What No One Tells You About DIY Classic Car EFI Conversion

Almost every Classic car owner will agree, carburetors are "finicky" mechanical devices. Without getting into too much detail, they basically work on "averages" between hot and cold conditions, most people don't know how to properly tune them and their operational deficiencies can be summarized by an old saying "When they are good, they are very, very good and when they are bad, they are very, very bad".
If you have a pristine example of a perfectly preserved or factory-perfect restored Classic, no one will ever convince you to modernize the fuel system, nor should you. Because it will lower the value of the car rather considerably. 

But if you own more of a "garden variety" Classic, it probably has a V8 with an aftermarket intake manifold and a Holley 4-bbl. We say that because of our observations; if there are 100 cars, parked hood-up at a cruise-in, over 90% of them are equipped as noted.
Over the past 5 years or so, the market has introduced EFI conversion kits. The earliest required piecing the system together and the ability to tune the system using a laptop. But the latest versions are available as an entire kit with ("almost") everything you'll need and are "self-tuning".

“We usually see an improvement of two or three miles per gallon after the EFI conversion. We had one conversion that gained seven mpg, but that depends on a lot of factors. How well the carburetor was tuned before you make the swap is a big factor."

Our research showed as they correct many "tuning" deficiencies, almost every article included significant increases in power, up to a 30% increase in fuel economy, and will start every time; hot or cold. Sounds great, right? 

Maybe, maybe not. So let's look at some of the things you need to know should you plan a DIY effort and before you put your carburetor "out to pasture".

STEP ONE - Decide "Do I really want to do this?" 
Regardless of what anyone says, "it ain't easy" if you take the "full frontal" approach depicted by several manufacturers. We included a very well done installation overview video below.  Our take is it was challenging even though the individual had done numerous "upgrades". So you need to evaluate the process, your skills, the cost and the end result.

True, "beauty is in the eyes of the beholder", but no matter what you do, excluding a custom install costing thousands of dollars, the additional parts COULD stand out like a sore thumb and, to many,  obliterate the "classic" underhood appearance. But if you plan well and take your time, the change is barely noticable.

While the installation can be completed by a person with above average mechanical skills, very few of these more rudimentary skills will help in the event of component failure. Who's going to fix it and how much will that cost? One thing none of the installation guides could confirm is is the "tuning head" will act as an ODB guiding a person to quickly diagnose which part has failed. If the comments warrant additional details, we'll get that answer for our readers.

As these systems become more advanced, there is the potential to upgrade the ECU and TB injector unit as a means of staying current. If possible, the cost is significant and may require a new ECU, wiring harnesses and other sensors or parts. Nobody wants an iPhone 3.

While some buyers might seek an EFI converted Classic, if they do they may be sensitive to the age of the install. If a newer version of the ECU and TB are available, they may include that in setting their price limit. 

Similarly, a shopper that regards an EFI conversion "sacrilegious" may choose to walk away regardless of price. In other cases, they may remain interested, but only if the price is so low they can factor in a full reversal of the modification.

If you've decided going EFI is what you want, here are some things the Marketing people never tell you.

First, Find Someone Who Has Completed an EFI Conversion
It might just be the best thing you can do to avoid numerous unpredictable errors and planning mistakes. Even better find and speak with as many "Conversionists" as possible. In that way, you can gather details from several experiences and further evaluate to effects of the conversion.It would also be a good idea to speak with at least one local shop that completes these conversions, look at their work and get a price for the whole job.

Second is to Decide Which Kit is Right For Your Classic
There are numerous manufacturers now offering "plugNplay" EFI kits. Most are between $1,999 and $2,500, a few higher. We also found this chart as an example of popular kits now on the market. There are more, but this should help you to understand the basics. While their individual marketing departments note their system is better than anyone else's, there may be a "market favorite". So choose wisely.
There are numerous other manufacturers offering EFI Conversion kits
Third Is To Decide What Type of System You Will Install

All of the kits are made to fit an intake manifold supporting the so-called square Holley flange (5 3/16 x 5 5/8 inches). If the one on your car does not meet this requirement, you'll need to purchase and install an acceptable replacement. Approximate cost is between $175 and $300. It will take the better part of a day to do it yourself and you need to have the necessary skills. Should you not want to do this work yourself, labor will run in the $100-$400 range. Some manifolds can be converted with an adapter plate, for far less.

All EFI conversions require an electric fuel pump and the removal of your mechanical fuel pump. At a minimum this will require removal of the pump and push rod (if so equipped) and a fuel pump block-off plate (about $10). You also need to remember, you'll need to plan how to wire the electric fuel pump regardless of style chosen.

Most kits are available in multiple configurations affording some choice regarding the fuel lines and tank. The choices include:
  • No return line w/ outside mounted fuel pump
  • No return line w/ in-tank fuel pump
  • Return line  w/ outside mounted fuel pump
  • Return line w/ in-tank fuel pump
In-Tank Pump Setup
The basic requirements are to modify the fuel tank to accept an in-tank setup and a return line (best choice) or buy a new tank manufactured as such ($900 to $1,400). You may not have a choice if none of the local shops understand and have experience welding a gas tank or if upon inspection declare the tank unusable. If yo need a replacement tank, they are $200 or less. We were unable to find an estimate for tank modification, but considering it is a time consuming job, we'd figure in about $200 labor.

