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Old 02-21-2009, 09:02 PM   #1
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Location: Dayton, Ohio
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Car: 1990 Firebird
Engine: 6.0L LQ4
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Correct Spark plug for 350 Vortec Head and Cam setup???

Hello fello Tgo members,

I recently acquired an 87 Regal off my brother. It has a 350 SBC with the following mods done to it;

Flat top pistons
Vortec Heads(64cc 1.94 in/1.55ex)
Comp cams 286H-10 Cam (.490/.490 286/286 duration 110 lsa)
981-16 valve springs(heads modified for flat tappet cams)
Edelbrock RPM Air Gap intake for Vortec Heads
Edelbrock 1406 600cfm carb w/ electric choke
Hedman LT Headers

My question is, what plug should I run and @ what gap should I run it?? It had some accel u-groove plugs but when compared to a NGK TR55 plug(recommended for 96-00 5.7L Vortec 5.7's), the electrode on the recommended NGK sat about 1/4" deeper into the combustion chamber.

The factory 5.7L Vortec engines also recommend a .060" Gap, typical SBC builds use around .035" right??

Thanks for the help!!
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Old 02-21-2009, 09:45 PM   #2
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Re: Correct Spark plug for 350 Vortec Head and Cam setup???

Pratically the same setup (350 Vortec heads xr276hr 9.9:1 scr).
ACDelco R44LTS @ .035" before MSD. .45" after MSD.
Always spotless. Great mileage too.

Last edited by skinny z; 02-21-2009 at 09:56 PM.
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Old 02-22-2009, 08:46 AM   #3
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Car: 1988 Firebird S/E
Engine: 406Ci Vortec SBC
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Re: Correct Spark plug for 350 Vortec Head and Cam setup???

Champion RS12YC gapped at .035" is best.
The OEM GM L-31 vortec heads use a 14MM .708" reach spark plug with a projected tip.

Recurve the distributor's mechanical advance for 24-26 deg intial timing at idle and 34-36deg at max advance (3000rpm +/-) You have to limit the advance travel to achieve this curve.

Last edited by F-BIRD'88; 02-22-2009 at 08:58 AM.
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Old 02-23-2009, 04:52 PM   #4
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Re: Correct Spark plug for 350 Vortec Head and Cam setup???

Quote:
Originally Posted by F-BIRD'88 View Post
Champion RS12YC gapped at .035" is best.
The OEM GM L-31 vortec heads use a 14MM .708" reach spark plug with a projected tip.

Recurve the distributor's mechanical advance for 24-26 deg intial timing at idle and 34-36deg at max advance (3000rpm +/-) You have to limit the advance travel to achieve this curve.

Thanks for the info! Im new school and got this car so I could learn the carb setup in and out. Im used to Turbo Buicks and LSx based cars and trucks.

How would I go about limiting the advnance travel on my HEI?
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Old 02-23-2009, 07:16 PM   #5
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Re: Correct Spark plug for 350 Vortec Head and Cam setup???

Quote:
Originally Posted by cabech984 View Post
How would I go about limiting the advnance travel on my HEI?
There's an article in the Chevy High Perfromance book 'Small Block Chevy Engine Buildups' about welding up the HEI distributor advance slot to limit total mechanical advance.
There's always the aftermarket. MSD has adjustable mech and vacuum advance. Very handy.
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Old 02-24-2009, 10:13 AM   #6
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Re: Correct Spark plug for 350 Vortec Head and Cam setup???

see the pic

Just swapping the advance limiter bushings will not limit the advance enough to allow the required base idle timing. The fatest bushing will allow 18initial. You need 24-26 initial. 34-36 total or 10deg of travel.

Where you locate the stop screw will determine the advance limit (left screw in the pic) You can grind a flat on the side of the screw head to fine tune the amount of advance travel.
Disassembling the distributor and welding up the advance pin slot works too.
Attached Images
File Type: jpg HEI advance.jpg (146.0 KB, 74 views)

Last edited by F-BIRD'88; 02-24-2009 at 10:23 AM.
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Old 02-24-2009, 04:17 PM   #7
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Re: Correct Spark plug for 350 Vortec Head and Cam setup???

Looks like some good info! Im gonna have to take mine apart and see what I got as a base.

I ran the car around the block after swapping just the plugs. For having 2.56 gears in the rear axle, this thing is faster than my perfectly running 95 Suburban 350! I wonder what itll do with my rebuilt holley, new plug wires, MSD 6AL, MSD Cap & Rotor. This carb needs tuned as well as the timing set correctly.
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Old 02-24-2009, 04:17 PM
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350, 57, 57l, cam, head, heads, ngk, plug, r44lts, sbc, spark, sparkplugs, tr55, vortec, votec
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