The pull of the dark side, 5 cylinders...

[silverbullet]

Well here's a fine dilemma, I can't believe that I'm even contemplating this but here goes...
Since the SA is languishing with a suspect (read broken) ecu, I need - for my own sanity - to weigh up the options and work out where I'm going with the thing.
The bones of it are this: stick with petrol/lpg or contemplate the unthinkable and install 2.5 Tdi from an Audi A6. There, I've said it.
LPG has been a disappointment for me even if the conversion has at least paid for itself in fuel savings, but the pence/litre difference is closing.

So it's time for a pros and cons list:

2.6i petrol.
Pros.
No engine purchase necessary; stick with the lpg and improve with an aftermarked ecu (megasquirt?) that has dual fuel/ignition maps; Sounds really cool when you give it the beans.
Cons.
Petrol/lpg dual fuel is always compromised as you can't optimise for either; lpg range is very poor (150 miles at best) compared to petrol, needs a second tank but then there goes the spare; Damn thirsty, only returns 20p/mile even on lpg and that's rising all the time; ECU, wiring and rolling road time to optimise means more expense. Vehicle not repairable by roadside recovery etc. (no different to now)

2.5 Tdi.
Pros.
Lots of torque and smooth with it, great for when 7-up and luggage; totally standard engine and ecu; massive range from the huge 85litre fuel tank; the odd gallon of veg oil is an option; engine is virtually a straight swap for the 2.6i as MG proved with Limey; sell off 2.6 engine and Longlife exhaust (but keep all mounting hardware); I have got a compact charge cooler good for at least 320 bhp (petrol)
Cons.
Purchase donor vehicle, try and pick a good one, strip it out; charge cooler and pipework needed; Lots of wiring to suss out. New exhaust (again). Painful pump price of fuel. Ideally wants a 7/29 cwp in the gearbox, to make the most of the low revs, so more costs.

[mrhutch]

Whats the issue with the ECU? is it foobarred?? If it will provide a spark then option D

sort the tank situation out PROPERLY, have at LEAST 120l in tanks and refit the LPG with a decent closed loop system. Loose the petrol tanks altogether

[Aidan]

downside of the TDi engine - will eat the gearbox, will vibrate and generate a lot of heat, won't do much over 30mpg, heavier, will get emmisioned off the road before the petrol does, will be noisy, smelly, dirty, need I go on

Mike Ghia has said he'd never do it again, Russel won't do them......there's a challenge thrown down....no seriously if you want to go oil burner stick with AFN with as much of it's original intake and exhaust as possible and Vagcom
but if there's nowt wrong but the ecu then I'd get that fixed/replaced and keep it stock; if you want fuel economy buy a new vehicle, if you want low depreciation and a nice bus then pay for the fuel and enjoy, there isn't really any other choice as any pursuit of fuel economy costs big money which could just be spent on fuel in the first place for the cost of a full blown TDi conversion done right you could fuel the drive to China and back

[silverbullet]

Obviously this is all thinking out loud, it's just been a bit of a pisser that just as it was settled down, it went pop.
Here are some fag-packet benefit-of-hindsight sums that I should have done before now, based on my regular motorway run at a steady 60-65 mph and light right foot:

LPG @ 77p/litre = £3.50/gallon
36 litres = 150 miles OR 19mpg if I'm being generous (18.75 really)
This adds up to 18.5 pence/mile.

Derv @ £1.40/litre = £6.37/gallon!
To get the same pence/mile, dividing 19 mpg into 6.37/gal = target figure of 33.5 mpg. That feels like a lot to ask from a 2.5 diesel pushing a brick.
If I factor in reclaiming the vat on the derv then it starts to look a lot more attractive, at first glance.

Gas capacity is always going to be the problem as the range is a joke. Ditching the petrol tank won't achieve anything because as we know, the regs won't allow underfloor tanks other than a donut in the spare wheel storage because of the 200mm clearance rule. OK on a Disco but no good here.
There's no point filling the inside up with gas tanks if we can't all get it!

I've read through the Limey thread a few times (original format and current) and I had presumed that the substantial torque output was down to a re-map boosting it well above OEM spec. What did that engine produce in standard form? I know MG had also put on that external oil feed system to the gearbox with a degree of success, but again it's a lot of work and ultimately still pushing the transmission beyond it's limits. I had heard that given the time again he'd have gone with a 2.3 turbo petrol...

