Fuel Injecting MGB's with SU carbs

I recently modified a set of Zenith Stromberg carbs to hide the fuel injectors on the underside of the setup. Not surprisingly,I found the car ran well using the same tuning parameters on the Megasquirt. It did require modifying the carb body, but the result is cool looking.

I have now found I can do the analogous thing with the SU carbs originally used on the car. It requires some drilling, cutting and simple shaping to remove the floor of the carb and to modify the integral float bowl to make room for the injectors. For the sake of comparison, I'm posting a setup which has one stock carb and one converted to fuel injection.

The air filter hides the front view, and all the rest is hidden beneath the inlet system.

As a secondary note, you'll notice I used two 19#/hr injectors (because they are so plentiful and cheap "previously owned" on ebay), but one can use a single injector of larger capacity (35-40 #/hr). Such injectors are widely available and occasionally come up on ebay. They are popular for high performance big V8's (Ford nd GM), and cost about $50 each.

I will be happy to supply details if anyone is interested.

Man, there's something about destroying a set of HIFs that bothers me. Would it not be better to use a set of wore out HS4s instead? Or a single block of aluminum machined to take the injector with a butterfly for throttle?

Hi Scott
I have several old HS4 and HIF carbs and a couple of intake manifolds hanging around and I might be interested in trying this FI idea you have been working on. I have a few questions. Are you using any of the following in your design? :
Knock sensor
Idle air control
O2 sensor
Ecm model (1227747 GM?)
Distributor (computer controLled advance)
EGR
MAP
MAF
TBI fuel pump?
THe final question is how do you inform the computer of vehicle speed/load?

Thanks

SORRY if I offended someone's sensibilities about HIF's. Nonetheless, this pair will now work better than they did while lying on the ground in an open field, and they'll even work better than they did when they were new at introducing atomized gasoline into the motor.

I'll probably get around to the hs4's in a bit. I had a set of hif's around which were corroded beyond utility. The risers were stuck solid, and the throttle shaft was badly worn.

Answer to above post: (All this info below is on my previous posts on this site or on the megasquirt.info site)

Are you using any of the following in your design? :


Knock sensor can be added. Megasquirt can handle it
Idle air control Not needed
O2 sensor Yes.
Ecm model (1227747 GM?) No. I used MEGASQUIRT ECU
Distributor (computer controLled advance) Megasquirt can do this. I will do it next month

EGR if you like you can add it back
MAP MEGASQUIRT
MAF not needed
TBI fuel pump? N o. Hi pressure EFI pump. Most TBI injectors only run at 12- 14 psi. I am using port style injectors which run at about 30-45 psi
THe final question is how do you inform the computer of vehicle speed/load?

The ecu tracks manifold pressure and rpm. It can also, if you like, use additional info (water temp, air temp, throttlle position, etc.)

Thanks

Scot, nice work.

I have a friend who is going to do a EFI conversion, and I've looked around a bit....

I did find this TBI setup for $545 http://www.extrudabody.biz/servlet/the-135/Twin-SU-SU%27s-MGB/Detail

It needs ECU (megasquirt) and injectors, and sensors to complete it....


utube video of a running setup is here: http://www.youtube.com/watch?v=kHR8_fCylEA


keep working Scot, looks great!

Thank you for your kind words.

The extrudabody setup is really nice looking first class aluminum extrusion approach.

I did notice that it interferes with the brake booster which are common on later cars, so some changes will be required for a B with power brakes.

It might be cheaper to use 175 zenith strombergs and go with the adapters from Rick Patton (~$350), or about $20 if you copy what I've done.

When I get tired of driving and building, I think I'll start trying to post examples of the car on youtube.

Would it work to mount the injectors in the manifold just downstream of the carbs rather than in the carb, and then just use the carb bodies for throttle?

Scot, I'm not familiar with the adaptors from Rick Patton....how do I find out more?

Thanks.

Mounting the injectors into the manifold downstream from the carbs does not work well with 'siamesed' motors because there is not enough mixing volume before the intake valves. There are a number of reported attempts which dont work well.

Placing the injectors before the throttle plate eliminates that issue and makes for the smoothest running setup. There is enough air volume to insure good mixing before the air and fuel are drawn into the combustion chamber.

I chose to use injectors which are normally used near the intake valves ("port style" injectors) because they have a great spray pattern, whereas the common throttle body injectors have much less efficient spray patterns. I also prefer the port style injectors because they are high electrical impedence- which means the port style injectors draw much less current, so they are easier on the ecu and also run cool.
Tbi injectors are usually low impedence, so they take much more current to operate, requiring cooling, and they do not give a fine spray pattern. They were the first attempt GM made to convert their carburetted cars to fuel injection.

