Got the GT6 back together this afternoon after replacing the manifold gaskets. However it's still pinking and making a noise under load. I'm pretty sure the noise is coming from under the bonnet rather than the exhaust system and it seems to be associated with the pinking,.
I did do a compression test while I had the manifolds off as I was a bit concerned that the noise could have been a blowing head gasket and I didn't want to have to take the manifolds off again if it turned out top be the head. Obviously as the car was apart the engine was stone cold when I did this so there was quite a lot of variation in readings, however none were really low so I carried on and put the manifolds back on. Anyway now the car is together I've done a hot compression test and it looks ago to me, readings are:-
There is less than 10% difference between highest and lowest which is within tolerance. Readings look pretty high but that could just be the gauge, the cheaper gauges don't tend to be calibrated and accuracy in terms of actual pressure is debateable, but the important thing is there are no cylinders with considerably lower pressure or any big variation. For the hell of it I did squirt some oil down the plug holes of the cylinders with the lowest readings and they did improve (up to c270 psi so there may be a little wear in the rings/bores but nothing too serious.
The ignition timing is around 10 deg BTDC at idle tested with a strobe, this is about right but I will try retarding it slightly to see if that sorts the pinking. The rasping noise is a bit of a pain though as I can't find where it's coming from...
I thought the Engine had about 85,000 miles on it but checking the MOTs it looks like I've only done about 55,000 miles since I fitted it the Engine in 1993 so it's not a particularly high mileage unit so I'm hoping it doesn't have too much of a carbon build up as I know that can be a cause of pinking.
All my recent fill ups of fuel have been Shell V-Power so I don't think is a crap fuel issue.
I'll also give the carbs a tune.