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[Jobbie]

Hi guys

I moved years ago to a country that has extremely restrictive import rules of vehicles with engine capacity exceeding 2000cc way back since the 80's, so most cars since then have always been imported with the smaller engines, and rarely would you see an large engine vehicle here. Infact, most manufacturers exclusively built engines for these markets with smaller capacities, such as BMW/Volvo etc)

Since the late 90's however, the engine modding/reboring market was born, haha! For example, the BMW 520i engine was bored and rebuilt frequently to the spec of the 530i, or the Volvo (2.0T) 5 pot engine was rebuild to the higher 2.5T spec etc. As the parts are modular and simply requires a wider boar and aftermarket engine sleeves. So its all been extremely fun. (FYI this market has slowed considerably since the advent of really powerful sub-2.0 litre 4 pot engines on the market these days.)

Anyway, the only problem is, I have never seen this done to the Omega V6 engine. Its rare to find the 2.5 V6 but it does crop up now and then. I just checked the market and ZERO 3.0 / 3.2's exist. If it does, I've never seen it.

From my basic research, the 2.5 / 3.0 or the 2.6 / 3.2 is a modular engine.  Just different bore/stroke. My question is this, can anyone, in theory at least, tell me any problems that I may face? As it seems pretty straight forward.

[Jobbie]

Sorry, I forgot to mention, you can NOT swap in another engine into the vehicle. So buying a 3.0 / 3.2 and dropping it in is out of the question. The engine code MUST match the one originally sold in the vehicle. These are the rules and is checked yearly come inspection time. Human nature is a funny thing though, and we love to figure out ways around things. 

[Doctor Gollum]

2.5 it is then... Not much to be done as the bores are cast as part of the block

[Jobbie]

2.5 it is then... Not much to be done as the bores are cast as part of the block

But with all the correct components sourced, can an engine rebuilder not thin/widen out the block to increase the capacity? I mean there is a specialist market here for just these things. I have approached many of them and none of them have worked on the Omega V6 sadly, but they all said if it is modular, then it can be done with ease.

[Diamond Black Geezer]

You could (I think) take a crankshaft from the 3.2 and turn the 2.5 into a 2.7(ish) That's a relatively simple (massive stretch of the meaning of the word 'simple') way of increasing engine displacement.

Personally I thought the 2.5s and 3.0s were the same block, just with more bored out - which would I suppose technically make the 'smaller' engine 2.5 actually heavier than the 3.0 - but someone will be along in a sec to prove me wrong as I say I only assume this, I have no personal experience of comparing blocks. If Dr Gollum says not I'd be inclined to agree 

check out the wiki page https://en.wikipedia.org/wiki/General_Motors_54%C2%B0_V6_engine for info regarding bore and strokes of each respective engine.

[Doctor Gollum]

It's possible that whist they are externally the same size, the blocks might be more lightly cast, which would be bad for boring...

That said, the 3.2 crank is forged which is good, also fitting  a set of G cams and porting it along with a 3.0 ecu (chipable too) then you might see some useful gains without actually machining the block

[Doctor Gollum]

From a UK perspective it is easiest to drop a 3.2 lump in, but thanks to the Vectra B there is plenty of scope for the 2.5...

[Jobbie]

It's possible that whist they are externally the same size, the blocks might be more lightly cast, which would be bad for boring...

That said, the 3.2 crank is forged which is good, also fitting  a set of G cams and porting it along with a 3.0 ecu (chipable too) then you might see some useful gains without actually machining the block

This is all sounding very sexy indeed! You mention G cams, are these by any chance the same ones used by MSD? Another source says they are simply the stock 3.0 cams:

https://www.pressreader.com/australia/performance-vauxhall/20180801/281543701774503

Out of curiosity, what about the stock conrods?

You guys don't know how excited I am right about now. A facelift 2.5 V6 just popped up with 168,000km for sale by the second owner. It looks to be in mint condition with the sunroof too! (rare option here) !!

[Doctor Gollum]

Others more knowledgeable should be able to help with the more detailed things tuning was never really my 'thing', all my proper Omegas had the 3.2

I believe there is/was a member here who had a part in the MSD Vectra B

As far as the ecu side of things goes you need the ecu, transponder ring and key chip in order to swap the ecu for a 3.0 one if you can get the donor car pass as well, then that makes life a bit easier re programming extra chips for any replacement keys.

