Spark Plug Indexing

njk53 · 12-31-2012, 01:31 PM

My brother and I had a conversation the other day about the horsepower and performance gains from indexing your spark plugs. If you read articles on the internet you will hear of a different ranges of gains.

My brother said he read an article by Smokey Yunick who said he tried different variations of spark plug indexing and yielded absolutely nothing and wasn't worth the effort.

Does anyone know of anyone who has test data to prove if indexing is worth it?

art leong · 12-31-2012, 01:34 PM

From what I have gathered. Indexing is more for clearance than anything else.

richie 2 · 12-31-2012, 02:05 PM

promotes an efficient flame travel resulting in a more complete burn of the air/fuel mixture.

Dwight Southerland · 12-31-2012, 02:27 PM

Considering the myriad of combustion chamber designs coupled with an almost infinite variety of piston tops and adding in the countless bore-stroke-compression ratio-valve size combination and then the many ignition systems and spark plug designs, there is no hard a fast rule. If you want to know if it works, try it. Keep good records.

Steve Williams · 01-03-2013, 01:13 AM

Nelson,

I assume you have a Chevrolet small block. What I found out concerning indexing and plugs is real simple. There is a small difference in power when used with timing change. The plug can be modified and combined with indexing a little more can be had. I tried different types of plugs. ground strap designs and gaps. Some of the plugs that people are/were paying big money for were absolute junk. One particular plug actually made less power by almost 10hp and it was the rage for about two years. Until word got out about how cheap they were. I modify my plugs ground strap and index all mine. I also use plugs that are not as expensive as many out there, but have good quality. As far as printed test data, I am sure it is out there in some publication. Indexing for clearance is something that many aluminum rod engines should do to avoid possibly nicking a plug.

SGSST109E · 01-03-2013, 07:13 PM

The biggest gain is the removal of the risk of closing a plug gap and losing all the HP in that cylinder.

njk53 · 01-08-2013, 02:02 PM

Our car is a big block (402 CI) Chevrolet. From the comments I gather that with the forward or open part of the spark plug facing the intake valve, this position will promote more efficient combustion which yields an increase in energy, translating to more power/performance correct?

Would an engine with a lower compression ratio yield better performance than one with a higher CR? Or doesn't it matter?

I have a kit that I'm going to use to index our plugs. I'll keep records and let you know what we come up with.

12-31-2012, 01:31 PM	#1
njk53 Senior Member Join Date: Jul 2007 Location: East China, MI Posts: 504 Likes: 0 Liked 0 Times in 0 Posts	Spark Plug Indexing My brother and I had a conversation the other day about the horsepower and performance gains from indexing your spark plugs. If you read articles on the internet you will hear of a different ranges of gains. My brother said he read an article by Smokey Yunick who said he tried different variations of spark plug indexing and yielded absolutely nothing and wasn't worth the effort. Does anyone know of anyone who has test data to prove if indexing is worth it? __________________ Nelson Kowal Stock 345

12-31-2012, 01:34 PM	#2
art leong VIP Member Join Date: Dec 2001 Location: Richmond Hill, Georgia Posts: 2,003 Likes: 0 Liked 1 Time in 1 Post	Re: Spark Plug Indexing From what I have gathered. Indexing is more for clearance than anything else. __________________ Art Leong 2095 SS

12-31-2012, 02:05 PM	#3
richie 2 Senior Member Join Date: Feb 2009 Posts: 916 Likes: 319 Liked 155 Times in 71 Posts	Re: Spark Plug Indexing promotes an efficient flame travel resulting in a more complete burn of the air/fuel mixture. Last edited by richie 2; 12-31-2012 at 02:08 PM.

12-31-2012, 02:27 PM	#4
Dwight Southerland VIP Member Join Date: Dec 2001 Location: Arkansas - In the middle of everything. Posts: 1,980 Likes: 52 Liked 724 Times in 177 Posts	Re: Spark Plug Indexing Considering the myriad of combustion chamber designs coupled with an almost infinite variety of piston tops and adding in the countless bore-stroke-compression ratio-valve size combination and then the many ignition systems and spark plug designs, there is no hard a fast rule. If you want to know if it works, try it. Keep good records.

01-03-2013, 01:13 AM	#5
Steve Williams Member Join Date: Aug 2007 Location: Detroit, Michigan Posts: 352 Likes: 0 Liked 1 Time in 1 Post	Re: Spark Plug Indexing Nelson, I assume you have a Chevrolet small block. What I found out concerning indexing and plugs is real simple. There is a small difference in power when used with timing change. The plug can be modified and combined with indexing a little more can be had. I tried different types of plugs. ground strap designs and gaps. Some of the plugs that people are/were paying big money for were absolute junk. One particular plug actually made less power by almost 10hp and it was the rage for about two years. Until word got out about how cheap they were. I modify my plugs ground strap and index all mine. I also use plugs that are not as expensive as many out there, but have good quality. As far as printed test data, I am sure it is out there in some publication. Indexing for clearance is something that many aluminum rod engines should do to avoid possibly nicking a plug.

01-03-2013, 07:13 PM	#6
SGSST109E Member Join Date: Jun 2007 Location: NJ Posts: 342 Likes: 54 Liked 124 Times in 58 Posts	Re: Spark Plug Indexing The biggest gain is the removal of the risk of closing a plug gap and losing all the HP in that cylinder.

01-08-2013, 02:02 PM	#7
njk53 Senior Member Join Date: Jul 2007 Location: East China, MI Posts: 504 Likes: 0 Liked 0 Times in 0 Posts	Re: Spark Plug Indexing Our car is a big block (402 CI) Chevrolet. From the comments I gather that with the forward or open part of the spark plug facing the intake valve, this position will promote more efficient combustion which yields an increase in energy, translating to more power/performance correct? Would an engine with a lower compression ratio yield better performance than one with a higher CR? Or doesn't it matter? I have a kit that I'm going to use to index our plugs. I'll keep records and let you know what we come up with. __________________ Nelson Kowal Stock 345