A smart roadster turbo upgrade focused on intercooler pipework and silicone hoses is the highest-value first modification you can make. Replacing the ageing rubber boost pipes eliminates chronic boost leaks, restores lost power immediately, and is essential groundwork before any remap. Cost is typically £80–£150 for a full silicone kit.
The Smart Roadster’s 698cc turbocharged triple punches well above its displacement, but that performance depends entirely on pressurised air reaching the engine cleanly and consistently. After two decades, the original rubber boost hoses have hardened, cracked or collapsed under heat cycling — and a single pinhole leak can rob you of 10–15 hp before you even touch the ECU. This guide covers every element of a practical smart roadster turbo upgrade on the induction and boost side: what fails, what to replace it with, how to find leaks, and what to buy first to make your money count.
Why the Smart Roadster’s Boost Pipework Fails
The Roadster’s engine bay is a hot, cramped environment. The 698cc Mitsubishi-derived three-cylinder sits mid-rear, and the Garrett 1238S turbocharger is nestled tightly against the bulkhead. Boost pressures range from 0.89 bar on the 45 kW Lite to 1.43 bar on the full 74 kW Brabus — and every millimetre of pipework between the turbo compressor outlet, the intercooler, and the throttle body is under constant thermal and mechanical stress.
The factory rubber hoses were adequate when new, but they were never intended to last 20 years. Heat cycling causes the rubber to harden and lose elasticity; the clamp collars bite into brittle material and create micro-cracks. The most common failure points are the small-diameter breather and wastegate actuation hoses, the main intercooler-to-throttle pipe, and the elbow connecting the turbo outlet to the intercooler inlet. Any one of these can cause the ECU to see inconsistent boost, triggering conservative fuelling or even limp mode.
Understanding exactly how the 698cc engine’s forced-induction system is laid out makes diagnosing and replacing these components far more straightforward — it is worth reviewing that architecture before you start pulling pipes.
Smart Roadster Turbo Upgrade: Silicone Hose Kits Explained
Silicone hoses are the obvious upgrade over original rubber, and for good reason. Reinforced silicone withstands continuous temperatures above 180 °C, resists ozone degradation, and maintains its shape under boost pressure rather than ballooning. For a smart roadster turbo upgrade, a full silicone kit typically includes:
- Turbo outlet elbow — the first pipe after the compressor housing, subject to the highest heat
- Intercooler inlet and outlet hoses — larger bore, often with 90° bends
- Throttle body inlet pipe — connects the intercooler outlet to the throttle
- Breather and vacuum hoses — small-diameter but critical for wastegate operation and crankcase ventilation
Colours are a matter of taste — black is subtle, blue or red are popular. What matters far more is wall thickness and braid reinforcement. Budget kits use single-ply silicone; choose at least three-ply for the main boost pipes. Stainless-steel T-bolt clamps are vastly superior to the original worm-drive clamps: they apply even clamping force around the full circumference and will not corrode.
If you are planning a larger intercooler alongside the hose swap, read our analysis of whether a front-mount intercooler upgrade genuinely delivers gains before committing to a specific pipe routing.
How to Find Boost Leaks on a Smart Roadster
Before spending money on new parts, confirm exactly where your boost circuit is losing pressure. There are three reliable methods:
Smoke Test
A smoke machine connected to the intake post-throttle body with the engine off is the fastest professional method. Smoke escaping from any joint or hose pinpoints the leak immediately. Many independent garages offer this as a £30–£50 diagnostic service.
Pressurised Air Test (DIY)
Block the intake pre-turbo and the wastegate port, pressurise the boost circuit to around 0.8 bar with a hand pump or regulated compressor, and listen carefully. Spray soapy water on joints to reveal bubbles. This works well on the bench if you have removed the pipework for inspection.
Data-Logging Approach
A persistent gap between requested and actual boost, visible in ECU live data, is the electronic signature of a leak. Monitoring boost pressure in real time allows you to correlate power loss with specific RPM ranges where a leak opens under load. Our dedicated guide on how to monitor and interpret boost pressure data walks through the exact parameters to watch.
What Happens If You Ignore Boost Leaks Before a Remap
This is the question that matters most to anyone close to a tuning purchase. A boost leak does not just reduce power — it actively corrupts the ECU’s ability to control fuelling. The Bosch MEG 1.1 ECU uses manifold pressure as a primary load input. If actual boost is lower than commanded, the ECU runs a leaner mixture than intended at high load. On a standard map that means sluggish mid-range; on an aggressive remap it can mean detonation.
