Spark plug question..
February 15th, 2019, 01:26 PM
#1
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Spark plug question..
I was checking the plugs in my 72 Supreme the other day, and noticed they were Autolites. Being a purist, I would like to switch to AC Delco, and even more to the point, would like to get period correct plugs. Question is, which ones would be period correct (pics would be appreciated) and is the technology different from today's copper plugs vs OEM? Also, what would be the correct gap for a U code 455 with a cam and .030 bore? I also have HEI ignition and the current plugs are Autolite 86.
Thanks,
Dave
Thanks,
Dave
Last edited by 72455; February 15th, 2019 at 05:01 PM.
February 15th, 2019, 04:03 PM
#2
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I use the AC Rapid Fire plugs, cost a little more, but you won't be changing very offen. I would check them, and see what they are when you get them, if they are close to what your old one are. Order some for a HEI year car,see if they are different, then old.If different, run them the way they came in the box.
February 15th, 2019, 07:45 PM
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Nope...l like the HEI...I'm a purist, but not a fanatic...lol. The R45 is a heat range 5 plug and the Autolites in it now are heat range 6, so to keep the same heat range I would need R46.
February 15th, 2019, 10:08 PM
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Why go for "period correct" spark plugs if you are using the HEI distributor? Doesn't make any sense to me.
Whatever, just set the gap between .035" and .045" - DO NOT use the "period correct" gap for HEI as that is either .060" or .080" depending upon the year, and that wide gap is for igniting the lean mixture on a low compression engine with EGR.
Whatever, just set the gap between .035" and .045" - DO NOT use the "period correct" gap for HEI as that is either .060" or .080" depending upon the year, and that wide gap is for igniting the lean mixture on a low compression engine with EGR.
February 15th, 2019, 10:38 PM
#7
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I am missing the "period correct sparkplugs" that are hidden by sparkplug boots when an HEI is far more obvious as being "incorrect". Back in the day I preferred AC and Champion sparkplugs. I will be running AC's in all my Oldsmobiles. 45's were kinda hot. I imagine I'll be using AC 44's gapped at .030" for conventional distributors and .035" or so for the one car with HEI.
.........Just my two cents worth.
.........Just my two cents worth.
February 16th, 2019, 04:56 AM
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The car has Autolite 86 plugs which is heat range 6. It has a cam and is .030 over so obviously it's not stock. There is a reason the engine builder used heat range 6, so that's why I want to stay with heat range 6.
HEI produces better spark, is more durable, and is more efficient than points/condenser. Yes, I am a purist, but I also want the best performance, so that's why I'm staying with HEI.
I only started this thread to get advice. If I had known I was going to get all the commentary, then we wouldn't be having this discussion.
Thanks,
Dave
HEI produces better spark, is more durable, and is more efficient than points/condenser. Yes, I am a purist, but I also want the best performance, so that's why I'm staying with HEI.
I only started this thread to get advice. If I had known I was going to get all the commentary, then we wouldn't be having this discussion.
Thanks,
Dave
February 16th, 2019, 05:50 AM
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February 16th, 2019, 06:17 AM
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February 16th, 2019, 07:42 AM
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February 16th, 2019, 07:55 AM
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AC DELCO plugs have more heat ranges, or at least they used to i.e. the Autolite 86 (I believe) is a replacement for each of these AC DELCO spark plugs - R45S,R46S,R47S. Spark plug manufacturers neither follow any universal guidelines nor do they cross-reference specifically to any other manufacturer. That's why you often see one plug replaces several of another. Some manufacturers have more choices (heat ranges) while others do not. You'd think at some point in the industry they'd agree on a universal adherence to manufacturing guidelines. I've never found any, if you find any let me know. 
February 16th, 2019, 08:08 AM
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Will do 👍 .all I know is the with Autolites and AC Delco the second number designates the heat range...IE "86" Autolite had a heat range of 6 and AC Delco R46 also has a heat range of 6.
