Cut-back plugs?
Thread Starter
Drifting
Joined: May 2002
Posts: 1,581
Likes: 2
From: The Motor City
Cut-back plugs?
This may sound like a stupid question, but what are 'cut-back' spark plugs?
Everyone keeps saying how it's a good modification, but I don't know what it is. Can somebody please explain for those of us who don't know? Pics would be great too...
Thanks.
:cheers:
Everyone keeps saying how it's a good modification, but I don't know what it is. Can somebody please explain for those of us who don't know? Pics would be great too...
Thanks.
:cheers:
Le Mans Master
Joined: Mar 2001
Posts: 7,999
Likes: 14
From: Life is just one big track event. Everything before and after is prep and warm-up and cool-down laps
Cruise-In III Veteran
Cruise-In IV Veteran
St. Jude Donor '12
Re: Cut-back plugs? (TheCorvetteKid)
Description:
Take a look at the ground electrode on a normal spark plug. See how it completely covers the center electrode? The spark jumps the gap betweek the electrodes and not much of it is exposed to the air-fuel mixture. Now Imagine if you cut off the ground electrode so that one half of the center electrode was visible. A lot more of the same spark is now exposed to the air-fuel mixture.
Use a cut off wheel on a dremel or other rotary tool, clean up the cut with sandpaper, gap the plug and put them in.
On my car it probably took 30 min to do it and another hour + to put them in the car (1988, L98)
Take a look at the ground electrode on a normal spark plug. See how it completely covers the center electrode? The spark jumps the gap betweek the electrodes and not much of it is exposed to the air-fuel mixture. Now Imagine if you cut off the ground electrode so that one half of the center electrode was visible. A lot more of the same spark is now exposed to the air-fuel mixture.
Use a cut off wheel on a dremel or other rotary tool, clean up the cut with sandpaper, gap the plug and put them in.
On my car it probably took 30 min to do it and another hour + to put them in the car (1988, L98)
Thread Starter
Drifting
Joined: May 2002
Posts: 1,581
Likes: 2
From: The Motor City
Re: Cut-back plugs? (jaa1988)
OK, that makes perfect sense - expose more of the spark to the air/fuel charge by removing some of the ground electrode. Brilliant!
But, wouldn't the same effect be achieved with those new Bosch +4 platinum plugs? They have 4 ground electrodes all placed around the centre electrode. The centre electrode is totally exposed.
Either way though, I think I'll try this before I put my plugs back in.
Thanks guys.
:cheers:
But, wouldn't the same effect be achieved with those new Bosch +4 platinum plugs? They have 4 ground electrodes all placed around the centre electrode. The centre electrode is totally exposed.
Either way though, I think I'll try this before I put my plugs back in.
Thanks guys.
:cheers:
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Cut-back plugs? (TheCorvetteKid)
Well that's the principle of the Bosch plugs anyway.
My time slips show a 1mph gain in trap speed from cut-back AC Delcos vs Rapid Fires.
I've never tryed the Bosch 4-electrode; cut-back (got a pic on my site) works for me.
My time slips show a 1mph gain in trap speed from cut-back AC Delcos vs Rapid Fires.
I've never tryed the Bosch 4-electrode; cut-back (got a pic on my site) works for me.
Team Owner
Joined: Mar 2000
Posts: 83,383
Likes: 87
From: Boston, MA
Re: Cut-back plugs? (TheCorvetteKid)
But, wouldn't the same effect be achieved with those new Bosch +4 platinum plugs? They have 4 ground electrodes all placed around the centre electrode. The centre electrode is totally exposed.
Safety Car
Joined: Feb 2000
Posts: 4,230
Likes: 0
From: VA
Cruise-In II Veteran
Re: Cut-back plugs? (65Z01)
This is an old hotrodding trick. It's been around for years.
:yesnod:
Not only can you do this, You can also dial in your plugs. Ever hear of that? :yesnod:
Dialed in plugs are plugs that when torq down has the open area of the tip and prong facing the more open area of the chamber. If the plug sat in the middle of the cylinder like a Hemi motor it would not matter much.
The plugs are dial in using washers to adjust where it stops when it is tighten down. gabeash!
