Droaning noise with sports manifold

[engineman]

Following a recent total rebuild of my engine and the fitment of a pair of stainless 4-branch manifolds and I am experiencing a loud droaning noise from the exhaust system at 25-30mph at low engine revs, before the refurbishment the car did not emit this noise with the standard exhaust manifold and Holley Carburettor. I have spoken to Mick at EJ Ward on this subject, he also experienced a similar problem with his car which he overcame with the fitment of a bespoke exhaust system made by a company in Nuneaton. I have spoken to this company and they have quoted me a price of approximately £600, ouch!! I have experimented trying to change the back pressure in the system by drilling holes in various places in the exhaust system with no effect.

I am trying to find a cheap solution, has anybody experienced this problem and what did they do to overcome it??

[GDPR]

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Welcome to our happy fold

My guess is that it's not a back pressure problem but one of resonance - the exhaust is vibrating at a given frequency, possibly down to the exhaust being under some form of tension due to poor alignment, or it is touching as it goes through the rear subframe and those awful mounts.....

Pipe resonance can sometimes be killed by sticking exhaust clamps in random places along the pipes - this alters it's natural resonant frequency and moves it hopefully to a range that you can't hear.

Russ:dude:

[V Mad]

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I think Russ is on the right track.

If you get someone to rev it at standstill until the vibration comes in, then hold a screwdriver onto the pipes at various positions-you may be able to feel where the vibration is worst?

The original cast manifold is more rigid, compared to the tubular ones, so I would also trysome extra clamping at the front near the manifold.

[stagmuffin]

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hi had this many years back with an early stag i fitted tubular headers to, and cured it with exhaust bandage wrap killed two birds with one stone .it made the system more efficient by encouraging scavengiing and reducing heat loss into engine bay.lots of suppliers out there but prices vary so you need to shop around...........steve.

[StagnJag]

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Some (most?) Tubular manifolds pass really close to the steering column. It could be touching there with the engine running.

Dave

[mjheathcote]

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Resonance I am sure will be the problem.

I have heard that clearance is tight with the Phoenix manifolds against the steering shaft, maybe the noise is contact with the shaft which then transmits the sound straight into the cabin?

[mjheathcote]

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StagnJag wrote:

Some (most?) Tubular manifolds pass really close to the steering column. It could be touching there with the engine running.

Dave

You thought about that at the same time as me don't you:P

[StagnJag]

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mjheathcote wrote:

StagnJag wrote:

Some (most?) Tubular manifolds pass really close to the steering column. It could be touching there with the engine running.

Dave

You thought about that at the same time as me don't you:P

Yup!

This would probably be felt through the steering wheel if this is the problem.

Dave

[Kevin Garrod]

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Have you seen this thread?

http://stagownersclub.mywowbb.com/vi...uling+steering

[engineman]

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Steve, thanks for the info, I have fitted heat wrapping on the manifold, I will try some clamps on the exhaust pipe as a next step.



peter

[engineman]

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Russ, thanks for the idea of clamps on the exhaust pipe, I will trysome, I will also check again thatthe pipes are not knocking againstanything.



Peter

[engineman]

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I notice that you seem to have a modified Engine , what carburetta do you have fitted and does your air filter touch the bonnet insulating pad ??

[GDPR]

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Sorry Peter - who was that directed to?

[Kevin Garrod]

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I'm assuming it's me?

It's a Weber and the low rider filter clears the bonnet OK, same with a Holley.

[engineman]

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Kevin,

I have a Holley 4150 fitted to my Stag , the Holley is fitted to the inlet manifold via an adaptor plate and an additional 7 degree wedge, a shallow Edelbrock Air Filter is fitted, the air filter touches the bonnet insulating pad, the overall height of the Edelbroch is about 2 inches, I am interested to know why you should have a small clearance between the pad and filter and I do not? I have recently fitted new engine mountings maybe my engine sits higher than yours? I notice that Monarch stags sell an adaptor assembly that has been machined to have the 7 degree tilt incorporated into the design, maybe the overall height of the adaptor is smaller and would allow the Holley and air filter to sit lower?

I may have to purchase the Low Rider air filter does it have a provision for the Camshaft cover air breather pipe to connect to it ?

Regards

Peter