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[Diamond Black Geezer]

Lots has been spoken about taking various versions of the V6 but I've been looking at the internal dimensions and got wondering if it would be possible, by using the crankshaft and/or conrods from a 3-litre in a 2.5 (whichever alters the stroke) and making another 'Dr Frankenstein's Monster' of the 2.5 

Because...
X25XE = 81.6 mm bore  79.6 mm stroke
X30XE = 86 mm bore 85mm stroke
Y32SE = 87.5 mm bore 88mm stroke

The displacement would be increased from 2498cc to ...
3.0 crank/conrods = 2668cc
3.2 crank/conrods = 2762cc

for the purposes of this I'm asking no-one chip in with 'it's not worth it, just buy a 3-litre' etc, because I'm theorising, only. Certainly not the time or resources to do it!  Just a bit of engineering fun. The road of 'what can you swap between the V6s?' is a well-trodden one, It just occurred to me that I don't recall anyone mentioning this particular change. 

[Doctor Gollum]

Changing the crank is an effective way of 'stroking' an engine... A commonish mod on the Ford Cologne lump... Took the 2.8 to 3.7, with a useful increase in oomph.

Hypothetically, a 3.2 crank, in a 2.5 block with ported 2.6 heads, 3.2 manifolds, 3.0 injectors, throttle body, inlet and chipped 3.0 ecu with sports cats ought to shift...

Whether it would keep a manual 3.2 driven with no mechanical sympathy honest, or not, is anyone's guess...

[BazaJT]

Wasn't changing crank/rods the way they took the straight six 3l motor up to 3.6l for the LC?

[Nick W]

There's a load of other things you might need to consider before you create combinations that actually work: piston deck height, conrod length, compression heights, etc etc. The usual reason for doing this sort of job is to create combinations tailored to specific competition classes. So by fitting a shorter stoke crank in a big bore engine you could build a similar capacity engine that revs better - big bore means the potential for bigger valves and better topend breathing, combined with a shorter stroke crank that  is less likely to break at those revs. Some of the famous engine capacities are a result of such parts matching: 302 and 327 Chevys, 340 Mopars, 1293 Minis, 1700 Crossflows, 2.1 Pintos and 2.0l Avenger engines(both of which use the 2.8 Cologne V6 piston) etc etc.


The other thing to bear in mind for your X27XE(    ) engine is you need access to both the big and small engines to build one. It would need to be noticeably 'better' - different is probably more likely - than an X32XE to be worthwhile.

[omegod]

Pretty sure Daz combined a 3.0 bottom end with a 2.6 top end for some reason

[Diamond Black Geezer]

All interesting, and very helpful info, thanks, all.

Maybe some of this comes about from the 2.5 being 'tunable' whereas the 3.0/3.2 you can't fit the high-lift cams from the 'bigger engine' - because it already is the bigger engine, etc.  Actually, may I ask why do you say ported 2.6 heads, Gollum? As far as I was aware the 'Y' engines have a lower compression ratio, so to pop one of them on a 'X' engine would actually cut power a chunk. Not nitpicking, just curious 

Oh, and does anyone know whether it's crank and conrods, or just one, or the other to 'stroke' the engine, in this case? See to recall 3.0 cranks are 'stronger' though I'm not sure what the metallurgical difference is between 2.5 and 3.0? 

[Nick W]

Swapping the cams is done because it's reasonably good value for the increase.
You can buy aftermarket performance cams, but you'll easily spend ten times as much on them. Tuning modern engines is an expensive business for small gains.

[Diamond Black Geezer]

Found on a Vectra forum that the actual engine they benchtested and got the '195bhp' on ST200 and GSi was actually fitted with Piper cams (or was it Courtney, anyway) but the 3.litre Omega cams being about 99% the same were actually fitted on the production line, presumably meaning Vauxhall could simply dip into a parts bin, rather than purchase hundreds of specially-made cams from an independent company. Actual GSi / ST200s are menat to be 192bhp because of this. And then we get into that no two engines are the same anyway. Some might do 200bhp, some might do 180bhp and so on...

