[ANSWERED] Indexing Spark Plugs
08-31-2017, 12:37 PM
#1
Tech Contributor
Thread Starter
Member Since: Mar 1999
Location: Northern VA
Posts: 10,057
Received 3,787 Likes
on
1,139 Posts
"Ask Tadge" Producer
[ANSWERED] Indexing Spark Plugs
The original question is here.
grcor asked:
Every year or so the topic of indexing spark plugs comes up on the Forum. Some say don’t bother as it makes no difference at all, others say it will add a couple of horsepower and to position the spark plug gap towards the intake valve or position the spark plug gap towards the exhaust valve. I know that when you are designing a new engine a lot of super computer time is dedicated to combustion chamber design and spark plug placement. Could you please ask the engineers who are involved in combustion chamber design if they would comment on indexing spark plugs? We would like to know if it makes a difference, if so how much of difference (a few, 5, 10 horsepower?), and what is the correct orientation of the spark plug in the combustion chamber. If possible a picture or drawing showing the correct orientation of spark plug in the combustion chamber would go a long way to eliminate any confusion coming from a written description.
Every year or so the topic of indexing spark plugs comes up on the Forum. Some say don’t bother as it makes no difference at all, others say it will add a couple of horsepower and to position the spark plug gap towards the intake valve or position the spark plug gap towards the exhaust valve. I know that when you are designing a new engine a lot of super computer time is dedicated to combustion chamber design and spark plug placement. Could you please ask the engineers who are involved in combustion chamber design if they would comment on indexing spark plugs? We would like to know if it makes a difference, if so how much of difference (a few, 5, 10 horsepower?), and what is the correct orientation of the spark plug in the combustion chamber. If possible a picture or drawing showing the correct orientation of spark plug in the combustion chamber would go a long way to eliminate any confusion coming from a written description.
Tadge answered:
This is not a Corvette specific question, but I did exactly what you asked and consulted the experts on combustion optimization. Here's what they had to say:
Indexing the spark plug has been a topic of discussion for decades now. Theoretically, you would think that the spark plug position would have some impact on combustion and performance, and it may have had an affect years ago on poorly developed combustion systems and low energy ignition systems. However on modern engines, like the Small Block Corvette engines, significant engineering work is done to develop the combustion system. We use Computational Fluids Dynamics, Combustion Performance Analysis, Single Cylinder Engine combustion development, and engine testing to optimize combustion performance. This significantly decreases the benefit, if any, of indexing a spark plug in the chamber. In effect the combustion system's design ensures thorough mixing of the air and the fuel in the chamber rendering indexing to be of little benefit. Since the plug initiates flame propagation from near the center of the chamber and all other parameters are optimized around that location, complete combustion of all the air and fuel occurs in the minimum amount of time. Once you have achieved that, there are no more benefits to be gained through other design or geometric changes.
This is not a Corvette specific question, but I did exactly what you asked and consulted the experts on combustion optimization. Here's what they had to say:
Indexing the spark plug has been a topic of discussion for decades now. Theoretically, you would think that the spark plug position would have some impact on combustion and performance, and it may have had an affect years ago on poorly developed combustion systems and low energy ignition systems. However on modern engines, like the Small Block Corvette engines, significant engineering work is done to develop the combustion system. We use Computational Fluids Dynamics, Combustion Performance Analysis, Single Cylinder Engine combustion development, and engine testing to optimize combustion performance. This significantly decreases the benefit, if any, of indexing a spark plug in the chamber. In effect the combustion system's design ensures thorough mixing of the air and the fuel in the chamber rendering indexing to be of little benefit. Since the plug initiates flame propagation from near the center of the chamber and all other parameters are optimized around that location, complete combustion of all the air and fuel occurs in the minimum amount of time. Once you have achieved that, there are no more benefits to be gained through other design or geometric changes.
The following 11 users liked this post by jvp:
Bad Dad (09-03-2017),
daleong (09-01-2017),
doorgunner (09-03-2017),
Fastmikefree (09-07-2017),
FortMorganAl (09-05-2017),
and 6 others liked this post.
09-02-2017, 06:28 AM
#3
Dual electrode plugs have been shown to produce a small hp increase in high performance motorcycle engines and are used in engines producing 3 hp per cubic inch normally aspirated.
09-06-2017, 10:15 PM
#4
E-Ray, 3LZ, ZER, LIFT
Member Since: Sep 2007
Location: NE South Carolina
Posts: 29,441
Received 9,603 Likes
on
6,616 Posts
Cylinder from WWII Engine as used in the Corsair fighter! Have valves (NOS, came in original boxes,) pushrods and rocker arms. Started accumulating parts after getting one used exhaust valve!
Next to it is a master connecting rod and one of 8 other articulated rods from one of two banks of 9 cylinders. Both rods have pistons from this dual 9 cylinder radial. A piston pin has aluminum buttons pressed in the ends, no retaining clips it floats and the aluminum rides on the cylinder walls! Started life in 1939 with 1900 hp and by Wars end had been modified so it could produce 2800 hp for a short burst when evading an enemy in a dog fight! But then it required a rebuild!
Amazing things were done with piston engines in WWII. The 46 Liter engine has sodium cooled exhaust valves.
Behind the engine is one of it's two stage supercharger impellers.
Last edited by JerryU; 09-07-2017 at 07:11 AM.
09-08-2017, 07:34 AM
#5
Le Mans Master
..... How about a pic of the 4 electrode spark plug ? ..... and to Tadge , does the discounting of indexing plugs also apply to drag racing engines ? .....
Last edited by C409; 09-08-2017 at 07:36 AM.
09-08-2017, 03:42 PM
#6
Melting Slicks
About drag racing... a friend of mine once worked on a top fuel crew for a few years. He said the ignition systems on those motors are so powerful that the spark plugs don't have a ground electrode -- the spark grounds anywhere and everywhere inside the combustion chamber. In other words, the spark plug creates a lightning storm inside the combustion chamber, much more than just one spark at the center.
09-08-2017, 04:12 PM
#7
E-Ray, 3LZ, ZER, LIFT
Member Since: Sep 2007
Location: NE South Carolina
Posts: 29,441
Received 9,603 Likes
on
6,616 Posts
TOP: NOS Plug Came in Sealed Package!
Middle: End View Showing 4 Electrodes
Bottom: Plug in Cylinder. Note Threaded Wire Connection From Magneto Visible.
Last edited by JerryU; 09-08-2017 at 04:16 PM.
09-20-2017, 07:44 AM
#9
E-Ray, 3LZ, ZER, LIFT
Member Since: Sep 2007
Location: NE South Carolina
Posts: 29,441
Received 9,603 Likes
on
6,616 Posts
