Engine - "Where does this thing redline?"

Funnily enough the engine is probably the last thing you need to worry about when building an offroad car. In reality, it's usually the first and everything else is built around it!

There's one thing to be said for offroading. It's rough.
The only way you can win races, is to finish the race.
The easiest way to finish is to drive around at a sedate pace and keep the car together; except you won't win.
The easiest way to to maintain a sedate pace is to put a reliable moderately powered engine in the car.
A moderately powered engine means you won't be shearing flywheel bolts, prop shafts, differentials, half-shafts, stub axles, wheel studs and the like.
This means you might have some chance of finishing.

But enough of this drivel. If you wanted to go slowly, you'd go a ride a bicycle.

13B Extend Port

Our motor selection arose from my experience with a friend's 12A powered RX2, 13B powered RX4 (thanks Gordy!) and my own 13B RX4 and 13B turbo series 4 RX7. I like driving rotaries. They have an amazing power band and pull everywhere from 3000 to 9000 (and upwards) RPM. The great advantage of this is the lack of gear changing. As changing gears takes time, the less gears you change the faster you'll go.

The engine is a 13B extend port, built for us by Formaz. We went the extend port way as we had previously decided that reliability was a higher priority than performance.

It generates about 180HP (134KW) and pulls from about 3500RPM through to our self-imposed red-line of 8000RPM (the engine will keep on going way past this limit, however the MTBF reduces exponentially with every RPM beyond the engine's build limit).

This power is probably a little too much for what the car can handle, in an offroad situation. Because of the inconsistencies in racing surface, the drive-train is subject to stress extremes and as a result you'll start snapping things. The easiest way to avoid this is to cut back on the power. Needless to say, this didn't happen...

When building a rotary, go the new housings. There's nothing more annoying than having an engine expire halfway through a race just because you can't spend the extra bucks at build time. A set of brand new housings is money well spent.

Whilst on the engine side of things, we had a couple of dual belt pulleys spun up for us. We haven't actually lost a belt yet, however the load on the alternator is considerable when the driving lights are powered up. We made the crank pulley a bit smaller than normal, but I'll go into the reasons why in the cooling and electrical sections.

Just be careful if you change the pulley!!! There is a key in the crank-shaft that can drop into the sump (relatively annoying to get out) or worse you can dislocate one of the crank-shaft end-float needle bearings. If you do this and don't notice it (which is entirely possible unless you know it can happen), your crank will grind up the bearing, spit out the pieces and proceed to float around all over the place. This requires removal of the oil pump cover (not a timing cover! Remember rotaries don't have valves and cam-shafts) and replacement of the deceased components. This is not a good job to undertake the night before a race, without the parts!

One last note, rotaries (like other engines) don't like dirt. Offroading is a dirty sport. Ensure that there is no way that dirt can get into the motor. Our engine is presently lacking a decent air box, however due to dirt ingestion reasons we will be building one soon.

Sump Reversal

As part of the installation of the 13B into the Datsun it is necessary to reverse the sump to clear the suspension cross-member. This is a fairly easy job and just requires flipping the thing around, redrilling a couple of holes and shortening the oil pickup (and turning that 180 degrees as well). Just remember to replace all those little pieces of support metal that brace the corners/sides of the sump. Because of the redrilling, some of the sump isn't going to seal as well as the original so it requires the additional support.