Thread: Toyota 4.5L TDV8 "Dissapointing" When Towing

When assessing an engine you can't just look at peak power and torque. There's also the number of gears and their ratios. The 76 is a 5-speed manual, and is quite low-geared so it should work pretty well, and it's relatively light at around 2000kg tare, around 200kg lighter than the Pajero.

But a look at the torque curve for the engine relative to others would probably explain a lot about driveability.

Having driven a 76 in deep sand I was very impressed with its ability to just keep lugging in first and second high no matter what. But that doesn't translate to the ability to tow at high speeds.

The 76 makes its max torque of 430Nm @ 1200rpm. The Pajero makes 441 @ 2000rpm. Max power is 150/3500 and 147/3800. Hence, in low speed in sand, I was getting all that 430Nm very easily and loving it. The Paj wouldn't have given me the same torque at that RPM.

But towing at speed up hills is a matter not just of torque, which provides the force to move, but also power which is how quickly that force can be delivered. There is no point a car having 2000Nm of torque at 2rpm, you'll be able to climb walls but at a snail's pace and clearly that's not what you want on a freeway. And if you gear it down so the power (in effect how fast the wheels turn) improves you'll lose torque in the process (big cog turning small cog).

The Pajero delivers slightly better torque 800rpm higher, so when its maximum turning force is achieved the driveline is spinning faster, thus the car can go faster. If the test was conducted again but over very slow going, say towing in sand, I predict a different result in favour of the 76 where it would use less revs for the same effect.

We also need to look at how flat that torque curve is, and how it falls away with increasing RPM in both cases.

Someone write a letter to the editor please ;-)

Originally Posted by rick130

Not if the bottom end is designed to take it.

Regardless if it's an NA engine or uses forced induction, if you are making 700 odd Nm's of torque the rods, crank, bearings, block will need to be designed to take it. ie they will be the same/similar size and design, it's just that the NA engine will be considerably larger overall as the swept volume will have to be huge to produce the same grunt.

It's not the bottom end that going to be the problem, usually anyway. The forces applied to the compression rings and the force for the piston into the cylinder wall/liner and then all the way down it's stoke. Unless the it's got offset gudgeon pins and crank.......