R34 GTT Auto High Revs 'Mystery Noise'

[MikeR34GTT]

R34 GTT Auto High Revs 'Mystery Noise'

Hello experts,

I'm experiencing a very strange problem with my R34 GTT (Auto Tiptronic) at high-revs as I change between gears, usually between 3 & 4 but can't say for sure (I've not driven it for quite some time as the water pump has gone and I'm waiting on parts as it'll be a full 100k service anyway so I cant say for sure).

Basically, If i plant it, I hear a unique "BRRRRRRT" sound between some gear changes and sounds like its coming from underneath the car (the A/T?) and is usually followed a puff of black smoke out the back of the exhaust, like its delayed that fraction of a second and the exhaust gases have backed up. I know she's running a bit rich, it's mostly stock but this is something that I really noticed after I had most the stock exhaust system replaced (X-Force 3.5 Catback, Venom 5" Cat - yet to fit a dump to complete the system).

My gears change just fine under normal load/cruisey driving, I dont have any issues or lag between changes, and I dont often flog it as its a daily driver (only every now and then to clear out the crap and whenever there is some p-plater pleb in a commy at the lights trying to get a rise out of me).

As I'm at 197,000k's (and just done a water pump), I'm conducting half the 100k service myself for the minor things such as oil & fluids, filters, radiator flush and my local mechanic will do the water pump, timing belt, seals etc - would it be worthwhile having it booked in to have the A/T serviced or is this issue cause by opening up the exhaust a bit.

Any light anyone could shed would be fantastic - it's not overly problematic, but it can be quite embarrassing really.

Cheers!

Mike

[GTSBoy]

This is usually an exhaust heat shield.

[MikeR34GTT]

2 hours ago, GTSBoy said:

This is usually an exhaust heat shield.

There was one on the stock cat, but nothing on the Venom now - do you recommend having a shop custom make one for my cat (or an area of the exhaust as you say?).

Also, from your recommendation and putting down to an exhaust heat shield, whats happening down there to make it cause that noise?

[GTSBoy]

It's usually that one is loose in some way and buzzes when the harmonics are right.  Low revs, mid revs, high revs, whatever it takes to get it buzzing.  If you don't have any heat shields down on the exhaust, then it won't be one of them.  It might be one on the manifold or turbo.  Or it could be the exhaust touching something, like at the mount on the gearbox crossmember.

Or it might not be the exhaust.  It could be the tranny.  In which case........manual conversion time.  It's the only way to be sure.