February 16th, 2019, 08:36 AM
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I may be incorrect stating the Autolite 86 is equivalent to the R45S, R46S & R47S spark plugs. That is 'if' the information on this site is correct regarding cross-reference.
http://www.angelfire.com/extreme4/sk..._REFERENCE.htm
They show Autolite 77 = R47S, Autolite 86 = R45S, Autolite 87 = R46S
I am not certain if the heat ranges 'align' 1:1 (it's a bit more than I care to dive into on a Saturday)
Also, be mindful of what Kenneth suggested regarding your HEI ignition system and the gap. I mention this because I believe AC DELCO makes the same plugs but with the wide gap specification - designated by the letter 'Z'. So, I believe you'd probably want to look for maybe a R46SZ plug? If you use a conventional plug to open the gap from a suggested 0.030 to say 0.060, the actual 'gap' will not be square. You'd prefer a square gap. I'm not an expert on HEI and gaps, so I'm not the one to make suggestions here. Although, whenever you widen a gap beyond it's normal recommended range, if a wide gap plug is available, I'd choose the wide gap plug because the length of the electrode will protrude further creating a better 'square' gap (as opposed to a more obtuse gap).
http://www.angelfire.com/extreme4/sk..._REFERENCE.htm
They show Autolite 77 = R47S, Autolite 86 = R45S, Autolite 87 = R46S
I am not certain if the heat ranges 'align' 1:1 (it's a bit more than I care to dive into on a Saturday)
Whatever, just set the gap between .035" and .045" - DO NOT use the "period correct" gap for HEI as that is either .060" or .080" depending upon the year, and that wide gap is for igniting the lean mixture on a low compression engine with EGR.
Last edited by Vintage Chief; February 16th, 2019 at 08:38 AM.
February 16th, 2019, 08:38 AM
#20
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I may be incorrect stating the Autolite 86 is equivalent to the R45S, R46S & R47S spark plugs. That is 'if' the information on this site is correct regarding cross-reference.
http://www.angelfire.com/extreme4/sk..._REFERENCE.htm
They show Autolite 77 = R47S, Autolite 86 = R45S, Autolite 87 = R46S
I am not certain if the heat ranges 'align' 1:1 (it's a bit more than I care to dive into on a Saturday)
Also, be mindful of what Kenneth suggested regarding your HEI ignition system and the gap. I mention this because I believe AC DELCO makes a the same plugs but with the wide gap specification - designated by the letter 'Z'. So, I believe you'd probably want to look for maybe a R46SZ plug? If you use a conventional plug to open the gap from a suggested 0.030 to say 0.060, the actually 'gap' will not be square. You'd prefer a square gap. I'm not an expert on HEI and gaps, so I'm not the one to make suggestions here. Although, whenever you widen a gap beyond it's normal recommended range, if a wide gap plug is available, I'd choose the wide gap plug because the length of the electrode will protrude further creating a better 'square' gap (as opposed to a more obtuse gap).
http://www.angelfire.com/extreme4/sk..._REFERENCE.htm
They show Autolite 77 = R47S, Autolite 86 = R45S, Autolite 87 = R46S
I am not certain if the heat ranges 'align' 1:1 (it's a bit more than I care to dive into on a Saturday)
Also, be mindful of what Kenneth suggested regarding your HEI ignition system and the gap. I mention this because I believe AC DELCO makes a the same plugs but with the wide gap specification - designated by the letter 'Z'. So, I believe you'd probably want to look for maybe a R46SZ plug? If you use a conventional plug to open the gap from a suggested 0.030 to say 0.060, the actually 'gap' will not be square. You'd prefer a square gap. I'm not an expert on HEI and gaps, so I'm not the one to make suggestions here. Although, whenever you widen a gap beyond it's normal recommended range, if a wide gap plug is available, I'd choose the wide gap plug because the length of the electrode will protrude further creating a better 'square' gap (as opposed to a more obtuse gap).
February 16th, 2019, 08:40 AM
#21
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Dave,
You're running HEI, and typically the gap for HEI is more than a conventional points distributor. Have you checked the gap on your existing plugs? I'm guessing they are set for around .060 (+/-). If you were running a totally stock 455 the stock plug gap would be .040. My opinion is to leave the existing spark plugs as are; that's what the engine builder determined would be plug of choice when the engine was done. Stick with what works, and don't worry about being purist in this category. The HEI and plug wires are dead giveaways that it's not stock anyway.
