RR 4.6 engine-carbi???

[malibu9]

The Rangie I bought a few months ago has a 4.6l motor in it runnining on the twin carbi set up. I just had a thought would the carbi's on it be off the old 3.5l motor if so this would severely hinder the performance of the vehicle wouldn't it? If htis is the case is there a carbi set up for the 4.6l or would I have to have the one on it rejetted?

[Maggot4x4]

I would get a 4 barrel manifold and put a quadrajet on it, but thats just me.

[Bush65]

The 4.6 is fuel injected - yours probably had the 4.6 short motor with 3.5 stuff added to compete it.

I doubt you would need to rejet the carbs.

Jaguars use the same kind of carbs in a larger size. Or get a quadrajet (Holden v8 for example).

[up2nogood]

You'll need to get it dynoed to make sure it's not leaning out at high revs, otherwise all that good work on the conversion can be undone by burnt valves.

Then rejet what you have if required or use a different carby.

[Aquarangie]

I would get your stock carbs rejetted if possible. I know of a few people who have had them done and the performance for a strommies set-up is quite good. All these aftermarket jobs sound inticing but at the end of the day, your off-road ability will suffer without a doubt.

I know there are blokes who have 4 barrel carbs, Holleys and the like and have no issues, but best left to blokes who know what they are doing. The stock carbs are restrictiove but provide no hassles in off-road situations unlike the aftermarket or alternative set-ups.

The reason I say this is that I have seen too many fourbys with aftermarket carbs (mainly Rangies) which die up/down hills, get vapour lock and are just a headache to get set-up right. I think LR were onto a good thing with the twin strommies and still IMO are the best off-road carbies bar none.

Some may beg to differ, but I really don't care. Each to there own I say, and what works for one may not work for another.

Good luck in whichever way you go.

Trav

[Bush65]

The Stromberg main jets are adjustable. Pre pollution control the adjustment was external (underneath float bowl). A special tool is required to adjust the later carbs (through the damper).

[justinC]

Trav is on to the money.

BUT, The needle profiles are all important.

I have just solved an overheating, pinging leanout problem with a 3.9 short in a county by using 'Richer'needles in the original 3.5 jets. It solved the problem Immediately and not only does it pull up hills better, but uses less fuel and runs cooler.
Basically, for a larger capacity engine, The profile of the needle needs to get smaller faster when the piston is lifting. The needles I fitted to the 110 were at least 2 sizes along on the chart, and were supplied by Michael at Barry Cooper Automotive in Hobart. He has been very helpful with SU setting up, as I have just done a similar thing with a new 4L short in a '81 RR.
Don't be tempted with Holley or others, HOLLEY'S ARE A GOOD CARB TO SET UP AND RUN WELL ON THE ROAD, BUT BECAUSE rANGIES ARE SO GOOD OFF THE ROAD, THE ANGLES YOU CAN GET TO mean flooding is common.
Quadrajets are an excellent choice for economy as their primaries are small and secondaries are HUGE. I've heard a 4.2 VC-VH Commodore quady has about the right metering for a 3.9RR V8. I can't comment on their flooding issues though.
I would call around locally to someone who has SU or CD175 tuning experience and the needle catalogue/ selection chart, and get some needle profile numbers off them, you will have to read yours first as a comparison. The needle has to be removed with its holder and alpha-numeric part number is stamped on side.
If you can get some genuine SU's from a Rover P6b V8, then they seem to perform even better in a Rangie than the CD175 Strombergs IMO.
The jet adjustment Bushy65 taked about usually isn't sufficient to overcome an engine capacity change this large, and some needles like the 79 - 82 RR were dangerously lean for emission control etc. If you move the jet or needle using this method, you get too rich an idle in an attempt to richen the entire range, which is not helping when pulling uphill in 4th with a boat on in hot weather! Also, Try looking on some of the UK performance websites, as they still use them quite a bit over there. I think Warwick Motors, the old JE performance engineering company may help with this, as they were fitting JE 4.5 engines to early disco's with twin carbs in the early 90's, and they if anyone would've played with enrichment considering their heads and cams etc were works of art for these engines.

Regards, JC

[Bush65]

Thanks for that JC.

[malibu9]

Thanks for the responses guys it has put a whole new light on the subject.
Next question does anyone know of a place in Sydney preferably in the Windsor/Penrith area that tune SU carbs?

[Rainbow Warrior]

Get them rejetted or adjusted to suit, I had no problems when mine were adjusted for the 3.9 short motor, I also improved the flow a bit on the manifold. You can also squeeze a 3rd air filter in between the other 2 to help it breathe better, get a spare set of the filter holding plates and join them back to back with some big holesaw holes in through them. Also get some electronic ignition.