Group buy / order: 0.65 / 0.643 5th for TDI
- Thread starter bretti_kivi
- Start date
the grim reeper
A2OC Donor
Hey Mike you said on the phone about it spinning the wheels, is there a lock on the box to stop this from happening or is it just put a wedge of some sort under the wheel???
Cheers Phil
Cheers Phil
Skipton01
Admin Team
No time this weekend Dan - service tomorrow and then prepare for Monday, as well as give a little time to Ang!
I would have liked to get it all done and dusted too - a 400 mile run would have been great info on how the gearing would suit others, but best laid plans and all that!!
Phil, yes, it was spinning the wheels, when I used the breaker bar, but a foot on the brakes, or a pusher would do the trick. I'm going to try using an electric impact wrench next week when I've got the correct spline bit.
This should stop the spinning.
Cheers,
Mike
I would have liked to get it all done and dusted too - a 400 mile run would have been great info on how the gearing would suit others, but best laid plans and all that!!
Phil, yes, it was spinning the wheels, when I used the breaker bar, but a foot on the brakes, or a pusher would do the trick. I'm going to try using an electric impact wrench next week when I've got the correct spline bit.
This should stop the spinning.
Cheers,
Mike
Disapointing
, however like you Mike when i was in the habit of doing major works on my Audis etc had similar problems. Remember setting out to replace valve stem seals and the cyl head bolts were different to those in the manual..... Hopefully will all go smoothly when you get chance next week. Looking forward to feedback and getting mine underway!
, however like you Mike when i was in the habit of doing major works on my Audis etc had similar problems. Remember setting out to replace valve stem seals and the cyl head bolts were different to those in the manual..... Hopefully will all go smoothly when you get chance next week. Looking forward to feedback and getting mine underway!Driveability will be the most interesting feedback for me. Maybe now with you car 'standard' you can record rough times for, 40-60mph / 50-70mph in 5th. Then repeat with the new gear.
I think the economy test will have to be conducted over a longer period than a single journey. I've been seeing 10% variation in economy over the same journey these past few weeks alone.
I think the economy test will have to be conducted over a longer period than a single journey. I've been seeing 10% variation in economy over the same journey these past few weeks alone.
I'm not sure just how much economy will improve due to the higher gearing.
Take legal motorway cruising for example. According to Audi, a standard TDi requires 75 hp to reach 108mph (flat road, no headwind) As power is proportional to speed cubed, it only needs 20 hp to do 70 mph. The car still needs 20 hp to maintain 70 mph but the higher gearing will reduce the engine rpm. The only improvement in economy will therefore be from reduced engine friction losses and with a little luck, the engine will be operating in a more efficient zone on the part load fuel consumption curves.
I'd guess a 2 or 3% improvement in economy so for me, the mod is more about more relaxed cruising.
Finally, for those with chipped 75 hp TDi's, 103 hp gives a theoretical top speed of 120 mph and Mike's 130+ hp rocket ship should be good for over 130 mph with the right gearing.
Cheers Spike
Take legal motorway cruising for example. According to Audi, a standard TDi requires 75 hp to reach 108mph (flat road, no headwind) As power is proportional to speed cubed, it only needs 20 hp to do 70 mph. The car still needs 20 hp to maintain 70 mph but the higher gearing will reduce the engine rpm. The only improvement in economy will therefore be from reduced engine friction losses and with a little luck, the engine will be operating in a more efficient zone on the part load fuel consumption curves.
I'd guess a 2 or 3% improvement in economy so for me, the mod is more about more relaxed cruising.
Finally, for those with chipped 75 hp TDi's, 103 hp gives a theoretical top speed of 120 mph and Mike's 130+ hp rocket ship should be good for over 130 mph with the right gearing.
Cheers Spike
Pugliese
A2OC Donor
Now I am not technically minded so feel free to shoot me down, but I have been giving this some thought and if that is correct, then would travelling at 60mph in 4th gear produce the same mpg as driving at 60mph in 5th, apart from the 2 or 3% improvement mentioned?
Swalsey
Member
I am no authority in this, but my own thinking would be that at 55-60mph, mechanical/tyre loss will be the major efficiency factors, but at higher speed where more air resistence takes its toll on our blunt A2s, the air resistence would be a bigger factor... with this line of thinking, the biggest gain in fuel efficiency would be at slower speers where the reduced revs would have their largest effect.
