Had couple of folks PM me with questions which go like "My car does not seem to be as fast as yours", or I dont know what the petes box does for me, I cannot feel any difference, etc. So before I get accused of making all this up, clarifications are required.
Wanted to explain as best as I can how to get the best out of the Elantra. And some of these tips apply in general to other turbo diesels as well. Anybody with ideas/experience with this, please feel free to chime in.
And I am not sure this is the right place for this info, moderators, please feel free to move this to any place where it fits.
Now, I feel one of the first things you need to see are the curves. Ok, not as interesting as the "other" kind of curves, but still absolutly required if you want to extract the best out of the car. And the curves of the Elantra are below, and it is from the PSI motorsport site -
Standard : 113 HP 83 kW 255 Nm
PSI (RED): 131 HP 96 kW 305 Nm
For people moving from a petrol to a diesel, or even trying to test drive this diesel after having a petrol for daily use, the first thing to understand is, power comes in really early, and ends really early too. To be precise, 1750 - 4250 is the usable rpm range. Compare that to some high performance petrols, where the power band might start after the engine crosses 4000 rpm.
Before we move further, we need a spot of turbo knowledge. Turbos are driven by exhaust gases. And it consists of a turbine, and at the other end of the turbine shaft, a compressor which actually pressurizes the air going into the engine intake. Unlike a super charger, the power output from a turbo engine is not really linear. When the engine is idling, it does not produce enough exhaust gases to spin the turbo fast enough to produce sufficient boost. Two things need to happen before the turbo boost comes on. One, the engine rpm needs to rise so that it produces enough exhaust gases to spin the turbo to its usable boost range, and two, the turbo/compressor has intertia, so it sometimes take couple of seconds to overcome the inertia and gets the turbo spinning fast enough. If the engine rpm is already above 2000, the turbo is spinning fast enough, and if you floor the throttle, it will provide that grin inducing acceleration as the turbo is able to provide max boost almost instantly.
So if you are cruising, and the engine rpm is below 2000 rpm, there will be a slight delay before the car starts accelerating. That is referred to as the turbo lag, and the car will start accelerating fast only after the turbo starts providing sufficient boost, as explained earlier.
Lets look at the other problem. At what rpm do you upshift? The engine idles at around 1100 rpm. And redlines around 4500 rpm. Lets look at the power and torque characterestics. The torque peaks very early, at around 1800 rpm, stays almost flat till 3000, and slowly drops until 3750. And then it is a steep drop down. The bhp starts incresing right from the moment the turbo starts providing boost, and keeps increasing linearly till almost 4000.
The elantra gear box makes it easy to calculate the right upshift rpm. For most upshifts, the engine will drop 1000rpm in the next gear. If you shift up from 3rd to 4th at 4000rpm, once the car is in 4th, the rpm will be 3000.
All this provides for 2 ways of up shifting for the Elantra CRDi.
If you are largely cruising, shift at 3000. The rpm in the higher gear will be around 2000. That leaves the car right at the start of the meaty torque band, and leaves it rightly poised for either cruising, or if required, responsive to throttle inputs as well.
If you want all out acceleration, shift right after 4100. Because anything higher, there would be a sharp drop in bhp, and probably the turbo rpm (that is not the engine rpm) redlines there as well. So if you upshift around 4100, rpm in the higher gear will be just above 3000. Perfect since it gives you the most meaty part of the BHP curve, and leaves enough space in the higher gear to keep accelerating away.
I know I might not have cleared this up fully. If you have doubts, please ask away. Even if I dont know the answers, I am sure there are so many folks here who actually build turbo charged cars, at least they will know the answers.