Fuel injection choices: manifold, carb bodies etc

I’m posting this in response to several emails and questions I’ve received concerning the choices of carb body, manifold, injector, holder, etc. for converting MGB’s to fuel injection. I've been exploring ways for someone with only simple tools to inexpensively retrofit fuel injection to cars with various SU and Zenith Stromberg carbutetors.
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There are several ways for converting an MGB to fuel injection using commonly available British car parts. The choices are a matter of convenience, performance, economics and appearance goals.

There are a number of intake manifolds which work. The manifolds which were originally supplied with twin 1.50 SU’s are plentiful, cheap, and work fine. The (somewhat rarer) manifold for twin 1.75 SU’s is also good. (I have not used any manifolds for only one carb because the common setups for single carbs generally starve the motor for air flow.)

There are two kinds of holders for the injectors I have made and used:

The easy, cheap, fast and reversible approach uses the “Top Down” holders. The holder is made from a couple of pieces of flat stock, and it bolts onto the top of the carb body in place of the “dome”. The “dome” can be left off completely or modified so the finished setup is reminiscent of the stock appearance. Alternately, a flat cover may be used (picture below).
The second way is the “Bottom Up” approach. The injectors are mounted so they inject from below the Carb body. This approach requires modifying the carb body, and takes about an hour or so per carb, but the result is a very neat , very ‘Stock Look”. Both of these ways perform about the same.

I have used different carb bodies: 1.50 SU’s and 1.75 Zenith Strombergs. The 1.75’s give the best performance so far. The top down and bottom up holders give equivalent performance. I converted a 1.50 Zenith Stromberg (made both “Top down” and “Bottom Up” holders, but did not mount or test it . I had found the much better performance from the Zenith Stromberg 175’s, so went no further. The 150 Zenith Strombergs require making an adapter plate to mount on the twin SU manifold.

There are at least two choices of injectors. I’ve used cheap ‘previously owned’ injectors (approx $2 each) from GM and Ford which are high impedence and rated at about 19#/hr. I’ve used 2 injectors per carb. I’ve preferred the shorter style ones (2 1/2 inches end to end or shorter) for the “Bottom Up” application, but ones of most any length are also OK for the “Top Down” application . Incidentally, there are single injectors of suitable flow rate (38-45 #/hr) available (so it would only take one injector per carb body). Those injectors are usually much more expensive, even “previously owned”. They are common in racing and performance applications for larger, high horsepower motors. There are also some very small ones of high flow ratings, but they are more expensive.

My choices, based on my experience: If I were just starting, I assemble a manifold and carb setup, and use the top down holders first. They are so quick and easy to make. You might download the patterns, print them out to proper scale, and then paste the paper pattern directly to a piece of sheet metal. Cut and drill. Bend the finished metal piece to fit in place. Mount the injectors, etc. and its g2g (good to go) You can always spend more time later to make a pretty setup, but getting running on EFI sooner is really great. The 1.75 Zenith Strombergs are such lousy carbs and so cheap, I'd use them. They are usually $5 a piece-sometimes less.They are also a little easier than the 1.5 SU's to modify for "Bottom Up" Injecting. They do look cool...

I'm attaching a few pix for comparisons.
The top left set shows the Top down on ZS 175's. The rt carb has a decorative flat cover on it. One can use a cut out Dome for the sake of appearance (I posted a picture of that earlier)
The top right setup is a pair of 1.50 SU's with "Top Down" holders.
The bottom left is a pair of HIF4's with "Bottoms Up" holders

Legal disclaimer: These comments are my opinion and a recount of my experiences. Enjoy these comments but use them at your own risk. I assume no responsibility whatsoever for what you do with this information. Working with automobiles and flammable materials puts one at risk of personal injury, property loss, or death. Don’t sue me.

Very interesting. I have been following these posts for a week or two now and I am very intruigued. You make it sound so easy but I am sure I would make a mess of it. Love to read about it and keep up the good work. Hopefully someday you like some of the others on this board will put together a kit to sell to us lesser mechanics.

Several people have approached me to provide a 'kit'. I have done this research/development activity for purely personal interest and have no desire to run a business. I feel the route I have taken most anyone can do with modest tools. I am happy to provide all the details that make it work for me. I am also not interested in the headaches or the liability exposure of such a business. I am a 65 year old retired technical professional with a love for certain cars.

I might be willing to provide a video to show what I have done for each of the steps in the whole retrofitting and also provide a list of all the parts. Would this suffice? It would save me buying and inventorying almost all the expensive parts, to which I add no direct value. The expensive parts are the fuel pump ($50-$100), variable pressure regulator ($40-$60), the electronic ignition (optional) and the the megasquirt computer. An inline fuel pump is just that: any anyone can pick one up locally. The megasquirt can be shipped to someone directly, rather than to me first. There isnt much reason to ship megasquirts from one place to another, except to give the shipping services a second chance to damage or lose it. I get all my sensors from a junk yard or from ebay, and shipping is often more than the cost of the items.

What I have done is found ways for someone of average ability to use very cheap and readily available materials, and modify some of them somewhat to make a unit of significant value in use. I have used very inexpensive materials (less than $50) to make a set of carb bodies into a fuel injection device. I have also learned how to tune cars using the Megasquirt. It is quite easy to get pretty good results with very modest effort.


I would appreciate some feedback on this topic.

I very interested in this, thank you for sharing, for now I would like to just enjoy my newly rebuilt everything B.

Scot....thanks for continuing to post your experience here. I've been following all your posts and am intrigued by your simple approach.

I'm going to replace my DCOE with a DGV soon, so I may try to see if a similar approach is feasible with a DCOE. I've also got an SU manifold, but no carbs or linkage.

It would be nice if your entire series of posts were available for easy reference either in a journal on this site, or hosted on another site. Being able to follow your efforts from start to finish in one place would be a great help to anyone going down the same trail...

That is an excellent thought, Joe. An awful lot of exceptionally good info is still floating around the internet, buried in the archives of threads on BBSs, some of it not even searchable. That is truly unfortunate, but it is the nature of what happens on bulletin boards and those who post things. The best that I do is collect stuff into my MG Files, but I am no better at organizing it than simply shoving the stuff into folders on a topic. It takes time and effort to compile stuff into some sort of cohesive and coherent form and not all of us are willing to do that. Probably the best venue for compiling such info is the website, owned and constructed by the author, but even that can be outside of many people's skill or budget. I guess we need better search engines.