LPG or Quad ??

3.5 v8 on carbs, in a 1985 RRC 4dr. 5 speed manual (ie: No injection or computers, or even electric windows, etc.)

To improve the 13mpg running costs I've been looking at LPG, but have been advised that a Weber 4 barrel would be similarly ecconomical and give better towing power.

New 4 barrel and manifold = around £850 (DIY).
New LPG fit out = £850 (DIY), or £1k plus (pro).
Of course a 4 barrel + LPG sounds even better, but very expensive.

I'm naturally looking at 2nd hand stuff as well, but this ol' bus is an appreciating 'Classic' and probably worth spending a few bob on. Though at 67, I'm more of a mind to keep it for 'life' now.

Any one got any opinions?

Johnny.

jwm said:

3.5 v8 on carbs, in a 1985 RRC 4dr. 5 speed manual (ie: No injection or computers, or even electric windows, etc.)

To improve the 13mpg running costs I've been looking at LPG, but have been advised that a Weber 4 barrel would be similarly ecconomical and give better towing power.

New 4 barrel and manifold = around £850 (DIY).
New LPG fit out = £850 (DIY), or £1k plus (pro).
Of course a 4 barrel + LPG sounds even better, but very expensive.

I'm naturally looking at 2nd hand stuff as well, but this ol' bus is an appreciating 'Classic' and probably worth spending a few bob on. Though at 67, I'm more of a mind to keep it for 'life' now.

Any one got any opinions?

Johnny.

Click to expand...

I can't see a 4brl carb truly making it hugely more economical. More tuning potential for sure and maybe more efficient, or at least you'll not have to drive so hard to get the same performance, therefore mild mpg increase.

Swapping too an efficient EFI setup like Megasquirt will offer improvements. But realistically if you are getting 13mpg now, then I doubt any RV8 powered RR will offer you anything more than around 18mpg tops average.

LPG is an option and will reduce cost per mile. But remember you'll not see as good mpg on it and you'll lose some power. I'm also lead to believe the motor will run hotter too.

That said I think LPG can be a good idea, but probably a pucker multipoint EFI setup.

Have you priced up swapping in something like a chipped Td5? Might not be much more costly, offer up similar or better performance and mid 20's mpg.

On LPG you'll probably get about 11mpg so cost wise compared to petrol you'll do 19 miles for the 13 you do on petrol.

300bph ...
That said I think LPG can be a good idea, but probably a pucker multipoint EFI setup.
Have you priced up swapping in something like a chipped Td5? Might not be much more costly, offer up similar or better performance and mid 20's mpg.

Thanks for your opinion, but my RR is computer free, and it will be staying that way.

Mogwyth ... LPG isn't a great improvement then? I start to wonder if the expense is worth it ! DIY with second hand kit can be dodgy and difficult to get certified too.

So I guess I'll be looking out for a second hand 4 Barrel and manifold.

Any one on here got any experience of these beasties?
Rimmers seem to rate the Weber better than the Holley.

Johnny.

The best thing to do is to scrap the engine and fit a 200/300 tdi
Does not matter what you do the v8 is just to juicy.
Had one or two and that was before fuel costs were what they are now.

jwm said:

300bph ...
That said I think LPG can be a good idea, but probably a pucker multipoint EFI setup.
Have you priced up swapping in something like a chipped Td5? Might not be much more costly, offer up similar or better performance and mid 20's mpg.

Thanks for your opinion, but my RR is computer free, and it will be staying that way.

Mogwyth ... LPG isn't a great improvement then? I start to wonder if the expense is worth it ! DIY with second hand kit can be dodgy and difficult to get certified too.

So I guess I'll be looking out for a second hand 4 Barrel and manifold.

Any one on here got any experience of these beasties?
Rimmers seem to rate the Weber better than the Holley.

Johnny.

Click to expand...

ECU's are fine tbh, 99.99% of all cars manufactured since the mid 80's have them.

LPG is good, but it's a trade off, to get the most from it'll you'll need to spend the money and get it setup right (IMO).

As for carbs, Holley is the better drag race carb but more likely to suffer fuel starvation on side slopes. So I'd go Edlebrock/Weber 500 every time.

Sorry Spencer, but I'm a die-hard old school petrol-head.
Diesels just don't have a place in my world.

300bhp [ECU's are fine tbh, 99.99% of all cars manufactured since the mid 80's have them.]

Apart from the wife's shopping trolley, this RRC is the first motor I've had that I actually have to pay road tax on.
(Which reminds me ... it's due this month. HOW MUCH ????) As I said ... I'm old school.

Or as the wife says "Old school? No Johnny, you're just old now!" :doh:

Johnny.

remember the cost to fit the LPG and the miles you will have to do in order to recover it.

fitting a 4 barrel carb will reduce mpg as it is a performance part.

POAH said:

remember the cost to fit the LPG and the miles you will have to do in order to recover it.

fitting a 4 barrel carb will reduce mpg as it is a performance part.

Click to expand...

That's an old wife's tale my friend. Yes, using all four barrels will of course vastly degrade mpg, but these are 'progressive' carbs. At low throttle only the smaller barrels are used, so as long as you are light-footed they can be more economical than the standard twin-carb set up.

With twin carbs, they are both feeding all the time, and to be anywhere near 'efficient' they need to be balanced. (Often)

To get your head around the 'Progressive' principal. think of it this way ... Your twin carbs are replaced with a small choke one and a large choke one. Most of the time you run on just the small one, but when you go above two thirds throttle the second carb starts to cut in.

