View Full Version : Carb upgrade for Rover V8

Two greens
18-10-01, 01:12 PM
Hi Guys,
Am new to this experience so be gentle with me!

Currently running a Sumo with a bog standard Rover 3.5 lump fitted with twin SUs which I am looking to upgrade. There seem to be two choices (Weber 500 (?) v Holley 390. Depending upon which distributors site I read, I get different recommendations.

I have three questions I would appreciate answers to:

1. Which is the better choice?

2. What sort of impact can I expect on performance?

3. Is it an easy job to do ones self (Cobra Cars say it is not a job they would recommend done by a layman).

Two Greens

18-10-01, 01:30 PM
Two Greens - (what, not satisfied with one??)

There will be lots of folk who like either the holley, or the weber. Me? Don't like Holleys, but that's just my opinion.

If you are a layman, and not likely to actually do the swap yourself( which will mean new intake manifold as well as carb), nor know how to tune it afterwards, my advice would be to find someone you are happy with to do the work for you, and who has a GOOD track record in tuning the make of carb they recommend, then go with their recommendation. At the end of the day, I am not sure why you want to move away from the original SU's on a standard Rover V8 - I would think they were sufficient until you had done other mods (cam, heads) to be giving you over 200HP. I am not convinced you will get noticeable extra performance just by a carb swap, unless the new intake manifold is a million miles better than the original, and you could lose out in terms of mpg. However, if you want to do it just for the looks alone, go for it.



18-10-01, 01:41 PM
I've fitted a Weber (Edelbrock) 500 to mine on an offenhauser jwr dual-port manifold (this is the lowest profile one - though I could have used the higher profile edelbrock performer one). Weber 500, according to RPI and also an american engine specialist who set it up for me, is much better (for a rover engine) than a Holley - Holley's are difficult to jet and very prone to flooding.
Impact on performance - especially throttle response is amazing - Chris at RPi tried to convince me when I bought it that it would make a great difference - I thought it was just his sales pitch, but it _really_ did!! :D Impact on fuel bill is also noticable. Apparently its better for economy generally than the SUs but the weber has a mechanical accelerator pump so if your prone to flooring it (who isn't!! :) ) then it really does quite literally pour the fuel in!!
Fitting it is pretty easy, though you need to spend a bit of time working out where your throttle & choke linkages are going to go and where to route the heater pipes (the bottom heater pipe no longer fits under the manifold) and the fuel inlet is now going to be on the driver side. Once you have this worked out it really is just a case of unbolt the old and on with the new and is dead easy. All common sense no specialist knowledge required. Not a plug for RPi but they were extremely helpful in the installation; Holly (the engine builder) answered all of my questions before I even asked them - Speak to Chris or Holly and they will let you know exactly what it involves.
Setting it up is again quite easy theoretically - I had the carb jetted by RPi before they sent it and they seem spot on- I did however need to take it to an engine specialist (conveniently over the road from where I work) to sort out the idle mixture as my CO meter wasn't really up to the job and I also wanted it set up for HCs - Much easier than the SUs I spent about 2 months and lots of needles trying to get them right and eventually ditched them!!

Hope that helps


18-10-01, 08:18 PM
when you replace the manifold look out for a pillar of alloy used for mounting the choke cable on the edelbrock performer it fouls the rh rocker cover and prevents it from sealing properly causing an irritating oil mist leak.

either grind a notch in the pedestal or the rocker cover as you like and this is one less ptoblem . I have a webber and edelbrock and am a happy bunny.

check your fuel pump is up to i recommend carter pump as it has preset pressure so no regulator is needed.

have fun and dont be frightened

18-10-01, 09:10 PM
Hi,have you thought about putting dellorto carbs on?.I run a rover V8 with quad dellortos and it is very rapid but a bit thirsty.

18-10-01, 09:13 PM
Sideoiler -good point, -a carb change alone will not result in much difference in output, although as has been mentioned, throttle response can improve over the standard SU's.

Twin Greens - the moral seems to be that a cam change at the same time would be a good idea!

I have the Edelbrock (Weber) carb on my engine (not a rover). I like the ease of tuning, and the fact that it holds tune well. Also so much easier to set float levels etc than a Holley. No nasty gaskets below the fuel level to leak. No nasty power valves to blow. Thats why I prefer the edelbrock to the holley. I notice you mentioned a "500" carb - if that is 500cfm, I would have thought that it's too much for a std Rover. Not sure if edlebrock make a smaller one, might mean you have to go for the 390 Holley after all?? Anyone know different??


