I have a 71 LT-1 and am running stock AC sparkplugs. Had a racing mechanic look at the engine--he said the black in my exhaust bezels indicates not all the fuel is being burned. He recommended switching to Autolite plugs. Said that was all he used in racing and they were more foregiving and would burn fuel better. True or not true? Would I notice any difference in performance? Car seems to run well except doesn't seem to have the power as it approaches higher RPMS--maybe just me--no missing, etc. Holley carb just rebuilt by Jerry MacNeish, all new plug wires and plugs, new TI ignition, has AIR system. Any thoughts or coments appreciated. I changed the springs in distributor so all in at 3000 rpms. Thanks

 

With your mechanic. The AC's are an ok plug but the autolites are better. It should be burning clean with new plugs though.

 

go for proper heat range.
on my L88 427 at 10:1 CR the 3 heat range works bad ( I tried AC R43xls and autolite 3923)
much better with 4 heat range: R44xls and autolite 3924.the autolite is best
I suppose that a proper wide gap is important too, but not as much as heat range

 

IMO 'wide gap' is a bit controversal.

for a given ignition system wide gap == weak spark.

a lot of weirdness (particularly up-top) can be solved just by tightening the gap a little bit.

 

Lots of advertising hype in plugs. I've run just as fast with cheap A/C's as NGK's. I run a pretty hot extended tip plug on the street. My race buddies laugh at them...but when I'm lazy and don't feel like putting in the colder *race* plugs....I go to the track with the 2 year old A/C's and never worry about it. They do fine.

How wide of a gap you can use is all about the ignition system. IF you have a stout one that can jump the gap with high cylinder pressures at WOT...it will make more power. If not...it will lose power and bang and pop.

There ARE some plugs that do better under mega heat N20 conditions and stuff like that...but for regular stuff...just use the right heat range...likely hotter than you think is good for the street.

Also really hard to tell on exhaust color these days with unleaded gas and no cats.

JIM

 

Any 'mechanic' that tries to recommend spark plug brands simply by looking at exhaust colour on a street driven car would get laughed out of a real garage.

Utter BS.

 

I tend to agree with Jim. When I had my 1967 327/300, and more ambition, I experimented with several plugs. (This is for sunny, Sunday afternoon driving; I do not push my cars.) The recommended was A/C R-43, a cold range. They fouled. I went hotter with R-44. Again they fouled. I switched to NGK B-4 (R-44 equivalent). They fouled. Based on advice from the C2 people here I tried R-45S, with extended tip. They were the cat's meow.

Fast-forward to now with a 1974 350. The recommended plug is R-44T and that is what the car came with when I bought it in 2008. It was not running quite "right" and as the Q-Jet was past its "best before" date I replaced it with a rebuilt unit. Still a bit off despite tuning efforts. Based on the experience with the 1967 I tried R-45TS. Again, the cat's meow. So the A/C "5" heat range is for me and my type of driving.

As to gap, I use the recommended 0.035" for a points and condensor ignition system.

I am a novice and your mechanic is a pro but I am skeptical about tail-pipe tests (unless the engine is obviously suffering from a bad carb, blown head gasket, etc.). I would imagine that colour will differ from city driving (lots of idle) and a 70mph, 60-mile highway trip (off-idle). The defining factor for me is runnability and for the moment my 1974 humms from idle to speed. While I must confess that I have never tried Autolite plugs, I am loath to mess with the current setup. Many times in the past I have tried to take a 95% (+) situation to 98%, mostly with unpleasant consequences. So I'll stay with R-45TS.

I did not answer your question but I did wish to comment on the heat-range matter advanced by Jim.

 

Plug gap and heat range make the most difference. Extended tips help on a lot of applications. If you can get away with them they help most Chevy engines because they get the gap closer to the center of the combustion chamber. If you have very high combustion temps over long periods such as road racing or land speed racing, they may not work because the strap will overheat.