Spike, am I talking rubbish?? I am no engineer, just a Science Teacher!
Irrespective of any of the above the economy gains from this mod will depend on the type of use and driving style of each individual owner/driver. For some owners there usage may only produce 2-3% gain where as others may get 10%. As Will states there are so many factors which can affect economy even on the same journey repeated in differing conditions. As most manufacturers are now accepting weight is also a significant factor with economy as is aerodynamics. Friction losses also contribute to the situation. The other 'mod' I would like to see adopted (if possible) would be 'stop-start' which for town drivers will make a big difference.
the grim reeper
A2OC Donor
Remember Adrian this only works when the engine is warm, so for like me and the trips i've been doing to work it would only just start to cut in as i got to work (or home on the return)
Phil
True Phil, however as i have posted elsewhere before ALL cars are actually fitted with this as a free option, its called the ignition key.... Seriuosly though there is no need to sit for long periods at red lights etc with the engine running. Simply making this mandatory on ALL new cars would do more to reduce Co2 emmissions from cars than most of the other rules they try and foist on motorists and it comes as a carrot rather than a stick (of increased fuel duty, lower speed limits, car use restrictions etc etc) insofar as everyone would save money by reducing fuel consumption, something I do not have any problem with even if I think man made Global warming is a load of rollocks...
Seriuosly though there is no need to sit for long periods at red lights etc with the engine running. Simply making this mandatory on ALL new cars would do more to reduce Co2 emmissions from cars than most of the other rules they try and foist on motorists and it comes as a carrot rather than a stick (of increased fuel duty, lower speed limits, car use restrictions etc etc) insofar as everyone would save money by reducing fuel consumption, something I do not have any problem with even if I think man made Global warming is a load of rollocks...
Skipton01
Admin Team
Trouble with using the ignition key to stop start is that it'll greatly increase wear on the barrell and also, I'm not sure that the A2 starter motor is up to the job - they play up just in normal use.
Also, the electrics need to be re-wired to prevent the lights from cutting out and the radio too (on re-start).
A button operated starter, as used on a lot of non-stop/start Audis now would be a better option.
Cheers,
Mike
Also, the electrics need to be re-wired to prevent the lights from cutting out and the radio too (on re-start).
A button operated starter, as used on a lot of non-stop/start Audis now would be a better option.
Cheers,
Mike
Hi Pugliese
The car would require the virtually the same hp to maintain 60 mph regardless of the gear ratio selected. In 5th gear it revs at 2200 rpm but in 4th its 2800. The higher the engine revs, the more power the engine wastes in internal friction and parasitic losses. Secondly, engines generaly run most efficiently around peak torque which is listed at 2200 rpm on the 75hp TDi so at 60mph in 4th, its operating well outside the optimim rev range for economy.
Cheers Spike
Hi Antony
I kind of agree. Worst case, our std 75hp TDi needs all those 75 horses to reach 108 mph.
At this speed, the higher gearing will lower engine revs from 4000 to 3450 and I'd guess this would reduce engine parasitic losses by 1 - 2 hp. The lower rpm should also allow the engine to run on a more efficient area of the fuel consumption curves but overall the % fuel saving won't be significant.
According to the cube law, the A2 only need 13 hp to do 60 mph so a 1hp reduction in the parasitic losses is an 8% improvement. The only unknown is with the higher gearing the revs at 60 mph drop below the 'official' peak torque rpm which may or may not be in a less efficient area of the fuel curve.
Cheers Spike
dan_b
A2OC Donor
I agree with Adrian, stop-start should be mandatory with all new cars - that would be a significant improvement in urban fuel economy and with it a reduction in urban noise, and urban pollution, with a relatively easy piece of existing technology?
I have found myself turning the motor off more often these days when I'm stationary in traffic, although as Mike mentions above, it's annoying that when you do, it cuts the radio and the lights when you re-start.
