Revo Performance Set-Up Guide (part 3)
Welcome to my third installment of my Traxxas Revo performance series of articles. Like my previous articles, I will be shedding some light on the tips and tricks that I perform on my own personal race trucks. In part 1, I showed you my complete guide to tuning the Revo suspension, and in part 2, I explained many of my steering and chassis tricks. In this installment, I will focus on the drive train, along with getting the most out of your engine and transmission. Racing the Revo is a lot of fun. There are many ways to tailor the Revo to your driving style, so be sure to check out the previous two Revo performance guide installments located above, to catch you up on everything that I do to my own Revo race rigs.
This starting system allows the removal of the EZ-Start onboard stating system, so that weight can be reduced from the chassis, while also reducing rotational weight from the crankshaft. This takes load off of the engine, which will increase acceleration, and allow the engine to run more efficiently.
I install my clutch shoes in the trailing edge (stock) configuration. However, the clutch shoes can be installed in reverse for a snappier bite, and/or modified for a different engagement feel. The clutch shoes can be shaved for a later engagement. This can be useful for getting more punch out of your engine. Make sure that you take the same amount of material off of both shoes, and be careful not to take off too much material, as this will soften the engagement too much, and accelerate shoe wear.
Traxxas clutch shoes (#4146X) are already cut from the factory, but you can experiment by shaving off a little more material for later engagements. The stock shoes (#4146) are uncut and will engage a little sooner than the cut ones. These can be helpful on a slick track with a lot of loose dirt on top of the surface. Be careful not to remove too much material from the shoes, as this will leave the shoes too “light”. They will not engage the clutch bell firmly, defeating your purpose of getting more punch out of the truck. Trim a little, and then try them out in the truck to see what works better.
There are quite a few different gear combinations available for the Revo. The chart below will give you a good idea of where to start for your local track. Remember, these are only suggested gear ratios. The actual track layout, jump specifications, surface conditions, and etc. will ultimately dictate what ratio is best for your track.
Your gearing should properly match the size of the track for fast and consistent lap times. You want to be able to efficiently use all of the power available from the engine. Being over-geared will put more load on the engine and clutch causing the engine to run hot with less power out of the corners. The idea is to get the engine to clear out before you get to the next corner. The engine produces its best power when it is burning the cleanest mix of air and fuel (not too rich & not too lean). This is normally found in the mid to upper RPM range.
On larger tracks it is ok to gear a little higher because the truck's cornering speed is usually greater. This keeps the engine in the best RPM ranges as described above. If the truck is geared too low on larger tracks, the engine will spend too much time in the upper RPM range. This will cause the engine to run hot, increase the danger of fouling the plug, and will affect top speed as well.
The placement of jumps on the track can also have an impact on your gear choices. A lot of tracks will have a set of jumps coming out of low speed corners, so good bottom-end punch is important to clear the set. What this means is that you may have to gear down to make certain jumps effectively. Your truck may be a tad slower down the straight, but it is now getting from apex to apex much more quickly. This set-up will be more desirable when your truck spends the majority of its time in the infield. Of course, this may change if you're on a more open course, with either smaller jumps or easier jump sets.
It's ideal to utilize a gear ratio that works best for the majority of the track. If the track has a long straight, but a tight infield, then gearing up to be the fastest truck on the straight is not necessarily going to be the best move. You'll need to maintain a fast pace through the infield as well. If you are coming up short on doubles, and bogging slightly out of the corners, then you can bet that all of the time lost in the infield will never be made up by the fraction of a second that you stand to gain on the straight.
Two-speed adjustments are necessary when changing the gear ratio between the clutch bell and the spur gear. Changing the gears on the clutch bell to a higher number of teeth, and/or changing your spur gear to a smaller number of teeth will give you a higher top speed. This will also take away a little bit of low end punch. This will affect your shift point by making your two-speed shaft turn at a higher RPM, thus causing the two-speed to shift sooner. If you are going to a clutch bell gear that has a lower number of teeth and/or a spur gear that has a larger number of teeth, then the two-speed will react just the opposite. Turn the adjustment screw clockwise for a later engagement, or turn the adjustment screw counter-clockwise for an earlier engagement depending on the need. Adjust the two-speed in small increments. Never turn the adjustment screw more than 1/8 turn at a time before testing the shift point. This is a fine adjustment, and can get way off base very quickly if large adjustments are made.
