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    A4 3.0tdi vs S4 gear ratios

    Hello, I was wondering about the actual theoretical performance difference between the diesel and petrol performance cars. In order to figure out the actual acceleration, one is required to also know the gear ratios. I have been assuming that the diesel has taller gearing in order to deal with the lower engine rpm limit. In that case, the higher torque figure for the diesel will be counteracted by the taller gearing.

    One can try to do a theoretical computation by assuming that both cars require shifting gears at the same speeds. For example, assume that the gearing in each car is optimised to attain 100kph as quickly as possible (for marketing purposes), i.e., each shifts the same gear right after 100kph.

    Since the A4 redline is approximately 5000 and the S4 is approximately 7000, this would imply that the TDI gearing is approximately 7/5 compared to the S4. Now the torque figures are 500Nm (1400-3250) for the A4 and 440Nm (2900-5300) for the S4. Assuming the gear ratios are as above, this would mean that the A4 would put 5/7 of its torque to the rear wheels compared to the S4, in particular, the effective torque of the A4 would be approximately 357Nm from 2900-3250 compared to the 440 of the S4, so about 81% the force to the rear wheels as compared to the S4. In this case, one sees that the S4 accelerates 20% more starting at 2900rpms.

    So an engine remap yielding 20% more torque to a supposedly impressive 600Nm, e.g., Sportec - Leistungsstufe 1 - 3.0 TDI 210kW (285 PS) MKB: CCW will simply allow the TDI to have equal acceleration to the S4 at 3000rpm.

    I have not been able to find the exact gear ratios of these two cars. If they are the same, then the diesel will accelerate faster at the same engine speed up till about 3250rpm's in first gear. Since the diesel has to change gears earlier, it will have to be in a taller gear compared to the S4 and will similarly be handicapped as above until the S4 has to change gears as well.

    My conclusion is that the diesel should pretty much always accelerate slower than the petrol engine simply due to lower rpm range.

    -ilan
    Last edited by Ilan; 11th April 2012 at 09:21.

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