Spark plug Bosch 4459 as replacement for NGK BR7EF

Buy me a set, and I’ll try them in my hot rod! :slight_smile:

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Hello Tex - 91:

Thanks for those specs- too often those details go absent in discussions and decisions on what to choose.

I bought a set of these after reading the very interesting thread on this on this site (well, the old site, if I am recalling correctly). I think if you search 4457 or Bosch 4457, you could probably find that thread and have a read for yourself. The gist was this, from my viewpoint: the person who mentions the plus 4 plugs indicated that he’d had direct communication with a Bosch employee or rep, who indicated that the Jag V12 took the 4457.

I am happy to know that the 4457 is heat range compatible with the NGG BR7EF. I don’t know what to say about running colder plugs on this motor; the last three sets of plugs I’ve used are the NGKs.

I will say that when I bought the car, it came to me as a write-off, a Marelli fire victim. I have the distributor cap and rotor (well, the pieces of the rotor, melted in half) from when I began the process of bringing the car back to life. When I pulled the plugs, one of them was gapped really wide- like 5 thou or more wide. I have always thought of that plug as the one that may have led to this failure.

But, I know that wider gaps (larger sparks) can do wonders. I figured that four gaps should be interesting, and so I bought a set. They are on my bench for this spring, as it happens, several years after having bought them. Too many things intervened to keep them off my to-do list for this car. Should be running them this season, tho.

I will post my observations and I do hope you will do likewise- user experiences are a big part of this list’s value, in my opinion, so I am interested to hear what you find.

Good luck!


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Mike90 - I should be doing the spark plugs soon as I am sure that they are needed to be changed - I have been trying to get to many things on my car, but keep getting interrupted with higher priorities between work and home duties - therefore my car is still just limping along - but since I have to drive it daily now, and my gas usage has increased, along with feeling like I may have a slight miss, I am going after the spark plug duty - I will post my results - thanks, Tex.

If you’re in Colorado, what you’re using isn’t rated on the RON scale, it’s (RON+MON)/2, also referred to as (R+M)/2 or AKI. The Jag V12 HE in US spec is 11.5:1 compression, which absolutely needs “high octane” (from a commercial perspective) fuel, which means 91 or 93 octane (Cali/West Coast vs rest of the US). Note that US 91 AKI is equivalent to 95 RON, and US 93 AKI is roughly equivalent to 98 RON… and 93 RON would be close to 87 AKI! Which is a total no-go for high compression engines of this technological era (modern ECUs with knock sensors and active learning and/or direct injection are obviously a different matter). I do agree that if the engine does not experience knock, then it does not benefit from higher-octane fuel, e.g. an engine designed for 87 AKI won’t make more power on 93, and an engine designed and tuned for 93 won’t make more power if you put 100 AKI race gas in the tank.

FWIW, my '89 (Lucas ignition, new cap/rotor/wires/plugs within the last year by previous owner) had noticeable knock using 95 RON (equivalent to US 91), and (gently!) running the tank empty and filling with 98 RON (US 93) had an immediate effect and virtually eliminated the knock. I did make a minor adjustment to dial back the ignition timing a smidge via the cam screw on the distributor and doing some road tuning, as I haven’t yet been able to get garage time to check with a timing light and mechanic in the seat to hold the revs at 3000 while she’s on the lift! About 1/16 of a screw turn of ignition retard got rid of the last vestiges of knock during throttle transition in the 2000-2700 rpm area. I still have some vacuum line double-checking to verify all bits of the timing system are bang on, but suffice to say that unless one is running significantly retarded ignition timing, the V12 should be fed “premium” fuel and not mid-grade.

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I think I already acknowledged up thread, that if a vehicle is experiencing detonation, by all means use high octane.

I’m not arguing that.

The only thing I’m saying is if a vehicle is running fine on midgrade or high-grade, without detonation, any higher octane, in and of itself, will not increase power.


After listening (reading) to what everyone stated, I decided that I would go ahead and give the Bosch 4457 spark plugs a try - in doing a purchase search, it seems that these Bosch spark plugs are very hard to find - I did find out that they are a suggested plug for use in the 6 liter v12 engine - my engine is the 5.3 liter V12 in my 1991 XJS, VIN ending 179190 - I did find 12 Bosch plugs and am now awaiting arrival - before I remove the existing spark plugs, I will do my best to make notes of performance and condition of everything - hopefully this will give me something to make a comparison to when using the Bosch 4457 spark plugs Tex.

Based on extensive experience in my Jaguar shop, I would not use a different plug than the Jag suggested NGK. Over decades we were given various “new improved” plugs of various brands including Bosch and I can’t recall any time it worked out well. The best result was when it wasn’t a problem. It isn’t that Bosch doesn’t make good plugs, it is a compatibility problem.

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Ditto, on many other marques that I worked on, including Jags. I still don’t buy this “magic plug” BS.

The only time I ever saw and experienced a noticeable difference was when you didn’t use the proper multiple electrode plugs on Mazda rotaries.

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I had several “noticeable differences”, all negative. They were mostly with modern thin wire and/or multiple electrode plugs on older Jaguars. The worst was Bosch thin wire electrode plugs in my XJ-12 Series 1 in cold weather after having 1400 miles or so on them. I had to go back to stock plugs in a parking lot in Jackson, WY in winter.
Another good example is that the early 4.0 V-8 Jaguars came with an Autolite conventional spark plug, which quickly were improved to an NGK Platinum plug. The latest 4.0 and the 4.2 came with a Platinum Iridium plug. Each one improved longevity but not performance. We recently saw a late 4.0 V-8 that had the Platinum Iridium plugs that took out one coil at 136K and the shop only replaced the coil. It came in at 143K with another intermittent failure and had taken out another coil. It received two new coils, the newly failed one and the aftermarket crap installed by another shop showing issues at 6K miles and a set of plugs. It really just needed a set of new plugs at 100K and would have never needed the coils or the wasted labor.


A few years ago, i swapped my NGK nickel tip copper plugs (NGK V power that many here use) with those Bosch four prong plugs. I didn’t notice any difference. About the only good thing was not having to adjust the gap twelve times.

Switched back to NGK V power. No difference.

Then two years ago, i tried NGK G power Platinum tip copper plugs. I have noticed a very slight improvement. More consistency too. IMO, those tiny platinum tips do better with my rich running V12? Don’t foul up as easy? Don’t know. But I’m sticking with them. Only con, you do have to be careful adjusting gap.


I agree with that.


I am VERY interested to hear what your experience is with those!


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Had to order the Bosch 4457 spark plugs from four different places - got 12 plugs for 48 US dollars - that was the total even with the shipping - apparently out of stock now - hopefully get them installed by tomorrow and will post how they work - Tex.

12 plugs including shipping for $US 48.00? I purchased a (read 1) plug for the Grandsons Mazda 3 2.3litre Turbo and it cost me over that in NZ $ and I received trade price!


NICE! I recall paying about twice that when I bought a set.


BEST LUCK!! “Half empty” thinking dictates-“if a better mouse trap, would not be developed, then discontinued”. Half full = “buy going slowly, you get cool plugs, cheaper than early adopters”. Hope “glass 1/2 full”, and you relay results, then supply demand makes them re-issued…

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