Scot,
you should follow Pattos design of TBI adaptor plates for ZS carbs and also for SUs http://sidedrafttbi.com/index.htm (each costs 125 USD). Adapter plate accommodates GM TBI 700 injector. Those injectors were in Europe usually used in Opel cars and you can easily find them in scrap yard with old cars.
I bought two adapter plates for SU carbs, but did modify them so they are completely hidden and you can not be recognized that car has TBI system and not standard SU carbs. Unfortunately I am moving very slowly so I am still far away from finished installation. I plan to feed fuel trough carb bowl from which I removed float and plug the overflow hole. In the carb body I made two holes, one to fed fuel from bowl and another for cables. I have now more or less al components and hope that will be project finished til summer.

more pictures

Scott and Tony, thank you both for doing is often only talked about. This sort of work is probably more interesting than restoration and more challenging. It is interesting that you have both been able to keep the costs down and that will appeal to many more people than most of the out of the box setups, given what they run.

I compliment you on the cute way of hiding the onjectors in the dome and running the fuel alongside the carb body.

I am well aware of Rick Patton's work. Nice parts, well machined. Costly and uses old fashioned type injectors. I chose to NOT go that route. Perhaps you might do an author search on my name and read the postings that discuss that issue and others.

I wanted to find an inexpensive way so anyone could do it themselves with simple tools. The entire system-computer, adapters, sensors and all cost about $400- a lot less than the $1500 to take Rick's route.

The ZS 175 conversion (Injectors from the from the bottom) takes about 2 hours to do complete. The conversion from the top takes about 20 minutes to make for any of the carbs.
Summary:

I do not want to use the old TBI style injectors, I didnt want to get trapped into using some reprogrammed computer I couldnt tune myself, and I didnt want to pay so much money.


I suppose I could have put the port style injectors inside the dome, but I chose to do it this way. Maybe I'll try that next...

Scott I agree with you regard TBI injectors, those are even low resistant so it will be alot of porgraming with MS EFI, but I put appearance in front of performance. My first idea was also to use modern Pico injectors (small and also with high flow rates - a lot of modern Fiat cars has them, no problem to find them here) but just can not find time to play.

The small injectors-about 40#/hr could well prove suitable in this application. One might make a single block and mount it to the center stem (suitably shortened) in the SU dome, or to the carb body. This block would hold the injector and also serve for the fuel feed connection. I would be tempted to run the line straight through the air passageway and out through the center hole in the carb body which was used for the jet. For the sake of simplicity, I've not drawn in the block.

In any case, this approach is more expensive and complicated than the simple routes I have chosen to explore. I have felt that a simple, inexpensive and direct route to getting fuel injection in place was an important goal to meet, since a number of people will not do a project if it is too expensive, or give up midstream if a project gets too complicated. An important thing to keep in mind is that the carb adapter is but one detail in the overall EFI retrofit, and it is easy to change later, after the car is running on EFI.

Cool injector Toni! Is there a website where one can source that type and the retainer?

Thanks!

There is many manufacturers of those injectors, Bosch call them EV 6 (standard not long body), Magneti Marelli marked them with IWP (on some markets are selling them with Weber name), and so on. I know that a lot of Peugeots, Mercedes, VWs, Fiats have them, but have no idea how is that at your continent.
Flow rates are from 0,33 l/min to 0,55 l/min and even more. For Europe I know few suppliers, but in USA I do no know them, you will have to Google a bit. Here are some links:
http://www.turbo-link.com/tlink/details/catS107.html
http://www.bosch-motorsport.de/content/language2/html/2610.htm
http://www.racetronix.com/S107FM.html
http://www.webercarburators.com/fuelinjection.htm

I am shore that you can find better offer than those from here. I bought injectors on e-bay for 20 € (used) and retainers from Burton (www.burtonpower.com) but if you look to this tech data http://www.racetronix.com/images/injectors/S107.pdf you can make them yourself.

I hope this would be of some help.

Scot,

Excellent work you've done here, I really look forward to a full writeup if you are so inclined. I have never much liked the finickiness of the SU carbs and would be very interested in trying out your system if I was able to get a good set of instructions/directions.

Thanks for all your hard work and keep at it!

Scott

Scot, I would like to add my name to the list for instructions.
I just rediscovered a set of SUs I was going to rebuild, but I think I would like to try
your way first. I have got a VP12 , port job, 040 etc., so I think this would wake the car up! Thanks for all your research, it keeps us old hot rodders interested.

Rich Hagon