FWIW, since the topic was broached, I found that using AC Delco copper core plugs in my 95 Regency Elite worked very well and that engine was 10:1 compression.
You're running HEI, and typically the gap for HEI is more than a conventional points distributor. Have you checked the gap on your existing plugs? I'm guessing they are set for around .060 (+/-). If you were running a totally stock 455 the stock plug gap would be .040. My opinion is to leave the existing spark plugs as are; that's what the engine builder determined would be plug of choice when the engine was done. Stick with what works, and don't worry about being purist in this category. The HEI and plug wires are dead giveaways that it's not stock anyway.
FWIW, since the topic was broached, I found that using AC Delco copper core plugs in my 95 Regency Elite worked very well and that engine was 10:1 compression.
February 16th, 2019, 08:54 AM
#22
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Dave,
You're running HEI, and typically the gap for HEI is more than a conventional points distributor. Have you checked the gap on your existing plugs? I'm guessing they are set for around .060 (+/-). If you were running a totally stock 455 the stock plug gap would be .040. My opinion is to leave the existing spark plugs as are; that's what the engine builder determined would be plug of choice when the engine was done. Stick with what works, and don't worry about being purist in this category. The HEI and plug wires are dead giveaways that it's not stock anyway.
FWIW, since the topic was broached, I found that using AC Delco copper core plugs in my 95 Regency Elite worked very well and that engine was 10:1 compression.
You're running HEI, and typically the gap for HEI is more than a conventional points distributor. Have you checked the gap on your existing plugs? I'm guessing they are set for around .060 (+/-). If you were running a totally stock 455 the stock plug gap would be .040. My opinion is to leave the existing spark plugs as are; that's what the engine builder determined would be plug of choice when the engine was done. Stick with what works, and don't worry about being purist in this category. The HEI and plug wires are dead giveaways that it's not stock anyway.
FWIW, since the topic was broached, I found that using AC Delco copper core plugs in my 95 Regency Elite worked very well and that engine was 10:1 compression.
My apologies to anyone who contributed and were inconvienced by my decision to stick with the Autolites. Sometimes my passion gets in the way of logic.
Dave
February 16th, 2019, 08:58 AM
#23
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I have a question for you and Allan.
Have either of you met this engine builder? Did either of you ask the engine builder if he chose those spark plugs? Was the engine builder the last person to install the spark plugs? I doubt the engine builder made the decision. Anyone who changes a stock contact/points distributor to HEI is not an engine builder. I bet the person who installed the Autolite 86 plugs was the person who changed to HEI.
But, your daddy has spoken, so you're back to square one - a non-conforming purist.
Have either of you met this engine builder? Did either of you ask the engine builder if he chose those spark plugs? Was the engine builder the last person to install the spark plugs? I doubt the engine builder made the decision. Anyone who changes a stock contact/points distributor to HEI is not an engine builder. I bet the person who installed the Autolite 86 plugs was the person who changed to HEI.
But, your daddy has spoken, so you're back to square one - a non-conforming purist.
February 16th, 2019, 09:17 AM
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I have a question for you and Allan.
Have either of you met this engine builder? Did either of you ask the engine builder if he chose those spark plugs? Was the engine builder the last person to install the spark plugs? I doubt the engine builder made the decision. Anyone who changes a stock contact/points distributor to HEI is not an engine builder. I bet the person who installed the Autolite 86 plugs was the person who changed to HEI.
But, your daddy has spoken, so you're back to square one - a non-conforming purist.
Have either of you met this engine builder? Did either of you ask the engine builder if he chose those spark plugs? Was the engine builder the last person to install the spark plugs? I doubt the engine builder made the decision. Anyone who changes a stock contact/points distributor to HEI is not an engine builder. I bet the person who installed the Autolite 86 plugs was the person who changed to HEI.
But, your daddy has spoken, so you're back to square one - a non-conforming purist.
