Spark Plugs, TBI Vortec L31, Heat Range

[Woods]

I know this has been covered a thousand times, my apologies in advance.

I have a stock L31 Vortec long block with a TBI mounted on it. 94 Chevy C1500.

I am currently running AC Delco R44LTS plugs, and reading the plugs, I would like to step down a heat range or 2? I am getting knock retard also, so am hoping a colder plug will help.

AC Delco for some reason quit making the R43LTS plug, I can still get the Marine MR43LTS (any difference other than being Marine version?).
Next step is R42LTS.
How much difference would 2 heat ranges make? (as I said, reading my plugs, I can go down in the heat range).
What are you guys running in your Vortec TBI motors?

Not a fan of changing plugs with the damn shorty headers in the way, so would like to get it right the first time.

Any advise and insight is appreciated.

Thanks

[ony]

I have a v6 vortec ac delco quit making the plugs that came in the engine. the best thing I have found to replace them on my truck is thin wired bosch.

[pmkls1]

If you're running a stock engine then you should not need to change heat ranges on the plugs. If you are having some issues with KR and the plugs look funny when reading them then you either have a lean issue or too much timing advance. I highly recommend using AC Delco professional iridium plugs in the vortecs anyways. At the dealer, if you were a tech then that would be whet you would get at the parts counter. Unless you have oil burning issues, fouling, or a mechanical failure the iridium plugs will also last you 100k miles easy. The pn# for the iridium plugs is 41-993. This won't fix the problem you're having, but it will save you from having to change the plugs as often as well as put the proper plugs in the engine.

[Woods]

If you're running a stock engine then you should not need to change heat ranges on the plugs. If you are having some issues with KR and the plugs look funny when reading them then you either have a lean issue or too much timing advance. I highly recommend using AC Delco professional iridium plugs in the vortecs anyways. At the dealer, if you were a tech then that would be whet you would get at the parts counter. Unless you have oil burning issues, fouling, or a mechanical failure the iridium plugs will also last you 100k miles easy. The pn# for the iridium plugs is 41-993. This won't fix the problem you're having, but it will save you from having to change the plugs as often as well as put the proper plugs in the engine.

SOOOO, what heat range would the very expensive 41-993, be compared to the r**lts AC Delco plug.
Sorry, I will never run a plug 100,000 miles.

[pmkls1]

They are the O.E. heat range for the engine so they would be the same as the r44lts. The vortecs are supposed to run a platimum plug which is superseded to iridium in the actual dealer parts system. The exception to that would be some of the early vortec 4.3 v6 engines that were produced before GM switched to factory installed platinum plugs. Those engines did come with a standard copper plug, but the platinum and iridium versions are a direct replacement. Only aftermarket parts systems show the r44lts as an option for the 5.7 as they will fit, but you are using an inferior plug by doing so. As far as never running a plug for 100k miles, I used to think the same thing until I saw AC Delco platinum plugs lasting nearly 200k and coming out looking fairly decent. The iridium plugs are even tougher. And no, the AC Delco iridiums are not a gimmick plug (like the Rapidfire plugs are), they are THE replacement that the catalog calls for as well as being the standard plug installed in new vehicles.

[Fast355]

They are the O.E. heat range for the engine so they would be the same as the r44lts. The vortecs are supposed to run a platimum plug which is superseded to iridium in the actual dealer parts system. The exception to that would be some of the early vortec 4.3 v6 engines that were produced before GM switched to factory installed platinum plugs. Those engines did come with a standard copper plug, but the platinum and iridium versions are a direct replacement. Only aftermarket parts systems show the r44lts as an option for the 5.7 as they will fit, but you are using an inferior plug by doing so. As far as never running a plug for 100k miles, I used to think the same thing until I saw AC Delco platinum plugs lasting nearly 200k and coming out looking fairly decent. The iridium plugs are even tougher. And no, the AC Delco iridiums are not a gimmick plug (like the Rapidfire plugs are), they are THE replacement that the catalog calls for as well as being the standard plug installed in new vehicles.

Heatrange is very subjective anyway. I generally run a heat range or two cooler than recomended because I am always on the throttle and drive at sustained high speeds often. I ran R42LTS plugs in my G20 and have the Rapidfire equivalent in my Express. Platinum and Iridium plugs are prone to creating detonation when the thin electrode starts to act like a glow plug at sustained high speed. Rapidfires are not a gimick plug, they work great.

[RobertISaar]

unless things have changed since i last looked, the original rapidfires were a uniquely shaped electrode, copper design. i want to say it had a few serrated edges?

anyways, those got replaced with other rapidfires, normal looking copper plugs, but with a platinum pad on only one side of the plug.