I'm still going to do the 5th gear mod though despite concerns over real-world economy gains. I tend to cruise somewhere above what I should do on m-ways (years of driving my S2 has given me bad habits which I struggle to break) and if nothing else, it would be good to reduce the noise and vibration at cruising speed. But I still believe that seeing a 400-500rpm drop at 77.7mph (honest guv) will produce a significant, and worthwhile improvement in fuel economy. I must admit I was surprised the 70mph rpms were so high in the TDi when I bought the car - I always thought that diesels always had longer gearing and that the low cruising speed rpms from diesels were one of the reasons for higher economy, never mind the thermodynamic efficiency of the engine itself.
Looking forward to reading about the first box mods in due course. Once I've done my brakes and got the car through it's MOT, bring on the gears. And maybe some additional home-brew aero mods
I have found myself turning the motor off more often these days when I'm stationary in traffic, although as Mike mentions above, it's annoying that when you do, it cuts the radio and the lights when you re-start.
I'm still going to do the 5th gear mod though despite concerns over real-world economy gains. I tend to cruise somewhere above what I should do on m-ways (years of driving my S2 has given me bad habits which I struggle to break) and if nothing else, it would be good to reduce the noise and vibration at cruising speed. But I still believe that seeing a 400-500rpm drop at 77.7mph (honest guv) will produce a significant, and worthwhile improvement in fuel economy. I must admit I was surprised the 70mph rpms were so high in the TDi when I bought the car - I always thought that diesels always had longer gearing and that the low cruising speed rpms from diesels were one of the reasons for higher economy, never mind the thermodynamic efficiency of the engine itself.
Looking forward to reading about the first box mods in due course. Once I've done my brakes and got the car through it's MOT, bring on the gears. And maybe some additional home-brew aero mods
I've read the same too. In my 75PS after a remap I've also read that peak torque would begin nearer 2000rpm. So at 60 mph with a 90PS 5th gear cog the rpm would reduce roughly from 2200 to 2000rpm. So the engine peak efficiency can be maintained, so leaves the question; how significant are frictional losses in engine fuel efficiency?
ps. this has to be one of the best motoring threads I've read in a long time
so leaves the question; how significant are frictional losses in engine fuel efficiency?
ps. this has to be one of the best motoring threads I've read in a long time
I've got no data on Audi engines but would guess the 1.4 TDi requires about 12hp to spin it over at 4000 rpm (I do know an 11 L truck engine takes over 90 hp to turn at its rated speed). This would include internal friction losses plus the fuel,water and oil pumps, alternator running unloaded and balancer shaft etc.
The lower the engine speed, the less power is wasted.
Cheers Spike
I used Mike's previous data to draw a gearsplit chart for the 75hp TDi. This shows how the revs drop when changing to a higher gear. The unwritten rule is you should not drop below peak torque revs at any change point during full bore acceleration. The 0.65 5th gear is also shown, and as others have pointed out, it may be difficult to run smoothly at 50 mph in this 'overdrive' ratio.
I've not seen the details but a 7 speed DSG box could be the dream transimssion for our A2's as it would be so easy to keep the engine operating in the 'sweet spot' for optimum fuel economy.
Cheers Spike
I've not seen the details but a 7 speed DSG box could be the dream transimssion for our A2's as it would be so easy to keep the engine operating in the 'sweet spot' for optimum fuel economy.
Cheers Spike
In case anyone has missed it, this thread may be of interest to some:
http://www.a2oc.net/forum/showthread.php?p=96875#post96875
I agree with Spike, that since the torque curve is very steep at low revs I think 50mph might be difficult with a much longer ratio. Even after a remap the torque changes little, if at all, under 1500rpm.
But at 60mph it looks very feasible, even more so after a remap
http://www.a2oc.net/forum/showthread.php?p=96875#post96875
I agree with Spike, that since the torque curve is very steep at low revs I think 50mph might be difficult with a much longer ratio. Even after a remap the torque changes little, if at all, under 1500rpm.
But at 60mph it looks very feasible, even more so after a remap
I agree, without a re-map i doubt a '75' would be comfortable at more than 0.70 or a '90' more than 0.65 at the most. I admit i am still debating between 0.689 and 0.65 gearset for my 'mapped '75'. The 0.65 will be great on the m/way but the 0.689 is much more expensive and so close to the '90' ratios is it worth it? I suspect what would be ideal is probably something around 0.67.