And if I'm a non-conforming purist, then so be it...my Cutlass still brings a smile to my face😀
February 16th, 2019, 09:31 AM
#25
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I have a question for you and Allan.
Have either of you met this engine builder? Did either of you ask the engine builder if he chose those spark plugs? Was the engine builder the last person to install the spark plugs? I doubt the engine builder made the decision. Anyone who changes a stock contact/points distributor to HEI is not an engine builder. I bet the person who installed the Autolite 86 plugs was the person who changed to HEI.
But, your daddy has spoken, so you're back to square one - a non-conforming purist.
Have either of you met this engine builder? Did either of you ask the engine builder if he chose those spark plugs? Was the engine builder the last person to install the spark plugs? I doubt the engine builder made the decision. Anyone who changes a stock contact/points distributor to HEI is not an engine builder. I bet the person who installed the Autolite 86 plugs was the person who changed to HEI.
But, your daddy has spoken, so you're back to square one - a non-conforming purist.
February 16th, 2019, 09:38 AM
#26
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There is nothing wrong with using an Hei. Just remember that the original timing settings are N/A because an Hei has a different timing curve. A .045 gap is more than sufficient for an Hei using stock plugs. Reading your plugs best way to determine if they are the correct heat range.
February 16th, 2019, 09:49 AM
#27
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Well, I was happy to see you chime-in, Allan. I was considering heading out to purchase & ship a butt-plug to Dave; I'm glad that will no longer be necessary. 
Dave, you're doing a great job on your modifications, upgrades & maintaining a classic. Adding to Allan's comments (in my own words, of course) - unless you're planning to be judged at some CCCA event, there are many routine maintenance items which you're going to have to lovingly endure - "period correct" spark plugs is not something to be concerned with unless you plan to have a ritualistic antique revival museum ceremony each morning in your garage and never drive it.
I commend you on doing what you believe is best.
As I see the - (other) Eric just posted, the most important consideration is the condition of your spark plugs - use what's best for your vehicle.
Finally, there were hundreds of thousands of both bbo & sbo engines modified for racing prior to 1975 - most of them did not have an HEI ignition system. My point is, unless you know specifically when your engine was modified, you really woudn't have a leg to stand on with me. That engine could have been modified in 1973 prior to any HEI ignition. Thousands ran on contact points in racing prior to any HEI systems. It may not have been modified. Someone may have tossed on the HEI in 1989, then modified the engine in 1999. Nothing but assumptions and conjecture unless you were there (like Allan).
Dave, you're doing a great job on your modifications, upgrades & maintaining a classic. Adding to Allan's comments (in my own words, of course) - unless you're planning to be judged at some CCCA event, there are many routine maintenance items which you're going to have to lovingly endure - "period correct" spark plugs is not something to be concerned with unless you plan to have a ritualistic antique revival museum ceremony each morning in your garage and never drive it.
I commend you on doing what you believe is best.
As I see the - (other) Eric just posted, the most important consideration is the condition of your spark plugs - use what's best for your vehicle.
Finally, there were hundreds of thousands of both bbo & sbo engines modified for racing prior to 1975 - most of them did not have an HEI ignition system. My point is, unless you know specifically when your engine was modified, you really woudn't have a leg to stand on with me. That engine could have been modified in 1973 prior to any HEI ignition. Thousands ran on contact points in racing prior to any HEI systems. It may not have been modified. Someone may have tossed on the HEI in 1989, then modified the engine in 1999. Nothing but assumptions and conjecture unless you were there (like Allan).
February 16th, 2019, 09:58 AM
#28
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Well, I was happy to see you chime-in, Allan. I was considering heading out to purchase & ship a butt-plug to Dave; I'm glad that will no longer be necessary.
Dave, you're doing a great job on your modifications, upgrades & maintaining a classic. Adding to Allan's comments (in my own words, of course) - unless you're planning to be judged at some CCCA event, there are many routine maintenance items which you're going to have to lovingly endure - "period correct" spark plugs is not something to be concerned with unless you plan to have a ritualistic antique revival museum ceremony each morning in your garage and never drive it.