FAST also makes a tank modification kit but it does require a significant amount of specialized tools, time and fabrication skills. If this is something you will consider, remember any leftover fuel/vapors can cause a fire/explosion. The proper method would be to remove the tank and have it "steamed" to extract all leftover fuel and "boiled" to remove rust and debris. You'll notice that in the following video, they are using a new replacement tank.
Did you notice the "Dual Quad" EFI? Yes you can add a two carb system
Outside Pump Set-up
This might seem the "lesser of two evils", but it has it's own issues. Pumps mounted outside the tank are noisey and run hotter. It's a pretty straightforward process, but requires significant care to mount the pump where is is well protected from road hazards.

Single Line vs. Return Line
All of the kit suppliers recommend a set-up with a return line, similar to modern cars. Pro's include a cooler operating fuel system and zero chance of "vapor-lock" (when heated fuel vaporizes inside the line). Con's are mostly related to increased vapor accumulation inside the tank due to the increased agitation of the returning fuel.

This may be a simple fix for some, installing a vented gas cap. But if the filler neck is mounted too low (e.g.-behind the rear plate) a vented cap can cause gas to pour out every time you accelerate or when the fuel expands due to outside temps. We found all types of suggestions online, but none conclusive.

Fuel Line(s)
All of the kits include flexible braided steel fuel lines and AN fittings to re-plumb your fuel line(s). This step requires some planning as the line MUST be routed and installed properly. Frankly, we really don't like the use of braided line exclusively, but as a DIY'er, there's not much choice. Should you feel the same, we recommend speaking with an experienced shop to learn what options might be available.

We figured by this time, you might want to give up completely because the concept of draining and dropping the fuel tank, modifying the tank, installing an additional fuel pump, installing flex hose fuel lines front to back, wiring, clamps, etc. might make you throw in the towel.

Edelbrock Sump Kit
Here's what most companies don't tell you. You can completely ELIMINATE dropping and modifying the tank, running new fuel lines and wiring up a remote fuel pump. Edelbrock offers a "hybrid" configuration. It can be used with ANY EFI conversion. Their Universal EFI Sump Fuel System Kit is an under the hood option. It's size is 13" H x 7.75" W x 5" affords numerous underhood locations. We couldn't help envisioning moving the battery to the trunk and installing this pump where the battery once sat. Hiding it inside a fake battery case also seems possible.
FiTech Sump Kit
In brief, it uses the mechanical pump to fill a fuel reserve tank. The tank has a built-in electric pump with a return and vent line. Voilà, all issues tackled in one fell swoop. Two possible drawbacks; it's almost $600 and if only your engine is under 600HP. But considering all of the work and complications it eliminates, we'd buy it in a second.

In addition FiTech offers a similar solution for engines that are up to or over 600 HP. Even better it's universal and under $400.
Fourth is to Review And Be Aware of Other Mandatory Changes
Regardless of which system you choose, you'll need to have your exhaust system modified to accept an O2 sensor. This requires a hole to be drilled in the "header pipe" or header collector and to have a "bung" welded in.What we found rather confusing is all of the kits we researched rely on a single O2 sensor vs. two. What that means is the system is guessing the conditions on the opposite cylinder bank 100% of the time. We don't think this is really any kind of issue as the EFI is a throttle body. If it were a port-injection version, two sensors would be mandatory.

While allowing your distributor to control timing and advance appears to be possible with reviewed conversion kits, doing so introduces a potential flaw in controlling the EFI. With no ability to control the ignition, an EFI system can only adjust the fuel mixture. Installation instructions include the suggestion to replace or modify your distributor to enable the EFI control unit to also manage timing. In all cases this requires additional items which vary in cost. Most importantly, an error in wiring the ignition will "fry" the ECU (not a warranty item). Replacements are over $1,000.

Without itemizing every item, a qualifier DIY'er will have to spend about $3,000. That's presuming you have all of the necessary tools, etc.

Time to Complete And Level Of Difficulty
Several reviews commented the time for a seasoned professional to complete once all parts are in order and all the planning details have been completed is about 8 hours. 

They also noted a person with adequate mechanical skills and knowledge should plan for a minimum of 2 days, also excluding any planning time. 

If you're a stickler for detail, plan even longer. As the saying goes, "Measure twice, cut once". Based on our evaluation, here is a very thorough overview of what it takes to install a "common" EFI Conversion Kit following conventional installation suggestions.

Break Even Point
As noted, you may experience as much as a 30% increase in fuel economy, but with limited driving (2,000 miles a year) even at $5 a gallon the change from 11 MPG to 14 MPG will save you about $200 a year. So the break even point will not occur for 12+ years if you do the work yourself. If you have a specialist shop complete the install, it's likely to add another 10 to 12 years.< Are There Alternatives?
As we noted at the beginning of this article, most people don't know how to properly tune a carburetor, select the right jets, accelerator pump cam, linkage clearance, etc. We also noted in each of the install videos we reviewed, the "post conversion" HP and Torque rose dramatically. That indicated none of the cars were properly tuned.

Therefore, we'd recommend considering a visit to a shop that specializes in the tuning process. Our research indicated it may take a few hours at a cost of $300-$500, but when done it may rectify many of the ills you are experiencing. 

Every article and video we reviewed had nothing but excellent reports of the post-conversion experience. We think it's something worth considering. If you have completed one of these conversions and have either good or bad experiences to share, please do so in the comments section below

Until Next Time
The Garagistry Team