Question about spark plug gap - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Jimbotronics · 10-30-2004, 03:46 PM

Not long ago, I installed new spark plugs. I believe by recommendation of the board I gap the plugs at 45. Anyway a few weeks a go I had a shop install my new headers, and the guy says he noticed the plugs were gapped wrong and re-gapped them to 35. I'm getting a little pinging if I really get on it - could this be part of the problem?

btw my engine is an 87 350 w/HEI

Brainchild · 10-30-2004, 03:51 PM

I always gap the plugs at 45 with an HEI,and 35 with points.Never have a problem.

Jimbotronics · 10-30-2004, 04:06 PM

Thanks Brainchild - I was second guessing my thoughts. It may not be the problem but I think I'll change 'em back to 45.

Mudder · 10-30-2004, 05:28 PM

I've always gapped my plugs (hei) at 045 but I was just looking at the spc sheet on my motor and it says 060.

Brainchild · 10-30-2004, 06:28 PM

Will it run better at 60? Anyone run thiers at 60? I know some of the smaller 4 bangers and stuff gap at 60,I think my minivan is one of them.I might try that one this week if there is no feedback.

Jimbotronics · 10-30-2004, 06:47 PM

I'm curious to know that answer as well

70c10 · 10-30-2004, 08:52 PM

I would go with .045 unless you are running a higher end coil, wires, module,etc.

CHEVYE · 10-30-2004, 09:03 PM

i gapped mine @ 60 with an msd 6al, blaster coil and billet dist. on 11.7:1 comp in my race car. you have to have alot of spark to do that though. i always do 45 on a stock engine with hei. they usually come pre gapped right out of the box and i`ve never had a problem.

cableguy0 · 10-30-2004, 09:05 PM

stock hei is .045 a really hot coil or an msd box you can go as far as .060. .035 went out with points except in a few chryslers

Jimbotronics · 10-31-2004, 10:28 AM

thanks guys!

I don't know what he was thinking, but he thought he was doing me a favor so I can't really be mad + he did an awesome job on the entire exhaust set up.

I'll gap them back to .045 today - question is. could that be cause of my pinging or is that something else. I've got the distributor just loose enough that I can't barely move it. I run down the road pull over and tweak it - get back in and floor it - pull over and tweak some more... can't get rid of the pinging. I've also set it with a timing light but that didin't do the trick either.

Longhorn Man · 10-31-2004, 10:36 AM

The first year or two of HEI, GM said .060. When they figured out that they were burning up coils and wearing out plug wires too fast, they chainged it to .045.
As far as your pinging....you may well need to fatten up the mixture on the carb. Did you just go from manifolds and singlr exhaust?

**Stocker** · 10-31-2004, 10:43 AM

I've always gapped at .035 (points) and .045 since I put in HEI, and I've been follwing this thread to see where it went. Andy, thanks for the info - it's appreciated!

Jimbotronics · 10-31-2004, 11:02 AM

Thanks Andy! I did a lot of changing at once so it's hard for me to relate the issue to one thing. I changed from a qjet to a dual-plane intake, a 600 cfm holley, and installed dynomax headers and exhaust.

**kwmech** · 10-31-2004, 11:25 AM

The change over to headers will lean out your mixture,[less back pressure] thus the pinging, you need to fatten up the mixture.

Jimbotronics · 10-31-2004, 12:02 PM

Meaning that I need to run a higher octane? I'm only running 87 right now. Even though he said it wasn't needed I'm thinking of installing an H or X pipe, would that help?

Mudder · 10-31-2004, 12:24 PM

I'm positive mine are gapped at .045. I remember getting into an argument with my ex-father-in-law about it. I just noticed last night that the sheet here in from of me says .060.

Longhorn Man · 10-31-2004, 05:55 PM

You probably don't need a higher octain...just need to make more adjustments on the carb. Need to richen the fuel/air mixture. Playing with the timing may/may not help too.
If you can't tune the ping out, then go to a higher grade of fuel.

Mudder, what is it you have there that says to gap like that? I was just going through my manual, and it was only in 75 that GM said to do that. 76 & up is all .045.

Mudder · 10-31-2004, 06:16 PM

Sheet that came with my motor......Gives all the specs. Trying to figure out a way to show ya.

Mudder · 10-31-2004, 06:20 PM

this is the motor I got from Performance Parts.