In rare instances I have seen a brand change make a small difference on the dyno, but it's not that common. Autolite plugs were the only plugs that I found that would stand up to nitromethane, although in recent years Champion has come out with some Top Fuel plugs that work well.

 

I had a very interesting conversation with a guy doing spark plug research at a university. He said that all the brands and designs (split electrodes and such) and materials (platinum, etc.) make virtually no difference in power ouput. So, I don't buy the "get xxx brand plugs because they run the best" argument.

 

This subject will always get a lot of different sides to it. I'm not really sure I understand why the same heat range plugs of different manf. will act different but they do from my own use. Though not a vett but my HD would foul a plug around the block and never foul a Autolite, my two stroke bike would run well on NGK for one ride then foul and then run at lease five rides or more with NP with Autolites. My race car (476ci Blown Chevy) will run almost 5 hundreds quicker with Autolite over everything else tried. Why? Don't know but would like to understand that better. As far as plug gap it takes ex amount of voltage to jump the gap and no matter how much voltage you have matters not, If it take 5,000kv to jump the gap with a 10,000kv coil or if you have a 40,000kv coil still takes the same 5kv to jump the gap. Now what does make a big difference is the amps of your coil.

 

I have also found the above to be true. You might consider going to an Autolite platinum which comes pregapped @ .044. I know this is wider than stock but it produces the same spark intensity plus the wider gap helps produce more complete combustion. It will still fire with the wider gap even with the stock coil due to the better conductivity of the platinum. Read this and it will make sense. It is about a different plug (NGK) but applies to other platinum plugs as well. One big plus to help justify the extra cost is they last over twice as long.
http://www.se-r.net/engine/platinum_copper_ngk.html

EDIT: I do agree with the others that posted about running the correct heat range for your application. Your symptoms could be from too cold of plug. Your driving style and city, highway or racing could all affect the heat range needed.

 

To put my comments above into perspective and with your EDIT comments, my highway temp is pretty steady at 180*F. In town with stop-and-go it can touch 195 or so, perhaps touching on 200 in July-August. The t-stat is 180*F. And that is with the "hot" R-45TS. And no fouling.

 

The important use of plugs is the proper heat range and gap. I found no difference between Champion and Autolite plugs. I had both reps present and used the plugs interchangeably and I won with both. For what its worth the plug gap of.035 is the standard you should be using whether points or electronic ignition systems. I also know that opinions vary as to gap, But you cant beat success.

All plugs start at the same temperature, normally the outside air temp. Its the function after warm up thats important. AC plugs of #45 is probably the best all around choice no matter what engine if its a street machine. Track use on a street car would be 44`s or 43`s. They operate cooler.

Champion is a better choice for racing because it`s easier to get a heat read on a Champion than a Black plug such as Autolite or AC`s.

All the rest of the plugs are just hype and price dont make any difference. Its like using premium or race gas for a low compression engine..A waste of money....However isn`t everyone loaded now since they got their stimulus money......

 

I will pretty much bet on the carb is running rich vs the spark plugs. Get yourself a wide band O2 sensor and dial the carb in. I don't care who it was built by it needs to be tuned to your engine.

 

I also have '71 LT 1, I had AC Platinum plugs in it. The plugs fouled and the car ran horrible. I switched to Autolite standard plugs last year( don't recall the part number off hand ) and the car has been fine since.

 

This has been my experience also with my 71 LT1, Autolites ran better and didn't foul. Both Autolite standard and platinum worked fine.

 

I put the E3 diamond fires in. They idle better and so far no fouls. I have had them for about 1500 miles so we will see. I have a 350/383, stock rebuilt carb, headers with cat muffler true duels.

 

So I guess there is no real answer in this thread. We tune to whatever we need with whatever product. Sounds reasonable.

 

The service manual calls for AC-R44ts.

 

There is an answer Paul, but not one that most people want to hear. It's more fun believing that there's a spark plug out there somewhere that has secret super voodoo mojo magic just waiting to unleash those extra ponies bottled up in our engines.

If only.