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.

[pmkls1]

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.

I have run the same engine both with the O.E. SCPI induction and with TBI as well. And while I disagree with just about all of that statement, I find it futile to continue to debate the subject as your opinion on the matter isn't going to change and arguing will not contribute anything useful to this thread. Let's just agree to disagree and leave it at that.

[Woods]

Thanks for the insight guys, if anyone else has thoughts, I would appreciate them.
Fast355, this is the type of hands on I was hoping to get, thank you


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.

I was on Jegs and found these engines kits based on the L31 long block

http://www.jegs.com/i/Chevrolet-Performance/809/12530282K1/10002/-1?parentProductId=813788

http://www.jegs.com/i/Chevrolet-Performance/809/12530282K2/10002/-1?parentProductId=813788

The spark plug they are using is with their kits is the NKG TR55. The AC Delco equivalent is R42LTS6.
I am thinking the R42LTS gapped at .35 will be what I am going to give a try.

If anyone has opinions, and hands on insight, it is appreciated.

Thanks

[1BadAction]

R42LTS are great running plugs. Ask if they have CR42LTS, that's a coated commercial version of the same plug. :thumbsup:

[Fast355]

R42LTS are great running plugs. Ask if they have CR42LTS, that's a coated commercial version of the same plug. :thumbsup:

He could alternately ask for the M version of the same plug. Many GM crate engines have specified "M" plugs over the years. My boat has MR42LTS

http://www.amazon.com/ACDelco-MR43LTS-Spark-Plug-Pack/dp/B0013WFURM

[1BadAction]

He could alternately ask for the M version of the same plug. Many GM crate engines have specified "M" plugs over the years. My boat has MR42LTS

http://www.amazon.com/ACDelco-MR43LTS-Spark-Plug-Pack/dp/B0013WFURM
Is that stainless? If so, that is one helluva good price. Last I bought SS Champions for my OMC 2 stroke (Yes, I hate champions, but OMCs love them) they were close to 10 bucks a plug.

[Woods]

Ran across these on Summit, MR43LTS $1.97

http://www.summitracing.com/parts/ado-mr43lts/overview/

[EagleMark]

If you look at application they are listed for a lot of 8.1L engines...

Then the mail in rebate...

http://www.rockauto.com/lang/en/promo.html#acdelco

[tayto]

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.
Fast, do you recommend a .035" gap on a 10:1 vortec headed TBI 355? I was told to gap them around .045-.055"... Have a brand new AC Delco coil, was told not to go with a MSD. Got the engine running on R44LTS and have a set of R42LTS that will be going in.

[pmkls1]

Fast, do you recommend a .035" gap on a 10:1 vortec headed TBI 355? I was told to gap them around .045-.055"... Have a brand new AC Delco coil, was told not to go with a MSD. Got the engine running on R44LTS and have a set of R42LTS that will be going in.

.035" would be the ideal gap on that engine. I prefer not to go much wider than that on most applications. I've heard both ways on aftermarket "performance" coils, but I've never seen any hard evidence for either argument. I've run MSD and Accel coils on TBI vehicles with no problems, but I couldn't say that they performed any different than the OE coil. That being said, the OE coil is just fine for your engine.

[Fast355]

.035" would be the ideal gap on that engine. I prefer not to go much wider than that on most applications. I've heard both ways on aftermarket "performance" coils, but I've never seen any hard evidence for either argument. I've run MSD and Accel coils on TBI vehicles with no problems, but I couldn't say that they performed any different than the OE coil. That being said, the OE coil is just fine for your engine.

I agree .035" is where I would run on that setup. A quality aftermarket coil never hurts, however the real thing holding back the small cap HEI is the module. I would use a Davis Unified Module and matching coil if he elects to upgrade. Keep in mind there are two different original EST module part numbers. One (369) that advances the timing up top and one (048) that retards timing. I will say that a MSD 6A box is a very noticeable different on a TBI truck. The idle was smoother, I could run leaner mixtures without misfire and it had sharper throttle response. I also run a MSD 6A box on my large cap HEI in my Corvette. However I use the HEI pickup coil to directly trigger the MSD box and run without a module. That engine (vortec head 305 with 216/216 @ .050 cam, single plane intake, holley 680, and 1 3/4" primary, 2.5" collector, 2.5" dual exhaust) has accidentally seen 6,500 rpm in high gear on the highway a few times and was still pulling hard when it ran up on the RPM limiter. I was out in front of the LS1 T/A when the governor kicked in, 140 mph speedo long burried.

[tayto]

I bought a new AC Delco module for a late 80s F-body. However they are no longer printing the "369" or "048" on the module like they did with the factory ones that I have pulled at the wrecker in the past. I remote mounted it on the passenger fender with a homemade aluminum heat sink. I would like to get the MSD 6A box, but I have spent WAY to much on this car already. Wish I would have know about the DUI stuff 2 years ago when I started this project. Live and learn (AND SPEND!).

[Woods]

Thought i would follow up on the thread.

I ended up installing a set of ACDelco MR43LTS plugs, gapped at .40. I was a little leery of going 2 heat ranges down (R42LTS). This plug has worked well for me. It has helped (almost eliminated) my knock retard, due to running the colder plug. The plugs I replaced where 3 month old R44LTS, so it is not an issue of needing a tuneup.

A colder plug for me, definitely helped.

[pmkls1]

All personal preferences aside, I'm glad that you found a solution to your problem. On a related note, I feel compelled to state that although I prefer to use iridium plugs and that they are the specified replacement plug for these engines, I never meant to imply that these engines wouldn't perform properly with standard copper plugs installed.

[tayto]

I finally got around to putting in a set of R42LTS into my Caprice. First off the R44s I pulled out were all black (carbon). Now my car is no where near tuned but it seemed to run alright. I also use to get knock counts like crazy before. Just did a trip from Vancouver, BC to Kent, WA to get my exhaust sorted out and over the 3 hour trip I think I had under 100 counts. Not great but compared to 1000+ within a 30 minute drive before. Have done a few learn runs with EBL and it was pulling fuel like crazy across the board so it seems to be a lot happier now.