Making the A-series quieter


The A-series is not exactly a wisper engine. At higher revs, it makes the ICE obsolete. Here are a few things you can do to make the engine more quiet. Also, you might want to consider good sound insulation in the engine compartment.

Quick & Easy

Alloy rocker cover
Replacing the standard rocker cover with an alloy one will cut down a bit on your rocker noise. This happens becuase the alloy is thicker, and absorbes more sound. This is probably the simplest engine mod sound-wise. Approximate cost of a new (quality) alloy rocker cover is currently 30 UKP.
Performance Filter Element
In pursuit of more horsepower, many people replace the standard air filters with a set of performance filters such as K&N or Piper. Filters such as these are known to let through a lot of induction roar. One way to get a bit of performance while keeping the noise down is to use the standard airbox, and replace it with a performance filter element. This gives improved air flow while maintaining a reasonable level of noise. About 20 UKP might be needed here.

Minor Mod

Roller Rockers
If you want to go for a small mode that cuts sound, and at the same time improves performance, then you might invest a bit into a set of nice alloy roller rockers. Based on adverts in Mini Magazine, I would estimate a set of new ones to be around 100-150 UKP.
Cam Belt
Quite a bit of the engine noise comes from a worn timing chain which tends to rattle. The performance guys fit duplex chains in order to keep the chain from stretching. Another way to go is to fit a cam belt. This almost completely eliminates this particular source of noise. The costs vary, but I recall seeing a figure of about 50-100 UKP for a conversion kit.
Electric Fan
Aparently a lot of noise is caused by the older metal radiator cooling fans. This happens especially at higher revs. It also robs you of a bit of top-end power. A solution to this is to convert to an electric fan. Price? About 60 UKP for a complete kit which hooks up to a thermostat.

Major Fun

Engine Balance
A fully balanced engine will run smoother, hence giving out less noise as it shakes. Good engine brackets won't harm either. This is pretty expensive joy though, and requires the lump to come out for a while. Prepare to spend all your christmass money on this.

Compiled from various sources