I commend you on doing what you believe is best.
As I see the - (other) Eric just posted, the most important consideration is the condition of your spark plugs - use what's best for your vehicle.
Finally, there were hundreds of thousands of both bbo & sbo engines modified for racing prior to 1975 - most of them did not have an HEI ignition system. My point is, unless you know specifically when your engine was modified, you really woudn't have a leg to stand on with me. That engine could have been modified in 1973 prior to any HEI ignition. Thousands ran on contact points in racing prior to any HEI systems. It may not have been modified. Someone may have tossed on the HEI in 1989, then modified the engine in 1999. Nothing but assumptions and conjecture unless you were there (like Allan).
Dave, you're doing a great job on your modifications, upgrades & maintaining a classic. Adding to Allan's comments (in my own words, of course) - unless you're planning to be judged at some CCCA event, there are many routine maintenance items which you're going to have to lovingly endure - "period correct" spark plugs is not something to be concerned with unless you plan to have a ritualistic antique revival museum ceremony each morning in your garage and never drive it.
I commend you on doing what you believe is best.
As I see the - (other) Eric just posted, the most important consideration is the condition of your spark plugs - use what's best for your vehicle.
Finally, there were hundreds of thousands of both bbo & sbo engines modified for racing prior to 1975 - most of them did not have an HEI ignition system. My point is, unless you know specifically when your engine was modified, you really woudn't have a leg to stand on with me. That engine could have been modified in 1973 prior to any HEI ignition. Thousands ran on contact points in racing prior to any HEI systems. It may not have been modified. Someone may have tossed on the HEI in 1989, then modified the engine in 1999. Nothing but assumptions and conjecture unless you were there (like Allan).
February 16th, 2019, 02:19 PM
#29
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Here's my experience with points systems vs HEI:
Back in the 80s I ran the factory points distributor in my 1970 Supreme 350. I used premium cap, rotor, wires, Accel performance coil, and 32 ounce Accel / Echlin performance points, and a recurve kit. The engine ran flawlessly and would turn 5800 RPM with no points bounce.
At some point a friend gave me a GM HEI distributor, which I set up with premium cap, rotor, wires, Accel performance coil, and recurve kit. The engine didn't run any different with the HEI distributor than it did with the points distributor. Same mileage, same 0-60 and quarter mile times, same everything. The only difference was no routine points replacement with the HEI distributor.
Back in the 80s I ran the factory points distributor in my 1970 Supreme 350. I used premium cap, rotor, wires, Accel performance coil, and 32 ounce Accel / Echlin performance points, and a recurve kit. The engine ran flawlessly and would turn 5800 RPM with no points bounce.
At some point a friend gave me a GM HEI distributor, which I set up with premium cap, rotor, wires, Accel performance coil, and recurve kit. The engine didn't run any different with the HEI distributor than it did with the points distributor. Same mileage, same 0-60 and quarter mile times, same everything. The only difference was no routine points replacement with the HEI distributor.
February 17th, 2019, 05:41 PM
#30
CH3NO2 LEARN IT BURN IT
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I've been running Autolite 86 or 87s(can't remember & to lazy to look) in my 400 since 1987. It was running OEM points in 87.
They run the best, last the longest verses other brands and are cheap too.
I run a DUI HEI (with a SUN curve) with 8mm Taylor Spiral cores and a .040" gap.
They run the best, last the longest verses other brands and are cheap too.
I run a DUI HEI (with a SUN curve) with 8mm Taylor Spiral cores and a .040" gap.
February 17th, 2019, 08:35 PM
#31
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Here's my experience with points systems vs HEI:
Back in the 80s I ran the factory points distributor in my 1970 Supreme 350. I used premium cap, rotor, wires, Accel performance coil, and 32 ounce Accel / Echlin performance points, and a recurve kit. The engine ran flawlessly and would turn 5800 RPM with no points bounce.
