Back to Knowledge Base

The Merlin Racing Exhaust Muffler

Racing Exhaust Mufflers

How much noise will the Muffler remove?

Noise testing and Merlin mufflers

We are based at the Castle Combe Race track in Wiltshire so we often have drivers rushing into our shop first thing in the morning after their car has failed the noise check.

To help, some years ago we designed a simple supplementary silencer/muffler. It is a round box 4 inches in diameter 8 inches long. It has 2 inch perforation in the bore and it is packed with E-Glass. We weld a short length of exhaust pipe at one end so that you can slip it over your exhaust. The end cap on the other end is tacked on with 4 welds so that it is possible to grind out the weld and repack the E-Glass.

The silencer comes in pipe sizes from 17/8 to 3 inches Outside Diameter in 1/8 inch increments so there is a good chance that we will have something to fit. The exhaust pipe wall thickness is 1/16 inch so a 2 inch OD pipe will have an inside diameter of 1 7/8 inches.

The muffler can fit over your exhaust in which case we can cut a slot to enable it to slide over the exhaust and supply an exhaust clamp. Alternatively the muffler can be fitted inside your exhaust and secured by drilling a small hole and using a self tapping screw. If you do this the scrutineer will require you to fit a hose clip round the pipe and over the screw to make sure that it does not vibrate out.

Advantages of the Merlin muffler

Unlike some other decibel reducers, which effectively block the end of your exhaust to reduce the noise thus causing an increase in back pressure, our Merlin Muffler is a straight through device. The 2 inch perforated tube through the middle allows the noise waves to be dissipated within the can and so can reduce noise levels without ’strangling’ the engine.

How much noise will the muffler remove?

It is impossible to say until tested, in some cases 7 Db and less often it’ll have no effect. Noise level (measured in dBA) values are not valued in a linear scale but an algorithmic scale. In layman’s terms, this equates to meaning that with every 3dBA decrease in measured noise, a 50% decrease in sound pressure levels will be achieved which in turn will mean a 50% decrease in audible sound heard by the human ear. For example: Reducing the decibel level produced by an exhaust from 103 to 100dBA may not seem like a major change, but it actually represents a 50% reduction in audible sound.

If the muffler is not effective then the silencer box in the system may need to be replaced either with a new one or a larger one. Silencers become less effective with time as the packing is blown out; Merlin racing silencers are designed so that they can be dismantled and repacked. We keep the packing materials in stock E-Glass & Basalt.

A few points to note - from our experience we have found that the mufflers do not offer much reduction on Porsche 911 variants because the exhaust systems on these types of cars are comparatively short. And also our Mufflers are round so will not fit oval outlets. Unfortunately we cannot offer anything for cars with exhaust larger than 3 inches (Subaru’s with 4 inch system will struggle to pass the noise test). On exhausts with rolled ends the muffler will have to be fitted inside.


Noise testing at Castle Combe Circuit

If you race locally and your car fails the noise test we are on-site and so can supply you with a muffler from our Merlin shop in the paddock. You can hold this over your exhaust (no need to fit properly) and take the noise test again. If it passes then you need to then decide how to fit it permanently (we can help you with clips and clamps) if it fails return it to us for a credit.

If you are concerned that your car will not pass the noise test you can always visit the circuit prior to your event and have the scrutineer make the check. It is far less stressful to have the noise problem sorted before you arrive for your event. At Castle Combe circuit during the summer the scrutineer is at the track several times a week. Ring Castle Combe Circuit on 01249 782417 to find out which days the scrutineer will be present.

If you are not local but wish to try out a Merlin muffler

Simply buy one and take it with you as a ‘just in case’ item. If you do not use it and it is returned to us in the condition in which you received it, we can refund you the cost of the parts within 30 days.

Testing days & noise levels

Testing days at the Castle Combe circuit fall into three noise levels

Track Day 100db (A) at 4,500 revs

Silenced Test 105db(A) at ¾ max revs

Pre Race Test 108 db(A) at ¾ max revs

Check the Cadstle Combe Circuit website for the full details - Testing at Castle Combe Circuit.

Other circuit’s noise limits will vary. The majority do run to a limit of some value.

Supplementary noise reducing systems - made to spec

Noisier testing days tent to be less frequent and more expensive. For regular noisier testing it may be worth manufacturing a supplementary system, perhaps fitted across the back bumper so that the car can be put through a wider range of test days. The cost of a supplementary system may even outweigh the cost of the noisier circuit testing fees longer term. Building a system such as this is a bespoke job and therefore it is hard to describe how it would work for your car and what parts would be required. Contact us on 01249 782101 and we would be glad to help you design and manufacture a system to suit your needs.

Archived in: Muffler

18th April 2023

Related products