Sniper XFlow Install: '74 Plymouth Duster

Posted by Joe Smith 09/17/20 1 Comment(s) Customer Rides,

We are glad to share this excellent restomod story from our friend, Jay Wright, who recently brought new life and Holley EFI to his family's treasured '74 Plymouth Duster. This write-up is well documented and full of helpful resources and wisdom that Jay learned along the way in his first EFI conversion. We are glad that Jay made EFI System Pro a part of his journey and we love seeing this generational family racer back on the strip!


My First EFI Conversion. The Good, The Bad, and the Ugly.

By: Jay Wright

I am a just backyard mechanic that has been tinkering with hotrods my whole life. My builds are always Hot Rod or Street/Strip builds and for me, it is Mopar or No Car. I have never done anything with any EFI system at all. I have always been a carburetor guy that just works on classic cars when I can.

Earlier this year, I was able to buy back an old family Street/Strip car that had been sitting for over 18 years. The car had a lot of sentimental value to me as my father and my brother both used to race it. It is a 1974 Duster with a 360 and 150 shot of Nitrous. It is and always has been an UGLY car but we kind of liked it that way. We have always affectionately called this car the Ugly Duster.


When I got the car, the wiring was a total mess. It had been butchered a lot over the years and a family member had started to “Rewire” the car when it was parked all those years ago and only got about 10% of the way done. In other words, they had just started snatching out all wires.

It was not much better under the hood.

My plan for the car was to bring it back to its former glory and still keep it ugly as it always has been but add a few more surprises under the hood. It was time for me to join the modern age and go EFI.

After researching all the current options, I decided to go with the Holley Sniper XFlow. The motor was in the 500 HP range and I planned on running a 150 shot of Nitrous. This put me past the 600 HP rating of the standard Sniper or Super Sniper so the Sniper XFlow seemed to be the best choice.

After research and shopping around, I decided to purchase from EFI System Pro. I am sure there are a lot of other great vendors out there, but I could not be happier with my choice to go with these guys. Chris from EFI System Pro was great to work with. Much more than just a sales guy. They took the time to answer all questions I had before, during, and after the sale. You just don’t find that kind of service anymore and it is appreciated.

I went all-in on the upgrade. I bought the Holley Sniper XFlow, Hyperspark Distributor, Hyperspark Ignition Box and Sniper EFI Coil, 6.8” digital dash, Tanks Inc EFI Fuel tank, Holley In-tank Fuel Pump, and Holley Filter Regulator. I wanted everything to be as plug and play as possible as all of this was new to me.

Before I could jump in on the install of all the new goodies, I had to address the wiring in the car. It is no secret that these systems are susceptible to RFI. Good clean wiring is the key to success.

My go-to for learning the best practices for wiring all came from Devin Vanderhoof. Devin has dozens of YouTube videos that are fantastic.

Most of his videos are for much higher-end cars but the principals he covers in each video apply to all builds. His video help was essential in learning the right way to approach this. I watched every one of his videos and some several times before starting this project.

I started by removing every bit of wiring in the main Harness. I left the harness to the rear taillights and to the headlights intact but everything else came out.

Originally, I had planned to install a new generic harness from one of the big suppliers but after watching one of Devin’s videos, I learned about Leash Electronics. They have a Pro Street Board that did everything I wanted. I would be able to build my own harness and still use Mopar factory Connectors to plug into the harnesses I left in the car. This tiny little box has all the relays, fuses, and flashers for all the basics in any car. Turn Signals, Brake Lights, Ignition, and some extra Inputs and outputs as well.

I mounted the Leash Electronics Board, The Hyperspark Ignition Box, and an MSD solid-state relay pack to a panel that would be mounted in the passenger side interior firewall. The MSD Relay Pack would use ground inputs from the Sniper XFlow to run my Nitrous, Purge, and two Fans.

From there, I built out the wiring harness and used the Mopar factory connectors so that everything was as plug and play as possible and would not require any wire splicing anywhere.

Next up was running power and grounds from the Trunk Mounted Battery. I also had an NHRA Kill Switch that had to be worked into the wiring as this was to continue being a Street/Strip car.

I ran 3 separate grounds from the battery using 4 Gauge welding cable. One to the Chassis, One to the Panelboard, and one to the engine block.

I ran two 2 gauge Positive Wires. One from the Battery to the Alternator and a switched wire from the Battery to the Kill Switch to the Panel.

With this done it was time to start installing all the new goodies. The new EFI Tank went in easily however I had a lot of trouble with the Filler neck gasket I bought. The first one I bought was an OEM Correct gasket that seemed to fit however it was very ridged and no amount of lube would allow the filler neck to slide in. Eventually, I went with a much cheaper filler neck gasket, and then the Filler neck slid right in.