As you say, gets expensive for very little gains. Actually hence why I'm shopping in the GM parts bin, so to speak. Get in at the right person and the right time and the price advantages are obvious.

[JamesV6CDX]

Actually, may I ask why do you say ported 2.6 heads, Gollum? As far as I was aware the 'Y' engines have a lower compression ratio, so to pop one of them on a 'X' engine would actually cut power a chunk. Not nitpicking, just curious 

The lower compression on the 2,6 and 3,2 is achieved by the dishes in the top of the Pistons, the heads don't play a part in lowering compression.

A late 2.5 x25xe head will be the same as a 2,6 y26se Head and is interchangeable. Same applies to a late 3.0 head is interchangeable with any 3,2 y32se

By fitting a 2,5 head to a 3.0, for example, this will increase compression due to the leaser volume  of the valve area

[tigers_gonads]

Pretty sure Daz combined a 3.0 bottom end with a 2.6 top end for some reason

The car started off as a 2.6 FL
He dropped the 3.0 engine and cats in. Fitted the 2.6's exhaust manifolds and kept the top bit for the ecu / dbw throttle iirc.

Engine came from "Vader" iirc 

[JamesV6CDX]

You can actually fit an early 2.5 head to a late 2.6. It will run fine but is considered a bodge as there are no bolt holes for the coil packs on early heads

[tigers_gonads]

Just drop a 3ltr long nosed engine c/w 2.6 / 3.2 manifolds and a proper gearbox.

Keep the 3.9 diff from your automatic then LPG the lot 

I've just done Skeg Vegas last week in the Mv6 and had a mixture of town work, sensible driving and    driving when the dog wasn't in the back.

Filled up yesterday and using the fill to fill method, I got 21mpg @ 51.7 pence a litre   

[Nick W]

A 300hp V6 shouldn't be too hard to build. Use a 3.2 block, crank and rods, with custom pistons. Some properly developed heads will be expensive, but necessary. Sticking your finger down a port isn't development! Custom ground cams to suit the heads and compression. Vernier pulleys to time the cams properly, which will be time consuming. Jenvey do a manifold for six throttle bodies, so I'd use that with an aftermarket ECU. Add some designed headers.

Sounds good to me, until you see a rough cost: I doubt you would see any change from £10k. When a 2.2 Astra turbo engine is a simple bolt-in and 350hp needs little more than a bigger turbo, it's never going to happen.

[Diamond Black Geezer]

More good info - never considered the lower CR was down to the pistons, that's worth knowing

To Nick, indeed. And it's always baffling when you see people sticking the V6 in Astras etc (I even saw one guy fitted a X25XE to a Frod KA!) when the power isn't really much, it's a big old lump, vs a 4-pot, and as you say, there's surely more compact and tuneable engines out there.

Tiger's - we know that The Devil's fuel is Diesel, but surely Judas Iscariot used LPG?  I like the sound of the rest, though, I've got the long nose plenum and G cams and now 2.6 manifolds.

Which is it that has sodium exhaust valves? the 3.0 if memory serves, or was it all the Y engines? Also why do I want sodium on my valves? 

[Shackeng]

More good info - never considered the lower CR was down to the pistons, that's worth knowing

To Nick, indeed. And it's always baffling when you see people sticking the V6 in Astras etc (I even saw one guy fitted a X25XE to a Frod KA!) when the power isn't really much, it's a big old lump, vs a 4-pot, and as you say, there's surely more compact and tuneable engines out there.

Tiger's - we know that The Devil's fuel is Diesel, but surely Judas Iscariot used LPG?  I like the sound of the rest, though, I've got the long nose plenum and G cams and now 2.6 manifolds.

Which is it that has sodium exhaust valves? the 3.0 if memory serves, or was it all the Y engines? Also why do I want sodium on my valves?

For cooling, in my youth training on Merlin and Centaurus engines, IIRC sodium filled valves were used somewhere, clearly not Centaurus, which were sleeve valve.