12355345 SP 350ci (300 hp)

Jimbotronics · 10-31-2004, 06:39 PM

Thanks Longhorn Man - I'll start tweaking on them and see what it does.

cableguy0 · 10-31-2004, 06:44 PM

jimbo your best bet is probably to go 2 jet sizes bigger and see if that fixes it. if not go bigger

tom hand · 10-31-2004, 08:02 PM

I agree on riching the carb cause of the headers...when HEI first came out GM said run .060 but I believe them backed off that because it was killing the coils.....Some NASCAR team did a test and found no horsepower gains at anything over .035

cableguy0 · 10-31-2004, 08:26 PM

i find it hard to believe that there was no gains with a gap over .035 i know one time i screwed up and gapped mine at .035 then when i checked i put em to .050 and it got better mileage and ran a hell of a lot better power wise

Jimbotronics · 10-31-2004, 08:58 PM

I've changed carbs but never broke into one - how do I change the jets?

cableguy0 · 10-31-2004, 09:09 PM

pull off the fuel bowl on the front 4 bolts. take on bottom bolt out and have a small cup or the cap to a can of carb cleaner under it when u pull the bolt because fuel is going to come out. then you will see the main body of the carb behind it. the jets come out with a straight blade screwdriver they are at the bottom. it will seem simple to ya once ya see it

10-30-2004, 03:46 PM	#1
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	Question about spark plug gap Not long ago, I installed new spark plugs. I believe by recommendation of the board I gap the plugs at 45. Anyway a few weeks a go I had a shop install my new headers, and the guy says he noticed the plugs were gapped wrong and re-gapped them to 35. I'm getting a little pinging if I really get on it - could this be part of the problem? btw my engine is an 87 350 w/HEI __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707 Last edited by Jimbotronics; 10-31-2004 at 08:59 PM.

10-30-2004, 03:51 PM	#2
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	I always gap the plugs at 45 with an HEI,and 35 with points.Never have a problem. __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

10-30-2004, 04:06 PM	#3
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	Thanks Brainchild - I was second guessing my thoughts. It may not be the problem but I think I'll change 'em back to 45. __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

10-30-2004, 06:28 PM	#5
Brainchild Still drivin' a Rat Rod Join Date: Sep 2004 Location: Monett Missouri Posts: 4,925	Will it run better at 60? Anyone run thiers at 60? I know some of the smaller 4 bangers and stuff gap at 60,I think my minivan is one of them.I might try that one this week if there is no feedback. __________________ Rusty Member #13872 Instead of saying.....you are a discomfort in the back of my front.....one should be able to say...... you are a pain in the a$# 71 GMC LWB 49 Chevy 85 Chevy G20 Check out my website

10-30-2004, 06:47 PM	#6
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	I'm curious to know that answer as well __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

10-30-2004, 05:28 PM	#4
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	I've always gapped my plugs (hei) at 045 but I was just looking at the spc sheet on my motor and it says 060.

10-30-2004, 08:52 PM	#7
70c10 67-72 Addict! Join Date: Feb 2002 Location: The TAX State! Posts: 7,857	I would go with .045 unless you are running a higher end coil, wires, module,etc. __________________ Jim 1970 C/10 Fleetside w/Ghost Flames Lowered 4.5" front and 4" rear (Raked) 355/350 Turbo w/shift kit 10" Redneck Performance Verter w/2500 stall Hooker Super Comps part#2808-1 Performer RPM Air-Gap 12 Bolt w/3:73 gears- Eaton Posi Comp Cams XE262 with 1.6 Crane Energizers, Road Demon 625 and Brodix IK 180 heads

10-30-2004, 09:03 PM	#8
CHEVYE my gas saver Join Date: Sep 2003 Location: Clarksville, TN Posts: 2,046	i gapped mine @ 60 with an msd 6al, blaster coil and billet dist. on 11.7:1 comp in my race car. you have to have alot of spark to do that though. i always do 45 on a stock engine with hei. they usually come pre gapped right out of the box and i`ve never had a problem. __________________ 85' SWB, 4.3/TH350, getting ready for paint 84`SWB, 462ci./TH400, cowl hood, 15" billet spec., flows, blazer buckets/console, flat black 71`SWB, project ebay feedback

10-30-2004, 09:05 PM	#9
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	stock hei is .045 a really hot coil or an msd box you can go as far as .060. .035 went out with points except in a few chryslers __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

