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MG MGB GT V8 Factory Originals Technical - Which carburation

I have decided to join the V8 conversion fraternaty with my 74 GT. I have read the the book etc, but im unsure which carb set up is going to be best, ie the copy of the original SU set up that somebody markets or the carter (Webber) or Holley. All im worried about is clearance and relliabillity with minimal maintenance, power and fuel economy come second in my opinion, obviously if i can get something that does all these things than all the better.

Thanks in advance Dean.S
dean stanton

You will not beat an Edelbrock on an Offenhauser dual plane manifold. I got mine from RPI engineering.
For comparison, I also have an RV8 and my conversion is about as quick and much more economical (30MPG minimum). The carb is slightly lower than a Holley, and mine started and idled smoothly straight from the box. I got it tuned at BHB in Southampton.It has been totally reliable. As you are in Hants. I am happy to show you the set up if you want. Good luck with the conversion. It will cost you much more than you think, but it's worth it all.
Simon Denney

Thanks for the advice funnily enough i live in Southampton and BHB look afetr a race preparred midget for me, i would like to see the carb set up if posible
dean stanton

Hmmm, my vote would be for a smaller carb like a Carter 400 (which is basically the same as a Weber/Edelbrock) as I think you'll find the low to mid range much more precise. The Weber 500 cfm carb is pretty sloppy on a Rover because those primaries are so big (they're quite a bit smaller on the 400). That was my experience and appears to be widely shared. Maybe OK if you have a hugely overbored and stroked V8 like a 5.0 liter with big valves and serious headers. Otherwise I'd try to get hold of a Carter, I really would. Admittedly, they are somewhat rare and expensive.

As to manifolds, the best by far -- I have never heard anyone really argue against this -- is an Edelbrock Performer dual-plane. It is just a *frac* higher than the Offy but it'll all still fit. It's not materially more costly -- really is well worth it; a much more modern design.

Go Carter/Edelbrock.

I have a Holley 650 for my 302 and I had tuning problems. I dropped a Carter on and it ran right off the bat.. Vac Secondaries is a must..
Larry Embrey

I have Emailed you my number, happy to discuss the conversion. Cheers, Simon.
Simon Denney

Hi guys,

Forgive me for pointing this out, but the Edelbrock and the Offy manifolds are very different. The Offenhauser JWR (John Wolfe Racing) manifold (I have one) offered by RPI is a 'Dual Port', the Edelbrock (I think the part number is 1404) is a 'Dual Plane'.

The dual port runs seperate primary and secondary fuel to all eight cylinders and hence has siamesed (as in twins) ports on each corresponding cylinder head opening. ie. all the primary fuel goes to all eight cylinders and all the secondary fuel, seperate from the primary fuel, goes to all eight cylinders.

The dual plane runs one primary and one secondary venturi to separate banks of four cylinders ie. the carby is divided in half essentially and operates its own side of the engine.

Offenhauser also has another older design which is the '360' which is a dual plane, similar to the Edelbrock.

From the research I did before my purchase, I prefered the Edelbrock, but as I have a chrome bumper front crossmember and have space issues, I went with the 5mm shorter Offenhauser.

I agree with Ted, not that I am a manifold design guru mind you, but the Edelbrock will give better middle and top end perfomance apparently, and the Offy better bottom end torque. I also agree that 500CFM is a little too big, but it is the smallest that Edelbrock makes(unfortunately) and I have one of these too.

Best bit about the RPI deal is that it comes as a complete kit with the jetting that you tell them you want. Then again Dean, if you order from Summit or somewhere else in the States then you get it Tax free. Your choice.

Just my 2 cents worth. HTH


I have heard of a cross-ram setup that employs 4 Weber side-draught carbs. The maniflod I was told was lower than any quad. unit with air cleaner. Anybody know of this manifold setup and have any idea where I might find one? Marc - Los Angeles
Marc Judson

Marc, you're talking about the Boxer manifold or one similar to it. I have to admit, it looks absolutely _amazing_, but keeping the four carbs in tune can be a bit daunting on a road car, and many say that they don't sufficiently tie together the two sides of the "vee" and your alu engine block can flex quite a bit -- a regular intake manifold bolts into the block with, IIRC, 12 fairly large bolts, adding considerable stiffness to the construction. For racing, the Boxer setup would be awesome but I don't think it would provide good service on a road car.

Right now, I've got a Triumph TR8 manifold with dual HS-6's on top of my engine! But, I also use an MGC hood.
Tony Barnhill

Not that this really matters, but just the other day, the long empty Carter Carb factory building here in St Louis burnt down.

Robert Rushing

Just a mad question Dean. But why convert a BGT in the UK, especially a 74 car, when there are stacks of good factory V8 cars around, both for restoration and perfect examples.
KD Rowson

Thats simple because ive just bought the car as a completley disasembled unit ie bodyshell with all the alterations done and all the bits in boxes nearley all of which are new from a guy that had started six years ago and lost interest i Have lots of new V8 bits from clive Wheatley still wrapped and a second hand SD 1 engine and box all of this came cheap and i cant afford the price of an original V8.The car is in primer at the moment and is to be re sprayed BR Green soon and then i will start the long road of putting it all back together.All i need is the 3.07 axle and the lower carb set up and a lot of patience.
dean stanton

Also on reflection this car is going to cost me as much as a rough genuine car but the reason i took it on is not for the car but to have a nice project/hobby in putting it together and learning how these cars tick. Also hopefully it will end up nearly a new car as such, like anything you cant beat the real thing although i hope to end up withc a nice Mg with the sort of drivability they all should have had
dean stanton

Sounds good mate, keep us informed how it goes OK !!
KD Rowson


Holley - drag - higher
Webber - race - wider
SU's - road - no idea

Budget and compromise


Hi Dean,

I don't want to get too far off track with your original question, however, when I was in the UK (the last 3 years), I found it very hard to find a company that would shorten a rear axle(as in Sd1). I did find oil rig support companies very helpfull mind you, particularly around Aberdeen, so this may be a good place to start asking. ie. you have a small job compared to what they do normally so maybe they could do a good deal.

Failing that, talk to Dave vale at V8 conversions and get him to hunt around. I don't have anything to do with his company but he is most excellent when it comes to V8s. HTH


This thread was discussed between 23/08/2002 and 30/08/2002

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