Howling at 2k RPM

[TVRCHIM400]

Hi All,

Just a quick one to see if anyone has noticed what can only be described as a howling exhaust note at 2000 RPM. Its present on my Chimaera 400 which is a stock car. The noise is present if I hold the RPM at 2k and dip the clutch which hopefully eliminates a transmission / diff issue. All the oils have been recently changed and no major issues where reported during the service.

I am thinking that this is just a characteristic of the vehicle and the exhaust note at this RPM, I was just wondering if anyone else had noticed it and if they had managed to come up with a remedy.

If I increased the RPM to over 2300 in any gear the noise disappears however it just so happens that in 5th gear at 2k RPM road speed is 60mph so I tend to sit with the howling noise most of the time which if I am honest is starting to give me a bit of a headache.

Hopefully someone has the answer or at least experiences the same thing to put my mind at ease this is something I ll have to live with,

Thanks all

[Classic Chim]

Sounds like you have a decatted Y piece and or de baffled exhaust.
Both are known to cause a droning noise at certain revs.
What is your set up?

[TVRCHIM400]

As far as I am aware the exhaust is completly stock, its a good shout though and wouldn't take much to take the y peice of to investigate. I am assuming I there is a honeycomb type arrangement in the y peice which would be missing or badly knocked through.

[Classic Chim]

Very early cars so registered before 94 come non Catted as standard and have a different manifold / y piece arrangement and should not boom or drone.

Many later cars that come with what’s sometimes referred to as the dustbin Y piece and yes inside that dustbin contains a big cat.
Some people cut open this dustbin section and remove the cat or far more favourably replace the Y piece for a shiny stainless one which is designed more like the earlier Y piece with a narrow section where the cat would normally sit.
This offers slightly less back pressure so more power 5-10 hp max.
The downside is it can often create a resonance or set of frequencies that result in a very poor sound at the revs you mention.
The answer is usually to drive faster or put a Catted Y back on.
Can you post a picture of your Y piece.

[TVRCHIM400]

All good info, thanks, I ll post a photo shortly

[TVRCHIM400]

[Belle427]

May be unrelated to the exhaust.
Not something like the alternator or belt is it?
Belt can be removed to test if required.

[TVRCHIM400]

I ll take the y piece off next week and do some investigation but if that looks stock I ll try the belt suggestion for sure

[Jordie Barretts sock]

No need to take that off. If it's been decatted it will have to have been cut open and rewelded. Clearly it hasn't. There is no way to remove the cat without cutting it open.

[TVRCHIM400]

Fair point, I ll inspect it more closely in the daylight and look for any signs that it's been played with, do you have to cut open to take pre cats out as well?

[Jordie Barretts sock]

No, they're in the manifolds. I took mine out and all it did was make the exhaust a bit louder. And the under bonnet temps are less.

My guess is the centre box under the car has been opened and 'emptied' rather than sleeved. Sleeving it moves the noise behind the car, emptying the Bix would make it quite 'boomy' I'd think.

[TVRCHIM400]

The more I think about it Belle's suggestion of the belt or one of the auxiliaries running on it having a failed bearing does make complete sense

[Belle427]

Mine had an unusual howl at idle once, took me ages to find it but it was coming through the air filter for some reason and related to the induction noise?
Weird but vanished on its own.

[Classic Chim]

Check your tensioner pulley and water pump bearings run free.
In your photo your Y piece appears to have some wadding where the r/h exhaust clamp resides. What exactly is going on there?
You appear to have a Catted Y so the noise is not that going by the picture.
If you are not mechanically savvy your best bet is to get a known respected Tvr mechanic to take a look.

[TVRCHIM400]

Thanks Classic Chim, I am going to check all those today and maybe just find the fault. I would expect however if a bearing had failed you would hear a noise all the time and not just a specific rev range. I am pretty savvy when it comes to mechanics, one of the main reasons for the thread was to see if this was more a characteristic of the vehicle before I delved in but it seems not and there is an issue somewhere.

[Classic Chim]

What’s that wadding by the exhaust clamp?
For your information the manifolds to Y piece are a face to face fit ( no gasket ) and need to be lined up correctly for clamp to draw them tightly together.
This can only be done one of two ways.
Loosen manifold bolts in the heads until they are loose enough to manipulate Y piece and manifolds together then re tighten heads bolts or use a ratchet strap to draw manifolds together then clamp them.
Your r/h clamp has a new nut and from the position of that nut it suggests it’s not tight enough and that suggests that side manifold is not necessarily lining up with the Y piece mating surface.
I can tell you from experience you won’t draw them together using clamp strength alone if they are not lined up. This is where the ratchet strap should help.
If that wadding is interfering with this clamp it will never seal properly imho

Edited by Classic Chim on Sunday 15th January 09:50

[Jordie Barretts sock]

Agree. But that will give a ticking at best, a woofly blow at worst.

[TVRCHIM400]

The wadding is in place purely to stop a slight leak. As you say the clamps are no way near strong enough to draw the manifold and y piece together and knowing how much of an arse it is to slacken the manifold bolts to achieve a good fit I ve left it alone. Knowing that the noise was present before I meddled I ve eliminated this as being the cause. Ratchet strap is a good idea and may give that a go at some point, thanks

[Classic Chim]

Jordie Barretts sock said:

Agree. But that will give a ticking at best, a woofly blow at worst.

True and howling does support the idea of an air leak somewhere.

O/P is this howling present in every gear at those revs and can you hear it when cars stationary?
Is the noise in front of you or sort of in the cabin. At those revs in 4th gear at a constant speed if you manipulate the throttle position does the pitch change or is it a constant noise until revs have changed.

I’d still want to sort that clamp out sooner rather than later though as fumes and black filth will spill allover the engine bay eventually.

Is the car generally very loud?
It’s looks like your car is Catted so if it has a standard exhaust it won’t be overly loud.
If the exhaust is sleeved it will be very loud at all times.
So assuming your exhaust is also standard I’m also leaning towards some other issue rather than it being because the exhaust system has been tampered with which is usually why booming as I tend to call it can create a resonance at certain revs within the car.

[ChrisW500]

I had exactly the same issue on my 400 as mentioned it was the tensioner pulley… easiest test is get hold of a rod stethoscope and have listen to the bearings on it and the water pump and alternator easy to do they are cheap to acquire and eliminates this without pulling stuff off
I did the tensioner and did the alternator clutched pulley mod at the same time!