If it aint broke - dont fix it!
If you've got the thing working on EFi, then rejoice and enjoy!
If its giving 'hassle' or not passing emmissions, then some justification for going carbs, but just means you are starting over with a new set of probs.
Dizzy and ignition can stay as is, if you go carbs, you then have conundrum of what carbs and what manifold, then jetting and setting.
Note the carburettors do NOT 'give' the car power, they can merely limit it by restricting the flow of charge into the engine.
Nor do they give or rob ecconomy, they simply mix the air and fuel in the right proportions to make a charge.
Carbs that supposedly 'give' better economy tend to do so by choking flow and restricting power; carbs that are suggested 'give' power tend to do it the other way by allowing greater flow, which can only give power if the rest of the engine can actually exploit that flow, and usually throw fuel metering to the wind, chucking excess juice down the bores under acceleration to give the impression of added power when accelerating....
As for specifics:-
Easiest would be pre-Efi stromburgs; that's what was supposed to live under the bonnet; work at Rangie inclinations etc, dont suffer fuel surge or anything, only real gripes with them is they dont flow enough air for a tuned motor, but adequete for a reasonably standard one. Not the 'best' for ecconomy, either, but a good compromise.
They do suffer a couple of known maledies, first of which is that the diagphrams perish, second is that the slides can 'errode' due to grit and grud in the air-stream, particularly on Range rovers, and worse on ones that have been off-roaded, especially worse on ones that have been run filterless for extra power, on knackered filters, or dubiouse quality aftermarket filters.
If you go Stromburgs I recomend a full overhaul; kits do a pair and are about £20ish, last time I looked, but dont unfortunately include teh slides, which if bad, really ougt to be renewed.
Once fettled, easy to set up though.
SU's; standard fit to the earlier V8's installed in saloons; two resons the Rangies didn't get them as standard; first was that they had a tendancy to suffer fuel surge, a problem that had been known about for years on sportscars, that could run up to three of them, where fuel starvation would cause them to stutter coming out of tight corners under full throttle. On a Rangie, the G-forces that caused such surge were not so previlent, but unusual angles of inclination were and induced the same phenomina.
Other reason they weren't used as standard was to do with space and possition. Basically SU's like to sit vertically, or near vertically, and the V8 has two banks of cylinders inclined at 45 degrees, which made manifolding them neatly and efficiently awkward, while the high dash-pot also gave clearance problems.
Later SU's, as used on Montegos & stuff in the 1990's were a lot more refined than earlier carbs, and the last of the breed had electronically controlled stepper motors to adjust the jetting 'on the hoof' sort of like a half way house between a carb and EFi.
Flow cabability of the 1 3/4" SU is good for around 120bhp, maybe a tad more, on a normally aspirated motor, so a pair of them are more than adequate for up to 250bhp on a RV8, BUT, like the Stromburg CV, they rely on the dash-pot 'lag' in the slide opening under acceleration to give enrichment, and on more 'sporting' applications of four pot, twin SU's were favoured becouse they made the engine a tad more 'responsive' and hence delivered more power more immedietly when asked, though they tended not to actually offer more peak power, and knocked a lot of ecconomy off the motor, through twice enritching the mixture during acceleration.
Which suggests on a tuned RV8 a quad SU set up, which isn't that common, as the SU's are notoriousely awkward to 'balence', the mixture being dependent on manifold vacuum, and each needing the same vacuum 'signal' to carburate evenly and deliver the same micture; hence popularity of multi-barel carbs like Webbers or Holley's, as they prove cheaper and easier to set up, than a bank of SU's.
A twin SU set up, though, can be pretty good; a bit more of a faff to set up than a Stromburg, and effectiveness of the set up very much depends on what manifold you mount them on; but choice of stock options that should work well, if you can squeeze them under the bonnet, or bulge it in the right places.
Using later HIF series carbs, fuel surge isn't a significant problem; plenty of compers use them, and reckon that they cope with the forces and inclinations of a hill-rally, so in more moderate road use, shouldn't make any deficiencies felt.
Webbers........ Well you have a whole host of options here; but the main thing is that they are straight venturi or 'slide-less' carburettors that rely on chokes and vacuumes through variouse holes in the carb to meter fuel through a multitude of little jets..... these are a right royal PITA to jet correctly for ANY-Bludy thing!
Simplest are the single venturi carbs, as used for ecconomy on old Ford Escorts or VW Golfs, thier only saving grace being they only have one hole to worry about and only about five jets for it, so the number of permutations to worry about are limited!
Next up is the ubiquiteouse double-barrel Webber, available as a down-draft for slant and V configuration engines, or the side draft, for vertical ones.
One carburettor body with two chokes in it, and a common float bowl, normally arranged like a twin single barel carb set up, each barel feeding two ports of a four pot motor, or paired, so that each barel feeds just a single cylinder, like a motorbikes bank of individual carbs.
