EFI for 400 (6.6L)

omologato

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I can attest to the Holley Sniper EFI system, I have installed a few on customers cars and the results are always stellar. I'm eventually going to be doing the conversion to my own 66' GTO.

Most of the ECU sensors are built into the Sniper unit, you only need to work out the air/fuel sensor and engine coolant Temp sensor which is pretty easy. If you are mechanically inclined and do your own work you can install the coolant temp sensor yourself but I suggest bringing the car to a custom exhaust shop for them to install the bungholes for the air/fuel sensor. For the air/fuel sensors you want high quality wideband sensors.
 

avell007

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Another option Msd Atomic , we just put one on our roadrunner , Getting another one I was so impressed . I like the fact it uses one fuel line with pulse tecnology rather than a return line, I think it is made by holly . Steve Mags has a install video on youtube check it out.
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omologato

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Another option Msd Atomic , we just put one on our roadrunner , Getting another one I was so impressed . I like the fact it uses one fuel line with pulse tecnology rather than a return line, I think it is made by holly . Steve Mags has a install video on youtube check it out.

"On demand" or no-return fuel systems are the more advanced system which pulse width modulates the fuel pump to meet fuel demands. Low fuel demands the pump is demanded "on" for less time, when fuel demand is high the "on" time is longer. It's just all around the better system.

BTW, this has been the norm in EFI for the last 20 or so years, I haven't seen a return line in a car produced in the last couple decades. Also the Sniper is also PWM no return type EFI system also. Both systems can be run without the PWM controller and just power the pump like the old days but then you need to run a return line and install pressure regulators. There are some builders I have run into that do not like the PWM for whatever reason and run a return line. I do remember this was for engines running >600hp and I don't remember the argument but for our street rides with less than 600hp the no return PWM systems are just so much better. Less evaporation, cooler gas temps, more efficient, etc.......

The sniper and Atomic are basically the same in operation and both are great. Since Holley makes the Atomic it stands to reason that it's just a sniper made for MSD to run with their distributor spark advance systems. If you have an MSD distributor and ignition system then go with the Atomic. If you do not have an MSD distributor and ignition system then it doesn't really matter which one you get.
 
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