300hp + Spark Plugs. Alfa Romeo 155 Q4

[g.kinazoglu]

Which, spark plug should be used over 300 hp.

[kunev]

As the heat and pressures in combustion changer will be noticeably higher than originally then colder plugs will be better in my opinion. For Q4 is recommended 6 hear range by NGK, 20 by Denso, ... different brands use their own ratings
sparkplugheatrating-copy-1024x652.jpg
Spark plugs with electrodes from more precious materials will be better and will last longer, but by not much and are much more expensive.
Last time when plugs was changed on mine I decided to go with one step colder copper (normal) Denso three electrodes (as originally) plugs on a car with tubular exhaust manifold, sports cat, some part of exhaust after it changed for 2.5" stainless steel and soon installed Squadra Tuning chip. Maybe not needed to change from standard in my case.
If you experience misfire on boost you may change/reduce the gap of electrodes. I have read about 0.6-0.7mm to be good value. Checking and changing of gap on multi electrodes is not so easy.
In my opinion one step colder than what is recommended standard by chosen manufacturer will be be good and cheap and frequent change after that.

[g.kinazoglu]

I understand , thank you very much.

[g.kinazoglu]

Platinum spark plug works in all kinds of difficult conditions. I would like to prefer Platinum spark plug instead of Iridium spark plug. Do you think that's true?
BPR7EVX.

[Steve Webb]

I think in your case you are going to have to try a brand/model of plug, see how the engine performs with them, and then adjust the temp of the plug to get the best performance.

Personally I use NGK B8EGV and they seem to work well. But saying that I wasn't running 300bhp.

But I guess when you get the engine all back together, you aren't going to jump straight in and try to get max power out of it from the start, so that should give you an oppotunity to tune the plugs as you develop things.

[kunev]

From what I have read iridium plugs are better in general than platinum and are more expensive. There is also a combination between them - iridium center electrode and platinum ground/side one. I see that NGK have new RUTHENIUM technology, which they advert as superior to iridium and platinum.
The best options have to be such with precious metal electrodes - platinum, iridium, ruthenium. Such plugs will be several times more expensive than normal copper ones and will last longer than them, but not as long as price increase.
What I would do in such case is to check sites of big manufactures (NGK and Denso with priority) and look what is recommended for my vehicle in their product finders. Generally they recommend 2-3 models for a vehicle in factory heat range - one standard and 1-2 more advanced and expensive. Will be noticed that not all type of products are listed for particular application. Then will look for 1 range colder from chosen model (if there is such) and will compare sizes against standard recommended model also. Can be looked for other manufacturer's models which should fit and for that have to be checked naming convention of manufacturer and recommended models to be explained against it. Some part of the recommended models names probably will be common. Then search for models which have such part in the name and check dimensions against recommended model.
And here is a example of such research:
Denso
-Standard: W20EPB (3 ground/side electrodes)
-Advanced: W20TT
-More advanced: IW20TT (iridium tip and platinum ground electrode)
W20 is common between them. W is for thread diameter and hex size and 20 is for heat range (from naming convention). Colder than that are 22, 24... (as per chart in earlier my post). If we choose "the best" option will search for model IW22TT, but there isn't such. Then lets look for models with W22 in the name, which look closer to names of recommended. I see:
- W22TT - colder than recommended advanced (twin tip) model
- IW22 - Iridium Power model
- VW22 - Iridium Tough model
For all above dimensions are like recommended.
NGK
-Standard: BP6ET (3 ground/side electrodes)
-More advanced: BPR6EIX (iridium)
Here BP and 6E is common. B is for thread diameter and hex size, P is for projected insulator, E is for thread length and 6 is for heat range. Interestingly standard plug doesn't have resistor and iridium one have. Again if choose "best option" then have to search for BPR7EIX and there is such with same dimensions like recommended. There is also:
- BP7ES - standard single copper electrode
- BPR7ES - standard with resistor
All above are with same dimensions like recommended.

Mentioned by Steve model (NGK B8EGV) is very popular among owners of other Italian cars with that Lampredi's 2.0 16V turbo engine (Fiat Coupe, Lancia Delta Integrale). These are old model racing competition plugs with gold-palladium center electrode and are recommended by NGK for some motorcycles. From what I have read look like when these models appear more than 20 years ago and was started to tune them was found that this model behave good on modified engines and that info spread across and was stated that this is the model for these modified cars.

And what will be intended use for your car?

[g.kinazoglu]

I decided. I'il put the B8EGV on and try.
Thank you very much for your interest.