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Author
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Topic: reading spark plugs 101
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chips67
Journeyman Posts: 83
From: louisville, ky, usa
Registered: Jul 2001
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posted 08-18-2001 12:03 AM
   
actually this isnt a class but it can be if you guys who know your stuff will help out a brother. i cant honestly tell you if i was too fat or too lean tonight, but i can tell you what i been told and you can tell me if any of it is right, or none of it. initially i was told to run the car hard, shut it off at the top of the track, and coast to the pits. pull a lean plug (like #1) and a fat one (like #6) and look for a tan color on the insulator. with this in mind i tried it, my lean plug looked off white and the fat one was just slightly darker...lite tan i guess. so i kept going bigger on the jets. keep in mind my best mph was with 67/73's...came in the holley that way. i thought this might have costed me my head gaskets (probably didnt, who knows) so i kept going fatter. i was up to 72/78's and the lean plugs still looked burned 1/2 way across the electrode (that curve of metal on the bottom) plugs were slightly darker...barely. i stuck the 74/80's in and went tonight. best mph has been 85.93 verses the 86.2 i had with 67/73's. now what? you lose mph with better traction/et so this whole experiment has been a wash up for me. my 85mph was .02 quicker than my 86mph et. so i have a 1.91 60ft. with 8.26 @ 86.2mph ------and-------a 1.89 60ft. with 8.24 at 85.98mph. OK FORGET THAT....back to reading plugs. a guy with a 5 second car told me that redaing plugs was better than using an egt. he said i want the ground (curved end) to look burned all the way back to the threads...dont worry about color of the insulator so much. another guy with a 5 second mustang said if it aint missing at the top of the track its probably not too lean...said you wanna run a naturally aspirated car as lean as you could. ok, its YOUR TURN....who is right? what is the correct way to read plugs?????? ------------------
67 coupe, 650dp and rpm intake on 5.0 with afr 165 heads, 4 speed, 4.11's.....best so far is [email protected] in 1/8 mile with 1.91 60ft. time.
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steve'66
Gearhead Posts: 2808
From: Sonoma,CA,USA
Registered: Mar 2000
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posted 08-18-2001 12:39 AM
I'd run 70/76s for a while and check the plugs after a few runs. Today's oxygenated fuels don't show on plugs the way the race gas or old leaded fuel did/does. Jet for max mph, which is h.p.  Of course the air has a lot do do with jetting, did it change during your runs? SteveW
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kid vishus
Gearhead Posts: 1149
From: a bad scene from "children of the corn"
Registered: Oct 2000
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posted 08-18-2001 08:15 AM
If it wasnt missing at the big end, it wasnt too lean like the fellow said. If it is too lean, it will pop out headers and you will feel it. I would put the jets back the way you originally had them. If it wasnt banging out the headers, or getting hot really quickly, it wasnt lean.Make a baseline pass or two when you first get there, then change the jets but leave everything else alone. If it slows down at all, et or mph, you went the wrong way. As for the difference in ET, the air quality plays such a major role in how fast teh car will go. One week the air could be good, you make some changes the following week expecting the car to run faster. The air is substantially worse and the car goes slower. So you think your changes didnt do any good and you put it back the way it was when in reality, your changes made the car faster but the air is what slowed it down. Confusing?
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chips67
Journeyman Posts: 83
From: louisville, ky, usa
Registered: Jul 2001
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posted 08-18-2001 01:56 PM
steve, i know you're right about the mph = hp and thats what i want with jetting. the air went from mid 80's and humid to mid 70's and little less humid by the end of the night. mph was high 85 (almost 86) at the start of the racing and the car was op. temp each run. the car never hesitated or missed at the top end so its probably not too lean then. the thing is the car was down to 84.88 mph by the last run but i cant say what that means because by then the 60 ft time improved by almost a tenth which could account for the mph drop. also the timing was 2 degrees higher at 36 total vs. the higher 85.98 mph with 34 degrees total at the beginning of the night. will go leaner next time and take jets with me. should i keep going leaner 2 jets at a time till it started missing and popping, then back up? on reading the plugs, is it ok even if the ground tip looks burned and the plug is just off white? the air here is consistant mid 80's and little humid in the day, mid 70's and less humid in the evening if this helps. ------------------
67 coupe, 650dp and rpm intake on 5.0 with afr 165 heads, 4 speed, 4.11's.....best so far is [email protected] in 1/8 mile with 1.89 60ft. time.
