The 3.2 in the Signum/ Vectra C is not the same as the Omega (hence Y & Z engine code)
The latter supposedly has less power, but with the 5 speed autobox, my Signum was quicker than my Omega - had both 3.2s for a while.
the Z32 has a precat in each of the manifolds that the Omega doesn't and it goes to a single pipe just after the manifolds with a 3rd cat
Coil packs are the same and have the same issues and same oil cooler and cam cover gasket problems.
It doesn't have the bagpipes and twin butterfly throttle body, just single butterfly and the multi ram is different - you can take the top off and have a proper look and clean inside
3.2 Signums all had 314mm diameter front brakes early Vectra Cs had 308s, and at some point they changed to 314mm but there is no definite point this happened.
The 3.2 has an option of the AF32 autobox and it has issues with the gearbox oil heat exchanger in the main radiator, the seals fail and water gets into the box which kills it, the only resolution is full core rebuild or new box - 7 years ago this was over £2k - mine was done under warranty - new boxes didn't exist then so now a decent box will be almost impossible to find
Even with the auto box it spins the front wheels really easily in the wet and understeers like nothing on earth - a set of Eibach springs made a huge difference to the handling and was the best thing I did to it
The dropped the 3.2 when the cars went full canbus, this happend very late in the prefacelift and can tell by buttons (part can) or scroll wheels (full can) steering wheel controls for the stereo - also headunits changed from NCDC to CD reference
My 3.2 was written off when a lorry drove into it so I replaced it with the Elite spec 2,8 V6 turbo Signum - basically the de-tuned VXR - this one has the bullet proof AF40 6 speed box - VXRs and the Elite spec cars come in manual and auto - its got full leather, colour sat nav, bluetooth phone, TPMS, electric windows all round, electric mirrors, factory fit parking sensors front and rear and duel circuit climate control amongst other things. Its a March 2006, but was forst registered 20th March 2006 so comes into the lower RFL band, the same as the Omega, not the £500+ band
They NEVER made a Signum VXR so anyone selling one is talking balls.
They never made a prefacelift 2.8 turbo in either Signum or Vectra C
The VXRs were 250 and later 280bhp, Elite spec Signums and Vectra Cs were 230 and 250bhp. The only difference in early cars was the engine map, later cars (250 & 280bhp cars) had a different cam profile and air box, but its the same basic block on all.
My 2.8 Signum is much much quicker than the 3.2 and thanks to a simple Superchips Bluefin semi custom re-map, its pushing near VXR power - with non switchable TC/ ESP and auto box its almost impossible to RR for exact figures, but, even with the auto box it will do 60 in under 6 seconds and give 330 BMWs a run for their money in a straight line!
It spins the fronts in the wet but with OEM 18" wheels the handling is better, due to snapped springs its got Eibachs again on the rear but haven't got round to changing the fronts or all the powerflex bushes.
I've had it for 5 years and was using it as a daily driver, but its now time so my Signum is going up for sale, only looking at £1500-1600 for it with loads of spare parts, as with the Omega it isn't getting used so off it goes. A lot of car for not much money
If you want a diesel, bin off the Vauxhall option and get a late Alfa 156 16v JTD multijet- same 150 brake Fiat engine, BUT doesn't have the crappy M32 6 speed box, doesn't have a DPF and oddly doesn't have the problematic swirl flaps. Just be warned, the 156 was also available as a 16v 140 brake 5 speed - avoid this at all costs