Amc V8 Gets Holley Efi

I recently added EFI to the AMC 304 that is in my jeep. I had been running a Holley truck avenger 470 for about 3 years that I had tuned pretty well, but between vapor lock issues and seeking out better MPG so I can get more range out of my fuel tank, I was ready to switch to EFI.

Ultimately I decided to go with the Holley Sniper system because of the amount of support for it, and I was really intrigued by another feature it has, electronic timing control. This would allow me to tune my engine to sync the timing curve perfectly with the fuel mapping for the best results, and the sniper automatically would adjust the timing to give a more stable idle.

I started with removing the TA 470 carb I had been running and removing all of the old fuel lines. I plan on listing it for sale in the classifieds soon, if anyone is interested PM me I'm hoping to get around $350 for it.

I dropped the new sniper throttle body on and used a 1/4" open phenolic spacer. I have an edelbrock dual plane intake, and I had read the sniper can have issues being mounted directly to a dual plane. Interestingly the sniper throttle body seems a bit smaller than a traditional square bore carburetor.

With my carburetor I had been using an external electric fuel pump which I think was responsible for some of my vapor lock issues as well. I went ahead and got Holley's in-tank fuel pump unit for CJ's. It uses a standard walbro 255 lph pump, and the fuel return is part of the sending unit so it returns all of the excess fuel directly into the tank. I liked this because it allows me to not run a return line.

The sending unit's fuel level float is also allegedly more accurate than the stock one when paired with Holley's fuel level gauge. I'll be adding the gauge soon so I can finally know how much fuel is in my tank, as my previous sending unit did not work.

All installed, I ran my new fuel system with 3/8" steel hard line and used short pieces of vapor guard high pressure hose for the connections. Not pictured is the Wix #33482 10 micron post filter I used. The new fuel pump is a lot quieter than the external one I had and I cannot hear it at all with the engine running. It pressurizes the fuel to 58 psi.

The next step was to replace my old GM HEI unit. It provided a strong spark and had served me well, although I found the process of changing weights and springs to adjust the timing curve to be troublesome and never felt it was quite dialed in how I wanted it.

The MSD distributor holley sells for use with the sniper was quite a bit smaller and comes with a tool to make phasing the rotor very easy. You put the engine at TDC on the compression stroke of the #1 cylinder, and then line up the distributor so the clear cap fits over the rotor just right. Once that is done you lock down the distributor and the ECU will control the timing from there.

I used an MSD 6EFI CD box and coil in conjunction with their distributor. The MSD box fires multiple sparks in each cylinder under 3000 RPM's, which ensures the air fuel mixture will be ignited reliably. It also provides a very strong spark so I increased my plug gap from .040" to .055" for better ignition of lean mixtures.

Now my one gripe I have with the sniper is that adding the timing control is not simple. They very much advertise the sniper EFI as "plug and play", and perhaps it would be if you were only doing the EFI without timing control. I found that the base timing table provided by Holley is god awful and it is necessary to use their software on a PC to make a better table. It took me a few days of reading forums to figure out how to achieve this. I will say the software holley provides is pretty good and gives you full control of the EFI unit.

I spent last weekend creating a custom timing table, fuel map, and a target Air/Fuel Ratio chart. You just need to get the fuel map in the ballpark, and the sniper will self learn the rest while you drive.

Overall I am pleased with how the engine runs, and found much better performance on the highway and cold starts. I'll be testing the fuel economy soon to see if it improved at all over the carb.

The sniper also came with a handheld controller that shows a lot of good data while driving. Once the unit is fully tuned I shouldn't need the handheld, but I will probably keep it in the glovebox so I always have it. I added a spare walbro 255 fuel pump and a wideband O2 sensor to my spare parts kit, as those parts failing could be problematic for the EFI. The unit should be able to resort to a "limp" mode if any one sensor fails and at least get me home.

 

This is so awesome and on my list of near future upgrades.

 

Thanks for this post. I'm likey to put a Sniper EFI on my Buick 350 some time next year. Lots of good info!

 

One thing I forgot to mention is the throttle linkage that the sniper comes with opens the primary and secondary barrels at the SAME time, which makes the power come on really hard. It's way too easy to bark the tires taking off from a stop sign.

Theres a progressive linkage for about $15 I'm ordering that will not open the secondaries until the primaries are 40% open, so the power should be much more linear and not so aggressive.

 

Any reason you went with the 4 barrel vs the 2 barrel?

 

Is there an option to run the msd integrated distributor rather than the distributor and ignition box? I haven’t googled its availability for amc but that’s what we went with on the wife’s 460 to replace the 6al. The in-laws are running that on their Ford as well now.

Super cool upgrade though. Has me seriously thinking….

 

The sniper efi is really tempting especially with the in tank pump/sender. Since the pump does its own return what did you do for the return outlet at the throttle body?

 

I looked into the two barrel as well but my engine already had the edelbrock square bore intake, and holley's techs recommended the 4 barrel sniper.

The sniper came with a small coil module in the box that you could use to trigger the distributor without an MSD box, and I have read about people converting the coil on top HEI units for use with the sniper timing control. I don't know a whole lot about how that works. I've lost two coils on my HEI so I don't have a lot of faith in them being reliable when I'm way out in the back country.

I just put a plug in the return end, so all the fuel return happens inside the tank. I had a large hydramat in my tank before, which was nice because it could pickup fuel at any angle...hopefully this setup doesn't have any issues. I did notice that the return dumps almost directly onto the pickup sock which should help.