Indexing question
Thread Starter
Racer
Joined: Apr 2004
Posts: 250
Likes: 0
From: Binghamton NY
Indexing question
While some engines like the spark plug's gap open to the intake valve, there are still other combinations that make more power with the gap pointed toward the exhaust valve. Has anyone experimented with this on the base 5.7L ? Details would be appreciated.
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
Its usually done on Very High compression ratio racing engines to clear the Intake valve & Piston dome top.
Like 14.0 - 18.0 : 1 static compression ratios.
My old Pontiacs liked the spark plug electrode openings towards the intake valve.
Never picked up any noticeable HP increases.
But engine idled slightly better & throttle response was slightly better when I took the time to index those spark plugs in.
At WOT I never felt any power increases to speak of from the driver's seat.
BR
Suckin' gas, haulin' ass.
Joined: Apr 2010
Posts: 1,100
Likes: 8
From: Newport News Virginia
I don't think its worth the time & effort indexing spark plug electrodes on a stock C4.
Its usually done on Very High compression ratio racing engines to clear the Intake valve & Piston dome top.
Like 14.0 - 18.0 : 1 static compression ratios.
My old Pontiacs liked the spark plug electrode openings towards the intake valve.
Never picked up any noticeable HP increases.
But engine idled slightly better & throttle response was slightly better when I took the time to index those spark plugs in.
At WOT I never felt any power increases to speak of from the driver's seat.
BR
Its usually done on Very High compression ratio racing engines to clear the Intake valve & Piston dome top.
Like 14.0 - 18.0 : 1 static compression ratios.
My old Pontiacs liked the spark plug electrode openings towards the intake valve.
Never picked up any noticeable HP increases.
But engine idled slightly better & throttle response was slightly better when I took the time to index those spark plugs in.
At WOT I never felt any power increases to speak of from the driver's seat.
BR
Give it a try, the shims to index are cheap. Though I doubt you will pick up significant gains, you may see a couple of HP, and some improved efficiency.
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
Actually it's indexed to open the spark plug electrode to face the piston so that the flamefront travels faster and more evenly in the combustion chamber. IE, the flamefront doesn't have to travel around the spark plug and electrode to get through the whole combustion chamber.
Give it a try, the shims to index are cheap. Though I doubt you will pick up significant gains, you may see a couple of HP, and some improved efficiency.
Give it a try, the shims to index are cheap. Though I doubt you will pick up significant gains, you may see a couple of HP, and some improved efficiency.
They relocated the spark plug hole on the 1970 Pontiac Ram Air IV - 4 cylinder head.
Clear shot at the Intake Valve.
Little know fact but what I have on my 70 TA.
Worked best igniting the fuel & air mix on that engine as I stated.
Save up for a camshaft, stoker crankshaft kit, better heads, Cylinder head porting & intake porting, long tube headers, NOS, Blower, Turbo(s), Better ignition system, ect.
You will see better gains in Power that will flatten your eyeballs from " 0 to 140 MPH).
Indexing spark plugs on a L98, LT-1, LT-4 may net you 1 or 2 HP.
Big Deal.
BR
Safety Car
Joined: Sep 2001
Posts: 4,150
Likes: 551
From: Glenbeulah Wi
In a stock car it may make a few HP difference but I doubt you will be able to tell a difference.
Race Director
Joined: Jun 2004
Posts: 13,942
Likes: 705
From: WI
Whenever this topic comes up there's always someone that sneers at making the engine work better which surprises me.
Here is what I do, use a marker and color a line on the plug that follows the ground strap. Install the plug with the line as close to up as you can. If the line is on the bottom, unscrew the plug and start the threads in a different place. Using slightly more/less torque can also help.
Here is what I do, use a marker and color a line on the plug that follows the ground strap. Install the plug with the line as close to up as you can. If the line is on the bottom, unscrew the plug and start the threads in a different place. Using slightly more/less torque can also help.
Team Owner
Joined: Oct 2004
Posts: 81,241
Likes: 3,062
From: altered state
St. Jude Donor '05
Waste of time generally speaking unless its an all out thing and youre searching for the last 1hp out there. It wont hurt to do it but as said above if youre looking to do it and hope to feel something when you hop back in your car forget it. Youll feel better eating a good cheesburger instead 
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
8 Coolest Corvette Pace Cars (and Replicas) of All Time
Verdad Gallardo
Top 10 Corvette Engines RANKED by Peak Torque (70+ Years of Muscle!)
Joe Kucinski
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
Melting Slicks
Joined: Nov 2008
Posts: 2,765
Likes: 5
Moroso sells Spark plug indexing washers made of annealed copper.
They are made in the classic flat washer style & the GM "Peanut" taper seat style spark plugs.
I think its a complete waste of time to index sparkplugs on a bone stock C4 sbc engine.
You may pick up 2,000+ HP and even scare John Force & Eddie Hill.
Let us all know your torque & HP gains after spending 2 or 3 hours.
Will take you longer than 15 minutes it takes me.
Your 1st time indexing spark plugs.
BR
They are made in the classic flat washer style & the GM "Peanut" taper seat style spark plugs.
I think its a complete waste of time to index sparkplugs on a bone stock C4 sbc engine.
You may pick up 2,000+ HP and even scare John Force & Eddie Hill.
Let us all know your torque & HP gains after spending 2 or 3 hours.
Will take you longer than 15 minutes it takes me.
Your 1st time indexing spark plugs.
BR
Race Director
Joined: Jun 2004
Posts: 13,942
Likes: 705
From: WI
Team Owner
Joined: Jan 2003
Posts: 20,293
Likes: 240
From: Summerland B.C. Canada
