Spark Plug of Choice

[LTZ C20]

Hey all, I'm experimenting with which spark plugs I want to use in my mild performance street engine. I've used the stock AC Delco plugs, AC Delco rapid fires, I currently have the Accel Shorty Header plugs in.

My buddy has the E3 plugs with 3 electrodes and the baseball diamond shaped plate, he said they run great and he has a Comp cams top end kit with an intake and holley carb.

My engine is a 355 with Dart aluminum hi flow heads, oversized int. and exh. valves, comp cam, edelbrock dual plane performer rpm intake, GM Performance HEI, Hedman headers, true duals and a throttle body fuel injection kit.

What's your guys opinions,  preferences,  recommendations?

[bd]

Assuming 14mm X 0.750" reach, projected tip, gasket seat, 5/8" hex, and minor clearance issues with headers - Champion 3071 Platinum regapped to 0.045" or Champion RC9YC5 (alternate #426) copper core gapped to 0.050" or Autolite 3924 copper core gapped to 0.045".

Currently running the RC9YC5 in a 355, 10.0:1, zero deck, 0.039" quench, forged/forged/H-beam, AFR 195 centerbolt (2.05" x 1.6" x 65cc), Comp XFI 0.560" lift roller, Crane 1.6 Gold Race rockers, MSD distributor & wires, Crane HI-6/LX92 CD ignition, and TBI w/Edelbrock MPFI conversion.

[LTZ C20]

That sounds pretty good. Thanks. What octane are you running? How's the fuel milage?

[bd]

Runs 93.  Mileage is atrocious at ~11 MPG around town with 3.42s and 31x10.5-15.

[LTZ C20]

I'm sure your tires aren't helping any. I have 265/75R16, running 91 octane and 4.10s. I'm not sure what my exact is but I do know my old motor with same tires and a th350 was suckling down 3/4 tank in like 3 days. Now I can go a week, sometimes 7-8 days on 1/2 tank, that's with a new 700R4 to.

[LTZ C20]

Also, what would be the best position for the j strap to "face" or "point" inside the combustion chamber. I believe it's called "indexing"??

[LTZ C20]

Have been doing a lot of research about indexing of spark plugs. Very interesting practice for sure! Not so necessary for street use but very useful on the strip.

A new question to ponder is, do I use the stock AC Delco R44TS plugs or the AC Delco 41-803 plugs for a 89-90 5.7L TBI truck. I ask this because I have a TBI kit on the truck from that model year, bought kit from Howell Engine Developments. Very good product!!!

[bd]

For the Dart aluminum heads?  Dart indicates 14mm x 0.750" reach flat-gasket spark plugs for their performance aluminum heads.  Which heads by part number did you install?

The Delco R44TS is a 0.460" reach tapered seat plug.  For factory heads use Delco R43CTS, Autolite 24 or Accel 0574S shorties if headers limit accessibility. 

Don't use a 0.460" reach plug in a 0.750" reach hole or you'll shroud the spark.

[LTZ C20]

Yes for the dart aluminum heads. I installed the biggest and baddest of course lol. Part number 127322.

I thought those 2 AC Delco plugs would be ok because, 1 - the heads have stock style plug location, 2 - R44TS is the stock plug for my truck, 3 - if the heads have stock plug ports, I should be able to put the stock plugs in. Also, I see there is a small tapered area at the top of the hole so I thought tapered plugs would be ok. So having almost shot myself in the foot, I now need to figure out what AC Delco plug is a 14 mm hex gasketed .750 reach plug and if possible one that if ment for a TBI engine.

Sorry for my blunder as I am still learning, not an expert yet lol. That's why I ask you guys!

[LTZ C20]

Using summits search filters, I found this.

An AC Delco,  14mm, .750 reach, gasket type plug. AC part number 41-106, GM part number 12610767.

Will this plug be good for these heads?

[bd]

You should have received important reference pages with the heads, similar to those attached, below.

I recommend you put together a binder to organize and keep all important information and details regarding your build for future reference.

Seems like you're predisposed to AC Delco plugs.  Use a manufacturer's cross-reference to find plugs similar to those I posted for you earlier.

[LTZ C20]

Yes I have 2 of those papers, 1 came with each head. I have all of my engine build papers in a zip lock bag labeled "ENGINE". For example though, the exhaust gaskets recommended are a Fel Pro with part number. It says what dimensions of plug to use just not a part number which erks me a little because I know for sure I saw an Accel part number somewhere on the paper work for those heads. Been all over and can't find it, if I had the Accel number I was gonna cross it to AC Delco and be done.

I am predisposed to AC Delco yes, but I work in a Chevy service department so parts are close and easy and if there's ever a problem easy to get replacements.

Your recommendations crossed to ACD numbers.

Champion 3071 platinum - ACD 5
        "       RC9YC5 - no ACD equivalent

Autolite 3924 - ACD FR1LS, FR3LS, FR5LS, FR3CLS, 5, CFR3CLS, FR2LS, FR3LSK, 41-629, 41-603 & 41-611

[LTZ C20]

I spent some time googling the specs for the large list of plugs. Most of them are pretty close in dimmensions, some i couldn't find all of the dimmensions for. The biggest factor is the varying heat ranges.

I want a plug that is the proper dimmensions for the heads, and has the best heat range for a TBI engine with aluminum heads.

The ACD number i posted earlier that also has the 8 digit number fits all specs but is a 12 on heat scale i believe.

[bd]

Every manufacturer has their own proprietary heat range scale that relates strictly to their offerings.  Heat range assignments do not directly relate between manufacturers.  Bear in mind that "4" in Delco does not correspond to "4" in Autolite, Champion, NGK, Bosch, etc.  Each has a unique numbering system.  And, finding an accurate chart that cross-references heat range between specific manufacturers can prove frustrating.  Nonetheless, an Internet search will usually provide what you're after. 

With some manufacturers, the heat range of their plugs relate directly to the spark plug part numbers.  For instance, an AC Delco R44TS runs hotter than an R42T; a Champion RC12YC runs hotter than an RC9YC.  With other manufacturers, NGK and Denso for example, the heat range of the plug increases inversely with part number - that is, decreasing spark plug number relates to increasing heat range.

Then of course, some manufacturers produce a narrower selection of plugs than others, so you encounter one part number of Brand X crossing to half-a-dozen part numbers of Brand Y.  So, keep "plugging" away and you'll find what you're after.   

[LTZ C20]

Ok let me ask you this then. What would the best heat range be for a TBI engine with aluminum heads running 91 octane gas. Should I use the heat range for the year of the truck or the heat range for the TBI or does it not matter at all. This all of course will be an AC Delco plug so we shall stick with there heat range scale.

The plug I mentioned earlier, part number 41-106 or 12610767 meets all physical dimmensions and spec for the cylinder head but is I believe a heat 12.

The R44TS, obviously is heat 4. Is 12 ok for TBI and aluminum or is that too hot and need to down around 4-6?