How is plug gap determined?
Thread Starter
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
How is plug gap determined?
Just curious.. not familiar with 'cold' vs 'hot' plugs and heat ranges. How is sparkplug gap determined?
I'm asking because everything in my new 388 is new.. ported heads.. 11.5 cr.. mixture will be different etc. Is there a method or way of knowing which type or gap should be used?
I'm asking because everything in my new 388 is new.. ported heads.. 11.5 cr.. mixture will be different etc. Is there a method or way of knowing which type or gap should be used?
Le Mans Master
Joined: Apr 2002
Posts: 5,726
Likes: 46
From: Waukesha WI
St. Jude Donor '15
I don't know about hot v. cold plugs either but it seems like the gap is mainly determined by the power of the ignition system. For example, a stock single coil setup (Like the L98) should probably stay at .035 or so. Adding a hotter coil and/or MSD box lets you open it up to maybe .045. Going DIS with multiple coil (think LS1/Delteq et al.) can get you into the .060 range.
I may be way off base on this so feel free to contradict...
I may be way off base on this so feel free to contradict...
Racer
Joined: Jan 2005
Posts: 476
Likes: 0
From: Tucson, AZ. L98-85 AUTO COUPE: 120k MILES: daily driver. SOUND OFF IF YOU'VE BEEN THERE. Ex-Jumpin' Junky-82nd Airborne-2/505 PIR: 1st ID-1/16th Inf: Recon Marine Retread. GOD BLESS GRUNTS.
watch out.
different plug manufacturers may recommend a different gap than your stock ac ones.
this may have to do with different brands' plug resistance, insulator length etc., all of which can effect current flow and heat. go with the recommended gap. if you don't trust what they tell you at pep boys, go look at the man's site. i double checked, after entering my car's year and model on ngk's site, and it verified the gap .045 recommended at the parts store.
also, if you are running aftermarket heads, check what the head man. recommends for that head. plugs are meant to protrude into a combustion chamber a specific distance. the wrong plug will be to short or too long--too much or not enough heat. bad medicine. heads like what goldylocks likes.
hot and cold plug recommendations, and allowance to open the gap due to high powered ignitions come from plug reading after the right plug and gap are installed.
check out this site for simple stuff:
http://www.ngksparkplugs.com/techinf...200&country=US
if you're ready for some serious info:
http://www.4secondsflat.com/Spark_plug_reading.html
different plug manufacturers may recommend a different gap than your stock ac ones.
this may have to do with different brands' plug resistance, insulator length etc., all of which can effect current flow and heat. go with the recommended gap. if you don't trust what they tell you at pep boys, go look at the man's site. i double checked, after entering my car's year and model on ngk's site, and it verified the gap .045 recommended at the parts store.
also, if you are running aftermarket heads, check what the head man. recommends for that head. plugs are meant to protrude into a combustion chamber a specific distance. the wrong plug will be to short or too long--too much or not enough heat. bad medicine. heads like what goldylocks likes.
hot and cold plug recommendations, and allowance to open the gap due to high powered ignitions come from plug reading after the right plug and gap are installed.
check out this site for simple stuff:
http://www.ngksparkplugs.com/techinf...200&country=US
if you're ready for some serious info:
http://www.4secondsflat.com/Spark_plug_reading.html
Last edited by parafrog; Mar 17, 2006 at 04:35 AM.
Melting Slicks
Joined: Jan 2002
Posts: 2,238
Likes: 4
From: Milan
It's true you can enlarge the gap with a better ignition system, it's imperative also to reduce the gap if the compression is raised.
A stock engine with a raccomended gap of .040 with better ignition and raised compression can continue to use a 0.040" gap.
A stock engine with a raccomended gap of .040 with better ignition and raised compression can continue to use a 0.040" gap.
Thread Starter
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
Spark Plug Specs (Denso Iridium)
Make: CHEVROLET
Model: CORVETTE
Sub Model:
Displacement: 5.7
Engine Type: V8
Plug Number: IT16 (Click to Purchase)
Gap: 0.06
Ignition Wire*: 671-8048
* Optional
Just looked into these plugs im going to try and they reccomend a .06 gap. i believe a stock 93 gap is .055 if i remember right. the website also says to go a step colder every 75-100 hp. so i think im going colder 3 steps on this one. Only problem is i dont know how or where to look for a plug for my app.. but colder. anyone know?
btw intereresting links posted above ty!
Make: CHEVROLET
Model: CORVETTE
Sub Model:
Displacement: 5.7
Engine Type: V8
Plug Number: IT16 (Click to Purchase)
Gap: 0.06
Ignition Wire*: 671-8048
* Optional
Just looked into these plugs im going to try and they reccomend a .06 gap. i believe a stock 93 gap is .055 if i remember right. the website also says to go a step colder every 75-100 hp. so i think im going colder 3 steps on this one. Only problem is i dont know how or where to look for a plug for my app.. but colder. anyone know?
btw intereresting links posted above ty!