Next, I mounted the Holley Filter Regulator and ran new fuel lines. I wanted all braided hoses and all new AN fittings. The AN fittings were a pain to deal with at first getting on the braided hoses until I discovered something called a Koul Tool. This is the best $30 I have spent in a long time. Makes assembling AN Lines much easier.

Then I installed the Hyperspark Coil on the firewall and installed the XFlow. Because I had planned out everything in advance, that part of the wiring was fairly easy.

I ran power and ground from the XFlow and the Hyperspark Ignition box all the way back to the trunk-mounted battery and they were connected to the side post terminals. Everything else I ran off the top posts keeping the EFI stuff as isolated as I could. I leak tested the fuel system, primed the oil pump, set the distributor using the plastic cap, and then ran the Holley setup wizard.

This motor had sat for over 18 years without being fired. I hit the key and It fired immediately and ran. I was amazed that it was running again after all these years without a struggle. That was the good news.

I pulled a few data logs and went to review them. Yep. RFI was definitely there. After all I went through to avoid it, I failed somewhere. I sent my data logs to Chris at EFISystempro and he confirmed it was RFI and gave me several helpful suggestions.

I honestly can’t say exactly what the cause was as I kind of went into shotgun mode while fixing it. I rerouted a lot of the wiring, I checked every connection, I went back and put dielectric grease on all the spark plug boots (I had new MSD superconductor wires already installed) and I added some of those Amazon Ferrite clamps to the XFlow wiring.

After all of this, No more RFI. Not sure if it was wire routing (I did have some wires routed right over the Ignition Box initially) or the ferrite clamps or the dielectric grease that solved the problem but it worked.

Now that the car was running and the RFI issues seemed to be addressed, I installed the 6.8 Digital Dash. This was probably the most disappointing part of my build. I was very excited about this dash and had high expectations.

The first thing that really set me off about the Digital Dash was that I wanted to run a fuel gauge. The problem was I would need two pin connectors to hook one up. Holley wants over $40 for a box for these pins. All their other Holley pin connectors run $10 to $20 a box. I had already bought several boxes of various pin connectors throughout my wiring process. Now having to go buy another box of connectors for the 2 connector pins I needed for $40 just did not sit well with me. I had paid $1,000 for this dash and to use a fuel gauge with it, I had to spend $40 more for a box of connector pins.

I bit the bullet and bought the pins, Wired it all up, and then the next disappointment. The 6.8 Digital dash only kind of supports the Sniper. It is really designed for the HP and Dominator systems. I knew going in that the playback functions did not work with the Snipers.

What I did not know was that the record function on the digital dash is disabled when you use it with a Sniper XFlow. If you want to record data logs, You have to buy a splitter and run both the handheld and the Digital Dash.

I did eventually find an experimental setting that the manual expressly tells you not to use that will enable the record function on the digital dash. I was disappointed that I spent thousands of dollars on stuff and the only way to make it work as expected was to do something that the manual tells you expressly not to do. But if you have an Xflow and a 6.8 digital dash you will not get the record option unless you ignore the manual and change the setting on the dash to enable the Experimental option.

Now back to some of the positive. The car was running and sounding pretty good. I was learning to use the Holley software to make changes. Overall, I was very happy. I took the car to the track and made some Non-Nitrous passes. Car was a little slower than expected but ran good and very consistent. We had never really run this car without Nitrous before so it was not all that surprising.

Knowing there was a lot more in this car, I reached out to Nick Langen at Mad Science Motorsports to help me with my Tune. I sent him some data logs and we went over the setup for the car. He sent back a new base tune. I was fairly happy with the car before. I thought it sounded good and ran well. I uploaded Nicks tune into the car. WOW!! What a difference. The car sounded amazing and the throttle response was incredible. This is only the first shot at it. I now have several more tunes coming from him once I get more data to send back. Money well spent.

Yes, the car is still ugly and always will be but it is back on the street and on the track after 18 years. Like my father always said, Pretty doesn’t win races.

My advice to others considering a Sniper conversion?

1. Buy from the right vendors. Make sure your vendor is knowledgeable and willing to help out. Holley support is very difficult to reach. You will have much better luck contacting your vendor if you run into issues. My choice was EFI System Pro and I could not be happier.

2. Watch all the videos on YouTube by Devin Vanderhoof. So many great tricks and tips that will make a huge difference in your installation.

3. No matter how careful you are, you still might end up with RFI. If you do, do not get frustrated and give up. Go back and check everything and it can be fixed.

4. Once you get it running, even if you think is it is running great, Call or email Nick Langen at Mad Science Motorsports and use his services. Amazing results.


EFI System and components:

1 Comment(s)

Chris Myer:
10/2/20, 09:09:14 PM,

Absolutely amazing job Jay. What a great honor to work with you on this project!

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