I know this has been discussed before, but all the threads seem to have conflicting information depending on who asks and who replies..

What is the current general consensus on the best plugs and leads to go for in a 3.9 EFI, running on petrol, not LPG?

I have heard that champion plugs are tat, is this true?

some people say only genuine leads will do, others say that 8 mm leads make a noticeable difference. presumably the 8 mm refers to lead diameter.. what diameter are genuine leads? is bigger always better? why not 9mm leads?

presumably genuine leads are boring black, are there any good after market 8 mm leads that are around the same money as genuine ones that come in bright colours to make my engine look a little bit more like a hotrod engine?

my truck currently has blue aftermarket leads on it, and it runs quite well, but there is nothing in the paperwork that I got with it to suggest that the plugs or leads have been changed in the last 5 years or so, so is it worth replacing them anyway?

thanks all

I spent a lot of years tuning and dyno testing engines for a living, and testing everything under the sun, and I have never seen, nor heard of, any dyno test that demonstrated ANY aftermarket plug lead producing any measurable gain in power or torque over a properly functioning OEM wire. Replacing leads with new OEM parts will be as good and anything else.

For performance, anyway. Appearance is another matter, and if you get a good quality aftermarket lead, like Nology or MSD, they will be good too. Cheap, Chinese-made eBay leads that trade more on price and bright colors than on performance can actually decrease spark energy to the combustion chamber and/or increase RFI, so I'd stay away from those.

I thought that might be the answer, thanks

any thoughts on the plugs themselves?

I am fairly new to all this and only really know of paddock spares, and they have 3 different temp ratings of plugs listed for the 3.9 EFI. I know LPG requires a higher temp rating, and that low compression engines and high compression engines also take different plugs, but assuming my 3.9 is a high compression which ones will work the best? Or maybe on a very lightly stressed engine like mine it simply doesnt matter?

also, paddock only have champion plugs (and also don't seem to have dizzy cap or rotor arm?), should I be buying from elsewhere if champion plugs really are a bit crap?

DeadTom said:

I thought that might be the answer, thanks

any thoughts on the plugs themselves?

(and also don't seem to have dizzy cap or rotor arm?), should I be buying from elsewhere if champion plugs really are a bit crap?

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I don't know much about plugs, run mine on Bosch super 4's and had no issues, in fact I don't know when I put them in, must be a good couple of years but I don't do many miles, probably only about 3k a year.

The big thing is dizzy cap and rotor arm. Don't put pattern parts on, trust me on this. Genuine parts are more expensive but so worth it. My 3.9 hates pattern ignition parts, it sulks and refuses to work properly. Once it chewed up a new (pattern) rotor arm in less than 5min, had to put in an old well used genuine arm to get me going and that lasted for ages! Also don't be tempted to put a "performance" coil on it, stick to standard spec anything else is a bit of a waste of time. HTH.

thanks kev, i'll make sure I use genuine rotor and dizzy cap if i need to replace them

I think I remember you offering wise words last time I was on here with my first RRC a few years ago. glad to see you're still around.

I'll get some Bosch plugs for it :tea:

ngk plugs (copper cheap ones,NOT anything flash ie should cost £2 each)

They are the best..i run boost nitros and lpg and they survive that..champion bosch didnt..ie still good at 20k!!!( though changed anyway cos so cheap)


Re leads as standard anything branded..oem expensive and no better than bosch etc
Magnacore ate excellent..but you dont need them..so i would go best you can afford

You DONT MENTION rotor arm and dizzy (assuming you not got gems or thor)
MUST BE genuine LR..no arguements, end of! Soz if not read proper and you got a p38( no dizzy)

DeadTom said:

any thoughts on the plugs themselves?
should I be buying from elsewhere if champion plugs really are a bit crap?

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Each to his own but I have used Champions in many vehicles (LR products & others, both carb/efi fuelled) over the last forty plus years & rarely had any problems.