Racer
Joined: Jan 2005
Posts: 476
Likes: 0
From: Tucson, AZ. L98-85 AUTO COUPE: 120k MILES: daily driver. SOUND OFF IF YOU'VE BEEN THERE. Ex-Jumpin' Junky-82nd Airborne-2/505 PIR: 1st ID-1/16th Inf: Recon Marine Retread. GOD BLESS GRUNTS.
Originally Posted by DieL
Spark Plug Specs (Denso Iridium)
Make: CHEVROLET
Model: CORVETTE
Sub Model:
Displacement: 5.7
Engine Type: V8
Plug Number: IT16 (Click to Purchase)
Gap: 0.06
Ignition Wire*: 671-8048
* Optional
Just looked into these plugs im going to try and they reccomend a .06 gap. i believe a stock 93 gap is .055 if i remember right. the website also says to go a step colder every 75-100 hp. so i think im going colder 3 steps on this one. Only problem is i dont know how or where to look for a plug for my app.. but colder. anyone know?
btw intereresting links posted above ty!
Make: CHEVROLET
Model: CORVETTE
Sub Model:
Displacement: 5.7
Engine Type: V8
Plug Number: IT16 (Click to Purchase)
Gap: 0.06
Ignition Wire*: 671-8048
* Optional
Just looked into these plugs im going to try and they reccomend a .06 gap. i believe a stock 93 gap is .055 if i remember right. the website also says to go a step colder every 75-100 hp. so i think im going colder 3 steps on this one. Only problem is i dont know how or where to look for a plug for my app.. but colder. anyone know?
btw intereresting links posted above ty!
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by DieL
Spark Plug Specs (Denso Iridium)
Make: CHEVROLET
Model: CORVETTE
Sub Model:
Displacement: 5.7
Engine Type: V8
Plug Number: IT16 (Click to Purchase)
Gap: 0.06
Ignition Wire*: 671-8048
* Optional
Just looked into these plugs im going to try and they reccomend a .06 gap. i believe a stock 93 gap is .055 if i remember right. the website also says to go a step colder every 75-100 hp. so i think im going colder 3 steps on this one. Only problem is i dont know how or where to look for a plug for my app.. but colder. anyone know?
btw intereresting links posted above ty!
Make: CHEVROLET
Model: CORVETTE
Sub Model:
Displacement: 5.7
Engine Type: V8
Plug Number: IT16 (Click to Purchase)
Gap: 0.06
Ignition Wire*: 671-8048
* Optional
Just looked into these plugs im going to try and they reccomend a .06 gap. i believe a stock 93 gap is .055 if i remember right. the website also says to go a step colder every 75-100 hp. so i think im going colder 3 steps on this one. Only problem is i dont know how or where to look for a plug for my app.. but colder. anyone know?
btw intereresting links posted above ty!
After my mods I started out with IT20.......then went to IT24....the IT24 is a totally different electrode design intended for track applications....I then went back to IT20's....
Denso recommended I use the as shipped gap setting of .044 on the IT20's......IT24 are factory set at .032 since they are intended for high compression applications.....
I would suggest you contact Denso for their guidance, but my opinion would be you go with the IT22 and leave the gap set to .044(as shipped)..
Race Director
Joined: Feb 2004
Posts: 12,518
Likes: 19
High Compression, Nitrous, turb's superchargers etc all build additional cylinder pressure. This pressure tries to blow out the candle(plugs). I reduce gaps slightly in this case. I have a 10.7:1 motor with a 150 shot, and keep the gap around .030
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Thread Starter
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
Originally Posted by parafrog
they might be talking about 75-100 hp over stock. if in doubt, give them an email. if they're expensive, you'll be happier. plus if you like them, it'll be a confirmation.
i know
its a 388 11.5:1 solid roller. Calling them does seem to be the best bet and i'll be doing that today.
Safety Car
Joined: Sep 2000
Posts: 3,524
Likes: 4
From: Hinckley Ohio
Originally Posted by DieL
i know its a 388 11.5:1 solid roller. Calling them does seem to be the best bet and i'll be doing that today.
its a 388 11.5:1 solid roller. Calling them does seem to be the best bet and i'll be doing that today. AARON_BROCK@denso-diam.com
Was very helpful...
Thread Starter
Melting Slicks
Joined: Mar 2003
Posts: 2,472
Likes: 0
From: Toronto ONTARIO
Originally Posted by LT4BUD