10-31-2004, 10:28 AM	#10
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	thanks guys! I don't know what he was thinking, but he thought he was doing me a favor so I can't really be mad + he did an awesome job on the entire exhaust set up. I'll gap them back to .045 today - question is. could that be cause of my pinging or is that something else. I've got the distributor just loose enough that I can't barely move it. I run down the road pull over and tweak it - get back in and floor it - pull over and tweak some more... can't get rid of the pinging. I've also set it with a timing light but that didin't do the trick either. __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

10-31-2004, 10:36 AM	#11
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	The first year or two of HEI, GM said .060. When they figured out that they were burning up coils and wearing out plug wires too fast, they chainged it to .045. As far as your pinging....you may well need to fatten up the mixture on the carb. Did you just go from manifolds and singlr exhaust?

10-31-2004, 10:43 AM	#12
Stocker 20' Daredevil (Ret) Join Date: May 2003 Location: Jefferson State Posts: 13,694	I've always gapped at .035 (points) and .045 since I put in HEI, and I've been follwing this thread to see where it went. Andy, thanks for the info - it's appreciated! __________________ - Mike - 1972 K20 LWB 350/350/205 RIP El Jay

10-31-2004, 11:02 AM	#13
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	Thanks Andy! I did a lot of changing at once so it's hard for me to relate the issue to one thing. I changed from a qjet to a dual-plane intake, a 600 cfm holley, and installed dynomax headers and exhaust. __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

10-31-2004, 11:25 AM	#14
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,599	The change over to headers will lean out your mixture,[less back pressure] thus the pinging, you need to fatten up the mixture.

10-31-2004, 12:02 PM	#15
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	Meaning that I need to run a higher octane? I'm only running 87 right now. Even though he said it wasn't needed I'm thinking of installing an H or X pipe, would that help? __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707



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10-31-2004, 12:24 PM	#16
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	I'm positive mine are gapped at .045. I remember getting into an argument with my ex-father-in-law about it. I just noticed last night that the sheet here in from of me says .060.

10-31-2004, 05:55 PM	#17
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	You probably don't need a higher octain...just need to make more adjustments on the carb. Need to richen the fuel/air mixture. Playing with the timing may/may not help too. If you can't tune the ping out, then go to a higher grade of fuel. Mudder, what is it you have there that says to gap like that? I was just going through my manual, and it was only in 75 that GM said to do that. 76 & up is all .045.

10-31-2004, 06:16 PM	#18
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	Sheet that came with my motor......Gives all the specs. Trying to figure out a way to show ya.

10-31-2004, 06:20 PM	#19
Mudder Registered User Join Date: Feb 2001 Location: East Central, MO Posts: 11,336	this is the motor I got from Performance Parts. 12355345 SP 350ci (300 hp)

10-31-2004, 06:39 PM	#20
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	Thanks Longhorn Man - I'll start tweaking on them and see what it does. __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

10-31-2004, 06:44 PM	#21
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	jimbo your best bet is probably to go 2 jet sizes bigger and see if that fixes it. if not go bigger __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

10-31-2004, 08:02 PM	#22
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	I agree on riching the carb cause of the headers...when HEI first came out GM said run .060 but I believe them backed off that because it was killing the coils.....Some NASCAR team did a test and found no horsepower gains at anything over .035 __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

10-31-2004, 08:26 PM	#23
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	i find it hard to believe that there was no gains with a gap over .035 i know one time i screwed up and gapped mine at .035 then when i checked i put em to .050 and it got better mileage and ran a hell of a lot better power wise __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

10-31-2004, 08:58 PM	#24
Jimbotronics YA YA Join Date: Aug 2004 Location: Rockledge, Fl Posts: 1,273	I've changed carbs but never broke into one - how do I change the jets? __________________ Jimbo '72 SWB - 350 (frame-off resto in progress - donations accepted) '04 Chevy Avalanche '03 Cadillac CTS (wife's ride) Restoration progress - http://67-72chevytrucks.com/vboard/s...d.php?t=335707

10-31-2004, 09:09 PM	#25
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	pull off the fuel bowl on the front 4 bolts. take on bottom bolt out and have a small cup or the cap to a can of carb cleaner under it when u pull the bolt because fuel is going to come out. then you will see the main body of the carb behind it. the jets come out with a straight blade screwdriver they are at the bottom. it will seem simple to ya once ya see it __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

Register or Log In To remove these advertisements.