Autozone guy gave me R43TS delco plugs instead of R42TS version for 88 V6. I had a spare 42 left over which is how i caught it. They look identical. Would it be okay to continue on with install?

One is one heat range hotter or colder than the other. Usually the higher the number the hotter the plug, I don't know about AC. Larry

Yeah I read that delco higher means hotter. Is that going to affect mpg, knocking, acceleration in a negative or positive way?

Usually a hotter range plug is used when you have a worn engine. Helps to burn any oil pulled into the cylinder. It just sits a little deeper into the combustion cylinder to get a better ignition. Advance told me that the 42's weren't available. They gave me 43's also.

Unless you are right on the edge of preignition one heat range will probably not be noticed at all. Take a look at one after a couple hundred miles and see how it is. Larry

Enough reason for me to return them. https://www.fiero.nl/cgi-bin...6293&style=printable

Okay so I returned them to Autozone. The guy initially thought I was trying to pull a fast one until he went back to the drawer and found the R43TS plugs stored in the R42TS box. So they gave me 10% off for my trouble. I got them installed and will see how it drives tomorrow.

The cooler plug is wiser for the Fiero because it does not have a knock sensor, the 3.4L does in the F-body.

quote Originally posted by Joseph Upson: The cooler plug is wiser for the Fiero because it does not have a knock sensor, the 3.4L does in the F-body.

Yes but the engine does have a distributor. If the 42s are no longer available and you have to use 43s instead; if those hotter plugs cause knock you can always back down the timing to solve it.

quote Originally posted by lateFormula: Yes but the engine does have a distributor. If the 42s are no longer available and you have to use 43s instead; if those hotter plugs cause knock you can always back down the timing to solve it.

Provided you can hear it. I've logged lots of knock retard events in the past several months, some false and some real but I have not heard any and that's where the concern is, having a problem and not knowing it.

Also, retarding the timing due to higher compression may not cause a loss in overall efficiency, but having to reduce timing because a particular grade of plug is causing problems likely will as its tendency to cause spark knock due to its heat range doesn't mean it is lighting off the fuel earlier in a manner that will counter any timing reduction you add in a distributor motor which will be affected across the entire operating range, including those areas where there is no problem with knock.

[This message has been edited by Joseph Upson (edited 06-04-2013).]

What did the 42's look like when you pulled them? Do you know how to read a plug?

Edited due to smart phone autospell .......

[This message has been edited by olejoedad (edited 06-04-2013).]

You should be able to get pretty much any spark plug, just need to check more sources.

quote Originally posted by sricka01: Okay so I returned them to Autozone.

Wise move. Always use the recommended heat range plugs unless you have very specific reasons for doing otherwise, understand why you're making the change, and understand the possible adverse effects. Spark plug manufacturers will occasionally discontinue an entire design, but I've never heard of one dropping a single heat range value from the middle of a product line.

quote Originally posted by fierofool: [A hotter range plug] just sits a little deeper into the combustion cylinder to get a better ignition.

No. The tip protrusion into the cylinder remains constant for any given plug series. What varies is the distance from the tip of the insulator to where the insulator meets the outer body of the plug and/or the contact area between the insulator and the plug body.

quote Originally posted by lateFormula: ... if those hotter plugs cause knock you can always back down the timing to solve it.

Not necessarily. Retarding the ignition timing is a band-aid fix, at best, and it may have adverse effects on performance, exhaust emissions, fuel mileage, engine operating temperature, and cooling system heat load. The best solution is to use the correct heat range plug for your particular engine and driving conditions.

[This message has been edited by Marvin McInnis (edited 06-05-2013).]

I had no knowledge about this issue and I am sure many readers will be the same, so here is some background information....

http://www.ehow.com/list_72...-specifications.html

I love this forum! Nowhere else can you find technical nerds arguing over the merits of a $2.00 AC Delco spark plug long after the OP had returned them.

Technical nerd? Mea culpa. Arguing? Not intended. I just want to see correct information, for the benefit of anyone who may visit this thread in the future. Of course, everyone is free to use any plug they want. It's OK to experiment, but it's best to do so slowly and methodically.

[This message has been edited by Marvin McInnis (edited 06-05-2013).]

I was in auto parts for 20 years, the R42TS was among the most popular plugs for GM cars thru the 80's and 90's, I don't see it being discontinued, I checked with a long time friend who is still in the auto parts industry, (now at O'Reilys commercial accounts). He said they are still available, the popularity of this plug has dwindled due to the new types of engines so most places won't carry them any more but can order them and get them in a few hours.
Unless your engine is worn out, order the R42TS.

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'88 Formula, V6, Auto. (daily driver)
'86 SE V6, 4-Speed (rusty parts car)

Thanks for the correction, Marvin. I always thought the tip and insulator was just slightly longer.

quote Originally posted by sricka01: I love this forum! Nowhere else can you find technical nerds arguing over the merits of a $2.00 AC Delco spark plug long after the OP had returned them.

I know, other forums seem so lame, once one has been to PFF.

quote Originally posted by fierofool: I always thought the tip and insulator was just slightly longer.

You were probably thinking of a "long-reach" or an "extended-reach" plug. There are several potential problems using a plug with longer (or shorter) reach than stock:

1) It moves the point of ignition to a place different than the cylinder head is designed for. This may result in pinging, incomplete combustion, higher emissions, and/or poorer fuel economy. (I once tried some short-reach NGK plugs in my Porsche 911S ... which had come from the factory with CD ignition system and some of the very first, and very expensive, Bosch platinum-electrode spark plugs ... and with the short plugs it would barely run below 3000 rpm.)

2) A longer reach may bring the tip of the spark plug dangerously close to the piston crown at TDC. Spark-plug-to-piston contact is bad.

[This message has been edited by Marvin McInnis (edited 06-05-2013).]