MGB V8 - Twin pipe exhaust system

I was very disappointed with the previous exhaust on this car - it was an aftermarket sports system and completely the wrong shape - it sat about an inch from the ground.

My rear suspension modifications have made room for twin silencers mounted where the leaf springs used to be, so the twin pipe exhaust system on this car is custom.

I have fitted flexible joints after the manifolds to allow the exhaust system to be softly mounted without risking fatigue of my newly made manifolds. The pipe diameter is 50mm which is perhaps a little excessive.

The oval silencers in the photograph were part of the mark 1 design which was revised following the rear suspension changes.

Having replaced the leaf springs with 4-link rear suspension I have room for twin silencers at the rear of the car. This required centralising the fuel tank by moving it about 3 inches to the left.

The photograph shows a section cut out of the boot floor and welded in 3 inches inboard to place the filler neck in the right place. The stainless steel fuel filler pipe is new I'm hopeful that the angle isn't too shallow.

Messing around with an acoustic model proved that the best place for the silencers is at the back of the car (where everyone else has been putting them for years). This is mostly because the gasses are colder at the back of the car so the speed of sound is lower, and the silencer can be shorter.

The silencer in the photograph is a mock-up made from cardboard just to make sure everything fits. I'm not going to fit the centre silencers but will leave package space just in case the car is too noisy without them.

The exhaust in one of many trial fit sessions. All of the pipes are in place (held together by masking tape), and just need slight adjustments prior to welding.

I've added a balance pipe right at the front of the exhaust system under the gearbox. These are said to increase power, and also have advantages in noise reduction.

The twin silencers really add to the appearance of the car.

The silencers were assembled from two half skins, two end pieces, and a perforated tube. I decided to make my own silencers as I wanted to offset the pipe as it entered the silencer to improve ground clearance. The standard MGB silencers were too long and didn't really have enough volume.

The photograph shows stainless steel wire wool wrapped around the perforated pipe to prevent the e-glass from blowing out.

Stuffing the silencers with e-glass is great fun. I did manage to get the end plates on without leaving too much sticking out. E-glass will help reduce the high frequency noise in the silencer. I think the e-glass has blown out of my MGA silencer as it's sounding very roarty.

Once the end plate is welded on I'll be able to move on to the exhaust mountings.

The mid exhaust mounting is very much the same as MG's effort. I wanted a very stiff mounting so that I could mininise exhaust movement, and hence the clearance between the exhaust and the car.

I've been trying to use MGB parts where possible throughout the car as parts availability is, and should continue to be, very good for the MGB.

There wasn't a great deal of space at the rear of the car for the exhaust mountings. Having spent several weeks wondering how to mount the rear of the exhaust I ended up using the rear spring hanger and bushes.

The exhaust will get longer when hot due to heat expansion, so the lower fastening of this mounting is a sleeved bolt that will allow the connection to pivot to take up the movement.

The completed exhaust in place. I'm quite pleased that the whole exhaust from the engine to the back of the car is completely custom and built to my own design.

I'm an automotive acoustics engineer by training, and have done some predictive design work to make a low back pressure exhaust that sounds nice but is quiet enough not to be embarrassing or annoying when cruising. Having said that, if it's too noisy I still have space for the oval silencers under the floor.

The whole exhaust was made in one piece. There seems to be enough flexibility in the flexible joints to allow fitting and removal on the manifold joints.

I'm pretty pleased with the exhausts. They really add a sense of purpose to the rear of the car without being too outlandish.

The exhausts seem fairly quiet on the road with no obvious booms, however there is a constant low frequency throbbing within the cabin which I'm reluctant to put down to intake noise. Maybe my exhaust mountings are just a little too stiff. I'll do some development and update this page when I find out more.

Above 2000rpm engine noise is nicely balanced and has a very nice V8 character. The engine sounds much more like a V8 now than before the modifications. I guess a lot of that will be due to the twin exhaust system.