NC Mk 3.5 Scrutineering

Technical Area Motorsport & Trackday Preparation
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  1. My model of MX-5 is: NC Mk 3.5__
  2. I’m based near: Salisbury__
  3. I’m looking for technical help or recommendations on: __
    More scrutineering advice 6 years later from original post!
    I now have an NC Mk 3.5 which I use for occasional hill climb outings. Last weekend at the last meeting of the season a scrutineer decided that the rear bulkhead between the bootspace and the fuel tank are was not sealed and therefore would not be regulation compliant. I run in a road going production class. Has anyone else had this issue?. All the plastic boot trim is in place ( I am not bothered about how many kg are saved by removing it) and shining a powerful torch in the boot does not result in any of the light being seen from the Driver /passenger compartment. It is a soft top model
    I have read the 2025 M’sport uk regulations virtually from cover to cover and I can see nothing about sealing the boot in a production car- certainly nothing in Chapter 14 Sprint/Hillclimb regs.
    General consensus was amongst others on the day was that I am running a car as produced by the manufacturer which must have passed all sorts of safety tests, so what’s the problem?
    I used to run an NB Mk 2.5 sport and the configuration of the boot bulkhead is different to the NC - it also had “carpet” boot space trim so I sealed any holes or gaps round the tank filler pipe with expanding foam sealant, whereas the NC has plastic covers firmly fixed to the bulkhead. Any practical advice will be welcomed.
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If anyone has a template for a cover for the Fuel filler pipe etc where it passes through the NC 3 boot bulkhead, which can be sealed in place then that would be brilliant (or indeed has a cover they are looking to dispose of). In conversation with the club today it is obvious that this requirement is a local scrutineer thing and if I am to run next season it is something that must be addressed! PM me if you can help please

Scrutineering advice
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Sorry I can’t help with the template, running a completely OEM . 2.5 and had this issue come up a couple of times at Llandow, Harewood and Castle Combe in 2024, they allowed me to compete with a promise it would be sorted next time. Not been competing this year. To see the reg that is being enforced go to Appendix J, Section 5 Technical, it used to be 5.2.1 from memory.

Hope that helps and you get it sorted.

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Thank you very much for the prompt reply. Unfortunately the Appendices in the 2025 Motorsport UK NCR’s are no longer in Alphabetical order, but numerical and I can’t find anything that seems relevant, apart from Chapter 7 Appendix 4 1.2 which says “Every effort should be made to isolate fuel tanks and pipes from the Driver/Passenger compartment”
This is what the bulkhead behind the seats does, so this is where the difficulty with the relevance of the concern about the boot bulkhead stems from. If I find an answer before next April I will post it under this topic.
Thanks again

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This is all a matter of interpretation. The scrutineer says in order to comply with Chapter 7 Appendix 2 6.1 Of the 2025 MotorsportUK NCR’s the boot bulkhead should be sealed against fuel tank leakage.However the “cockpit area” behind the seats is completely sealed against the fuel tank so I tend to disagree with the interpretation. Will see what happens at the first meeting next season!

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I tend to agree, remember when I changed my NBFL hood noting how well the cockpit is sealed from the fuel tank…. :+1:

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Does the fuel filler pipe pass through the boot area? If it does then one could argue that if the filler were to become detached in an accident then fuel could flow freely from the tank into the boot area and from there into the cockpit area.

This has always been a contentious point.

In the Caterhams I used very wide stick backed aluminium foil to bridge any gaps.

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I’ve had sealing the boot for fire mentioned once in six years of sprinting / hillclimbing, from memory at Shelsley.

If it is a local ‘thing’ I’d do one of the following…

I’d either take it to a garage that prepares race cars and ask them to seal it (as it must come up all the time for circuit racing).

Or I’d try and seal it myself using suitable foam or tape. A quick look on Demon Tweeks shows some foam and tape that looks like it’d work.

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Thanks to everyone for thoughtful help and advice. I suppose the question I haven’t asked the event organisers is why? because it would be helpful to know if we are dealing with petrol escape/ fire or both!

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