F355 coil-on-plug conversion

May I add that the 5V design of the combustion chamber may be even more efficient at pushing the mixture towards the centered spark plug as the piston goes up during the compression stroke than more conventional 4V combustion chambers.

 

@redwedge
Here are some pictures. It looks just the same as previous installs.

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@f355spider

I happen to have right now in the garage NGK PMR7A, CR7EIX and CR8EIX lying around. They all measure exactly the same.

 

What coils are those please @Timmo

 

The coils are the same Densos as used on previous installs.

FWIW here is a confirmation that everything is running well. The plugs now look the same as on my 550 which runs John's COP set up, whilst with the stock ignition on the F355 the plugs always looked richer than this. This sort of confirms my initial impression that 2.7 cars need this type of upgraded, stronger ignition to run the way they should always have.

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I was afraid you might say that. They're hard to come by new here in there UK.

 

Nice! I can't tell from this angle but do you need to run spacers for the covers?

 

Yes, as mentioned. Not sure yet where I'll have them made.

 

They are hard to come by new anywhere as they are not made anymore.

 

Thanks. Did not see you mention it unless assumed because of the same coils.

 

Interesting. I installed the CR7EIX many years ago (I didn't pay attention to any differences), and a couple years after, I had a major service performed at the Ferrari dealer and they removed them and showed me the nose projection differences and sent me photos. I should have saved the photos. The CR7EIX was clearly shorter. But perhaps the specifications of the CR7EIX has changed?

It was because of this thread I originally installed them in my car (5.2 Motronic). But after the dealer discovery I have stuck with the factory plug, until I later sold the car.

 

PMR7A application is Ferrari 355 and F50. That's it. This plug has a solid terminal and will not work with Denso/pencil style coils which require a threaded stud.

CR7EIX, (CR8EIX), CRP7EAIX-9, and CR7EIA-9 all have threaded stud; will fit and work.

Like the PMR7A, they all share
-19 mm reach
-1.0 mm pitch
-5k ohm resistor

PMR7A
-platinum center electrode
-platinum ground electrode
-.028" gap
-2.0 mm projected tip; but listed as non-projected

CR7EIX, (CR8EIX)
-iridium center electrode
-nickel ground electrode
.031" gap
-1.0 mm projected tip; listed as non-projected
(this is 1.0 mm shorter than oem)


CRP7EAIX-9
-iridium center electrode
-nickel ground electrode
-.035" gap
-3.0 mm projected tip; listed as projected tip
(this is 1.0 mm longer than oem)


CR7EIA-9
-iridium center electrode
-platinum ground electrode
-/035" gap
-1.8 mm projected tip; listed as non-projected
(this is 0.2 mm shorter than oem)

All must be gapped to .028"

By the numbers, CR7EIA-9 is the most similar to PMR7A. Only a 0.2 mm projected tip difference,
and iridium center electrode vs. platinum. Everything else is the same including platinum ground electrode.


@Timmo: why did you choose to go with CR8EIX? This plug is one number colder (8) than factory

 

The plug originally recommended for the F355 2.7 is the PMR8A, and the PMR7A for the 5.2.
The CR8EIX is simply the Iridium upgrade to the original PMR8A.

BTW the CR8EIX and CR7EIX I purchased came gapped to 0.7 mm / 0.028".

 

@Timmo thanks for clarification. Any idea why the 2.7 plugs are colder?

Do you have before and after fuel trim info? Would be curious to see that data.

 

@Carmellini
I do not think it is possible to get fuel trim info on pre OBD cars like the 2.7.
As for colder plugs I am not sure but logic would suggest a higher dynamic compression ratio, through a higher static compression and/or advanced IVC. The pistons seem to be the same for both the 2.7 and 5.2 but the parts catalogues show different part numbers for the camshafts.

 

The difference in the CR7EIX versus PMR7A seemed more dramatic than 1mm in the photos my dealer sent me. Looked like 2 or 3mm. Not sure what if any negatives there were to that. The car ran fine for a couple years on them.

 

Agreed. In this picture it looks like the reach of the threads is greater on the PMR7A (right)?

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I suppose pictures are worth a thousand words...

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As a follow up to installing COPs on my 2.7 F355 and in order to boost the coils which are paired in series, I added in the loop a HKS Twin Power ignition box, after successfully installing one my 550, as per John Cribb's initial set up. This has tightened up further the way the engine runs with the COPs and it runs yet a little smoother, with more instant torque down low, a slightly quicker throttle response and at last but not least a sharper and more precise engine note right up to 8500 rpm. The engine feels healthier and like it's not working as hard as before, if that makes sense.
A well worth and simple upgrade IMO that allows extracting more performance from the Denso coils.

 

I wrote an entire description of what I have and what I've done and it simply vanished so I'm just going to include the photos of my 2 stage coil conversion.

 

Bill,
I hope you will post videos when this is running on the track. The noise this car makes on a flyby must be amazing.

 

In regards to CR8EIX, NGK’s site lists it at .031” gap

https://www.ngk.com/ngk-4218-cr8eix-iridium-ix-spark-plug

Apparently, there are people selling them on Amazon with .028” gap.

https://www.amazon.com/NGK-CR8EIX-Iridium-Spark-Plug/dp/B000VZJ712




Either the seller is listing the spec incorrectly or he is gapping them to .028”. I’d want to double-check on that.




I run the HKS Twin Power and Iridium plugs on my FD RX-7 for 80k+ miles. Solid responsive, simple setup.



The HKS Twin power would do good for the platinum plugs as well.

 

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I also can’t seem to find them in .028” spec anywhere else other than Amazon.

 

I’m not finding any CR7EIX gapped at .028” either.


Someone should message the Amazon seller to double-check if he listed the spec correctly.