GT6 Exhaust

[Ian Foster]

I currently have the exhaust system off my GT6 Mk2 after an engine out clutch change.

My current exhaust is a bitsa, comprising a standard mild steel downpipe, a mild steel Mk3 centre box (chopped at the rear end) and a stainless wheelbarrow rear section. It sounds good and is not at all boomy, so the combination is actually working well.

A stainless 6-3-1 manifold is a future project, either waiting for someone to offer a good one commercially or for retirement and development of sufficient skills, equipment and energy to fabricate my own (could be a long shot that one !).

As a stopgap I would like to replace the existing downpipe with a new stainless item, as it has multiple crush bends which would appear to be an unnecessary restriction. The systems on offer from the usual culprits also seem to have even worse crush bends, so I’m considering getting something made from mandrel bent tube, which should hopefully be a relatively straightforward job for an exhaust fabricator, with the existing one to copy. Jetex make a round ‘bomb’ type silencer which is similar to the original centre box but is a straight item, which would fit nicely between the rolled edges of my chassis and plug straight into the rear section.

However, looking at the way the existing down pipe fits, it is apparent that the rear of the section which finishes just in front of the small cross member, is not on the centreline of the chassis (photo attached). The front pipe of my existing middle section has an offset kink which would appear to bring the centre section onto the centreline, but it is a bit close to the chassis at the join. Is this the standard set-up and if so why would this have been done? If I'm having something fabricated I can get it altered so it comes on centre (about 18mm towards centreline).

Could anyone with access to the underside of a GT6 Mk3 have a look at this area and let me know what theirs looks like.

Cheers

Ian F

[NonMember]

I think my GT6's exhaust is centred at that point but I've not crawled under to look for a while. They're not exactly a precision manufactured part and some fettling is often required. The flange studs allow a small amount of adjustment - should be enough to get that centred, I'd have thought. That's not true of the tubular manifolds, of course, which is why the one on my Spitfire got attacked with a big pipe bender when I fitted it.

[Colin Lindsay]

Mine is off-centre but not enough to touch the chassis. If you're concerned you can always fit a chassis bracket to straighten it.

[dave.vitesse]

I agree with both Colin and Robs comments. The other area that could cause the exhaust to be off centre is if the engine is not correctly mounted/aligned. This may have happened during the clutch change. The engine and gearbox may requires centring. Of course the pipe may have been wrong in the first place and the clutch change has highlight this.

Dave

[Pete Lewis]

yes if the mounts are shot nothing aligns,

one idea .   if the mounts are ok you could add a packer to lift one side a little thats  not easy with the Vee formation but a washer cut into a C will slide under the loosend  stud  as a trial.

pete

[dave.vitesse]

Pete, My memory may be playing tricks but the mount brackets on the engine are slotted to allow movement so you can centre the engine. As is the gearbox mounting plate.

The shims are to get the engine height right.  

Dave

[Pete Lewis]

Dave  youre lucky youve got a memory ,     mine keeps escaping .

pete

[Ian Foster]

Hi Guys

Thanks for the input so far and a Happy New Year to all.

The engine has gone back in as it was previously, using the same good condition mounts and same spacers.The front engine mounts would have to move significantly to move the pipe laterally by 3/4" and there is no lateral movement possible at the rear mount which is a bit of a special for the J type  O/D. The engine and box slotted back into position very easily, so I'm thinking the down pipe must have always been like this which would seem to explain why the front pipe of the centre section has a kink. The down pipe is actually a pattern part dating from circa 1980s, when you could still go into Thicktwit and get GT6 bits. The flange connection only allows very slight rotational movement.

Perhaps this kink 'feature' is to allow access to the overdrive pump/filter.

As I am intending to have a new downpipe made as per the above,  I have the option to get it onto the centreline and will probably pursue this course, based on my current geometry.

Ian F

[Colin Lindsay]

I doubt very much if the engine is off-line, certainly not enough to change the angle of the exhaust. It's probably just the angle of the downpipe / front pipe. By the time the tail pipe goes on there's enough flex / bend in the long centre pipe to straighten it back again for the rear box. Mine is on the Phoenix manifold system and has never moved any further than the day it was fitted (coming up on 18 years now!)