On a V8, they can be arranged in a number of ways; you COULD use a single down draft on an RV8, with a bigger 45mm choke, it probably 'just' has the flow capability for 160ish bhp, but more commonly they are set up as a pair, manifolded to supply four pots of each carb, or in abank of four, each cylinder getting its own barrel.
Setting up is still as niggly as any webber, compounded by the problem of having a LOT of them to set up, though technically each bareel should be jetted pretty much identically...... though in practice, they rarely do!
More complicated to set up, is the webber 'progressive'; has two chokes, a big one and a small one; the smaller one opening earlier than the larger one, which starts to open when teh smaller one is starting to struggle for flow.
Great idea, theory is, that under part throttle, little choke works like a small single carb, giving accurate metering and ecconomy and good throttle response; but when you give it 'large' the big choke opens up and lets the motor suck a chunk load of charge and go like the clappers........
Set up well, these can be wonderful...... trouble is, setting them up is a right royal PITA, as you now have two chokes of different sizes to play with, with the jetting effected by where you set the 'over-lap' of the second choke opening.........
there is also, I believe a Range of Webbers designed for American V8's I'm not so familiar with; one I know is a derivative of the DCOE arranged with four barrels around a common float bowl, like a Holley, another, I 'think' is called the 'concentric' and is a progressive twin choke, but with the small choke barell inside the middle of the larger one.......
These, like the holleys can be banked as single carbs on a common manifold, or twin carbs, again usually on a common namifold to aid balencing, though with twin four barells, they may be manifolded to feed individual carbs.
Bottom line, in my experience is that on big Yank V8's, they circumvent any subtlety in metering by using big choke sizes and small jets, augmented by big 'pumper' jets for acceleration......
They work well at full throttle, by dint of chucking huge excesses of fuel down the bores; and at part throttle by setting the base jetting via the idle air screw!
I would HATE to have to mess around with a twin progressive..... and my inclination, having been asked to try and 'sort' far too many Webbers or Delorto carbs has been to avoid them wherever possible!
A multi-barrel Holley or single concentric or four barrel Webber, on an RV8 IF you can get one pre-jetted roughly for your motor, may be OKish, but I'd not expect it to give its best unless the motor was tuned and be horendousely thirsty however tuned!
A couple of googlies I've come accross; Motorbike Carbs. The old Edward Turner, All alloy, Daimler SP250 V8 engine was noteable in the fact that Edward Turner, was Chief Engineer of Triumph Motorcycles in the 1950's, and when that was absorbed into the BSA combine, was asked to design an engine for a sportscar for the american market....
He alledgedly bolted four Triumph 'Bonaville' 650 engines together to make an all alloy V8 of 2500cc, and water cooled the result, producing a lightweight, short stroke engine..... with eight Amal mono-block carburettors!
Butiful sounding engine, thing revved to the incredible height of around 8,000rpm, unheard of in its day, though production engines I believe had to suffice with twin SU's rather than the exotic Amals that proved a RIGHT pain to set up and balence!
the engine, though was used in competition, and using Triumph Bonaville hi-po parts, and carbs, made lots and lots of power; and when the RV8 fell into the hands of fiddlers, those carb set ups were soon transcribed to it.
The Amal mono-block is still available; its a simple slide carb, worked by cable, which means a complicated arrangement of 'splitters' and adjusters to get all eight chokes opening in unison, and a lot of messing around to find the right combination of idle jet, main jet and needle profile....
Not as ardiouse as trying to set up a webber....... but I still wouldn't want to try!
Modern variation on the theme; Mikuni's taken from a Japanese motorbike. Seen a few examples; basically modern multicylinder bikes have banked carbs, usually CV types, thouh some slide carbs, usually with a neat bell-cranked linkage to aid balencing.
Flow capability of two banks taken from a suitable model of motorcycle, flow capacity for a V8 can be pretty well matched; something like a GSXR 750 makes aroun 120bhp, so two banks of Gixer carbs would have the flow for up to 250ish bhp.
My suspicion though, is that the jetting, for a highly tuned motorbike engine is WAY off as standard for a lumbering RV8, that takes a lot of big slow gulps of charge, where a bike takes a lot more, much smaller ones; but manifolded and jetted, sure they can work well, but again, I wouldn't like to try it.....
Well I would..... but only iof I had a dyno, a BIG chest of jets, and lots and lots of time to play!
Which ultimately means, its your call....... but if you want an easy time of it...... Keep it Simple.
By which, EFi if its there and working OK, leave it alone.
If you really want to go carbs, then a standard stronburg set up should drop on with least hassle.
An SU set up from a saloon, would be next, being a bit more hassle, and probably no great advantage.
After that, the 'tried & tested' Holleys or Webber's, but really only if you are camming the motor for power.... and can get a carb base-lined for your state of tune.
Beyond that, anything is possible......... but, to be honest, if you are masocistic enough for any of that, you're probably game for a Maga-Squirt EFi, which to be honest, has a lot to commend it, over ANY carb conversion, if you are game for it.
Complicated, but at least you can re-map at the touch of a button; Expensive, but comparitively, not much different to a carb conversion.........
