It's is very interesting the 5th to 6th gear conversion kit
Index | Eurotuning s.r.o.
1180€ + shipping + several workshop hours it seems very much compared with
337€ + workshop time on the 5th swap.
I did some fast calculation (my engine has Bosch VE rotary pump VP37, it's not a PD, cd lowered from 0.31 to 0.25) and 0.588 to 0.622 F.E. figures differences at constant speed are about -0.1 to -0.2 L/100km (best results in my car in mid range because of VGT) saving 0.1 L/100 kms at 90 km/h or at 180 km/h it'not very useful as an improvement.
Improvement of getting taller ratio
(0.769/0.588)*(44.5 km/h)/1000 rpm = 58.2 km/h looks very good and Seat Ibiza/Cordoba PD 131 Sport, Fabia Vrs <2004, Polo GT PD130 used to have 59 to 62 km/h/1000 rpm 6th gear ratio in firts versions (lasted with 50 to 54 km/h/1000rpm, so if you have lots of BHP it is very good to know and far easier than changing lots of things (inside or outside de gearbox, included or not).
But talking about my car, almost the same car as yours. Using Matlab i get this figures.
Comparing 0.622 (or 0.625) with standard 0.769 it's a very good improvement as an additional 6th gear, but not as a swap becasue of big gap on rpm. It saves 0.6 L/100kms at 90 km/h, 1 L/100kms at 120 kmh and 2.7 L/100kmh at 180 kph.
Swapping 0.681 (cd 0.25) into 0.769 (cd 0.31) gear will give to me with my current drags and improvement of -0.5L/100 kms at 90 kph, -0.7 L/100km at 120 kmh and
-2.14 L/100 km at 180 kmh.
I discarded 0.658 swap because at constant speed differences where 0.05 L/100km at low speeds between 0.681.
In Spain max speed is 120 kph (130 kph in project) so german Auutobahn drivers or very tuned 1.9 engines will notice a big improvement in fuel economy, top speed (if lowered drag it will be big improvement) and drivebaility
PD with more than 131 bhp also have 6 speed gearboxes.
But it is a very good alternative to full 6th gearbox swap as explained in spanish here
Instalación de la caja de cambio de 6 Velocidades en motores TDI 110cv o 90cv | www.fullcustom.es
that will cost almost 1200€ + workshiop time (1500$ on junk yard/ some news parts + workshop cost) or far more if using a refurbished gearbox or new one.
Click on the following almost white thumbs to get big images:
LEFT: Fuel Economy (in L/100km/h) at Full Load and at constant speed (in km/h), standard car vs aeromoded and 5th swap. Theoretical (but fuel consumption in standard car at ctt speed it is predicted +-1% error). Using BSFC map to convert torque in fuel mas per kilowatthour and diesel specs and data. RIGHT: efficiency at ctt speed no units 0 to 1 (not g/kWh, or us, uk units, 0 means 0% -fuel energy converted in heat- and 1 means 100% - fuel energy converted in work-)
Theoretical Power (in W,). at Full Load and at constant speed (in km/h), standard car vs aeromoded and 5th swap. Remmeber 1 kW = 1.36 bhp, so 81000 W are 110 bhp.