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Protecting drivetrain when mapping. Where don't you want torque?


Jono

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Hi,

 

I have seen it mentioned a few times that to protect the drivetrain you want to avoid torque low down in the rev range, but nobody has provided any good sources or sound engineering rationale for this info.

 

Is it just a widely propagated myth?

 

 

 

Is a torque value of X more harmful at 2000rpm than it is at 4000rpm?

 

Does it really matter if it comes in early or later in the rev range?

 

 

 A big blat of torque, (like the old PD engines) feels harsh to the flimsy human in the passenger seat, but does it really matter mechanically? Is it all about the peak torque rather than the rate of increase to get there.

 

Do components genuinely care if it takes half a second to go from 100-500Nm, rather than three seconds?

 

 

As an aside - what happens when you try to keep the torque up at higher revs on a turbocharged engine - Even if you are requesting max output from the turbo, does the boost pressure drop as the engine is gobbling more air?

 

Is this easier on the turbo than requesting a big boost pressure at low/mid revs?

 

How kind/hard on a diesel engine is keeping it pulling up to it's redline, rather than it tailing off at 75% revs?

 

 

 

Finally - DSGs - is there a more sympathetic way to map the engine to care for them? or is it all just peak torque that matters?

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  • 1 year later...

Surprised you got no answers, which is a shame as I'm interested in the answers to same questions! I suspect that your DMF is interested in the rate of climb of torque, and not the peak value. The question is the analysis of the difference in static strength vs dynamic load conditions wrt to durability of components. I'm reasonably confident that it doesn't matter what engine speed max torque occurs at, it's a max loading that will either break your engine or won't, unless things like coolant flow, oil pressure and temperature variation have an influence, and if they change sufficiently  significantly at different engine speeds. I'm sure the engine manufacturers have tested all of this and worked out their own proprietary target profiles 

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  • 2 months later...

Going to have a go at resurrecting this.

Can confirm from an engineering point of view that a big lump of torque shock loads the system causing thing to fatigue and eventually fail earlier than a similar setup with a smoother delivery. How measurable that is will we down to stats and big numbers that my head can't handle on a Monday evening.

It also puts a shock load through the clutch which will potentially cause slip therefore additional wear.

 

As for torque low down I would guess that if a smooth delivery then it shouldn't matter how fast the engine is rotating. Car speed will have a greater effect. A large dose of torque will damage the car more at a higher car speed due to the increased gearing. And it takes more force to accelerate at higher speeds (not 100% on this one. A check of numbers would again be required).

 

Diesel engine naturally like to stay at one speed and adjust the load via additional fuel.  The ideal 'box for a diesel car would be a CVT but these are difficult to get right.

 

As far as dsg go, I'm in the market for a dsg remap so I'll let you know.

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When I looked at mapping our FIAT JTD most tuning companies could easily get more out of it than the clutch could take. Tuned, they were particularly vunerable to clutch slip in 3rd & 4th gears ( I'm pretty sure the factory ecu was already boost limited in 1st and 2nd for the same reason).

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The rate of rise of torque is largely irrelevant. If you increase torture massively at very low revs, you may be subjecting the bottom end and gearbox to higher than design load at lower hydrodynamically lubricated speeds. In other words, low rotation speed may allow oil film in the gearbox and bottom end to fail.

 

If you run a turbo too hard, to maintain boost at higher revs, you get more heat from the compressor and it may go pop earlier than expected.

 

Limiting torque in lower gears helps protect the diff and driveshafts.

Edited by Chris GB
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Isn't this why diesel owners have DMF failures with or without remaps? Stamping on the power in high gears and loading up the gearbox and clutch at lower revs must be a recipe for premature wear unless the components are beefed up or designed to handle it. 

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DMF only really does anything with the firing pulses at low revs. Big torque can kill them quickly. "Two footing" (biting point and foot brake together) is possibly the quickest way to kill one.

Edited by Chris GB
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  • 4 weeks later...

Your drivetrain and greabox will take the increases in bhp and torque from a remap unless you have a high mileage engine already. The clutch is probably the weakest link.  And is also a part you can uprate when it starts to fail. it is a consumable as far as servicing goes.

You won't be constantly using the  extra power anyway  due to speed limits and corners and the  inevitable traffic jams. More torque at lower revs will mean you can stay longer in higher gears  rather than changing down so that should save you fuel.

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