Engine modifications are the single most important category to get right when declaring car changes to your insurer. They are among the most common categories of undisclosed modification, and a leading reason specialist claims are disputed. The right approach — full, documented disclosure — costs slightly more upfront but eliminates the risk of a large claim being rejected over an undisclosed camshaft.

What Counts as an Engine Modification?

Any change to the engine from factory specification is an engine modification. This is broader than many owners realise:

• Performance air intake or induction kit (including drop-in panel filter upgrades)
• Performance exhaust (headers, cat-back, downpipe, race pipe)
• ECU tune or remap
• Camshaft changes (bigger cams, different timing)
• Cylinder head work (ported and polished, bigger valves)
• Forced induction (turbocharger or supercharger — factory or aftermarket)
• Larger injectors or fuel pump
• Upgraded intercooler or charge cooler
• Nitrous oxide system
• Short-runner intake manifold or plenum swap

How to Document Engine Modifications

The more documentation you provide, the stronger your position at claim time:

1. Photographs: engine bay before and after each modification; label each component in photos
2. Receipts: parts receipts and installation invoices for all modifications
3. Dyno sheet: before/after power and torque figures with the dyno operator’s details
4. Build sheet: a written summary of all modifications with dates, part numbers, and installer details

How to Tell Your Insurer

Contact your insurer (or broker) directly — don’t wait for renewal. Provide the modification list in writing. Many specialist insurers can process a mid-term endorsement quickly once documentation is provided. You may pay an additional premium; you may also need to provide photos or a dyno sheet.

What Happens If You Don’t Declare?

At claim time, an assessor will inspect the car. Engine modifications are visible and impossible to hide. If undisclosed mods are found:

• The insurer can void the policy from its inception date
• You receive no payout
• Any third-party liability costs may be pursued against you personally
• In the UK, insurers share claims and incident data through the Claims and Underwriting Exchange (CUE), a shared industry database that helps insurers identify prior non-disclosure — a record there can affect your ability to get cover, or the price of it, in future.¹ Other countries have their own equivalent shared claims registers; ask your insurer what applies where you’re covered.

Sources

• GoCompare — Claims and Underwriting Exchange (CUE)

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“@type”: “Question”,
“name”: “Does a Stage 1 tune count as an engine modification?”,
“acceptedAnswer”: {“@type”: “Answer”, “text”: “Yes. A Stage 1 ECU remap is an engine modification regardless of whether it’s done through the OBD port. It changes the engine’s fuelling, ignition timing, and boost pressure. It must be declared to your insurer. There’s no fixed premium increase — ask your specific insurer for the figure on your car rather than assuming a generic percentage.”}
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“name”: “Do I need to declare a performance exhaust?”,
“acceptedAnswer”: {“@type”: “Answer”, “text”: “Yes. Performance exhausts (headers, cat-back systems, downpipes, decat pipes) are engine system modifications that affect the car’s emissions, power output, and noise level. All must be declared. Many insurers accept performance exhausts without significant premium impact if the rest of the car is relatively standard.”}
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“@type”: “Question”,
“name”: “What if my car was modified before I bought it?”,
“acceptedAnswer”: {“@type”: “Answer”, “text”: “If you bought the car with modifications already fitted, you still must declare them. The insurance obligation is based on the car’s current specification, not its original build. Get a full list of modifications from the seller before purchase and present them to your insurer from day one.”}
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