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There are a lot of old threads, and even then people seem to debate back and forth Bosch vs NGK, platinum vs. iridium.
What is the current consensus here?
Thank you,
Sixcarbs
I am sure you've experimented multiple combinations, here are my comprehensive notes opinions to help the A/F firing system.
> Stock Is Nearly Good
Long story short, my personal answer has been to experimentally under-gap my stock dual-iridium Bosch plugs.
> TIP OF ICEBERG
Spark plugs are an important topic because ignition sparks are essential for combustion to prevent misfires that derate output with common laggy accelerations.
To have a balanced stock mixture at 3500.Rpm you need a good neutral base mixture at 2500, at 1500, at 1000.R'... it's a smooth continuum.
The driveability mixture does not transition from lean to rich outside of accelerations. It has to be right to begin with.
There are experimental ways to turn around laggy output... a transformation "journey"!
The Bosch ECU is always going to inject the least amount of fuel for complete combustion. This is always close to misfiring and the penalty for misfiring is less gas yielding more misfiring... "catch-22" vicious cycle! We keep out as-if a mine-field...
The best spark plug is often the one your engine calls for: the OE P/N delivers stock experience.
Both NGK and Bosch make the best parts according to specs.
> Climbing the PINNACLE
When the results are not great then curious minds can search for better solutions. Is there a way to get reliable GDI ignition ??? The plugs are not entirely responsible for misfires, the engine system is.
You can have all new tune-up and still misfire!
Actually you want identical cylinder ignitions: the same everything old or new but identical so ECU can control it's end. Don't change one of anything change all or nothing else this stresses unbalanced cylinders.
> ELECTRODE SHAPE
For GDI engines you best not use stuby dual-platinum with multiple paths, it has to be a dual-irridiumneedle with a single path.
The stuby platinum plugs do ignite more reliably than iridium. Switching plugs type experimentally does reduce fish-bites on non-GDI engines.
So that shows the single needle is not the best igniter because the cylinder mixture is not too homogeneous.
Having multiple path all around the small stub is like having insurance to find a viable ignition path. The difference in size between platinum and irridium seems unsignificant but PRACTICALLY platinum electrode fires better than iridium needle does contrary to common belief.
The regular stuby electrode works like an array of 20 needles.
Then why use not so good "needle" electrodes??
They are not great at firing A/F mixture but guarantee exact timing control without any randomness. This provides great control to ECU logic to manage timings precisely.
To offset the fact they are practically not great at firing, you can experiment under gapping the electrode to help strike more predictable sparks the ECU works with better.
> PLUG GAP SIZE
A wider gap does NOT produce a longer spark for better ignition with excellent "high voltage COPS": nope!
A wider gap produces more random firing delays that screws up the ECU logic to lean out the mixture that guarantees misfires. Misfires > lean > Misfires: "Vicious cycle!"
Then where are the experimental limit ??
The key is to realize that bigger gap is not better spark.
Stock gap: is somewhat reliable (mixed results)
Over gap : is more misfires events (leaner mixtures)
Under gap: is less misfires events (stoichiometric)
> OUT OF MY SCOPE
-- I am not directly talking about turbo applications that may benefit from under-gapping.
-- I am not talking about the plug heat range to prevent destructive auto-ignition (better too cold than too hot!). Its actually interesting to realize its the messed up timings that cause destruction.
Something interesting there about the precise timing that gets quiet skirts under load.
The engine is noisy under load when timings are not precise due to drafty rings. Controlling that gets strong balanced, well ignited contributions.
-- Out of scope is the topic of GDI advanced multi-shots of fuel and sparks at various stage of the piston compression strokes. They require the additional timing precision we're dealing with - Non-GDI engine timings are more relaxed.
> EXPERIMENTAL SETUP
No mystery with experimental setup... stronger combustions have better driveability than misfired mixtures - We just please the ECU with better basics :
Then your GDI ECU will perfectly manage fuel+spark in micro-seconds for premium output. A great day for sure.
Decrease as many penalty factors to re-gain strong combustion performance.
Experiment tweaking the followings:
seal
spark
voltage!
cam positioning
...,
In main oiling thread I've shared my POV about misfires: A/F mixture Ratio + predictable compression timings + predictable spark.
> STABLE VOLTAGE
This post highlights the importance of all factors managed on time before TDC. The coil voltage affects that!!
-- The COPS are simple reversed transformers. They use two coil windings primary + secondary linked by a magnetic core.
-- A short primary pulse of 12V creates a 30kV spike given the right conditions.
-- Conversely the same pulse with higher primary makes an even bigger secondary voltage. Let's say 14V yields 45kV... a greater spark voltage.
-- Bigger is better here!
-- Q: If we already get reliable sparks at 12V why seek a higher voltage ?
-> A: this helps the needle electrode strike a spark through any poor conditions.
What we need is the most RELIABLY TIMED sparks.
The ECU hardly tolerates spark variations. This is very much like drafty cyl. randomness.
-- In the ignition spark topic variable chassis voltage acts like unpredictable drafy rings. You want to minimize all randomness for best contributions.
