Thread: Series Gearbox

Originally Posted by JDNSW

I suggest most UK owners have swbs, where most Australian owners have lwbs?

The gear ratio is the same so is it just the extra load you feel is an issue with a LWB ?

Interestingly the Isuzu C240 conversions by Dellow in Sydney were almost always in LWB's. This was probably due to the need to fit something for economical outback travel.
I remember Fred Smith telling me that my shorty should 'fly' which, relatively speaking, it does.
The motor in mine was from a LWB originally.


Colin

Originally Posted by gromit

The gear ratio is the same so is it just the extra load you feel is an issue with a LWB ?

...


Colin

The 109 has an empty weight about 150kg more than the 88, and a payload about 450kg more, for a total of 600kg more or, to put it in perspective, about 25% more than the 88 GVM. Perhaps more important, it has about twice the load area, giving much more scope for overloading. And the 109 is 10cm higher, adding 5% to the frontal area and hence aerodynamic drag.

So it is mostly the extra load, although I am surprised that the 109 is only about 150kg higher empty weight than the 88.

A secondary effect is that the standard tyre diameter on the 109 is 31", where the standard on the 88 is 28", although these days it is usually at least 29", meaning that the 109 is effectively about 6% higher geared due to the tyres. (of course if you use 7.50 tyres on the 88, then there is no difference)

Originally Posted by JDNSW

A secondary effect is that the standard tyre diameter on the 109 is 31", where the standard on the 88 is 28", although these days it is usually at least 29", meaning that the 109 is effectively about 6% higher geared due to the tyres. (of course if you use 7.50 tyres on the 88, then there is no difference)

My Isuzu powered shorty is running 7.50 x 16's and the HRTB isn't a problem so, potentially, it's only the weight difference in a LWB.

Colin

Yes, but the torque and power curves of the Isuzu are, I suspect, significantly different from either the petrol or diesel Rover engines. One of the key features of the Rover engine is its ability (even the diesel) to operate at high rpm (4,000rpm) without distress.

Originally Posted by JDNSW

Yes, but the torque and power curves of the Isuzu are, I suspect, significantly different from either the petrol or diesel Rover engines. One of the key features of the Rover engine is its ability (even the diesel) to operate at high rpm (4,000rpm) without distress.

Seems the C240 gives 54Kw at 3,800 rpm. There are a number of variants of this motor, the ones fitted by Dellow were from the Elf truck.
Isuzu Elf - Wikipedia


Colin

One of the problems with this sort of discussion is that typically, all the figures we can get on an engine are the peak power and torque figures and what rpm they are at. The problem with this is that the driveability depends also on the shape of the curve, in other words, how sharp is the peak. And even where we have these curves, it is almost impossible to guess how different engines compare.

If you take the Rover engines, the petrol one has peak power at 4250 and peak torque at 2500, the diesel at 4,000 and 1750.

Since power is the product of torque and rpm, power increases with rpm from peak torque until the fall off in torque exceeds the increase in rpm, although for many diesels, the governed maximum rpm also represents the maximum power. For a petrol engine, the torque usually drops off due to breathing restrictions, so there is no definite maximum rpm unless this is imposed by valve bounce or ignition issues.

In the case of the Isuzu diesel in Colin's Landrover, the fact that the peak power is at 450 rpm or about 10% lower than the petrol engine suggests that it would benefit from higher gearing, especially since (with standard gearing) the maximum rpm is probably easily reached at a road speed that needs less than the maximum available power.

I hope this lot makes sense!

Hi.
Thanks for the comments on the Ashcroft Kit.
I have to remove the Dreaded Output Shaft bearing.
Any one found an easy way to remove it ????
Have done one before using the Book, cold chisel method, but there must be an easier way ????

whitehillbilly

Originally Posted by JDNSW

One of the problems with this sort of discussion is that typically, all the figures we can get on an engine are the peak power and torque figures and what rpm they are at. The problem with this is that the driveability depends also on the shape of the curve, in other words, how sharp is the peak. And even where we have these curves, it is almost impossible to guess how different engines compare.

If you take the Rover engines, the petrol one has peak power at 4250 and peak torque at 2500, the diesel at 4,000 and 1750.

Since power is the product of torque and rpm, power increases with rpm from peak torque until the fall off in torque exceeds the increase in rpm, although for many diesels, the governed maximum rpm also represents the maximum power. For a petrol engine, the torque usually drops off due to breathing restrictions, so there is no definite maximum rpm unless this is imposed by valve bounce or ignition issues.

In the case of the Isuzu diesel in Colin's Landrover, the fact that the peak power is at 450 rpm or about 10% lower than the petrol engine suggests that it would benefit from higher gearing, especially since (with standard gearing) the maximum rpm is probably easily reached at a road speed that needs less than the maximum available power.

I hope this lot makes sense!

John,
I understand the theory but would like to hear from someone with a HRTB fitted to a LWB to get 'real life' feedback as I don't think it would be as problematic as you suggest.


Regards,

Colin