Has anyone converted their 331 engine to use Electronic Fuel Injection?

[TRLockwood]

I have a Cadillac 331 engine (from a 1954 Series 62) which I hope to convert to Electronic Fuel Injection. Currently, the engine has its stock Rochester 4GC Carburetor. I'm considering using the MSD Atomic EFI unit marketed by Holley. Has anyone out there done such a conversion? The most challenging aspect appears to be adapting the Atomic EFI mounting flange to the 331 intake manifold. Otherwise, this should be a very straight-forward upgrade that will offer numerous advantages.

The Atomic EFI unit uses standard Holley 4160 "square bore" stud spacing (5.160" x 5.625"), which is wider than the stud spacing used on the 1954 331 intake manifold (~4" x 4"). So, a custom adapter plate will be required. I'm curious to know if anyone has experience with this.

[TJ Hopland]

The first question with any EFI conversion is why?  Are you going for more performance? Better fuel economy?  Better starting and less chance of vapor lock?   Just hate carbs and think EFI is neat?

I don't know much about that specific system or engine and have not really kept up or stayed that active in the EFI community since I did my last one which was an FiTech which is more like the Holley Sniper.   I see the price has really come down on the Atomic which seems really strange since its Holley and they have the Sniper.   

I was looking for a quick comparison between the Sniper and Atomic but didn't find one.   Was there some specific feature of the Atomic that the others don't have?   I did the FiTech because Holley didn't quite have the Sniper to market yet and Atomic was still kinda a homeless stepchild no larger company wanted to take part in.   I'm pretty sure they had been around quite a while with some good ideas but just could not connect with the right group to get it to market and support it.  Looking at the quick recent history looks like MSD ended up with them and Holley ended up with MSD in 2015 which was about the time the Sniper came out so that explains why both products exist with very similar features and price points.


Anyway things you will have to deal with no matter which system you choose are the thing you mentioned about mounting which I would not think would be too big a deal.   Kinda surprised no one makes an adapter since both EFI now and square bore carbs are so popular to swap onto older motors.   Depending on your intake design you may also need to make your adapter higher to clear the intake since the throttle arm will have stuff hanging off the bottom that is used for some transmissions.   

Another thing you will have to make on your own is what ever linkage you need for your transmission.  What is there appears to be designed for something like a THM700 with a cable.   Not sure if it will be an issue with yours but people converting from Quadrajets always have to extend the throttle arm to mellow out the pedal response.  With the stock setup its almost undrivable.   

What are you thinking for a fuel supply?  A majority of the issues and complaints you read about on the forums are related to the inline fuel pump.    Short life, noise, loosing prime, and having to keep the tank 1/2 full and even then having issues.   Trying to run without a return also seems to cause issues so I would avoid that too.   The in tank conversions seem to work out OK but I have not done one myself or actually talked to someone in person that has done it or has one.   Those usually involve a foam like sump area thing you stuff through a new hole you drill in the top of the tank and then insert a new high pressure pump and sending unit.    If the tank is on the deeper side I could see this working pretty well.    Flat wide shallow tanks have the most issues with fuel sloshing around. 

Another option is something called a swirl pot or surge tank.   This is a small tank you mount up front somewhere that contains the high pressure electric pump.  You feed the tank with the original mechanical pump so the only change you may have to make to the original system is to add the return if it didn't have one.   Basically there are 4 ports on the tank.   One is the high pressure out from the pump and the other 3 are just open to the inside of the tank.   One is the inlet from the mechanical pump.   Another is the return from the rail/regulator and the last one is the return back to the tank.   Any air or excess fuel gets pushed back to the main tank.  This also keeps a constant flow going which helps keep temps down.   

Sounds perfect right?   Not quite, you do want to try and mount this as far forward as possible where it can't get any hot air from the radiator or you will easily still vapor lock on a hot day.   If you can get it in a reasonably cool spot it does work pretty well and can save you from having to modify or replace the tank and does seem to be much more reliable and a little quieter than an inline pump.    I used the older version of this one.   https://www.robbmcperformance.com/products/powersurge.html     

There are others just be sure to avoid the ones that have a float in them and claim not to need a liquid return line.    Those are way more complex and problematic than they need to be.   The float is one more possible problem area and then you don't get the circulation so you will have vapor lock issues on warm days.

Don't forget about your electrical system.  Is it up to the task?   Does it have an extra 10 amps or so capacity?  You have the electronics injectors and a fuel pump that will constantly be running along with anything else you added that wasn't stock.   Forums are full of people with issues that turn out to be electrical because they are starting with those 60's or 70's strip down cars that just don't have any power to spare. 

[Jay Friedman]

You might want to contact Art Gardner who did this to a 331 in a '49.  He is in the CLC directory in Georgia. 

[dinhnguyen57]

I don't have much experience with EFI, but I did try to install a Holley Sniper onto a 500 engine and I learned the same as mentioned above. 

The noise from the gas tank might be annoying.

An important point that does not seem to be mentioned by Holley but is mentioned quite a lot on other websites and by those who install these Holley EFI unit, is that a single plane manifold is better.  Some people even say it is required, as the sampling of the gas mixtures between the two planes may give erratic signals to the EFI computer.

