[nukeblitz]

Hello, I own a Tata Indica Vista and I've been trying to find the graph for the Torque curve so that I can finetune my gearshifts for maximum acceleration. I've looked around quite a bit but I haven't found one yet.

The TDi engine on my car makes max torque of 135 Nm at 2500 rpm. So, I've been trying to keep the tacho around that value. Problem is that turbocharged diesels usually make their max torque very early of around 2000 rpm or even before and have a flatter curve. I have no idea where 2000 falls on the curve. Not to mention the fact that turbocharged engines usually mess up the usual theoretical calculations you can do.

The gear ratios on my car are
3.42 : 1.95 : 1.13 : 0.74 : 0.636
Reverse is 3.58

My current shifts are at 3250. 3250. 3000 and 2750. Would appreciate it if someone could post the graph or point me to a website. Any advice would be appreciated too...

PS - Does someone know the differential ratio for the car?

[greenhorn]

3k rpmisa bit too high. You might wear out the clutch too soon.
Try shifting a bit earlier, about 2500

[nukeblitz]

Thanks but I know that. I shift at round 2000 rpm during day to day driving. Or at a maximum of 2500 rpm when I overtake. I'm trying to figure out how to get all the 71 horses and 135 Nm of torque outta my car if I wanted to....

PS the 4th gear is 0.78

[nukeblitz]

So, I looked around a LOT for the torque/power graph for my engine and couldn't find one.

And, I don't really have the resources to take my car to a dyno.

So, I decided to make one myself. I started with the values given in the manual.
70PS @ 4500 rpm and
135Nm @ 2500 rpm

I can calculate both the torque at 4500 rpm and the power at 2500 rpm

Also, from experience, I know that the turbo kicks in at round 1600 rpm and reaches it's peak at round 2000 rpm. I made the assumption that I could use values from the non-turbo 475IDI engine on the old indica for a fair estimate of how the curve would be before 1600 rpm. Also, the engine loses breath around 4700-4800 rpm.

Armed with this mix of facts and presumptions, I went ahead and made a spreadsheet on Google Docs. I'll upload it in excel format here. I'd like feedback from anyone who either has the dyno graph or has a better idea of now this works.... thanks

P.S. All values are in SI units (i.e. kW for power and Nm for Torque). This means that the formula Power (hp) = (Torque (lb-ft) * rpm)/ 5252 will not work without the suitable unit conversion and hence the power and torque lines will not cross at 5252 rpm.

P.S 2. You will notice from the images that on the Geared Torque and Geared power graphs, the rpm is that of a (hypothetical) first gear. You'll have to use the first sheet to calculate which rpm you'll be at in different gears

P.S 3. You may also notice that on the same graphs mentioned above, the third, fouth and fifth gears are sort of blocky. This is because I calculated the Torque at every 100 rpm and on those graphs, the rpm interval in fourth gear is much lesser than 100 rpm... I don't have time to correct this. i would appreciate it if someone else could do so...

P.S 4. The best gearshifts I have calculated from this are at 4800, 4800, 4750 and 4650.

P.S 5. As greenhorn pointed out, this would wear out the clutch plate. So, no, I do not do this in day to day driving and would not recommend doing it to anyone else either.

P.S 6 Oh, and if you do end up in a drag or are trying to get the best 0-100 times etc, you'd want to powershift which will put even more strain on the transmission and the clutch plate. Not to mention the fact that the 475IDI engine was probably not designed for that kind of operation by any stretch of imagination - it's a tata diesel for crying out loud....

P.S 7 Oh, and I'd probably be able to calculate the speeds at which you shift but I don't have the final drive ratio for the TA65 gearbox on the Indica Vista. It's mentioned in the Indica V2 turbo manual as 4.4 (175/70 R13) and in the indigo diesel manual as 4.64 (175/65 R14) but is curiously omitted in the Vista's manual.... I'd appreciate it if someone can tell me what this value is...