dominicbeesley

dominicbeesley

Well-Known Member
There's been a fair number of threads on here about engine swaps. I've been wondering which would be best value for money and decided I'd try and work it out. Now like Peter Snow used to say on election night, "this is just a bit of fun". I've knocked up a spreadsheet and got the results below...

I'm sure I've not guessed right for MPG figures or conversion costs, all depends whether your time is "free" or you pay a garage, if you can get the bits for cheap or not, etc...still instructive.

Be interested to know what other's think of the mpg / conversion cost guestimates. Excel spreadsheet attached if you want to try your own numbers...
 

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Well come on then if you know better let me know...I've never had a diesel for long but when I borrowed one I did spend most of the time flat out in first gear just to get up the sodding hills round here!

So what MPG would you get for a diesel, with or without overdrive?

What mileage do folks get with TDI's with and without 5-speed/overdrive. Seem to be a lot of people putting in tdi and claiming improvement but buggered if I'd fork out all that brass and time and then find out I'd have saved more money just sticking a pair of diffs on.

LPG conversion for petrol looks like the way to go to me.
 
Excellent spreadsheet! I was wondering if anyone could do this. The mpg figures will cause some debate, but in real life I suppose it's close.
 
Aye, it would be good if we could all pool "real life" mpg figures for our motors to get a good comparison of the likely savings each thing gives.

I've always been a bit dismissive of LPG but after doing some basic sums I reckon it might not be that bad an idea...
 
how did you get 13 mpg from lpg ?? even in the mountains i live in i am able to get 18 mpg and 19 mpg 18 is solex carb 19 is zenith carb but all in all thats a really cool spread sheet and pretty acurate workings out good stuff
 
That's gallons of LPG, the usual figure to use for LPG is 85% of the mileage you'd get with petrol. (Not the silly equivalent price of petrol mpg figure given by some companies).

Do you get 18mpg of lpg then? Happy to be corrected if it is!

D
 
yep had a 110 v8 lpg as well did numerous trips to poland in it would get just over 17 on petrol just under 17 on lpg and its around 15% power that you loose which you gain back by spending a bit of time on the engine setting it up to suit the LPG its like leaded and unledded petrol 3 and 6 degrees advance and ukraine petrol (nasty african like bad quality) you run 4 degrees because you dont get the same performance with normal BP real mc coy
 
i see alot of you say RR diffs improve mpg is it a thing i could do in my own garage or how much would i have to pay some one to do it for me
 
My real world MPG for 2.25 diesel is 28/29 This can go down to 26 in heavy traffic/ cold winter running but never any less. I sometimes run 50% biodiesel and save around £1.50 a gallon.
Rangie 3.54 diffs forget em unless you are running a petrol or tdi My diesel lost driveability when i tried them constantly running in 3rd gear around town and only got 30 mpg on a long run. Made a profit selling them though. Yes you can change diffs easy in your own garage try swapping the rear only and running it for a while. Just avoid four wheel drive cos you will break the gearbox if you try.
 
Thanks for that CJ2a, I'm surprised it is that close as LPG only has about 3/4 the energy density of petrol so realistically should give a substantially lower mileage though I suppose the gas conversion might well do better than a carburetor at metering...what kit do you have?

richbatch - if your engine is set up well and you don't have too many steep hills or do any towing then yes RR diffs make a difference. It's like all your gears go up by 1/2 a gear. More top speed or lower revs for the same speed. Not sure how much it would affect off road ability.

An overdrive is better but a lot more expensive. I got a pair of diffs off ebay for about £75 each delivered, a bit knackered but serviceable. Fitting is fairly simple. Back takes about half an hour to an hour. Front is more involved and requires removing stub axles but still less than a two hour job. Worth having another pair of hands as it is heavy work.
 
dominicbeesley said:
Thanks for that CJ2a, I'm surprised it is that close as LPG only has about 3/4 the energy density of petrol so realistically should give a substantially lower mileage though I suppose the gas conversion might well do better than a carburetor at metering...what kit do you have?

richbatch - if your engine is set up well and you don't have too many steep hills or do any towing then yes RR diffs make a difference. It's like all your gears go up by 1/2 a gear. More top speed or lower revs for the same speed. Not sure how much it would affect off road ability.

An overdrive is better but a lot more expensive. I got a pair of diffs off ebay for about £75 each delivered, a bit knackered but serviceable. Fitting is fairly simple. Back takes about half an hour to an hour. Front is more involved and requires removing stub axles but still less than a two hour job. Worth having another pair of hands as it is heavy work.
Click to expand...
petrol in theory can be as dense as it likes the liquid itself does not burn its the vapour that burns, what you would be looking for is like for like in burn properties and the energy that burning that fuel gives, LPG and petrol are pretty similar in energy given when burning and the state that it burns as its the vapour of the LPG thats the flamable bit too you just dont get quite the same bang from the same amount of it which is why you loose around 15% of power and the LPg is not injected on the carb fed landies LPG converted i have owned the LPG goes in to the top of the air intake so it fills the carb up allowing it to work as normal with the liquid (pretty similar to petrol really) and 1 i have is Lovato of italy and i will check the other one but both done in poland (bloody cheap at the time) and leaps and bounds ahead of the UK LPG scene as they have been running it here for 20years and its perfectly normal to find most normal cars to have LPG
 
dominicbeesley said:
Well come on then if you know better let me know...I've never had a diesel for long but when I borrowed one I did spend most of the time flat out in first gear just to get up the sodding hills round here!

