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Petrol vs Diesel @ Same BHP. Result = ?

Discussion in 'A3/S3/Sportback (8P Chassis)' started by emzino, Jul 30, 2007.

  1. emzino
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    emzino Active Member

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    I didn't know how to title this thread properly but hopefully this should explain it:

    Car A (FWD): Petrol, 1.8T @ 180bhp (stock)
    Car B (FWD): Diesel, 2.0TDI @ 140bhp mapped to 180bhp (everything else is stock)

    Which is more likely to win:

    a) Off the lights.
    b) Rolling.

    Now I know a Diesel is going to have much more Torque so would this make it faster in both scenarios?
    If so, how much more BHP does Car A need, to have the equivalent performance of Car B...?
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  2. Matt
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    Matt Active Member

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    At a guess I'd say the diesel would be faster from a rolling start as cos of the torque. But standing start not a clue, diesel probably needs more gearchanges to say, 60. Dont really know though.
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  3. Phil's Barber
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    Phil's Barber Top Gear

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    The diesel will also be heavier. My feeling is that petrol probably quicker to 30ish then the diesel will catch up. From a rolling start, diesel every time. This is based on nothing other than experience BTW.
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  4. marklad2020
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    marklad2020 1st Gear

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    Work Done = BHP X Torque. So if you know the torque figures of both cars then you can calculate what BHP figure you need to get the same Work Done figure.

    But as identified, there are other factors which affect the real world performance. Diesel engines are heavier which might blunt performance, but might also help traction of the front wheels off the line.
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  5. KRL
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    KRL Member

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    Remember the larger power band of the petrol should be taken into account as well. The Diesel will have run out of BHP by 4-4.5k rpm where the petrol will probably go on to 6-7k rpm. Main difference this will make is less gear changes will be required on the petrol. So the petrol would probably be quicker from the standing start and (as already said) the diesel will be quicker from the rolling start.
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  6. ManicMunky
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    ManicMunky Member

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    but if the diesel is mapped (like it says) then the powerband will be extended. still not as high as the petrol, but should pull hard to the red line.
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  7. KRL
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    KRL Member

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  8. Amchlolor
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    Amchlolor Active Member

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    I'm in a position to compare diesel v petrol for the same(ish) bhp quite often.
    I have a 140bhp diesel sportback,my colleague has a 150bhp Fsi 3 door.
    There is next to zero difference in straightline performance.
    Honestly,nothing at all.
    That's both cars,flat out from rest down a dual carriageway that enables speeds of up to around 110mph before you have to brake for a roundabout.
    (closed,private dual carriageway,of course).
    The difference comes once you get to the twisty bits.
    Anything that involves punching out of slow speed corners from low revs and the diesel pulls out a lead that the petrol cannot make up.
    The diesel is actually the easier car to drive in the twisty road scenario too,because gear selection isn't as important.
    Of course,this is comparing a turbo car with a non-turbo car.
    If both engines were turbo'd,the diesel's torque advantage at low revs would be negated,so it would probably just be a dead heat.
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  9. Phil's Barber
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    Phil's Barber Top Gear

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    There's one point your missing through the twisty bits though, on the edge, the diesel is far more likely to under-steer due to the extra weight over the front wheels, assuming of course both drivers have the same level of skill, throttle control, balls etc.
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  10. Detector
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    Detector Just waiting for the green light

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    I wonder how much heavier the diesel is compared to petrol, they're both alloy construction after all.
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  11. Macduff
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    Macduff Member

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    According to the Audi site a 2.0 TFSI is actually 90kg heavier than a 2.0TDI 170 (both A3 3dr).

    Just checked A4 weights and for same engines, the diesel is 25kg heavier. I think that's probably the correct weight difference.
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  12. ManicMunky
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    ManicMunky Member

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    so it's like having a 14 stone-ish passenger?
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  13. Detector
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    Detector Just waiting for the green light

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    A full tank of fuel or a passenger would make quite a difference, when I sprint my car I take everything out that's not needed, spare wheel, passenger seat, tool kit, empty the ashtray etc. etc.
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  14. Amchlolor
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    Amchlolor Active Member

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    I'm pretty confident that,all things being equal,a diesel with the same power/weight as a petrol will perform in a similar manner.
    If there are differences,they'll be so small as to not matter.
    The diesel will always give the better mileage at the same time though,surely ?
    So if you can get a diesel to perform the same as a petrol,but with better mileage,then why bother with a petrol ?
    It will just come down to personal preferences about noise etc.
    I remember an Autocar test of the Alpina BMW D3 (320 diesel,tuned by Alpina to 200bhp) and the bloke's summary was something along the lines of "honestly,if you can get a diesel this good,why bother with petrol".
    It's probably only a matter of time until supercars are fitted with diesel engines too.
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  15. Shades
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    Shades Member

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    :lmfao:
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  16. steve184
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    steve184 Active Member

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    nah i think hydrogen fuel cell vehicles will kick off in the nect couple of years and that will start to kill petrol and diesel engines in cars altogether - development in diesel technology and petrol technology will slow down in favour of fuel cell technology
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  17. emzino
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    emzino Active Member

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    Hydrogen fuel cell? Think that's stretching abit there Steve :think:

    Here's what I think:

    Petrol > evolve into the use of TSI technology

    Diesel > particle filters will be perfected. economy will continue to rise even with increases in engine size and power

    Hybrids > become more affordable but still be outnumbered in sales
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  18. ManicMunky
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    ManicMunky Member

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    well manufactorers are moving from larger N/A engines to smaller turbo-charged ones giving the same or increased power, more torque, with better economy and emissions, all combined with the greater control of direct injection.

    Autocar stated that VW are experimenting with hybrid petrol/diesel engines. apparently.
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  19. Amchlolor
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    Amchlolor Active Member

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    This is why VAG's 1.4Tfsi has always puzzled me.
    It seems to be all very clever.
    It gives the power and torque of a larger engine.
    However,it still has the emissions of a larger engine too....
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  20. mfspen
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    mfspen Member

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    Aren't you thinking of the VW 1.4 TSI (twincharger) engine ?

    The recently announced 1.4 TFSI is a standard turbo engine (developed from the 2.0 TFSI) and has quite reasonable (for petrol) emissions of 154g/km.
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  21. steve184
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    steve184 Active Member

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    no not at all - they have been playing with fuel cells for years now - and now know it is the 'only' viable way of going forward. Within the next 5 years or so i reckon they will start popping up - and at this point petrol and diesel development will reduce significantly
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  22. Macduff
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    Macduff Member

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    And none of the character. We had a Bora V5 and it really was a lovely engine. OK, you couldn't get much more power from it but it was so flexible and had a lovely sound. You won't get that from an anonymous inline 4.
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  23. Amchlolor
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    Amchlolor Active Member

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    It was the one with the supercharger/turbo I meant,yes.
    It's Co2 emissions aren't good at all.
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  24. Detector
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    Detector Just waiting for the green light

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    Didn't Alan McNish drive a diesel at the LeMans 24hr quite successfuly :respekt:

    The Audi R10 is a racing car prepared for sports car racing in the LMP1 class of the 24 Hours of Le Mans and other similar endurance races. The car was unveiled Tuesday, December 13, 2005 and went on to win both its maiden race at the 2006 12 Hours of Sebring and the 2006 24 Hours of Le Mans. It was the first diesel powered car to win either of those events. This is the most ambitious and the most expensive project ever undertaken by Audi Motorsport; the Audi R10 project costs Audi $15 Million a year.

    BUT THEY CAN'T CURE THE TRACTOR SOUND:motz:
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  25. si_reading
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    si_reading Member

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