Recently bottomed out my Z on a stupidly high speed hump and grounded the mid section of the exhaust. Now (especially when cold) it's making a loud rattling sound when revving.

 

Took it down my local Quick Fit(!) just to get it up on the ramps and have a look. No external damage visible, but if you bang the pipes, something metallic is definitely loose in there!

 

Anyone got any ideas what may have broken in the pipe to cause this and as a result, are there any performance or maintenance worries to consider? It seems to be running fine but it just sounds like a dog!

 

On the same subject, I was considering having the car decatted. However, it's a UK '93 vehicle and I've read somewhere that you can only decat pre August '92 cars (something to do with the MOT and emmissions??)

 

Any help appreciated guys... :confused:

Could be some heat sheild which you could have losend, or the middle silencer is broken or even some part of the cat is lose.

 

As for decatting there are pros and cons.

 

You cant legally decat a post 92K reg car if the original spec has them on. If you have a pre K reg 92 car you are legally allowed to remove the stock spec cats.

Removing the cats doesnt help the immissonions but you should still be able to pass it without them. How ever if the MOT centre notices you have gutted your cats on a post 92 you will fail regardless of whether your immissions are OK. On the other hand I only know of 2 people who have failed for gutting the cats.

 

For performance, your turbos will spool up quicker which means the power will come earlier. I noticed that the engine reved better and smoother. It also makes your car sound slighly louder and deeper. The theory also says that your car should get slightly better MPG. LOL, yeah right, but you may notice a slight improvment on longer runs.

 

On the downside gutting your cats puts more stress on your turbo seals because of the increased pressure when you let off the accelerator. Having your turbo seals leak means you will get oil dripping from your turbos into your exhaust. Not to much of a problem but will cause puffs of blue smoke every now and then, usually when you first start up in the morning. The leak will get worse and worse. Apparently the kit to stop them turbos leaking costs £40-50, but to have a mechanic do it for you will cost £400-£500 as it means turbos out.

I have had my down pipe decatted and I have had no problems. If you turbos are young enough and good condtion you will probably no no problems yourself. If you turbos are already leaking slightly, decatting will accelerate the problem.

 

Just giving you the facts.

 

Stuart

Thanks for that Stu.

 

The current turbos are stock and have done 75,000 miles so I'm a bit nervous about going the decat route. The car technically failed on emmissions at last year's MOT, but as it was borderline it was let through... I've since put a bottle of STP Complete Fuel System Cleaner through the system. Next MOT is at the end of this month :( so we'll see what the latest is.

 

BTW has anyone heard of an MOT failure due to (slightly ;)) warped front disks. Visually they look fine. Due to change them soon for APs, but wanted the MOT out of the way first...

 

Cheerz

 

Steve

No as long a the brakes brake hard enough you wont fail. They cant test for warped discs anyway unless they take it on the road which they dont ;)

 

There are also tricks to pass the immissions test too. :D

1 - removing the cats has nothing to do with the MOT test (whether its legal or not is another matter) as long as it passes the emmisions test.

 

2 - the 300zx is not in the emmisions database, so unless its an 8/95> car its tested as a non-cat vehicle anyway

 

3 - excessivly warped discs is a failure & will show up on the brake roller test as the needles fluctuating.

 

& 4 - yes, i am an MOT tester :D