[Diamond Black Geezer]

If you delve into the development of the Vectra GSi/Supertouring they made some high lift cams in development (Courtenay? maybe) but it was then discovered that the 3.0 cams were an almost exact match, so 'off the shelf' parts were used instead. Its a fallacy that they used a different map, people have swapped standard 2.5s with 'MSD' ECUs and looked over them with compooters and they're identical - although they even claimed it in the Vectra brochure! (Isuspect because they didnt want to admit that the ONLY difference between the standard rep's car and the 'specialist' racing engine, developed by a racing team, consisted of.....a bloke in Liverpool picking a camshaft off a different shelf. 

[Jobbie]

If you delve into the development of the Vectra GSi/Supertouring they made some high lift cams in development (Courtenay? maybe) but it was then discovered that the 3.0 cams were an almost exact match, so 'off the shelf' parts were used instead. Its a fallacy that they used a different map, people have swapped standard 2.5s with 'MSD' ECUs and looked over them with compooters and they're identical - although they even claimed it in the Vectra brochure! (Isuspect because they didnt want to admit that the ONLY difference between the standard rep's car and the 'specialist' racing engine, developed by a racing team, consisted of.....a bloke in Liverpool picking a camshaft off a different shelf. 

Hahaha! This is golden! Only in Britain! You just gotta' love it!

So a stock 2.5 simply using the 3.0 cams will bump up 25bhp? Lovely! If this is the case, why is this not a more common mod? I mean almost 200bhp from a cam swap is surely desirable. Little disappointed at GM for not making this the standard setup to begin with, thus putting it on par with the BMW 525i which it would have competed directly against back in its day.

[Nick W]

Hahaha! This is golden! Only in Britain! You just gotta' love it!

So a stock 2.5 simply using the 3.0 cams will bump up 25bhp? Lovely! If this is the case, why is this not a more common mod? I mean almost 200bhp from a cam swap is surely desirable. Little disappointed at GM for not making this the standard setup to begin with, thus putting it on par with the BMW 525i which it would have competed directly against back in its day.

it was quite common. But it required stripping the cams from a 3.0l, and if you had one of those it was better to fit the entire engine for an even bigger increase in power and especially torque with no downsides.

[Doctor Gollum]

What would the tax increase for fitting a larger engine vs the cost of rebuilding the existing one?

[Diamond Black Geezer]

Just to answer your point about the power increase it is something like 25PS as you say, however the X--XE V6s were designed for several things - broad torque, to replace the venerable CIH straight6s, economy (I know, doesnt feel that way but they were) and to suit both FWD and RWD applications.

Variable intake manifold helped the torque curve being nice and flat, economy -  managed 40mpg if you sit in top gear at 50ish mph, so pretty good all round, and the unusual 54degree angle of the vees made for a more compact package, it first appeared in the Calibra and Cav. However, everything's a compromise - 170bhp for a 2.5 wasn't much - the legendary 2.0 XE ran 150bhp - replaced with a version that had 136bhp! Vauxhall were directing their engines and engineers towards tree-hugging in the 90s.

I also suspect that a car range featuring a 2.5 with 195bhp, and a 3.0 with 204bhp....may have made buyers squint a bit...and wonder why they should pay more for the 3.0 with as little as NINE bhp...from 500cc more!? Very odd!

1. - Anyone will tell you the 2.5 and 3.0 is 'incomparable' in terms of power/how they feel, so I'm not saying that the 3.0 was pointless, but that this leads us onto the dark world of...
2. - Actual power outputs. So the Cav/Calibra and Omega both have the same engine... except the Omega has a far superior twin port intake system, versus the single butterfly of the former cars (smaller = fits under the Calibra's lower bonnet).. also a different and easier-breathing intake. Now how can they both claim identical power outputs? Like I say, dark world, and no-one's ever come up with an answer.

That's enough for now, off to the shop! 

[biggriffin]

Get a set of G cams, a pair of 3.2 manifolds,  fit 3.0 chip, later 3.0 long plenum,.

 As for msd, supertouring was all done in Milton Keynes, basically lightened and balanced, G cams.  A tweked ecu, , no cat in the exhaust, and the cars were a bit lighter, due to being stripped out, a few more bhp was achieved using 99/100 fuel.