Variable low voltage plus variable low oil pressure plus lossy compressions de-tune combustions to limit cyl. contributions.
> RESULTS BY TEST DRIVING
- To assess the A/F mixture is super simple. No need to read ECU fuel trims or gauges.
- The throttle response is the true result:
Lean is laggy
Strong is nimble
Pressure sensitive is GDI multi-shot cherry
It's clearlynot rocket-science:
- Throttle enriches the mixture to accelerate.
- Throttle response is the ECU matching the engine setup. To improve throttle, improve the engine.
- All experimental options are a personal choice. Don't change anything that's all good.
Helping ignition understanding shouldnt strike sparks... I am sure there are gaps in sparkplug topic.
To please MBW members alike unregistered readers: "my experimental opinions are non-professional advice" - Note: UNRELIABLE cars may cause FATALITIES - Personal OPINIONS and INPUTS shared in this forum by non-profesionnal should *NOT* be construed as ADVICE" - Do maintain your vehicle in STOCK condition by seeking PROFESSIONAL services from MB DEALERSHIPS. Any maintenance or experimental modification performed outside of factory network is UNDERTAKEN STRICTLY AT YOUR SOLE RISK."
Last edited by CaliBenzDriver; Oct 24, 2025 at 08:14 PM.
The bottom right is the owner's manual. You can see the two different OEM spark plugs.
Column 1 shows the comparison between the NGK (OEM) and the NGK BKR5EIX-11 (That I have purchased)- Says Suitable
Column 2 shows the comparison between the Bosch (OEM) and the NGK BKR5EIX-11- Says NOT Suitable
Column 3 shows the comparison between the NGK (OEM) and the Bosch (OEM)- Says Suitable
How can A=B, A=X, and B ≠ X ?
Also interesting is the owner's manual says the Gap is 1.00 mm and Google says the Gap for all of them is 1.10 mm.
I personally use the top quality(ie most expensive) NGK plugs in everything I own from lawn movers to the excavator to my 300 Benz with m276 engine to my sierra truck with 420hp LS engine to my race car that is 600cid and makes 1000hp on e85. They all get NGK plugs.
Both Bosch and NGK are OE suppliers to Mercedes. One of my cars has Bosch as the OE supplier, and my other car has NGK. For your engine, stick with what was originally used.
I had a M113 that used 2 plugs per cylinder. Is the M112 the same? I forget what I used with the M113, but I did stick with what was already there. I remember the plugs being iridium because I thought that they should be good for 100k miles and the dealer said to change them at 50k for only $600. 🤣
I would never trust AI data. I don't even look at it when it pops up. Trust the oem car data and the plug mfg data only. No manuals, not cross reference charts, nothing. There are a sht ton of plug part #'s and mistakes are made. I have no doubt AI makes the most mistakes.
Plugs are pretty easy since whatever the car mfg calls for is usually the best plug for it. Whatever other plugs you find on a cross-reference chart are generally as good or close enough, but you need to check that other plug mfg site to be sure the cross-ref was correct.
The heat range the car mfg suggests for your particular engine is going to be the best for 99.99% of people. If you put a blower on it or run nitrous or something you need to think about heat range, otherwise you're good. When engines start to burn a lot of oil people will sometimes run a hotter plug, which is fine, but you don't need to worry about that until you literally foul plugs from the oil.
The car mfg will suggest a plug gap, but I'm not sure I've ever used the mfg gap. I will either widen or narrow it depending on the ignition system. Your 1mm gap is more than enough, but bigger gaps like that are harder on the coils.
These modern car coils are BS because they are incredibly delicate, and from what I see they are designed to fail to extract more $ from you. You don't actually need a gap that big so why not reduce it? When my coils failed, a week or so after warranty per design, I swapped them and the plugs, and reduced the gap from the .032" it calls for to .025".
I had your engine in the past, and if I still had it I would go down to at least .030". I would also go with Copper plugs, which is safer and probably a third the price, which counts since you need 12. There is little need for exotic metals, and it wasn't that long ago they were thinking various ways to sell "better" (meaning much more expensive) plugs, like multiple grounds, or a V shaped ground. All were a complete waste of $, and like Slick 50, they made $ until people wised up. The rare metal just the latest "better" plug, but at least have the potential to last longer, kinda, but is it really worth it? A regular copper plug will last 50k no problem. If they don't last 50k then you have some other issue that would also kill an expensive plug.
I also wonder about the little Iridium tip because that looks like a hot spot to me. I don't think you'd need to worry about that, but they look very sketchy to me. I also wonder how many of those tips have popped off and trashed the engine. The Platinum looks a lot safer, but Copper is actually safe.
One thing you have to watch out for, with the more expensive plugs, is counterfeits. If someone in china make a buck, they will try to scam you. Some of their plugs might even be ok, maybe, but I wouldn't trust them. If the rare metal tip pops off it could F-up your eng in a second. So no plugs off Ebay, Amazon etc, especially if the price is a good bit lower than normal. To ensure legit plugs I'd go with an established and known car parts seller that has a reputation to protect.
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