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n2oMike
Gearhead Posts: 201
From: Spencer, WV
Registered: Jan 2001
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posted 08-19-2001 09:39 PM
Steve has a point about the unleaded gas and plug reading. Pump gas, especially when combined with todays high power ignitions makes plug reading a real pain in the *** . If I remember correctly, back when my car had the 650 double pumper on it, the engine liked more jet than what came in the carb... this was with the 12 second engine. But, that is a different engine. It's hard to say what YOUR engine will want.My advice is to go to a test and tune session with a jet kit (around $29 from Summit) and go richer and leaner a couple sizes at a time, and see what runs best. Make a 2-3 passes with each setup to check for consistency. Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/motorcitymustang/cmml/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
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chips67
Journeyman Posts: 83
From: louisville, ky, usa
Registered: Jul 2001
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posted 08-19-2001 10:49 PM
mike, i've got a jet kit already. what's hard to do is be sure what to look for on the spark plugs when you get a different answer no matter who you ask. even with the guys with quick cars at the track, each one says something different. i know that i dont want to burn a piston. i know how to get the plugs ready to read by shutting down directly after a pass and coasting to the pit area. i always run chevron 93 and i do have a full hot msd ignition system and i dont rev past 6100 when i shift. if i jet for best mph, wont the motor just like going leaner until i burn a piston? i can tell you that the first time i drove the car when i got my new heads this year that it run stronger that anything i've ever been in and the jets in the carb where 67/73's. it hasnt felt that good since and that ride only lasted about 30 minutes before the #8 intake lifter failed and wiped out my cam and appearantly i lost both head gaskets too (which i didnt find out till about 2 weeks ago) which were blown between the water jacket and cylinders on #1 and #8. to be honest, i dont know why i bought the jet kit other than the car just wasnt running like it did the first night. i mean when you can say that you actually could "feel" the car was quicker, thats something you can bet will show up on the clock! i dont know why the car blew those gaskets, but i know ive run it hard longer so far on this set and they havent blown yet. is it safe then to go as far as 67/73's again? if i can be sure the mph wont increase until the point that i hurt something by going to lean then i'll gladly leave plug reading to the experts. i can be patient a go 2 sizes at a time and reading the ticket is easier than pulling plugs, which i dont like doing on hot $1400 aluminum heads anyway. ------------------
67 coupe, 650dp and rpm intake on 5.0 with afr 165 heads, 4 speed, 4.11's.....best so far is [email protected] in 1/8 mile with 1.89 60ft. time.
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n2oMike
Gearhead Posts: 201
From: Spencer, WV
Registered: Jan 2001
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posted 08-19-2001 11:02 PM
You shouldn't be hurting head gaskets running naturally aspirated. A tad lean shouldn't hurt anything. I believe the carb came with the 67/73's stock. You won't hurt the engine with these.You had some kind of problem before. Just jet the thing until it runs best and be happy. As long as you don't run it into severe detonation, all will be fine. Good Luck! ------------------
Mike Burch
66 mustang real street
302 4-speed 289 heads
10.63 @ 129.3
http://www.geocities.com/motorcitymustang/cmml/cmml_mburch.html
http://www.fortunecity.com/silverstone/healey/367
IP: Logged |
chips67
Journeyman Posts: 83
From: louisville, ky, usa
Registered: Jul 2001
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posted 08-19-2001 11:27 PM
mike, you're right about the jets being 67/73's...thats what it came with. this year is my first of 8 years running that car that ive tried my hand at tuning the carb. wouldnt it be just a hoot if the carb ran best with 67/73's and i didnt even need to buy that brand new holley jet kit and reusable gaskets? it would be the story of my life, maybe i should hire somebody to weld the hood of my car shut so i wouldnt mess up all my good luck. didnt like carrying that spark plug wrench around while i race anyway, the weight factor. thanks for the help mike.------------------
67 coupe, 650dp and rpm intake on 5.0 with afr 165 heads, 4 speed, 4.11's.....best so far is [email protected] in 1/8 mile with 1.89 60ft. time.
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