2003 Arctic Cat Firecat F7 EFI

Our first look at a totally new engine design shows great potential
RELATED TOPICS: ARCTIC CAT | SNOWMOBILES | ENGINES
It has been a long time since we've seen a completely new two-stroke engine concept come out of the factories. We have seen new twins, new triples, new orientation and even a handful of new four-strokers, but nothing that actually changed the way the engine is designed.

Arctic Cat engine guru Greg Spaulding and his design team have brought us something totally new for 2003: the laydown engine. This is more than just an engine tilted forward or backward. It's an engine with the intake and exhaust coming through the same side. Cool, eh?

Air enters through the slits in the hood and travels through a trap before it enters the new airbox. It does its thing in the combustion chamber, is spit back out on the front side of the cylinder and exits through a tuned pipe that snakes up over the engine and out a muffler on the right side.
History Lesson
The laydown motor actually started with the 440 race engine. "One of the main challenges we had was how to get a motor that is lower and moved to a more central location," Spaulding explained. "We decided to lay the motor back.

"Once that was decided, we went about designing the engine to lay in the chassis the way we wanted to," he continued. "We actually made three protos in the process. We took a standard case, and we cut and we welded and we puttied. We had reed cages in a number of locations. Once we decided on a rough placement and concept for the motor, we sent it to be prototyped with Suzuki."

The 700 EFI engine uses a completely different case and stroke than the 440 and 500 motors. The bigger mill has a 70mm stroke, over the 63mm on the others. Its Nicasil cylinders have triple exhaust ports to help it breathe freely.

Cooling is Key
"If you're talking about making one or two motors, even four or five, it isn't that difficult to make this kind of horsepower from a 700, especially in the aftermarket," said Spaulding. "But when you get into a full production standpoint, you have so many other factors that enter into it. One way to get the kind of power we wanted out of the engine is to maintain the heat in the combustion chamber.

"What we decided to do was to reverse the conventional water cooling routing. On the laydown engines, we take the cool extrusion water and send it into the cylinder head first, so it cools the combustion chamber more so than the hotter water going up there last. That allowed us to use a broader range of ignition timing values for peak power and fuel combinations. That is one big change in the laydown motor."

To avoid cold seizures, the new engines use a positive water bypass thermostat system. When you start it up, the water only circulates through the head, the cylinder, back into the pump, back through the hose and back into the head. It's a very small amount of water circulating. There is only a little amount of water that leaks through a very small bypass hole in the system. Once it reaches operating temperature, the thermostat bypass opens up and sends water through the extrusion system.
On the Dyno
Since this is such a new engine, we had to work a little magic in order to get the test done. While we normally use Dynoport's facilities, we were forced to turn to the factory for a helping hand. When the F7's actually roll off the assembly line, we'll put one of those on the Dynoport bench as well.

Our factory dyno test of a final-stage preproduction motor showed the new 698cc laydown twin runs just as strong at the top end as the 800 standard motor, but with a longer, broader powerband. While it doesn't match the bigger sled's numbers all the way up, our seat of the pants testing showed that the Firecat's significantly lower weight allows it to get up and go much quicker than the traditional ZRs.

At 140.1 factory horsepower, the F7 EFI will certainly be the toughest 700 single pipe engine we've ever seen, if it comes off the production line in the same shape. Time will tell, but we've got a good feeling about this one.
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