Making a Bypass Valve Silencer

by Bryn Owen - E-mail myself or Doug with any corrections or additional info and we’ll keep it up to date.

If you have a bypass valve fitted to your Turbo Elan and find the ‘hissing’ on lifting the throttle is getting to you – there is an inexpensive way to reduce this to a more tolerable level – make your own bypass valve silencer!

The procedure detailed below describes the materials I used to do this one wet afternoon, using stuff I already had kicking around my garage. I am sure with a little more thought it would be possible to achieve a more professional construction, but the basic design here works fine and silences the valve to the extent that it is not intrusive, but you can still hear it working, giving you that reassurance that the valve is doing it’s job.

The procedure describes fitment to a standard HKS bypass valve when fitted to Bills Isuzuperformance intake pipe, the dimensions may need to be varied slightly if you are using an alternative set up.

Parts you will need:

Canister - for the body of the silencer, I used a discarded spray can approx. 140 mm in height & 60 mm in diameter. Once the painted label had been removed from the outside it left a nice stainless steel finish. Ideally you need to find a canister which has a metal ring on top roughly the same diameter as the plastic tubing (see diagram below).

You will see what I mean if you take a look at a few paint cans.

Plastic tubing – standard grey plumbing stock which is approx. 22 mm diameter; you need approx. 18 cm length of this.

Heater hose – standard diameter of approx. 24 mm used for automotive water hosing, available by the length from Halfords or any motor factor. You will need approx. 30 cm of this.

Drill bit – approx 5 mm diameter.

Hose clips – approx 24 mm diameter, 2 needed.

Long zip ties – x2.

How it goes together:

Punch a hole out of the top of the canister to the same size as the plastic tubing. If you managed to find a canister with a metal ring the same diameter as the tubing, it makes this an easy task.

Cut the plastic tubing to the same length as the canister plus approx. 4 cm.

Check that the tubing will fit into the hole of the canister, ideally this should be a very tight fit (so don’t push it right in yet!).

Drill a series of holes in the plastic pipe, the number of holes you drill here should be roughly equal to the total diameter of the plastic tubing (this avoids the silencer being restrictive in any way).

Drill a series of holes in the bottom of the canister, around the edge, avoiding the central 30 mm of the canister.

Push the tube into the canister and ensure it is butted firmly against the bottom of the canister (this is important, so the air is forced out through the drilled holes rather than the bottom of the tubing). If it is not a tight enough friction fit to stay in place, you can use some ‘chemical metal’ to secure the pipe where it exits at the top of the canister.

Fit your 30 cm length of heater hose to the plastic pipe and secure with hose clip or zip tie.

Push the silencer down to the right of the engine, it should sit somewhere just above the gear box, almost out of site.

Attach the other end of the hose to the bypass valve with a hose clip or zip tie.

Then strap the canister loosely with a zip tie to wherever you can. I used a bracket which sits conveniently on top of the gearbox for this.

Voila, you have silenced your bypass valve, so go for a spin and be amazed at the lack of sound from the valve.

Post script:

It should be possible to silence the valve further if you wish by drilling smaller holes in the pipe and canister. I opted to drill holes which gave approx. same overall volume as the valve outlet to avoid creating any backpressure which I figured may blow the silencer apart.    

Any queries, do drop me a note at bowen@wwwits.com