The shift point of the two-speed is not only important for optimum performance on the track, but it is very important for long engine life. If the transmission is shifting too soon, power will be lost, and the engine will over-heat quickly. If the shift point is too late, then the engine will be allowed to rev too high for too long. This condition can cause many problems like accelerated wear between the piston and sleeve, plug damage, poor fuel economy, and can also lead to very hot engine temperatures. The prime time for the transmission to shift is at the point before the engine is just about to “wind-out” or “peak”. You don't want it to actually reach its peak rpm, but you'll want it to get close. This will allow the engine to clear out (burn clean), and continue to produce good power on through the next gear ratio.
Now that you know how important the timing of the shift is, it is now time to learn what is happening to the truck when it shifts, and how it affects handling. When the two-speed shifts there is a noticeable “instant” boost in speed. This boost can upset your truck's handling before and through the turn. This can cause a greater chance of you over-shooting the corner, which adds seconds onto your lap times. For instance, if you're racing on a medium-sized track that has a long straight, but the rest of the track consists of many turns and switch backs, then there is a good chance that first gear will be able to handle all of the infield duties on its own. There is really no need for the transmission to shift until you're on the straightaway. In a situation like this, allowing the transmission to shift in the infield will more than likely hurt your lap times, by increasing the chance of the shift throwing your truck wide in a corner. If the engine is really revving out in an area or two within the infield, then it is ok to allow your transmission to shift; just use good judgment. You may also benefit from gearing up a couple of teeth on the clutch bell to get the rpm down through the infield portion of the track. This, of course, will depend on the track size and layout.
The best solution for getting smooth shifts is to install a close-ratio two-speed kit. This brings the second gear ratio closer to the first gear ratio. This helps with several things. Shift points are less critical in keeping the engine in the proper power-band. There is less of a ratio change when shifting, which makes for smoother shifts. This is what attributes to better chassis balance when shifting through a corner. A small amount of top end will be lost, but for most tracks, there is still plenty of speed with the close-ratio gear set. Also, the attitude of the truck is much easier to control when airing out on high-speed jumps.
Removing the reverse system is a big step to reduce rotating mass inside the transmission; along with the weight of the extra servo that is used to shift the system. A lightweight single-gear shaft replaces the entire system, and is located where the main output shaft used to be. This set-up eliminates reverse (which is not used during racing anyway), and provides quicker acceleration.
High Bite Tracks
Low Bite Tracks
A good starting point for the slipper setting on the Revo is threading the nut to where there is only about 1/16-inch of the slipper shaft is sticking out from the nut. Experiment with different settings for your track conditions to obtain optimum traction with as little wheel spin as possible.
Caution: Be careful not to run the slipper extremely tight or loose. If the slipper is set too loose, then this can cause excessive heat build-up and could result in a melted spur gear. If the slipper is set too tight, then not enough slip will be allowed to protect the spur gear from violently engaging with the clutch bell. This can chip the teeth of the spur gear, and will eventually strip all of the spur gear’s teeth.
The differentials of the Revo are filled with a thick lube to slow down the diff action. This will help prevent the diff from unloading when powering out of the corners. Any of the hobby-class differential lubes out on the market should be fine; the thicker the lube, the slower the diff action. Slowing the diff down will also make the truck's traction more positive on throttle. This will typically reduce steering entering a corner, but will actually increase the steering coming out of the corner. Heavier fluids are also beneficial for higher bite surfaces as well. Loose and bumpy tracks will want thinner oils in the differentials.
Thicker fluids – high-bite, smooth, high-output engine
Thinner fluids – low-bite, bumpy, lower output engine
Traxxas offers diff lube in three different thicknesses: