Product Evaluation SIMON SMART BOY Bolt-on performance for the Polaris RZR

q OK, fuel injection has been around long enough that we’re not scared anymore. We’re ready to look to it for real performance, not just lightweight remapping of the air/fuel ratio. Dave Simon was thinking the same way when he came up with the Simon Smart Body, which is the EFI equivalent of a new carburetor for the Polaris RZR. The Smart Body replaces the stock Keihin throttle body and offers more flow, better atomization and more performance.


The carburetor had actually evolved into a very sophisticated instrument before it was declared obsolete. What arrived in its place was the throttle body—very crude by comparison—which was deliberately made to save cost. The real technology of fuel injection is in the programming that tells the injectors how much fuel to spray. That information is attained through the use of a number of sensors and so on. But, the throttle body itself is no more sophisticated than a carb dating back to the ’30s. The most glaring evidence of that is the butterfly valve that regulates air flow.

The Smart Body is a billet throttle body that uses a guillotine valve instead of the butterfly. There are several advantages here, the most obvious is the total elimination of a very big obstruction in the venturi (there’s no more flap in the middle of things). No matter how flat that butterfly valve opens, it’s still there. There are other factors, too. A guillotine can regulate air flow much more precisely because it increases flow in a more linear fashion, whereas the butterfly allows air to flow around both sides, creating aerodynamic chaos on the other side of the valve. And with most systems, fuel is only sprayed from the top side of the butterfly—very sloppy.

Simon first developed the Smart Body for 450 motocross motors, but soon discovered that the Polaris RZR was a more natural application. With the RZR’s system, the injectors are located in the intake port rather than in the throttle body. He discovered that the best atomization occurred when the guillotine opened from top to bottom, because that’s where the injectors were located and that gave the air/fuel charge a direct shot to the intake valves. He developed the system to work with the Bazzaz fuel controller, but it will work with the stock fuel mapping or with any of the controllers on the market. As with most EPA-approved machines, the RZR is very lean in stock configuration, so there’s some performance to be gained with just a controller. That does, however, render the RZR non-compliant for emissions.


We got a chance to ride an 800 RZR in both stock and modified form back to back. In stock form, the RZR works well but is very mild-mannered. As far as the fuel delivery is concerned, it’s obvious that the machine is somewhat lean, but that doesn’t result in anything terrible. After a loop around the Anza Borrego OHV area, we took apart the RZR and installed the Smart Body with a Bazzaz controller. The process took less than an hour.

The difference was obvious as soon as we started moving. The mild-mannered RZR came to life. The difference was especially noticeable at the very bottom when you first open the throttle. Instead of slowly building revs, the Polaris barks. Then, it builds up to a strong mid-range before the rev limiter kicks in. On top, the top speed doesn’t change; that’s regulated by the spark advance. But with the Smart Body, it sure gets there faster. The performance gain is similar to what you might expect from a full-race exhaust system.

When you’re in rock-crawling mode, the RZR’s more sudden throttle response means you have to pay attention. The power delivery is more abrupt than that of a stocker—but that’s what comes with increased performance. You also have to deal with stiffer spring tension on the pedal, but you get used to it fast.

The Simon Smart Body impressed us and demonstrated that there are other paths to performance. The price is actually less than that of a high-end exhaust. The product sells for $595, and if you get the Bazzaz fuel controller at the same time, the total is $750. For more information, you can contact United Parts Distributing at (602) 353-1300. q
Traditional throttle bodies have a very obvious obstruction standing in the way of performance: the ancient and crude butterfly valve.
Dave Simon installed the Smart Body while we waited; it took him less than an hour.
The Simon Smart Body is a bolt-on performance modification for the Polaris RZR that provides similar results to a full-race exhaust system. Other applications are on the way.

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