Thread: Tdi into a petrol discovery?

Diff and T-case ratios are the same for diesel and petrol discos IRC. The (manual) gearbox ratios are slightly different, but not much. I believe you may need to swap the ZF auto to fit the tdi though. The bellhousing bolt pattern is different between the two engines, and I believe the shifting/kickdown is also quite different between diesel and petrol boxes.

This has nothing to do with your thread but your 4.6 should be getting better gas consumption then that.A 3.9 would be doing around that.And even less on cruise.

You would be better off selling the V8 disco as is and buying another tdi as by the time you do the conversion you would have spent 50% on top of the current value. The TDI ZF is completely different valving wise so you will need to factor in a matching transmission for the tdi. 20L/100 is normal for a 3.5 on lpg so i would think a 4.6 that wouldnt have to work as hard would do better than that.

Get yourself a lpg processor and oxygen sensor to match, you will pick up around 20% improved economy if you do. Makes all the difference. Ask your local gas fitter or post a pic of your setup so someone can advise.

Something sound wrong??

I have recently put a 4.6 in mine and Bee utey fitted gas to it, it is getting the equivelant of 10lt per 100km on gas in $$ and with total city driving or the Adelaide hills and driving it hard, which I do every day traveling to and from work. I get 20lt per 100km on petrol, if I drive more sedately this improves to about 17/18lt per 100km on petrol. I havent worked out the comparison on gas yet but I can increase the range from 250km per 60lt of gas to about 280 driven carefully in the above conditions.

Once I get used to the massive power increase from the tired old 3.9 I may start driving it for economy, but I am still having way to much fun with it

Blythe

Thanks for the replies. Sounds like it’s not a bolt on job.

I am not too sure on the responses about my current fuel use. My car is an automatic running lpg so to use 24/25 l/100km around town is pretty spot on. Hobart is quite hilly and I only do short runs. I went and pulled out the fuel consumption figures from RAVE which I copied into here. The first lot show for the 3.9 auto @19.6 l/100 km whilst the second set of figures show the 4.6 auto @22.9 l/100 km. these are for petrol too whilst my figures are for lpg. Real world figures are just about always worse than the figures achieved under the fuel consumption tests.

I speak for myself here, but sometimes it can be painful to look realistically at actual fuel consumption. It’s less painful to stop working it out and think oh well what ever it is the sound of the V8 is worth it! when I look at the cost to run the V8 compared to the tdi it makes me question this every time.

blythe - agree wholeheartedly, they are bloody good driving motors with their low down torque and purr. You will find though that your consumption is the same as mine. Your tank would be the same as mine ie 62 useable litres so if you get 250 km out of it then this translates to 24.8 l/100 km. Adelaide is a bit of a sprawl (please don’t take it personally) so you would find your economy worse over in hilly Hobart doing just city driving. If our lpg prices were a bit cheaper here it would probably make it ok to put up with. I had a look and currently your prices are around $0.57 whilst Hobart is $0.80 so whatever your fuel bill is now if you increase it by 40% then you’ll get an idea of the cost in Hobart. Unfortunately we get used to being ripped off down here. just had a look, melbourne is around $0.52, geez we get taken for a ride - 30 cents a litre to transport it to hobart who are they kidding the ******.

Bee utey – you’ve replied before to some of my questions re: narrow band oxy sensors for lpg as I’ve got injected lpg so don’t really need another lpg ecu. Per one of my posts on such, as a proof of concept I found I could manipulate the signal of the narrow band to the 14cux but to get a working “signal modifier” I would have to spec something up to get an electronics techo to design the circuit. It all takes time and there are plenty of other things I need to be doing rather than playing around with my car!


