HPI Nitro RS4/Nitro RS4 Racer

hpirs4r.jpg (32496 bytes)First of all, let me start off with my opinion of this extremely popular nitro touring car. Both versions are extremely well equipped and clearly demonstrate HPI's dedication and superiority in the field of pavement pushers.

Straight forward, quality parts a plus
You can tell a lot about the quality of design and materials when you get the opportunity to build one from a kit. Not only did I find this car very straightforward in it's assembly but required very little modification to make it RTR. It seems that so many kits these days seem to be chock full of addendums, requiring you to dramatically modify parts in order to make them work. Now, I'm not against modifications.. they are how some of the greatest innovations come to be, but when you are trying to build a kit, with it many complex parts and the painstaking and inevitable task of having to fit third party servos, radios and engines to the chassis, the last thing you want to have to deal with is referring to addendum after addendum about how to dremel parts to make them work. I didn't see this as a problem with these cars.

A picture is worth a thousand words
Now, many of you that may have built these kitss may feel that HPI's method of building instructions may leave something to be desired. I think I may have counted all of about 20 words in the racer manual. Brief it is. However, the saying that a picture is worth a thousand words clearly applies to their method. Systematic exploded views of each "section" concisely illustrates how each part interconnects. Additionally, with this method, you are not necessarily bound to the exact step-by-step instructions that normally are part of most manuals. I feel that this also gives you additional understanding of HOW your car works.  Afterall, this is the biggest selling point behind kits, vs. RTR's; so that you can gain a helpful understanding of how your car is put together so that you can make your own repairs and modifications.

The driving force
The Nitro RS4 (both standard and Racer) are built on a three belt, all wheel drive design. Although not as resiliant on gravelly pavement as drive shaft or other protected driveline systems, it does provide the smoothest and most quiet results. The natural dampening characteristics of belt-driven systems tend to help reduce premature wear by absorbing the relentless vibration that accompany nitro systems and increase efficiency of power to the drive wheels where they are needed.

Hit and Miss
I have to say I'm a little disappointed on their apparent lack of belt tensioners, even in the Racer kit.  Granted, most tensioners are more about improving the asthetics of the machine rather than providing any real mechanical advantages. In theory, this is just one more piece of machinery for the engine to drive and decreasing its overall efficiency. However, there are exceptions to this rule. An improperly adjusted belt can either increase friction at the bearings (if overtightened) as well as the belt itself. If too loose, the belt can "slop" around dragging or hitting nearby parts as it makes its journey from one gear to the next. On the Nitro RS4, the forward belt (the longest one) tends to aimlessly drag on the top of the chassic plate. Whether this really creates that much friction is debatable, especially since this drag is dissipated over several inches. The other solution to this would be to put a tephlon or silicon backed tape on the top of the chassic, just under the drive belt path. The more important concern with this particular belt is the sharp pinch it must make as it enters the forward differential assembly. A loosely stretched belt could, conceivably, not make that pinch either jam the entire works, or worse, cut the belt in half. I have to admit that this is not something I've personally experienced, but nonetheless, should be something worth considering in future designs. As of this writing, HPI does not offer a forward belt tensioner for the Racer. They do, however, offer a belt tensioner/gear brace for the middle belt that drives the exterior offset belt assembly. The purpose for this is truly two-fold. It acts as the only easily adjustable belt tensioner avaiable from HPI.  More importantly it acts as a much needed brace for the two drive shafts extending well beyond a structurally sound standard. Why HPI doesn't include this as part of this kit, I will never fully understand. I understand they are trying to keep the price of these kits down, but it seems to me that this is a mandatory part and tops my list as the number one most important hopup for the racer. Failure to install this device, puts an incredible strain on the shafts and bearings that exist, especially when considering that a belt is being driven between the two shafts, thus pulling the two shaft together at a force equal the the driving force of the drive-train.

to be continued....




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This page last modified: 07/26/11