Packard Forum Index » V-8 (1955-56)

Hello,Im finishing up building my 352 up and getting ready to install in car,and hopefully have running over the weekend!! My question is what should I gap spark plugs at??I had thought about 40 thousandths to compensate for unleaded fuel?? I have this car and engine on a project blog on here.This motor was rebuilt back in 1981 by someone other than me,and Im assuming there prob. was nothing special done during that rebuild to compensate for unleaded fuel(I really don't know) So I am assuming nothing was done. Also what other recomendations or simple adjustments do you have so that I can safely run engine on today's(Unleaded) fuel??Should I use a lead supplement? Thanks for all your input in advance!!!

Original specification was 0.035 plus/minus 0.002, and there is no reason to do differently today.

Thanks,Do i need to make any other adjustments,use additives,ETC in order to safely run engine on unleaded fuel?? Thanks again!!

Follow Owens advice. The .040 and wider that is used in modern cars is not due to fuel. The wider gap is due to e-ignition of modern cars because the e-ign throws a much hotter spark.

My personal preference is to gap standard ignition plugs at .028 - ,030 for faster cold weather start up and allows for longer range between regapping the plugs.

What spark plugs are u using and what is the number on them?????

Do i need to make any other adjustments,use additives,ETC in order to safely run engine on unleaded fuel??

0.028-0.030" in fine for flathead engines, but for my taste a bit too narrow a gap for the V8s. As to additives, if you're going to flog the heck out of the car on Interstates, I'd recommend using genuine tetraethyl lead, available from Jack Podell, or at the very least a lead substitute but I sometimes wonder if they're not just another "snake oil" with no benefit. If you're driving is occasional Interstate trips at about the legal speed limits, then I'd say no.

For a 1955 Packard 352,

Spark plug type = H10 (1955) N18 (1956)

Spark plug gap - .035

Points gap - .017

Dwell angle (points) - 31 degrees

Firing order - 18436572

Timing 5? BTDC

Battery ground and voltage -12


The reason they went to wider spark plug gaps in the 70s and 80s, had a lot to do with trying to fire a thin or lean mixture. They leaned out the carbs as far as they dared, for mileage and pollution control.

If you are using electronic ignition you might open the gaps a little but I wouldn't go more than 40 thou. Unless you change the distributor cap, rotor, and plug wires to more modern designs.

On the whole it's probably best to stick with the stock settings.

If you do not have hardened valve seats, it can't hurt to add some Marvel Mystery Oil, Redex, or other good upper cylinder oil to the gas.

But you won't hurt your engine if you don't, provided you don't run it too hard or overheat it. By run it hard I mean cruise over 80MPH for extended periods on a hot day, or tow a house trailer over the Rocky Mountains.

One correction there. The 1955s were 12+ Ground while the 1956s was 12- Ground.

Thank's to all!!!!!!

The timing on all but the earliest 56 374 engines was:
Timing 10? BTDC

There are a couple of other things to consider when selecting spark plugs for these OHV V-8 engines. Should one go with the standard exposure center electrode or a projected electrode (e.g., Y series Champions or S series ACs) spark plug? Also, resistor or non-resistor type? And what about the new platinum plugs with one, two, and more grounds? I would say go with a resistor projected electrode plug along with solid wire, non-resistor, high tension wires. The extra cost for the platinum spark plugs is probably not warranted due to the small amount of miles these cars are usually driven. The projected electrode type plugs will not work on the l-head straight 8s. Just some thoughts ...