[pmkls1]

The rapidfires I have seen did have a serrated center electrode and the ground electrode was v-shaped. I'm not sure about the material, though. I have never heard anything good about the rapidfires from a competent tech and there were parts counter guys that I respected that would not sell them at all. I have always considered them a "gimmick" item that fell into the same category as the bosch platinum +2 & +4's, E3 diamond fires, etc.... Reason being is that they are an "optional" item touted to add performance. Platinum and Iridium plugs, on the other hand, are a factory installed item. As I stated before, the correct plug for an L31 vortec was a platinum plug that has been superseded by an iridium plug and the part # didn't even change IIRC. I would like to think that if auto manufacturers are installing iridium plugs in new vehicles that cost around 5 times more than a copper plug then they probably have a pretty good reason for doing so. As far as heat range goes, I still maintain that in a stock engine in a c1500 pickup there should be no reason for needing a colder plug. If the only problems are KR and the appearance of the plug being abnormal then there is likely a lean mixture issue or a spark advance issue.

[Fast355]

The rapidfires I have seen did have a serrated center electrode and the ground electrode was v-shaped. I'm not sure about the material, though. I have never heard anything good about the rapidfires from a competent tech and there were parts counter guys that I respected that would not sell them at all. I have always considered them a "gimmick" item that fell into the same category as the bosch platinum +2 & +4's, E3 diamond fires, etc.... Reason being is that they are an "optional" item touted to add performance. Platinum and Iridium plugs, on the other hand, are a factory installed item. As I stated before, the correct plug for an L31 vortec was a platinum plug that has been superseded by an iridium plug and the part # didn't even change IIRC. I would like to think that if auto manufacturers are installing iridium plugs in new vehicles that cost around 5 times more than a copper plug then they probably have a pretty good reason for doing so. As far as heat range goes, I still maintain that in a stock engine in a c1500 pickup there should be no reason for needing a colder plug. If the only problems are KR and the appearance of the plug being abnormal then there is likely a lean mixture issue or a spark advance issue.

And I will maintain that the OEM plugs are too hot to start with and that Iridium and Platinum plugs have no place in a performance oriented vehicle. Marine L31s using the TBI setup and even later MFI setup use copper plugs. One of the reasons I always liked the rapidfire plugs is they they came with the center ground electrode cut back and rounded off smoothly, just like a person should do the the plugs on any performance minded setup.

[1BadAction]

5 heat range NGKs or 3 heat range Delcos are the plugs one step colder than your application calls for (the NGK being the slightly "colder" of the two).

I've never ran vortec heads so I'll leave that heat range argument to others.

[Fast355]

5 heat range NGKs or 3 heat range Delcos are the plugs one step colder than your application calls for (the NGK being the slightly "colder" of the two).

I've never ran vortec heads so I'll leave that heat range argument to others.

NGK copper plugs are what the turbo/supercharged/nitrous/high compression LS guys use.

[1BadAction]

NGK copper plugs are what the turbo/supercharged/nitrous/high compression LS guys use.

Yep, TR6... Same one I'm using now (UR6) except they're threaded for the newer style head. Mine run good but I want to try the UR5s. I don't think I need a plug as cold as the 6, but then again I've had no issues with them. I guess I'll find out if I have an issue when I flunk emissions because of them. lmao

[Fast355]

Yep, TR6... Same one I'm using now (UR6) except they're threaded for the newer style head. Mine run good but I want to try the UR5s. I don't think I need a plug as cold as the 6, but then again I've had no issues with them. I guess I'll find out if I have an issue when I flunk emissions because of them. lmao

You won't flunk due to plugs unless they just aren't firing because they are fouled. With your increased compression ratio you need the cooler plug. Constant load applications often have up to 3 heat ranges cooler plugs in them. A 1-ton truck will have several steps cooler plug than a 1/2 ton truck.

[pmkls1]

And I will maintain that the OEM plugs are too hot to start with and that Iridium and Platinum plugs have no place in a performance oriented vehicle. Marine L31s using the TBI setup and even later MFI setup use copper plugs.

That may be the case, but the OP is running a stock engine in a 1/2 ton pickup. There is nothing performance about it. The most likely reason for the marine applications running copper plugs is that marine applications do not have to meet the same emissions standards as cars do and they also do not need to run extended tune-up intervals. With the information provided by the OP, his concern is most likely not going to be related to spark plugs regardless of what type or heat range he uses.

[Fast355]

That may be the case, but the OP is running a stock engine in a 1/2 ton pickup. There is nothing performance about it. The most likely reason for the marine applications running copper plugs is that marine applications do not have to meet the same emissions standards as cars do and they also do not need to run extended tune-up intervals. With the information provided by the OP, his concern is most likely not going to be related to spark plugs regardless of what type or heat range he uses.

Having run his exact engine, the OEM plug is TOO HOT for that application....The dynamic compression ratio of a stock L31 is too high to be able to run enough timing to maximize the power potential of the vortec cylinder heads. The hotter heat range is likely contributing to his detonation issue. Not to mention the TBI ignition system is setup to fire copper plugs, not iridium or platinum both of which typically require more voltage to jump the wider gap. A properly gapped (.035") set of R42LTS plugs would work well for him.

The factory 195*F thermostat is also too hot IMO. I run a 170*F thermostat in my L31 and bring the fans on at 176*F for low and 180*F for high speed. I never get hotter than 182*F even in summer, pulling a load.