:lol:
[Modified by ConeKLR, 5:19 PM 7/23/2002]
:yesnod:
Not only can you do this, You can also dial in your plugs. Ever hear of that? :yesnod:
Dialed in plugs are plugs that when torq down has the open area of the tip and prong facing the more open area of the chamber. If the plug sat in the middle of the cylinder like a Hemi motor it would not matter much.
The plugs are dial in using washers to adjust where it stops when it is tighten down. gabeash!
:lol:
[Modified by ConeKLR, 5:19 PM 7/23/2002]
Safety Car
Joined: Feb 2000
Posts: 4,230
Likes: 0
From: VA
Cruise-In II Veteran
Re: Cut-back plugs? (scorp508)
But, wouldn't the same effect be achieved with those new Bosch +4 platinum plugs? They have 4 ground electrodes all placed around the centre electrode. The centre electrode is totally exposed.
Do you want one BIG spark or one little one? Electricity only follows one path at a time.
Do you want one BIG spark or one little one? Electricity only follows one path at a time.
Some people think all four fire up at the same time.
:crazy:
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Every 2027 Corvette Engine Explained
Joe Kucinski
Designer Imagines A Corvette That Looks More Like a Corvette Than the Corvette
Verdad Gallardo
10 Ugly Corvettes That We Still Kinda Love
Joe Kucinski
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Safety Car
Joined: Feb 2000
Posts: 4,230
Likes: 0
From: VA
Cruise-In II Veteran
Re: Cut-back plugs? (65Z01)
The cut-back "trick" is realy easy but dialing in (or indexing) on an L98 would be too much effort for me.
I did not say to do this. Was just bringing it up, you know trivia. :D
Have never tried it on an L98. But on my past Muscle cars, that a different story. :yesnod:
Thread Starter
Drifting
Joined: May 2002
Posts: 1,581
Likes: 2
From: The Motor City
Re: Cut-back plugs? (ConeKLR)
Actually, for me indexing the plugs would not be such a bad idea since I'll have the heads off of my car soon. But is there any real advantage to it? What kind of numbers are we talking about here - 5hp or maybe 8hp at the flywheel? Is it worth the effort?
I think that Summit Racing sells a plug indexing kit. Do you need this kit, or would any properly sized washers (of varying thicknesses) do the trick?
I think that Summit Racing sells a plug indexing kit. Do you need this kit, or would any properly sized washers (of varying thicknesses) do the trick?
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Cut-back plugs? (TheCorvetteKid)
With our Al heads you need crush washers for the plugs so not sure how easy it would be to index the plugs.
I too have not heard how much of a HP gain to expect from indexing them.
I too have not heard how much of a HP gain to expect from indexing them.
Racer
Joined: Jun 2002
Posts: 428
Likes: 0
From: Dallas Tx
Re: Cut-back plugs? (TheCorvetteKid)
Indexing plugs was reported in several build-up volumes to be worth 5hp at the 400-450hp level. No report of indexing vs. cut-back plugs (or both) is available.
Anyone with a dyno and an inquiring mind? Why not add the MSD box to the test and we can all benefit from some hard data.
If one had the heads on a bench, indexing would be a snap, and you could have a spare set of plugs ready to go. On the car, it is a royal PITA for the right rear plugs unless you have long headers and small fingers. For an extra "free" 5-10 hp I'd walk on hot coals, though, so I cut back the plugs, index, and use MSD..
Anyone with a dyno and an inquiring mind? Why not add the MSD box to the test and we can all benefit from some hard data.
If one had the heads on a bench, indexing would be a snap, and you could have a spare set of plugs ready to go. On the car, it is a royal PITA for the right rear plugs unless you have long headers and small fingers. For an extra "free" 5-10 hp I'd walk on hot coals, though, so I cut back the plugs, index, and use MSD..
Safety Car
Joined: Feb 2000
Posts: 4,230
Likes: 0
From: VA
Cruise-In II Veteran
Re: Cut-back plugs? (tkrussell)
Make sure you verify whether indexing can be done on the L98 type heads without leakage or stripping the threads. I have never done it before so I can't say.
