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MG MGB GT V8 Factory Originals Technical - 3.9 conversion from FI to carb?

Finally came across a complete and running Rover 3.9 in my own neighborhood. Snapped it up right away. Now the questions start.

1. Is it advisable/advantageous/difficult to convert from the FI to a carb setup?

2. What is the approximate value range of a complete FI unit with the computer, wiring, etc.?

3. What is the proven manifold/carb setup for a mildly rebuilt/tuned 3.9?

Thanks in advance. I'm sure I will have more questions later.

Michael Willis

Sounds like the perfect thing. I don't know about #2, but as to #1 and #3:

1. FI setups are pretty sweet, but to me -- and this may be only me -- they are rather out of place on a car of this vintage. Of course, who am I to talk -- the friggin' RV8 had exactly your setup. It's trivially easy to convert to a carb; much more complex to go in the other direction. FI setups usually get a little better gas mileage. They don't really offer the -Wow- effect of a big chrome air cleaner sitting there when you open the hood though!

3. As to manifold and carb, I'd put in a very strong vote for an Edelbrock Performer manifold and a Carter 400 carb. As a side note, you won't have to bulge the hood with this setup. You might have to with the FI, although you can get the plenum machined down and the air trumpets shortened so that it works.


I feel compelled to encourage you to keep the fuel injection mainly because it will likely produce lower emissions and that may become important in Phoenix. It would be a shame to put all the time and money into your project just to find DMV wont let you drive it. Finding the right buyer could bring in enough to cover the price of a new manifold and carburetor, but pessimistically I would expect you could sell it for less than you could buy another if you found you needed fuel injection to pass emission inspections.

The overall cost is difficult to predict because it depends on what you do and what deals you get at the time. It sounds as if the only thing youd need to utilize the fuel injection is the high-pressure fuel pump, swirl tank and a return line.

A big bright shiny chrome air cleaner does dazzle the eyes of onlookers, but beauty is in the eye of the beholder and many will be just as impressed with the technical look of fuel injection. They would be even more impressed if you replace the cover with one from Costello or got one for an RV8 with the large MG emblem. Both systems can be coaxed under the hood (bonnet) with the low air cleaner on a carburetor simpler to accomplish than the machining required for fuel injection, but the instructions are available so its not as if youd have to blaze a new trail. If youre considering a hood scoop or an RV8 style bulge then it doesnt matter anyway.

The only intake manifold Ive tried is the Buick that came on the motor. It has worked fine with both a Carter 400 and an Edelbrock 500, but doesnt permit the use of a Holley. Other brands are drilled for both carburetor sizes and probably flow better, but from what I recall reading here on this BBS, the original Buick manifold is the lowest. I have no doubt the Edelbrock that Ted recommends is an outstanding choice. There is another brand (the name of which escapes me) that is geared towards British applications that accepts British fittings such as the temperature sender and brake vacuum boost takeoff.

Many will agree that fuel injection seems out of place on a vintage car, but the same could be said of V8 engines, automatic chokes, air conditioning, Fiero seats, tube shocks, base coat/clear coat paint jobs, non-standard wheels and the list goes on.

Well, there are two quite different opinions. Lets see what other advice you get.
George Champion

On the dress up part,it just comes to $$. You can have an alum intake plenum looking pretty darn awesome if you want to. Look at all the mustang guys, they have shinny plenums, chromed billet inlet tubes, etc. I have heard of a few people Jet-Hot coating thier intakes and selecting the "chrome" finish, this comes out AWESOME, and helps keep the fuel/air charge cool..

That is one road I have not seen any MG V8 FI guys go, it to polish and dress up the mototr like the carb guys do, course we carb guys have the advantage thhat most carb car now-adays are "rare" and all the owners want to dress them up..
Larry Embrey

George's advice is very sound and Larry's reference to $$ is spot on. I have my own views about FIvCarbs but will keep them to myself**. It isn't the easiest conversion (nor the cheapest because you want an RV8 hood ) but you will very occasionally need some specialist backup - I would think twice about an FI set up unless there was a LandRover dealer within reach.


** but FI is the way things are going and in an MG generates much more interest than carbs - especially from the MGF fraternity.

Just to amplify what George in Yuma said about emissions and FI

If you go carburetor you will have to fit an airpump (if indeed the year car you put it in originally had one), which is a big pain. Az Dept of Environmental Quality will waive that requirement if you go with fuel injection.


As you have most of the hardware don't forget to consider after market control systems. The prices are lower over there but you should be able to get a control system with 3D spark for under $1000. That will give better spark than the dissie and free electric fan control, revlimiter, tacho output and no playing with carb jetts. A good conversation piece aswell.

I've gone down the FI route, the engine definitely gives more power than the average carb version, and is MUCH more fuel efficient (over 30miles per UK gallon on the motorway ).

2 problems, you will need the RV8 hood if you use the UK plenium chamber, but it fits OK and looks really nice on a B. You will also need a much modified fuel tank, with a swirl chamber and return pipe, I had difficulty getting a modified B tank, I gather the RV8 tank fits, but is smaller and very expensive.

Good luck anyway

Mike Barnfather
Michael barnfather

My 3.9 hotwire just squeeks under the standard '71 bonnet with the plenum castings trimmed per Roger Parker's instruction. The chrome bumper x-member was retained with about an inch of clearance between it and the sump pan. Next time, I'll use an extra UJ and steering pinion shaft (per Costello) and the engine could be dropped that much further. The limiting factor for me was the pinion shaft contacting the engine mount bolt where it passes throught the chassis bracket. Machining the plenum castings is far less expensive than an RV8 bonnet. You might get as much as $1,500 US for the whole system from a running engine if it's clean and pretty. I've read that the FI system offers capeability of managing up to 30% greater airflow over stock without modification or rechipping. That's alot of chrome!! I'll start the bidding at $800.

This thread was discussed between 15/01/2002 and 17/01/2002

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