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original post by fly71h on Yahoo 4BT site;

"The primary difference between an on road and off road engine is the function of the governer. The on road engine has what is sometimes referred to as a speed governer, which does exactly what the name implies. It limits the maximum rpm of the engine and nothing else. Actual engine speed (below max) is controlled by the throttle linkage on the injection pump. If the load on the engine increases, rpm will decrease unless the throttle is opened further by some outside influence. In the case of a truck engine, that influence would be the driver's foot. The off road engine has a load governer. It's purpose is to keep the engine at a specified rpm regardless of load. As load increases or decreases, the governer proportionally increases or decreases fuel delivery to maintain the same rpm without any movement of the throttle. What this means is, when your truck with the off road engine in it encounters a hill, it is going to try to go faster all by itself. I'm not saying it won't work, but it will be very "different" to drive, and could potentially be dangerous under certain circumstances.

original post by Bob Sova on Yahoo 4BT site;

"I agree with you and could not have said it better. You have perfectly described a "industrial stationary engine" in a power unit such as a pump or generator. They are designed to run at a fixed speed to prevent cavitations in the pump or to maintain the hertz frequency in a generator. There are however some non-stationary off road diesel engines that could possibly be adapted to function in vehicles. These would be found in wheeled and tracked tractors. These engines are designed to be run at variable throttle position speeds and the governor is designed to increase and maintain the engine speed only as far as the throttle is positioned. The major difficulty in using one of these engines would be emission certification requirements that our duly elected officials have established for our own protection."

The other giveaway is the on road Diesel will have a EPA tag stating approved for on road use

Steve
 

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I am going to add this to the FAQ at the top of the page, make it a "FAQ" thread...
 

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Just to muddy the waters.

All the isuzu engines are fitted with load governors, even the onroad light truck engines.
It is a completely different feel to driving a normal vehicle but makes holding speed on the open road nice and easy. Like cruise control but mechanical.
 
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