At some point a friend gave me a GM HEI distributor, which I set up with premium cap, rotor, wires, Accel performance coil, and recurve kit. The engine didn't run any different with the HEI distributor than it did with the points distributor. Same mileage, same 0-60 and quarter mile times, same everything. The only difference was no routine points replacement with the HEI distributor.
Back in the 80s I ran the factory points distributor in my 1970 Supreme 350. I used premium cap, rotor, wires, Accel performance coil, and 32 ounce Accel / Echlin performance points, and a recurve kit. The engine ran flawlessly and would turn 5800 RPM with no points bounce.
At some point a friend gave me a GM HEI distributor, which I set up with premium cap, rotor, wires, Accel performance coil, and recurve kit. The engine didn't run any different with the HEI distributor than it did with the points distributor. Same mileage, same 0-60 and quarter mile times, same everything. The only difference was no routine points replacement with the HEI distributor.
February 18th, 2019, 01:05 PM
#32
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I see Rockauto has one 46S plug left. The AC Delco and Autolite plugs aren't as good since going overseas for manufacturing. I used to really like them both but now prefer the NGK XR4 or XR5 plugs in mild Olds V8's. I actually noticed a smoother idle vs AC Delco 46SX plugs.
February 18th, 2019, 02:36 PM
#33
CH3NO2 LEARN IT BURN IT
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Good point. NO MORE OFFSHORE GARBAGE!!! NGKs it is. But they are offshore too....what isnt...GAH!!! I give up.
Had I known this 3rd world sell out would have been this systemic 30 years ago I would have stocked up. Hind site,
At least NGK has a proven track record.
I have a collection of used AC 44 45 and 46s from 30+ years ago. Looks like I have museum pieces. :^)
Had I known this 3rd world sell out would have been this systemic 30 years ago I would have stocked up. Hind site,
At least NGK has a proven track record.
I have a collection of used AC 44 45 and 46s from 30+ years ago. Looks like I have museum pieces. :^)
February 19th, 2019, 02:17 PM
#34
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The Autolite plug is very good IMO as are NGK. You cannot use the original R45S with HEI as gap will not open up far enough to get the HEI benefit without buggering up the side electrode. Use the R46SZ or R46SX if you decide to go with ACD sometime in the future.
.045 is a good gap setting for HEI. Wide enough to gain benefit from the fatter spark, and closed enough not to get misfire-- which the original .080 gap was notorious for. I have the tech bulletin from 1974 somewhere that instructed all dealer techs to set HEI plug gaps at .060 when an early HEI car was in for service or tuneup.
.045 is a good gap setting for HEI. Wide enough to gain benefit from the fatter spark, and closed enough not to get misfire-- which the original .080 gap was notorious for. I have the tech bulletin from 1974 somewhere that instructed all dealer techs to set HEI plug gaps at .060 when an early HEI car was in for service or tuneup.
February 19th, 2019, 07:22 PM
#35
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I have no problems with setting the gap to .045" on any brand spark plugs I have used since I installed the HEI back in 1982. I get the plugs specced for my engine and open the gap a bit. I should point out that I work the ground electrode so it is parallel to the center electrode.
February 19th, 2019, 07:32 PM
#36
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I have no problems with setting the gap to .045" on any brand spark plugs I have used since I installed the HEI back in 1982. I get the plugs specced for my engine and open the gap a bit. I should point out that I work the ground electrode so it is parallel to the center electrode.
February 19th, 2019, 08:13 PM
#39
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I don't grind the electrode. I bend it so that with the .045" gap it is still parallel to the face of the center electrode.
I suspect what you are referring to is shortening the electrode so the spark is not shrouded and theoretically better exposes the spark to the intake charge for improved ignition. Some folks even index the plugs so the open gap area is facing the intake valve, but I haven't experimented with that so see if it actually does anything. I'm not sure how to measure the effect of that.
I suspect what you are referring to is shortening the electrode so the spark is not shrouded and theoretically better exposes the spark to the intake charge for improved ignition. Some folks even index the plugs so the open gap area is facing the intake valve, but I haven't experimented with that so see if it actually does anything. I'm not sure how to measure the effect of that.
February 19th, 2019, 08:25 PM
#40
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