So I'm looking at spark plugins, trying to figure out the best ones to get for my new engine coming in within the next couple of weeks. And one thing I'm noticing is that spark plugs come in a lot of different reach (or thread length). From what I read if I don't get the right size bad things can result, two short ending up with deposits inside the threads making it very difficult to install the correct size later, and to long heating up the tip of the spark plug to much as well as getting deposits on the end of the threads making a high chance of stripping the threads in the spark plug hole when removing.

What I can't figure out is what the correct reach is. Is there a standard reach for a 350 motor, or does it vary by motor? I'm assuming the place building the engine for me will know and I will contact them Monday if I don't receive an answer here prior, but was hoping someone here had some insight.

Thanks!

 

Depends on the heads.

If they're stock heads, then the stock plugs that go with them will work fine. All you have to worry about is washer seat (heads from the early 70s or before) or tapered seat (everything since). You can just look at the seats and tell which ones they are, if you don't know what heads they are.

 

Ok guess I'll have to call the place building the engine for me and find out. Not even sure what size stock plugs are. I'm going to be getting a set of Accel plugs and wires from summit racing and after selecting all the features of my car and the engine size it still has .375 or .406" reach options.

 

If they're stock heads, just look at the seats, and see if they're washer or taper. Then go order plugs for a 69 something-or-other (say, Impala 350 4-barrel) or a 78 something-or-other (say, Camaro Z28 350). Major no-brainer.

Too easy. Not something to stress over. Don't bother with trying to outsmart the specs. Just stick with year-appropriate STOCK stuff and all will be well.

 

Sorry if I wasn't clear, but I don't know what STOCK is for this. As I said when I put in all the details on summit racing it shows two options still .406 and .375. Are one of these two stock? I have no clue. None of the ones available say STOCK on them.

I'm not trying to outsmart the specs, I'm trying to get the appropriate sized spark plug. Honestly I did not know there were so many different sizes before I started looking.

I don't even know what you mean by washer or taper on the heads. I suspect if I did I probably would not have to ask about the spark plugs lol.

I appreciate you attempting to help, but simply spouting off that it's "Too easy" and a "Major no-brainer" without giving any technical specifics besides "STOCK" doesn't help me at all. I'm doing an engine swap here, therefore what I'm putting in my car is absolutely not STOCK.

 

are you asking what heat range to go with? i use ac delco plugs. 45 would be hotter, more reach into the cylinder. 43 would be colder, farther from the cylinder. most factory cast iron heads use tapered plugs. most aftermarket aluminum heads use flat, washer style plugs, like you see in your lawnmower. every manufacurer uses different part numbers, so it can get confussing. id try & stay away from accel plugs. they have a reputation of looseing up where the wire attaches. some guys use theyre shorty version for header clearance cause, theyre the only one that makes a shorty version to my knowledge. there should be a ton of info about plugs on the net.

 

Don't worry about Summit and trying to look them up that way. Try Auto Zone instead.

STOCK = what came in a car. All you have to do, is know what kind of car to ask for the plugs for, to get ones that will fit your new heads, whatever they turn out to be. You MUST know that before you can buy plugs.

The difference between washer seat and tapered seat is how they seal to the head.

Here's a beautiful pic of a tapered seat one. Note how the plug's sealing surface looks alot like a lug nut. The place in the head is also conical like the holes in a wheel. All you have to do is LOOK AT YOUR NEW HEADS and see if they look like this. http://www.acdelco.com/parts/spark-p...-conventional/

Here's a similarly beautiful pic of a washer seat plug. This kind, the sealing surface on the head is flat. http://en.wikipedia.org/wiki/File:Sparkplug3.jpg

You are NOT READY to buy spark plugs if you don't know what heads you have. That is THE FIRST THING you need to find out.

If your heads have tapered seats, look up a car, or truck with a 350 or 350 - ANY car or truck, EVEN YOUR OWN - from the mid-70s onward.

If your heads have washer seats, look up a car, or truck with a 350 or 327 - ANY car or truck - from the early 70s or before.

I'm not "spouting". I'm trying to de-mystify you from something you have excessively complicated in your own mind, without realizing how SIMPLE it really is. I'm telling you, YOU DON'T NEED to know the measurement. All you need to do, is go to AZ, walk up to the counter, and say, "I need 8 spark plugs for a 19xx Xxxxxx with a xxx engine". Which could well be, "1986 Camaro Z28 305", if your new heads have tapered seat plugs. THey will then try to sell you whatever their highest-profit "gimmick" plugs are this week. AVOID that: none of it does A DAMN BIT of good. All you need, is yerbasic STOCK grade plug, from some one of the OEM mfrs; AC Delco, Bosch (but just the regular "platinum" and NOT "+4" or any of that), NGK, Denso, Motorcraft, or Champion. NOT, E3, Splitfire, etc. etc. etc.

This just isn't that hard. Once you identify which of the 2 incompatible families of them your heads need, a trip to the parts store will take care of it on the spot.

 

Ran stock plugs in my Vortec heads for a while not knowing they require Vortec specific plugs. Put the right plugs in and didn't notice a difference in any way and Vortec plugs are 1/8" longer, IIRC. Sofa has a very good idea, figure out what heads you have then shop for plugs. BTW, the Accel plugs suck, don't waste your money!

 

I am going to chim in here... who ever said that depth reach is not a concern and how simple it is... well you never ran much than stock. I am running a 67' cevelle 327 with shaved heads. I bought a set of the Accel 437SS plugs (silver tips) $150 for a set. THey are a projected plug that goes further into the cylinder than stock. They are right for a stock application. but any mod to the crank or aftermarket pistons or shaving the heads play a role. trust me
my pistons hit the new plugs!!! be careful