After multiple attempts, I gave up and went back to the carb set up.  I've been happy with my original carb set up since the costly lerning experience.

[phildeville@cox.net]

I installed an EFI Tech kit in my '54 2 years ago.  I regret not installing it 15 years ago....
I used a speed shop adapter.  Diecast crap...broke easily.  Was a bit more careful the next go around.  NO more stalls, hard starts for me!  Mileage went from 10 to 14 on interstate w/ a/c on.  Had to do some linkage, filter ring fab & relocate coil to reduce EMI.

GL,

Phil

[TJ Hopland]

I too have 'heard' you need a single plane intake but have never been convinced its really a problem.    The 'mixed' signals doesn't make any sense because its 2 from one plane and 2 from the other on each side and even if you are just monitoring one side or plane you should be getting the same thing from the other not to mention that as far as I know none of the systems have a way to adjust the sides independently so if there was a difference not sure what you could do about it.   

I have a stock dual plane on my 500 and as far as I can tell no issues in the 1000's of miles I have put on it so I don't think there is a difference to an average person.   I don't doubt on a track or dyno you may be able to tell a difference but for a driver car I don't think it matters.

I do really like having the EFI and never once thought of going back to a carb.   Ok maybe one time when I thought the fuel system was causing a problem but when completely changed it from a homemade one to a fairly new store bought one I had the same issue that turned out to be ignition I was glad I didn't switch back.    I have not had to do anything with my fuel system put put gas in it several years in a row now.    If / when I do another I will seriously consider the Sniper over the FiTech but don't think there is anything really wrong with FiTech either other than they don't seem to sell parts like Holley does.   

[55 ledsled]

I dumped the Rochester on my 54 and dropped a edelbrock 1406 on it. perfect starter every time!

[bcroe]

My engines start instantly if the carb is full of gas.  The problem comes
when the engine is not started for a while and the carb dries up.  An
electric fuel pump can cure that, but that doe not mean needing a whole
EFI system.  Bruce Roe

[Jay Friedman]

My '49 starts perfectly every time.  Its Carter WCD 2-barrel carb is the state of the art for the time, having been around for a number of years.  4-barrel were not introduced until '52 and, in my opinion, being brand new they, particularly the Rochesters, seem have some problems. 

I think another factor in ensuring good starting performance on my car is that I've cleaned up and improved all the ground points in the starting system.

[fishnjim]

I think this is better discussed on the "modified cadillac" section site or we'll be debating putting rocket packs on dynasoars next.
Talk to Holley, it's their product.   Who knows better?   All you'll get is sour grapes from purists and mis-installations, etc.   

[TRLockwood]

Thanks for all this input. The primary technical roadblock I've encountered is that the Holley and MSD EFI systems require a distributor with a phase-adjustable rotor. The only modern distributor upgrade for the Cadillac 331 is a Small Cap distributor which offers pointless ignition but does not have a phase-adjustable rotor. One could have a modern MSD billet distributor custom machined to fit the 331, but that's deeper than I'd like to go.

[TJ Hopland]

Computer controlled timing is for sure one of the benefits of an EFI system but I don't think is required for any of the systems you would be putting on an old engine.   I would also NEVER recommend to anyone considering this type of conversion to do the ignition/distributor at the same time.   You want to do these systems on a decent running engine that is past is break in and really runs pretty good.   Maybe not perfect but you don't want to be expecting to 'fix' any significant problems.   

As far as I know all the systems will even trigger off points if that is what you are running now.  So the thing to do is just do the fuel part of the conversion first and get it running.   DON'T even touch the distributor other than to hook up the tach wire.    Get it running at least as good as it was before with just the fuel part of the system before you even consider the ignition side of things.   Many people are happy at this point, especially ones that are not running engines where there are dozens of off the shelf ignition options.  Once you have it running good and you think you want more then go for the ignition conversion.

Because of things like the rotor phasing which for some reason is hard for apparently even the manufacturers to wrap their heads around and explain the ignition just adds way to may variables you just don't need when installing a system like this and since its not required to make the fuel system work it just makes sense to skip it at first.

Now once you get the fuel running and want to do the ignition......

Are you sure the only way is with an adjustable rotor?   It makes it easier but I would assume there is some sort of an offset you can program that will still allow you to get it set.  My FiTech has that.  Only reason Holley and MSD would not have it is they just happen to also sell distributors.   

It can be a hassle because what you have to do is change the offset which changes everything then you move the distributor which changes everything again.   Its a lot of back and fourth especially if the system doesn't let that change happen in real time.   I think on my FiTech system you had to shut the engine off then change the number then power cycle the system so it rebooted and used the new value.  You could then take readings and adjust again.

To do this setting I drilled holes in an old cap around one of the towers so I can point the timing light in and see where the rotor is when its firing.   If its at least close you can also see where its tending to operate once you get some miles on it by just looking for the corrosion on the terminals. 