19-10-01, 10:15 AM
Two Greens
I inherited A Holley on my rover on a converted SU manifold,which I changed for an Edelbrock performer.I could not get it to run right even after a complete carb rebuild.I agree with Wilf, get someone who knows to set up whatever you buy.My car went to Cheng at Thunder Road for a front suspension rebuild and whilst there he tuned the carb and did the timing etc. It is now a totally different engine, Good response and not as thirsty.Personally when I change my engine(next years project hopefully) I will get a Weber for ease of maintainence and performance.Anything looks better than SU's tho.

Happy Jim
19-10-01, 12:25 PM
I bought a part built GD with Rover V8 and Twin SUs (not running). Part of the deal was a new Weber kit (500 carb, Edelbrock performer manifold, pancake filter) all still in the box.

I consider myself a layman (I can weild a spanner and follow instructions) and no expert by a long shot.

I followed the instructions to the letter, spoke with Chris at RPI who suggested a suitable pump & Regulator, fitted the lot with no problems whatsoever.

I started the engine for the first time without having to touch any of the settings!! Which I guess says a lot for its ease of installation.

It looks as if its running rich, but I'll leave it a while before I find an expert to tune it (unless I get brave!).

Oh and it looks good too:7



07-11-02, 08:20 PM
The chart is taken from a 94 fast car magazine ,the three carbs (weber , holley , quad su and twin su) were fitted to a standard rover v8,second hand and of unknown quantity, with a real steel Hurricane cam fitted at @ approx 110
Graph colour as follows:-

Holley - green
Twin su - yellow
Quad su - red
Weber - blue

The Twin su was making 140 bhp
Weber made 176 bhp
Holley made 165 bhp
Quad su made 162 bhp

They concluded that the weber wins being the most complete package for your money

The scores out of 50
Weber 47
Holley 39
Quad su 32

The figures speak for themselves and the weber was easier to set up apparently

28-09-08, 05:42 PM
I notice you mentioned a "500" carb - if that is 500cfm, I would have thought that it's too much for a std Rover. Not sure if edlebrock make a smaller one, might mean you have to go for the 390 Holley after all?? Anyone know different??


Hi Wilf, the 500 is OK for even a bog stock 3.5 lump, Jim of JRV8 fits them to his turn key engines. I think that the priamries are smaller than the holley 390 so the motor "see's" it as a small carb until the the secondaries come in. The secondaries as you know are half mechanical, half vaccum. (I removed the vac bit on my carb and went for a spin....it was bloody terrible!).

I would definately do the "drill mod" to the manifold just behind the stat and also fit a 74 degree stat. The lump will then run at 80 degrees.

The 500 really does need a thicker set of needles, 67x55. Once that lots done (30 minutes work in total including the drill mod) you can fit then manifold, an insulator, and then the carb and "bobs your uncle" :D

The Thunder series 500 looks very interesting....more knobs to fiddle with!

Sideoilers post is interesting, everyone quotes figures over 200 BHP for the 3.5 but mine which also had typhoon (hotter than the hurricane) fitted and it only made 177 at the fly. (It was a bit knackered though and the timing was probably miles out!)

Real steel really take the pi55, they quote something daft like 254!


28-09-08, 05:47 PM
Another 2002 resurrected post?? :mrgreen:

Purple AK
28-09-08, 05:53 PM
Another 2002 resurrected post?? :mrgreen:
18-10-01 to be precise ;) Around about when I was firing up my engine for the first time :mrgreen: And Happy Jim was still running a RV8

28-09-08, 06:28 PM
I was going to say what dimwit brought this post back up.....it was me!

The thing is it showed up as a new unread post in "bold"....bloody computer making me look stupid!


28-09-08, 06:38 PM
Its not just the computer.;)

28-09-08, 07:19 PM
Its not just the computer.;)

Very true, I'm worried that I'm getting "tarred with the same brush" as some of the people that I hang about with. :)

28-09-08, 09:38 PM
I was going to say what dimwit brought this post back up.....it was me!

The thing is it showed up as a new unread post in "bold"....bloody computer making me look stupid!


Don't worry Pete, it came in useful, I posted a similar question yesterday evening.


30-09-08, 12:23 PM
Have you thought of this?

The cheapest carb setup is the one that is currently fitted to your engine!

I run a tuned RV8 with a pair of 1.75"SUs. They are heavily modified to flow better (actually flow better than stock 2" SUs). I read the Vizard books from cover to cover and then back again and then set off with the dremel and the wet&dry. The hardest part is finding needles to suit your engine, but the addittion of a lambda sensor helped no end.

I also port matched the inlet manifold, somthing worth doing on any carb setup.

I have never done a back to back flow test on my SUs v a 4 barrel, but I bet theres not much in it.

Although they don't generate massive HP, SUs are economical, simple, cheap to modify and if they break, cheap to fix, sets are always available on fleabay for no money and the new SU web site is excellent.

OK, I admit that they don't look like authentic COBRA fit, but in reality, how often do you run round with the bonnet open?