 2-stroke engines check this link out. It will be a big eye opener for a lot of you. They also have good info for blending your own nitro fuel.

Tips for setting the high speed needle

You really need to set the high speed needle before doing any other engine tuning. The high speed needle affects both the high speed and in a small way the low speed operation of the engine. You need a BIG and i mean big place to set your high speed needle. Most tracks don't have a big enough straight way for you to check the high speed needle setting. When you run your car at high speed on a large oval, you will be able to measure engine temps that are not affected by your low-speed needle. Adjust your high speed needle so the engine runs between 220-260. Once that has been set tune your low speed needle.

 You may need to adjust min-throttle position to get a good idle. Use a long screwdriver so you can adjust the low speed while the engine is running. Check your temps to make sure the engine doesn't cook while idling. Make short passes and test your acceleration. Adjust your low speed until you have a crisp idle and a fast reliable transition to top speed. Don't mess with the high speed needle when you are tuning your low-speed needle.

If your car runs great for the first tank and then dies on the second consecutive tank, you can rest assured that your engine is slowly overheating. Whether it's the bottom end that's too lean and the high speed is set rich to compensate or the bottom that's set rich and the high speed is set lean to compensate. You don't notice that the top is too lean because the straight away is not long enough. So the engine temps slowly rise as the race progresses and then at some point when you refuel or on the 8 minute mark your car flames out. This is the typical scenario because most people don't like messing with the low-speed needle so they leave it on the factory setting which most of the time is too rich for racing, it's actually meant more for breaking-in that anything else. They adjust the high speed needle until the engine accelerates smoothly and off they go cooking their engine after 3 min of running. Remember that Hot engines don't idle well, they just slow down and die. That could be a good indication that the engine is running too hot. Try the idle test at the end of the heat, it's a good way to compare how the engine behaves before and after 6 minutes of real racing.

Setting the engine idle speed and low-speed needle

The throttle stop screw or idle-speed screw (same thing) determines how far the carb barrel will be able to close when the servo is in the neutral position. Typically you set the servo/throttle linkage so that the carb will go from fully open when the trigger is fully pressed to fully closed when the trigger is in neutral. Then you would adjust the idle-stop/speed screw so that there is a 1-2 mm gap when the servo is in the neutral position. You might need to readjust the spring collars on the throttle linkage to force the throttle arm against the idle speed screw.

At this point you would start the engine warm it up and commence tuning. Adjust the low-speed needle clock-wise until the engine doesn't sputter when at idle. You want a fast idle, if the car wants to move forward a lot, then turn the idle-speed screw counter clock wise to lower RPM until the engine just barely want to engage the clutch. It may take a little time to get the settings right.

Remember you want the fastest idle you can get away with. It will make the engine more stall proof. Some engine will overheat if the idle isn't rich enough, you need to experiment to determine what's the right setting for your particular engine. When every thing is set right the engine will be able to idle through an entire tank without missing a beat.

Tip#1: There should be no speed change whatsoever when the car is in idle and when you hit the brakes. If the engine's RPM drop either your linkage isn't set right or the idle-speed screw is set too loose. Tighten clockwise until the carb barrel doesn't move when you go from neutral to full brakes.

Tip#2: Some RTR kits have servo horns that are to small. There is not enough servo throw to open the carb barrel, if you use servo trim to be able to open the carb fully, then when you go to neutral the carb doesn't close enough. To compensate for this the novice engine tuner opens up the low speed needle to drop the engine RPM so the car will stay still when at idle... The drawbacks of correcting the linkage problem with the mixture control is that now the low-speed is too rich and the car won't idle for more than a couple of seconds before the engine sputters and dies.

To fix this problem you need to get an after market servo horn, a really big T-Shape one that fits your particular servo brand. Now you can go from fully open to fully closed, without using trim. Now you wont have to compromise the carb settings because of lack of servo throw.

Note: if you have a slide carb you would use the long straight servo horn. Another option is to use a hole (or drill a new hole) on the carb throttle arm that is closer to the pivot point (center).