I think that I'm looking at going the MegaSquirt dual-map ecu route, fully sequential, COP and gas injectors in the manifold (like it should have been in the first place) possibly with a re-work of the manifold so more of the engine can actually be accessed!

Lots of wiring (but there would have been either way), extra sensors, coil packs etc but probably as efficient as it's going to get for a 10:1 compression engine plus the thing is actaully serviceable here in the UK. I know that real economy costs money and if I want mega mileage then buy a Smart

[ELVIS]

have Pm'd you megasquirt chaps number.

IMHO thats the option to go for. Surely with seperate map for LPG where you can optimise timing etc to make use of increased octane rating you will be able to get wayyyyyy better than 18/19 mpg ? Thats sort of figures chaps on open loop appear to be getting


Once you consider how many miles a year/month you do, cost of conversion and how many hours in the day you have to spare only you can decide. As you know any 'full on' conversion costs $ once you start looking at everything down to last nut/bolt/coolant etc etc How long will it take you to recoup cost? MS is looking good at under £600 installed and mapped. Aditional advantage of being the 'first' to do it for kudos points (and you can let me know before and after results for when i do it and also probably wayyy cheapest. IIRC i readf somewhere that LPG is price fixed or whatever the term is by the governement until 2013 at least where as petrol isnt.

Good luck whatever route you decide

[silverbullet]

Damn damn damn! Just hit the windows key and lost it all

Only one vote and that's for DERV?

In brief this time: MS dual map is probably as good as it will get, maybe 25 mpg fully sequential for both. Transverse 1000 x 200 or 250 dia tank over gearbox and donut up front = 90 litres wet for a range of nearly 500 miles and it still seats 7 inside

Diesel, last words (maybe)...Gunzl had a nicely done 50 degree 5 cyl tdi Carat at VF last year. Wonder if it was still auto to handle to torque?

Diesel auto, niiiice that's the way to go

Earliest Audi A6 AAT, 115 bhp, 265 Nm @ 1900 rpm (sensible?) later AEL 140 bhp, 290 Nm @ 1900

[lloydy]

2 litre turbo petrol, you know it makes sense!

[eatcustard]

I voted No 2

[ELVIS]

Me to!

Could i be cheeky and offer an extra to aftermarket ECU?

Research what from I5 Audi engines is interchangeable Find out if there is a slightly more *ahem* 'robust' cam or head you can fit?

There is a company in finland or sweden called KM or KN (cant find link) that do cams.

For the cost of full diesel and box conversion you are looking at having LOTS of spare if you went MS and extra/bigger tank.

A GOOD lpg set up at sub 80p/l cost will give v good mpg and it will take a long time to recoup diesel conversion cost.

[mrhutch]

properly setup and mapped gas system will give you more than 20mpg.. my 2E on the last run give 28Mpg..

[mrhutch]

and Charlie gets WAY more than 20 mpg on his SA

[silverbullet]

2 litre turbo petrol, you know it makes sense!

Not enough cylinders! 2.3 RR in S2 spec maybe

and Charlie gets WAY more than 20 mpg on his SA

That can't be right, he drives everywhere at 90!

Thanks for the input everyone, it's all good for the grey matter even if it's just shooting the breeze. That's the whole idea of a tech forum, isn't it?

I think that Hr. Gunzl's Carat was runnning a G50 gearbox, so that clearly states the level of financial commitment to the project.

It's ok, I will be sticking with sparks and doing a TRUE dual fuel setup, not a halfway add-on that clearly doesn't deliver. I'll also put the charge cooler at the back of a cupboard for a different engine project later on

[ninja.turtle007]

Mike Ghia has said he'd never do it again, Russel won't do them......k

I presume this is 2.5 tdi not 1.9tdi?

[silverbullet]

It's all about the smoothness of the 5-pot, Tom. The clue's in the title

Regarding torque outputs of tdi's generally, what sort of numbers do these mTdi engines produce (and at what rpm)?

P.S. the argument against a big, heavy, 5 cylinder diesel engine don't really hold up as I've already got a big, heavy 5 cylinder petrol engine

[ELVIS]

I too am at a crossroads.

Thinking of sorting cam/head/fanimolds/Megasquirt in the gti but working figures out i can sell my complete gti set up + money i would have spent on 'go faster' stuff and have a well sorted 20v turbo with slightly more bhp but more importantly oooooodles more torque.

Makes it even worse when i happened upon a 20v engine and adaptor plate the other day.

Decisions, decisions (oh and get my pay out aswell )