DHSE Chip vs Gearbox

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T

TCubed

Active Member
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Hello,

I'm just looking for some clarification regarding the effects of a chipped M51 on its gearbox. I've read that should one drive too hard the increased torque can lead to an early demise for the box.
I'm just slightly confused though as to how this works when the standard engine was a presumably more torquey V8? The obvious answer suggests a different gearbox, but I can't find whether that's the case in the info in the manual.

Thanks
 
TCubed you are confusing power and torque ;-)

The V8 makes more power (so is faster) but at higher revs (so no more torque than the diesel)

Cheers

Jerry
 
Torque and BHP are not the same, the V8 has more BHP so is faster. Torque is what breaks gearboxes. A chipped M51 exceeds the ZF4HP22's limit by around 15 to 20%.
The standard diesel is not that slow, it just has a strange throttle response, pedal to the metal and it goes!
 
The thing I still don't quite understand is how the increased torque from the engine maps to the various gears. As in, 4th high will have very little torque while 1st low's will be colossal. Is it therefore just the lower gears (and low range) which are at risk, and if so, are they only so if forced to undergo harsh acceleration?
(I'm a chemist, not a physicist!)
 
OK so I'm no scientist but when thinking about torque and power I find the analogy of a regular door to be the easiest way to get your head around it. In the door analogy you have the hinge (piviot point). The hinge is bolted to the door (we will come back to this in a second) and then there is you. assume that every time you push the door you do so with the same force. Now if you push the door at the handle it open easier than if you push with same force closer to the hinge.

Now if you think of the hinges as the wheels of the car and you are the engine then the door is the gearbox. First gear is out by the handle and as you change up you effectively move towards the hinge.

Now since torque is a measure of how much an object will turn when a force is applied then you must also take into consideration the internal torque characteristics of the engine (since it is a rotating body) but this is where it can get complicated.

I know this is over simplified but I think it helps most people get the idea.
 
BHP = torque x (rpm/5252)

'Power' is the ability to do work over time. More torque at higher revs = more power. If an engine puts out 200 ft lbs of torque, but only revs to 2626 rpm, it will only make 100 BHP. If it is able to maintain this level of torque up to, say, 8000 rpm, it will be developing 305 BHP. What you FEEL shoving you in the back is torque. BHP you cannot feel. The car with the 2626 rpm redline (or torque peak) will pull just as hard as the one that keeps going to 8000 rpm, but the 8000 rpm car will be FASTER - not because it pulls harder, but because it pulls LONGER. This is why diesels tend to feel like they are pulling harder than petrols - because they are. They are naturally more 'torquey'. But they dont pull for very long, and therefore don't develop as much power which is why they are, in fact, slower, in the main.

This is how a bike with a 1000cc engine can develop over 200 BHP.
 
Last edited:
with the auto boxes ,the weakness isnt overall torque load ,but the sharpness during gear change ,its allways been problem with lrs diesel autos
 
Best I get my slippy-jumpy 3rd-4th-3rd change sorted out then, before it breaks my gearbox! Know much about auto boxes, James, 'cos I'm clueless with them?
 
jt_armstrong said:
Now since torque is a measure of how much an object will turn when a force is applied then you must also take into consideration the internal torque characteristics of the engine (since it is a rotating body) but this is where it can get complicated.

I know this is over simplified but I think it helps most people get the idea.
Click to expand...

I love the door analogy - it's great! But torque is not a measure of how much something will turn with a given force.... torque is in fact just a rotational measure of force. If there is no movement, then you can have huge torque with no power. Power is required to move the object (accelerate it or overcome some resistance to movement, or usually both), torque cannot move anything without power (=energy over time).


HTH ;-)

Cheers

Jerry
 
mcapinha said:
Correct me if I'm wrong, but isn't the ZF4HP22 rated up to 380Nm, the same as the R380 manual box ? I've done a quick search on the interwebs and there are some posts agreeing with this. I then took a look at a remapped 2.5 DSE max torque and it was around 340Nm...
http://www.tecnauto.com/images/testes/RangeRover25dse_chip.pdf
Click to expand...

If that power curve is real, I want one of those chips.....

Has anybody ever had a chipped 2.5DT P38 on a dyno, ideally with before and after runs?

Cheers,

Jerry
 
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