General data
147
FUEL CONSUMPTION
300Tdi non-catalyst models Manual Automatic
Simulated urban cycle (l/100 km) 8.6 .................... 9.3
Constant speed, 90 km/h (l/100 km) 6.6 ................ 6.4
Constant speed, 120 km/h (l/100 km) 10.0 .............. 9.4
300Tdi catalyst models
Simulated urban cycle (l/100 km) 8.7 .................... 10.1
Constant speed, 90 km/h (l/100 km) 6.8 ................ 6.3
Constant speed, 120 km/h (l/100 km) 10.2 .............. 9.7
V8i non-catalyst models
Simulated urban cycle (l/100 km) 18.2 .................... 19.6
Constant speed, 90 km/h (l/100 km) 10.5 ................ 10.5
Constant speed, 120 km/h (l/100 km) 13.4 .............. 13.4
V8i catalyst models
Simulated urban cycle (l/100 km) 20.6 .................... 20.2
Constant speed, 90 km/h (l/100 km) 10.3 ................ 10.3
Constant speed, 120 km/h (l/100 km) 13.8 .............. 14.0

"All figures shown are produced in accordance with the Passenger Car Fuel Consumption Order
1983. They have been calculated using a standard testing procedure. Under normal use a car’s
actual fuel consumption figures may differ from those achieved through the test procedure,
depending on driving technique, road and traffic conditions, environmental factors and vehicle
condition."
FUEL
Diesel Diesel or Automotive Gas Oil (AGO) .................................................. ............
Petrol
Catalyst vehicles 95 RON unleaded ..............................................
Non-catalyst vehicles 90 RON leaded or 95 RON unleaded .......................................


General data
182
FUEL CONSUMPTION
The fuel consumption figures shown below have been calculated using a standard testing
procedure (the new EC test procedure from Directive 93/116EC), and produced in accordance with
The Passenger Car Fuel Consumption (Amendment) Order 1996. Under normal use, a car’s actual
fuel consumption figures may differ from those achieved through the test procedure, depending
on driving technique, road and traffic conditions, environmental factors, vehicle and load
conditions.
MODEL URBAN EXTRA-URBAN COMBINED
mpg l/100km mpg l/100km mpg l/100km
Petrol models:
4.0 V8 Auto 12.9 21.8 23.4 12.1 18.1 15.6
4.6 V8 Auto 12.3 22.9 22.7 12.4 17.4 16.2
Diesel models:
2.5 Tdi Manual 22.2 12.8 31.9 8.9 27.5 10.3
2.5 Tdi Auto 20.3 13.9 30.7 9.2 25.8 10.9
Urban cycle
The urban test cycle is carried out from a cold start and consists of a series of accelerations,
decelerations and periods of steady speed driving and engine idling. The maximum speed attained
during the test is 31 mph (50 km/h), with an average speed of 12 mph (19 km/h).
Extra-urban cycle
The extra-urban test cycle is carried out immediately after the urban test. Approximately half of the
test comprises steady speed driving, while the remainder consists of a series of accelerations,
decelerations and engine idling. The maximum test speed is 75 mph (120 km/h) and the average
speed 39 mph (63 km/h). The test is carried out over a distance of 4.3 miles (7 km).
Combined
The combined figure is an average of the urban and extra-urban test cycle results, which has been
weighted to take account of the different distances covered during the two tests.
NOTE: These figures should not be compared with the figures produced using the ECE/EEC
procedure previously required by The Passenger Car Fuel Consumption Order 1983. Because of
the changes in test procedure, even the urban figures would differ if the same car were subjected
to both tests.

Its horses for courses , Gas has its place where it is cheap and plentiful = major citys , On here you have the views of the v8 die hards and the oil burning rattlers .

I for one have owned both and am a diesel convert now , Simple answer is if you drive out of the comfort of your major city the savings of lpg reduce quickly which some dont understand
Look i love the v8 roar but hate feeding them , Mind you a Td5 with some exhaust mods doesnt sound too bad at all and they go well for a diesel aswell a Tdi is just good on fuel unless you fuel them up im a fence sitter

Brett, you may just need to look at other options by the sounds of it

but you already hve a tdi (manual), maybe thats the one you will need to do up like the v8 one?

This thread is something Timau13 needs to see as he too was contemplating a petrol to diesel swap, but also is auto so same issues here.

PS off topic: You decided on next weekends trip mate?