Extreme Soundproofing
Iím Pete Gildenhuys from Pretoria, South Africa. I bought a new Honda Jazz/Fit 1.4iDSI CVT in August 2005, and at April 2007 it has done 59000Km trouble-free. I originally bought the car for my son whoís attending University, but have since bought him a Honda CBX 250, for obvious reasons. Some of the modifications Iíve done may have impeded the carís warrantee, but what the heck. Iíve been driving Mercedes Benz cars for the past 30 years, and I wanted to see if I can make the Jazz as comfortable and as quiet. My latest Merc is an E320CDI (2007 model) with air suspension and allÖ

Modifications done to the Jazz so far: Leather upholstery and sheepskin seat covers (softer ride), anti-smash film on glazing and loose full-size pile carpeting (adds to sound-insulation), hand-operated throttle for long journeys, Unichip piggy-back programmable ECU, air intake duct widened (the headlight unit causes some restriction on the standard setup), Xenon headlights fitted, wheel tracks widened by 10mm (toe-in and camber set at zero degrees), Michelin EA3 195/55 R15 tyres on standard mag. road wheels (originals were Bridgestone 185/55R15). 50x5mm neoprene O-rings were added between damper bump-stops and car body (rear shock header bushes lengthened accordingly). All stowage compartments lined with felt-cloth, body cavities in vicinity of suspension sub-frames filled with liquid poly-urethane foam (taking care not to block water drainage holes), and further insulated with high-density foam rubber inside and out (most road noise enters the cabin via suspension mountings and wheel arches), rubber dampers fitted to torsion-bars and coil-springs to reduce metal harmonics. Rear swing arm filled with poly-urethane foam. All body panels (doors, quarter-panels, rear gate, under-bonnet) lined with 10mm high-density foam rubber (works better than commercial sound-deadening pads, and is much cheaper). I Also lined the inside door U-channels for reduced wind noise. Roof pillars, tail-gate and gate-cover, doorstep channels, part of rear roof, under-dash cavities all filled with 50mm low-density foam rubber or poly-urethane foam. The complete boot tub (a beeg sound box) lined with seamstress-type batting, moulded in place with white Castrol motor cycle chain wax. So, some parts have up to four layers of insulation. Tailgate-wing fitted (a la vtec). All panels, mounting pins, etc. was treated with wax before re-fitting, to prevent rattles and squeaks. Complete under-side of car, including rear wheel-arches, covered with 1mm PVC-sheeting and/or 4mm PVC foam-sheeting, lined with 5mm high-density foam rubber. (I made templates from card-board first.) Under-engine cover sculpted to aid air flow through the engine compartment. Standard engine splash guard tends to sag in the middle, so I stiffened it with aluminium channeling tied to the cross-member. Total added weight about 9Kg.

No holes were drilled in the car, all modifications can be undone and the car returned to standard. All mounting screws were glued to the car with epoxy putty or thermal glue. All body-mounted foam (except under front wheel arches which is glued in place) is fixed with removable double-sided tape. The only modifications readily visible from the outside are the slightly wider tyres and the tailgate wing.

The net result of it all? Dyna-tuning the engine with Unichip added almost 5kW and 9Nm @3000 rpm at the wheels, at 1700m above sea level (no noticeable improvement on fuel consumption, though). The Michelins (run slightly under-inflated for a smoother ride) are nothing short of superb (maybe I should have fitted 185/60 R15 for lower rolling resistance, but the increase in circumference bothered me). The low noise levels inside the car is almost eerie-like (I can almost hear my passengers breathe at 120Km/h, and I drive around without the tonneau-cover, which makes a whooping sound on bumpy roads. Still needs fixing). The sound of the doors, bonnet and tail-gate opening and closing, is Limousine-like. The under-body covers which started as an experiment have now become a permanent fixture: the cover between the rear bumper and rear swing arm had had a major impact on the carís aerodynamics. The widened tracks added to a smoother ride and exceptional directional stability, even while doing 212Km/h (Garmin Nuvi 300 GPS-measured) along a long, steep down-hill. The lower front-end cover disintegrated during that run, so I had to rethink its fitment. The modified engine air intake system allows for some hot engine compartment air to be sucked in, which slightly leans out the fuel mixture on hot days. Normal open-road cruising around 115km/h with two adult passengers plus luggage returns fuel consumption figures of 5,2l/100km (best achieved 4,7l/100km over 1500km round trip). Hand-throttle in tandem with CVT works like a charm. In-cabin noise stays virtually the same for wet and dry roads. Oh yes, I fitted a modified air filter element as a cabin air filter, as my wife is sensitive to odours and dust. (GUD AG868, side grooves removed, 2mm sealing strip added, plus 20mm foam strip at the back. It needs replacement every two months.)

I once fitted a 20Kg lead weight in the spare wheel well, between the wheel and jack: it smoothed out the ride even further, but adds a bit to the fuel consumption. And I still want to reduce the engine noise further by wrapping the front part of the exhaust system in suitable insulation material: couldnít find any to date. The hand throttle may be augmented by an electronic cruise control, but modified to keep the engine revs/load constant rather than the cruising speed. I still occasionally drive around in the Merc, just to keep its batteries charged. And when I have to show-off, of course...



10 mm foam rubber

1 mm PVC insulation

1 mm aluminium sculpting

50 mm foam insulation

Batting insulation

Bonnet insulation

Damper bumpstop

Damper insulation

Engine air intake

Engine Bay Insulation

Left rear insulation

Left rear wheelarch

Mounting wax

Right front insulation

View from left rear

Wheel arc joint