Equally problematic: a leaking wastegate actuator hose allows boost to creep above the target, potentially over-spinning the Garrett 1238S and shortening its service life. The 1238S is a small, fixed-geometry unit with real thermal limits — if you want to understand exactly where those boundaries lie, our deep-dive into exhaust gas temperature and thermal safety margins on the 1238S is essential reading before pushing boost further.
The conclusion is simple: no responsible tuner should flash a new map onto a car with leaking boost pipes. Fix the pipes first, verify boost delivery is consistent, then remap.
Smart Roadster Turbo Upgrade: Costs, Gains and What to Buy First
Here is a practical spending hierarchy for a boost-side smart roadster turbo upgrade:
- Full silicone hose kit with T-bolt clamps: £80–£150. Restores full factory boost delivery. Essential before anything else.
- Boost leak smoke test (if symptoms present): £30–£50. Confirms the problem before you spend on parts.
- Actuator hose and vacuum line set: £15–£30. Often sold separately; replace these at the same time as the main hoses.
- Intercooler upgrade (optional, above 1.3 bar): £200–£400 installed. Only relevant if you intend to run higher boost on a remap. The stock intercooler becomes a genuine bottleneck above Brabus SB2 pressure levels.
- ECU remap: see our performance packages. Only after all boost-side work is verified.
The 60 kW standard Roadster is the best starting point: it has the oil cooler absent on the 45 kW Lite, and its standard 1.09 bar boost leaves genuine headroom for a remap. The 66 kW SB2 and 74 kW Brabus are already running closer to the 1238S’s comfortable ceiling, so hose integrity matters even more at those pressures.
If cold-side airflow is your next priority after the boost pipes, our guide to upgrading the air filter and cold intake covers the induction side of the same equation and pairs well with this work.
For those ready to commit to a full performance package after completing the hardware groundwork, our ECU map packages range from 90 hp BASIC to 125 hp EVOLUTION and are built around a properly sealed, healthy boost circuit.
Choosing the Right Silicone Kit: Brand and Fitment Notes
Not all silicone kits are made equal, and fitment on the 452 Roadster is unforgiving — the mid-rear engine layout means several hoses must navigate tight radii around structural members. Key buying criteria:
- Wall thickness: Minimum 4 mm on main boost pipes. Thinner walls balloon under sustained boost.
- Reinforcement: Three-ply polyester braid as a minimum. Four-ply for the turbo outlet elbow.
- Temperature rating: Continuous 180 °C minimum, peak 220 °C. The turbo outlet sees the highest temperatures.
- Kit completeness: Confirm the kit includes the small-bore vacuum and wastegate hoses, not just the large intercooler pipes. Budget kits routinely omit these.
- Clamp quality: Stainless T-bolt clamps supplied or purchased separately. Avoid zinc-plated worm-drive clamps in the engine bay.
Reputable suppliers include specialist silicone hose manufacturers such as Samco Sport, who produce custom-fit kits for a range of small-displacement turbocharged engines, and general-purpose suppliers where you can cut-to-fit using their bulk hose and appropriate reducers. For technical background on silicone polymer properties versus EPDM rubber in automotive applications, the Wikipedia entry on silicone rubber provides a solid material-science grounding. The Garrett Advancing Motion technical library — including specifications relevant to the 1238S — is referenced throughout the Garrett Motion engineering resources.
Frequently Asked Questions
How much power does fixing a boost leak restore on a Smart Roadster?
A significant boost leak can cost 10–15 hp and noticeably blunt throttle response. On a 60 kW (82 hp) standard Roadster, that represents up to 18% of total output. Fixing leaking hoses restores full factory boost delivery and is often the single most cost-effective power recovery available.
Can I do a silicone hose swap myself, or do I need a garage?
Most competent home mechanics can complete a full silicone hose swap in 2–4 hours with basic hand tools. The mid-rear engine is accessible via the rear compartment lid. The main challenge is the tight routing around the bulkhead; patience and cable-tie management matter more than specialist tools.
Do I need to upgrade the intercooler at the same time as the hoses?
Not unless you are remapping above 1.3 bar. For a standard 60 kW Roadster on a BASIC or PLUS map, the stock intercooler is adequate. At 1.3 bar and above — SB2 levels and beyond — the stock unit begins to thermally saturate and a larger intercooler becomes worthwhile.
What is the best smart roadster turbo upgrade sequence before a remap?
Replace silicone boost hoses first, then verify there are no boost leaks via smoke test or data-logging, then upgrade the air filter and intake, and finally remap the ECU. Attempting a remap before fixing boost-side hardware wastes money and risks detonation under load.