So what MPG would you get for a diesel, with or without overdrive?

What mileage do folks get with TDI's with and without 5-speed/overdrive. Seem to be a lot of people putting in tdi and claiming improvement but buggered if I'd fork out all that brass and time and then find out I'd have saved more money just sticking a pair of diffs on.

LPG conversion for petrol looks like the way to go to me.
Click to expand...

Ok, I've a diesel 2.25 ,3 bearing fully rebuilt engine, in a LWB. I can average 27mpg on short trips, and 37mpg (best so far) on a 3.5hr trip mostly at 60mph, with occasional bursts up to and over 70mph. I've no overdrive and standard diffs. The whole thing is standard, no special gearbox etc etc. (and i don't use cooking oil )
I do put a small drop of two stroke oil in the tank from time to time, but I don't always remember!:D
 
mad git said:
Ok, I've a diesel 2.25 ,3 bearing fully rebuilt engine, in a LWB. I can average 27mpg on short trips, and 37mpg (best so far) on a 3.5hr trip mostly at 60mph, with occasional bursts up to and over 70mph. I've no overdrive and standard diffs. The whole thing is standard, no special gearbox etc etc. (and i don't use cooking oil )
I do put a small drop of two stroke oil in the tank from time to time, but I don't always remember!:D
Click to expand...

thats because diesel engines become better on mpg when they are loaded up meaning when the car / truck is carrying / pulling more weight rather than when they are unloaded or not carrying weight, a LWB landy is a lot heavyer than an SWB landy.

a couple of years ago now just after i bought my static caravan i sold a s11a g/box to a forum member and delivered it on my trailer on the back of my then 300tdi auto disco to devon as i was going to my caravan in perranporth in cornwall the same week so from home ( manchester ) to forum member in ( devon ) then onto my caravan in ( perranporth ) i did the full trip on 1/2 a tank at a steady 70 mph ( traveling through the night ), then later in the year i did a strait trip from home to the caravan and got there on 3/4 of a tank of fuel at a steady 70 mph.

so makes the car more economical when the car is pulling / carrying more weight :)
 
cornish rattler said:
thats because diesel engines become better on mpg when they are loaded up meaning when the car / truck is carrying / pulling more weight rather than when they are unloaded or not carrying weight, a LWB landy is a lot heavyer than an SWB landy.

a couple of years ago now just after i bought my static caravan i sold a s11a g/box to a forum member and delivered it on my trailer on the back of my then 300tdi auto disco to devon as i was going to my caravan in perranporth in cornwall the same week so from home ( manchester ) to forum member in ( devon ) then onto my caravan in ( perranporth ) i did the full trip on 1/2 a tank at a steady 70 mph ( traveling through the night ), then later in the year i did a strait trip from home to the caravan and got there on 3/4 of a tank of fuel at a steady 70 mph.

so makes the car more economical when the car is pulling / carrying more weight :)
Click to expand...

Defies logic...........but I'm not arguing:D
 
richbatch said:
i see alot of you say RR diffs improve mpg is it a thing i could do in my own garage or how much would i have to pay some one to do it for me
Click to expand...

this is how i swap front diffs, two axle stands supporting the vehicle and two more to support the brake drums/swivels etc'

Picture088.jpg


nothing needs fully removing except the old 4.7 diff, just undo the 6 bolts attaching each swivel to the axle tube pull them away from the axle by 3-4 inches each and support the brake drums on an axle stand this allows the halfshafts to pull out of the diff, when pushing back into place throw the paper gasket away and seal with instant gasket/silicone, one new diff gasket and refill with fresh oil

doing the job this way and you'll be completed in an hour/hour and a half if you get your finger out
 
Roughly how I did it but first time it took feckin ages because every single nut & bolt was destroyed either before or after I'd finished....if you need the thing up and running quickly order a new set of bolts, gaskets and a couple of decent cutting discs....

I'm due to swap the back one out then back in or maybe front to back. The back one on mine has a lot of backlash - when I refitted them I forgot to check which was worse and fit that to the lightly used front. I practised adjusting the bearing caps on my original diffs on the bench the other day and looks to be easy enough....anything I should be careful off when doing this?
 
personally i wouldn't attempt to adjust the backlash out of diffs, they've usually worn the teeth between the crownwheel and pinion gear and the wear is matched or the pinion shims have worn out due to lack of lubrication and/or water in the casing, adjustment is likely to unsettle this match and aggravate the wear rate

to set a diff up 100% correctly is quite involved

4.7 diffs can be as little as free and shouldn't be anymore than 25quid each secondhand

3.54 diffs are usually no more than 50 quid each secondhand

to me it makes better sense to just buy another if yours is badly worn
 
its not as hard as youd imagine ,pinion bearings if changed for timken should maintain pinion height and should be changed as a pair ,carrier is easy to set as ive explained in several places ,but only after ensuring the pinion bearings are good and no freeplay is evident with used bearings and smooth preload is with new bearings
 
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