Thread: Spark Plugs for Vortec?

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Building up a 383 with GMPP Vortec heads #12558060. Heads are designed for use on SBC 1958 and later. Block from a '71.

Static Compression Ratio = 8.6
Dynamic Compression Ratio = 7.4
180 degree thermostat
4 Speed manual
Daily Driver
Not high RPM, well maybe once in while
Want to use 87 octane

Probably start a little cool on the plug and get hotter as I see effect on plugs.

Anyone have ideas on particular plug part #'s I should start with using these particular heads and application? I hate to admit it but I'm clueless!

Thanks,

DoubleSun

here is a good info page regarding the heads:

http://www.sallee-chevrolet.com/Cyli...ads/Vortec.cfm

down towards the bottom of the page, they list some plugs
including Rapidfire #3 (an AC Delco plug)

From the plug length info on this page, you can do a heat
range comparison on your favorite plug brand's web page.

mike in tucson

Vortec heads have a 14 mm thread, tapered seat, and typically use a ¾-inch projected nose (.750) reach, small (5/8") spark plug socket. Some suggestions:

AC/Delco are the factory stock plugs and I have had good success with them.
R42LTS - Stock and a good place to start.
R43LTS (colder)
R44LTS (coldest)

NGK
TR5 (stock equivalent )
TR55 (colder)
TR6 (coldest)

Autolite
103 (stock equivalent)
AR103 (Racing)
AR104 (Racing)

AP605 (Platinum)
APP605 (Double Platinum – kinda pricey)
XP605 (Xtreme Perf)

Bosch (0.69" reach)
HR9DC
HR8DPX
4305
4458
4205

Here’s a good (really complete) xref:
http://www.angelfire.com/extreme4/sk..._REFERENCE.htm

Thanks, it's exactly the info I was looking for. However, I have a question on reach. I did a little more research and I keep coming across .708" reach as opposed to .750" given in your post.

The reason I ask is because I've seen some specs given as R44TS. You do say "typically use a 3/4" projected nose" which translates to a R44LTS, I think.

Are we talking a performance issue between the two or crash-bang?

Thanks,

DoubleSun

On AC plugs, prefix and suffix letters are used to identify a specific type plus the numbers relate to thread size and heat range. R44LTS breaks out as:
R = Resistor
4 = 14 mm Thread
4 = Heat Range
L = Long Reach, 3/4" (19 mm) reach, (14 mm) thread fineline (which these plugs are)
T = Taper Seat
S = Extended Tip

With a stock HEI you can run 0.040 or 0.045 inches of plug gap. A larger gap has the advantage of more complete burn of the air and fuel mixture, but it also takes more power to get a spark to jump a large gap.