I have not really paid close attention to this scene since I did my last one a few years ago but even then there were rumors that companies were working on a distributorless options.   It would most likely be an external module that takes the existing coil signal and converts it to the individual signals needed for individual coils.   You would then have the option to by new coils or go to a junkyard and pull them off something else.  The real DIY people were doing that when I did my first system over 10 years ago now. 

Not sure why the bigger companies haven't picked up on that yet.   Only real trick would be to make this work you would have to have some sort of sensor that told the system where #1 is which they don't have now.   All they know now is that they are getting a pulse every 45* of distributor rotation.  That offset I was talking about earlier is what tells it the relation of that pulse to the actual crank position. 

More modern engines have a crank sensor that has quite a few pulses plus a reference one to tell it the actual position so its pretty accurate.  The reference one only says that 1 and 4th cylinders for a V8 are TDC so that is where the crank sensor comes in to figure out which one is compression vs exhaust.   While its making that first spin to learn that it fires both spark plugs and the injectors in batches.  Once it learns where everything is it can switch to sequential injection and not wasting a spark on the exhaust cylinder.   Not that it is that much of a waste, 80's and 90's systems usually only had 2,3, or 4 coils and they always fired in pairs just to save money on extra coils.   

[51Chevy01$]

I have a Cadillac 331 engine (from a 1954 Series 62) which I hope to convert to Electronic Fuel Injection. Currently, the engine has its stock Rochester 4GC Carburetor. I'm considering using the MSD Atomic EFI unit marketed by Holley. Has anyone out there done such a conversion? The most challenging aspect appears to be adapting the Atomic EFI mounting flange to the 331 intake manifold. Otherwise, this should be a very straight-forward upgrade that will offer numerous advantages.

The Atomic EFI unit uses standard Holley 4160 "square bore" stud spacing (5.160" x 5.625"), which is wider than the stud spacing used on the 1954 331 intake manifold (~4" x 4"). So, a custom adapter plate will be required. I'm curious to know if anyone has experience with this.

Thanks for all this input. The primary technical roadblock I've encountered is that the Holley and MSD EFI systems require a distributor with a phase-adjustable rotor. The only modern distributor upgrade for the Cadillac 331 is a Small Cap distributor which offers pointless ignition but does not have a phase-adjustable rotor. One could have a modern MSD billet distributor custom machined to fit the 331, but that's deeper than I'd like to go.

[badpoints]

I converted my points and don't feel bad about it. I would not want to lose my carb. It would take away the nostalgia of the engine. I would rather have an LS engine than a fuel infected 429.

[Caddy Wizard]

I've had 22 antique Cadillacs from 49 to 62.  I have done EFI on one of them and it wasn't very hard, really.  I did it on a 49 331 which was getting AC and 12v.  The conversion was pretty straightforward and worked extremely well.  I kept the stock air cleaner (with some internal modifications), and the final result looked very, very stock. In hindsight, it was a bit overkill on the 49 engine as the Carter 2-bbl carb on the 49 331 is a great performer and rather trouble-free.  Not terribly prone to vapor lock (in part because the relatively low HP 49 engine doesn't create as much heat as the later 331s and 365s).


I am planning to put EFI on my 55 FW, for greater reliability, better economy, and easier starts between uses.  The 55 produces a LOT more power than the 49 engine and is much more prone to vapor lock.


The EFI systems now are essentially an electronic carburetor with a feedback loop (O2 sensor and computer).  Very simple to install.  You have to add a coolant temp sensor, an electric fuel pump (probably in the fuel tank), an oxygen sensor in the exhaust, and a little adapter on the throttle of the throttle body to accept the TV rod from your Hydramatic.  The last item sounds hard, but isn't.  All you have to do is to carefully note the exact radius (distance) of the TV rod connection from the throttle shaft and the clock angle of the same relative to the shaft when the throttle is closed and mimic that with your little adapter that you add to the throttle body throttle.  It is harder to describe than to do.  These kinds of systems can be retrofitted in a weekend for about $1500 in parts.  Given that a proper restoration of a Carter or 4GC runs about $450 and a new fuel pump is another $100, it is about triple the cost of redoing one's carb set up.  But it will start instantly, even after sitting for a month or two and will NEVER vapor lock on you, even in a parade on a hot 4th of July.

[jwwseville60]

Electric fuel pump and a return line. For older engines from the late 40's and 50s 2 barrels, drilling out the jets is the way to go.

EFI is not developed enough, and for really old engines its junk. Unless you really want to fiddle with it all the time.

[TJ Hopland]

Electric fuel pump and a return line. For older engines from the late 40's and 50s 2 barrels, drilling out the jets is the way to go.

EFI is not developed enough, and for really old engines its junk. Unless you really want to fiddle with it all the time.

You don't consider running wires, lines, and drilling out jets as fiddling? And I and I'm sure others would like to hear more about your statement about it being junk and having to fiddle with it all the time.  That hasn't at all been my experience.  I would really like to hear more about yours.        

[bcroe]

The variety of capabilities in EFI systems
since the 70s, is so great that it makes
little sense to just lump them all together
in one catagory.  Better to have discussions
on all the possible features.  Bruce Roe