Re-map....40nm torque....is that a lot?

DEBTMONKEY1A

Hi guys-had an eco-remap of my 75bhp corsa 3cdti (& yes the insurance company are aware!)...asked for the map to be for the best economy.

Car drives like a dream now-no flat spots-better pull up hills, more acceleration. Sorry for being dumb-but is an increase of '40 nm torque' a lot? On my receipt it says a 10bhp increase but on looking on some chip sites the 40 nm torgue goes hand in hand with a 25bhp increase?

Sorry guys....just getting confused with the jargon.....!!

Joe_Horner

As a rough guide:

Increased torque will improve "driveability" - including acceleration and ability to pull a higher gear (generally good for economy). It may or may not come with an increase, or even a decrease, in peak RPM. It's entirely possible to increase max torque AND reduce the revs it occurs at, but this will invariably reduce maximum power.

Increased power will improve top-end but not a lot else. It will usually provide an increase in the maximum torque but it will also come with an increase in the RPM that torque is available at. It will also usually reduce the range of engine speed that gives usable torque (so requiring more gear changes).

So, if you remap to increase power, you'll also get a certain increase in torque but driveability will suffer because the usable rev range will be higher and narrower.

If, on the other hand, you specifically remap to maximise torque, you're likely to get much less maximum power increase but you'll usually benefit in real-world driving conditions. It's better to be able to pass someone briskly, without multiple gear changes, and save fuel when cruising, than it is to be able to brag about the 140mph top speed that you can't use cos you just lost your licence

I don't know the Corsa engine well, but Google suggests standard torque is around 240Nm, in which case an increase of 40 is well worthwhile and has probably been done the "right" way for a road car.

DEBTMONKEY1A

Thanks-taht makes it much clearer! So 10BHP & decent tuning for economy can produece an extra 40 nm torque??? It feels so nippy that I thought they'd put 25bhp on instead of 10 (!!!!!!).

Delivery_Driver

Torque(lbft) is roughly 75% of Nm, so you gained 30lbft.It will have been achieved by increasing the boost pressure your turbo is running and increasing fuelling to match.
If you gained that amount on your car I am guessing it will have 150lbft or so as standard?So 30lbft would be a 20% gain in peak torque.As these remaps usually see more boost at lower revs too, you will have parts of the rpm range where there is more than 20% torque than you had previously(say 1k rpm had 80lbft before, it might be 120lbft now so a 50% increase) and its these rpms you'll notice it the most.
The bonus is, as well as making the car faster, you can now use less throttle to achieve the same acceleration as before the remap, saving fuel.Downside is some parts will wear more quickly obviously.

StrangelyBrown

Comparing horsepower (BHP) and torque isn't that straightforward and involves a bit of physics.

It's not like comparing miles and kilometres - torque is a measure of force (specifically a 'turning' force), where as BHP is about power.

It's also not just a single fixed number for your car - it will vary depending on engine speed and there's actually a very narrow range in which the engine produces 'useful' torque. You may have seen 'torque curves' when you were weighing up your remapping options - these would show the torque produced at the varying RPMs.

If you're already bored, stop now, else read on...

Because torque is affected by lengths of the 'lever' applying the force, angles and rotational speed, then you have to get your school textbook out and revisit everyone's 2nd-favourite 'pie': π (the first being 'steak').

So, if you know your torque value (in Nm) and you want to convert it to power (in kilowatts, kW), the formula is:

(TORQUE x 2π x RPM) / 60,000

So if you knew your (remapped) car produced 300 Nm at 5,000 RPM, you'd do:

(300 x 2π x 5,000) / 60,000
= 157 kW of power.

Of course, you want to have power in BHP so you need one more conversion. There's a lot of different definitions for horsepower and it varies by industry (horses weren't a great choice with hindsight) but in general we can just use 1 kW = 1.34 hp

So in the example above, you'd be getting 210 hp.

So now you can plug your before-and-after numbers in and see whether you think a 40Nm increase is a lot, relative to your car's normal performance!

DEBTMONKEY1A

Thanks SO MUCH guys! The re-map is a custom one done well within the safe limit for my car. I'm not a 'boy racer' but do appreciate how much better it drives. It's SO quiet as well-no flat spots. The economy is the next thing....will report back at 500 miles (!).

Joe_Horner

StrangelyBrown wrote: »

The more technical basics

Not to mention the fact that you can increase max torque while reducing max power, if the changes you make shift peak power lower in the rev range. As a general rule, this will give a wider useful torque curve, which is "easier" (and cheaper) for most road use.

Old trick for that used to be to open valve clearances a little to reduce overlap - more low torque but worse breathing, so less power, flat-out.

You could fill a whole library with the theory, not to mention the practical aspects of implementing that theory, and quite a few of the books would contradict each other - especially on the practical side

Which is why I tried to keep to the "very roughly" version

On the face of it, though, it sounds like whoever did the OP's car gave him just what he asked for rather than getting hung up on providing "impressive numbers". Pity all tuning places don't do the same!

Joe_Horner

DEBTMONKEY1A wrote: »

Thanks SO MUCH guys! The re-map is a custom one done well within the safe limit for my car. I'm not a 'boy racer' but do appreciate how much better it drives. It's SO quiet as well-no flat spots. The economy is the next thing....will report back at 500 miles (!).

Look forward to seeing the results. It'll be nice if they confirm that you've got what you wanted rather than what they thought you should have!

DEBTMONKEY1A

Hi! Yup-REALLY nervous about having it done. Seems bizarre that some guy plugs a laptop in-2 hours later a custom map is done..£150-bargain in my book! Won't put name on here cos of no advertising rule but its a place in a northern city starting with B & ending with D (!). Google it with the £150.....(!). For me the torquue makes it feel VERY punchy-I live in the pennines & hills that would have been 1st gear can now be done in 2nd & sometimes third. I'm gonna change oil/filter every 6 months & keep it well maintained.