The idea behind them of course, is that when big acceleration is required, wanging both chokes wide open (full throttle) you get the big push of a super slurper ... but if you treat them gently it's like having a smaller carb fitted (ie: one of your twins blocked off).

Of course, if you really want economy, try blanking one of the twins off, but don't even think about towing a caravan.

Johnny.

jwm said:

Sorry Spencer, but I'm a die-hard old school petrol-head.
Diesels just don't have a place in my world.

300bhp [ECU's are fine tbh, 99.99% of all cars manufactured since the mid 80's have them.]

Apart from the wife's shopping trolley, this RRC is the first motor I've had that I actually have to pay road tax on.
(Which reminds me ... it's due this month. HOW MUCH ????) As I said ... I'm old school.

Or as the wife says "Old school? No Johnny, you're just old now!" :doh:

Johnny.

Click to expand...

I admire you immensely Johnny. Most 67 year olds around my way own and drive Nissan Micra Automatics, those ghastly 'cube' things or other such nastyness...

BTW, fit a big four barrel carb n get a nice throaty exhaust, cos you only live once!!

Cheers Joe.

Pleased ta meet ya.

Allow me to introduce the Duchess to ya ...


She likes to drink a bit and roar at the neighbours too.

Johnny.

POAH said:

remember the cost to fit the LPG and the miles you will have to do in order to recover it.

fitting a 4 barrel carb will reduce mpg as it is a performance part.

Click to expand...

jwm said:

That's an old wife's tale my friend. Yes, using all four barrels will of course vastly degrade mpg, but these are 'progressive' carbs. At low throttle only the smaller barrels are used, so as long as you are light-footed they can be more economical than the standard twin-carb set up.

Johnny.

Click to expand...

Yep same was said when I replaced the 4.0 in my DII with a 4.6 but in fact it's does about 12% more to the gallon.

My 4.6 does around 19mpg on LPG, on diesel prices that's equivalent to about 33mpg so just as cheap to run and a darn sight more fun than the most TDis and TD5 even if they have had their pumps tweeked or been chipped.

Unless you are doing plenty of miles the best way to get LPG on a motor is to buy one already converted, otherwise you are looking at a long payback.

Nice Jag Pass your way on the A5 at least once a month.

Bill

jwm said:

3.5 v8 on carbs, in a 1985 RRC 4dr.
I'm naturally looking at 2nd hand stuff as well, but this ol' bus is an appreciating 'Classic' and probably worth spending a few bob on. Though at 67, I'm more of a mind to keep it for 'life' now.
Any one got any opinions?

Johnny.

Click to expand...

Reading the replies you've had so far Johnny (I'm in the same age bracket as you!) bear in mind that if you go down the diesel route the car will no longer be an 'appreciating asset' & you are very unlikely to do enough miles to get your money back anyway.

I looked at an tried a few deisel conversions before I found this one Norseman. Deffo won't be going down that route.

LPG is still a possibility, but only if a suitable second hand set up crops up. The savings just aren't enough to warrent the cost of a new fit. I was tempted by a rig on E-bay last week, but it was for an EFI motor, and didn't include a tank. Used tanks don't seem to crop up much, and adding in a new torroidal one pushes it into unrealistic realms again.

Fitting a 4 barrel is the most likely to happen (one day maybe), but these are hen's teeth on the second hand market. Again, I don't think the gains measure up to the cost for a new one. I'll have to start mixing it with the local 'Off Roaders' and keep me ears open for a 'write off'.

Joe1972's post set me thinking though ... I'm bloody sure there's a pair of Red Bullets out in the shed. Guess I'll wait for the existing pipes to blow out first though. It sounds pretty good already.

Johnny

my two pence worth , my 1972 manual with twin su carbs isnt bad on petrol- it was ont he old carbs but with the new ones when set up well its very good, much better than my 1990 3.9 efi.

hard bit is keeping the su's on top form which is prooving a PITA!

lpg is ok if you will do the milage to recover it which you have to work out before hand.

would be worth fitting the upper cylinder/valve lubricator with the lpg kit too!

I have just purchased one of my excustomer vehicle it has a 4.6 converted d2 with 300+ bhp and gas yesterday I went to Cambridge from Leicester and it was crap on gas poor performance and generally run very poor switching over to petrol and it was ace me personally now looking for a full petrol tank to remove the gas!
Don't fit gas spend some money have the engine overhauled and tweaked up and get some better mpg
I worked it out I got 25 on petrol and 12 on gas!

vougese39 said:

I have just purchased one of my excustomer vehicle it has a 4.6 converted d2 with 300+ bhp and gas yesterday I went to Cambridge from Leicester and it was crap on gas poor performance and generally run very poor switching over to petrol and it was ace me personally now looking for a full petrol tank to remove the gas!
Don't fit gas spend some money have the engine overhauled and tweaked up and get some better mpg
I worked it out I got 25 on petrol and 12 on gas!

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I think there might be a little artistic licencing to be honest.

300hp from a 4.6 is unlikely unless super/turbo charged or running a HUGE **** off cam. Either way I truly doubt a real 25mpg out of an RR.

As for gas, all that sounds like is a ****ty setup probably running a budget single point system rather than a multipoint.

LPG has an octane rating of around 114 RON, so tune the vehicle right and it can still make good power, very good power.

gas is half the price of petrol too.

jwm said:

Cheers Joe.

Pleased ta meet ya.

Allow me to introduce the Duchess to ya ...


She likes to drink a bit and roar at the neighbours too.

Johnny.

Click to expand...

A lovely old bird there. Always good to see a good 'ol classic.

a guy at work has got one of those too, he is also having fun with the twin SU's

he keeps borrowing my balencer lol

cars lovely though, 3.8