V6 tuning + will 2.5 heads fit a 3 litre block?

[cav_2.0_gli]

hello all,

right i have a few questions.

a mate of mine, has been discussing things to do to my cavy, while its off the road.

basically, hes trying to talk me into getting an omega 3 litre bottom end (block, crank + pistons), and then fitting my 2.5 cylinder heads, and using my 2.5 loom + ECU to run it.

will this work? what sort of power gains should i see?

will the engine run fine, and do i need to make any modifications to the 3 litre bottom end, in order to fit it to my car? will a lightened 2.5 vectra flywheel fit it? will my F25 gearbox fit it aswell?

also, is there any other modifications i can do to the engine?

ive already got:

3 litre G camshafts
3.8 bar FPR
ported + polished inlet manifold + throttle body + cylinder heads (well will be when i strip the engine)
shall be uprating to blue V6 injectors from my current black ones
superchip for the ECU
and custom made exhaust manifolds, and possibly a complete exhaust system.

cheers
Dave

[HAIRIBO]

People have used 2.5 heads before its lowersthe compresion ratio, but dont know what affect it has. I used 3litre haeds as they have stronger sodium valves and its matched to the Bore of the block. Look at the head gasket from a 2.5 (50p shaped) and the 3.0 (Perfect circle)

You''ll probles find an omega egine in a scrap yard with the cams missing. People often just strip the cams for a 2.5. but you already have the cams so you'd be sorted. You have to use everything off the cavs engine. Sump. and inlet manifold injection manifold. but you relly should use the 3.0 blue injectors as the engine doesnt like the 2.5's black ones.

And insurance is a nightmare to get. as most companies wont touch it. Then theres the expense of haveing the engine rebuild, as lets face it, you dont want to fit an engine just to find out its a duff. Shells and piston rings, wter pump etc. It gets very expensive. I'd say if you 2.5 is running fine and heathly then leave it in. unless you have the money and balls to chance swapping it. I only did it,as my 2.5 blew up leaving 2 fist size holes either side of the block.
well over £1000 for a rebuilt 3.0 fitted.

If you want more power from your car as it stands then, fit a panel filter in an airbox and 3pipe mod. and maybe a sports cat £170 and a cat back exhaust.£150+, Up rated leads plugs. Coulkd also fit the Fuel pressure regulater from a 2.6 or 3.2 v6, £25 from Vauxhall. its a 3.8bar compared to the 2.5 and 3.0 v6's which have a 3bar. Courntey do a 4.0bar for £45 but you dont really need it. Enlarged throttle body often on ebay. Omega plastic lower inlet divider.

Lots of ways to uprate your 2.5. onec they are all done, you could even do a 3litre conversion in timje to come, and at least you know you'd have all the uprated bits alreday on your engine to swap.!

[HAIRIBO]

As for gearbox and flywheel, wat ever set up you have on the 2.5 will fit staright on. If you get a 3litre block, make sure you now which cambeltkit and cambelt covers you need. as the cavaliers only had one set up. but the omegas changed twice. I found that out at my expense lol, as my cavs cambelt covers would not fit the late spec 3.0 block as the cam belt pully postions changed.

[cav_2.0_gli]

change of plan,


just gona fit a 3 litre crankshaft to my 2.5 block instead, and use my current pistons/conrods and the rest of the engine.

according to a mate of mine, this will work, as he did it to his vectra 2.5 V6, and then just use the rest of my 2.5 engine bits on it.

ive already got thr 3.8 FPR fitted to my engine.
i shall also be fitting a set of V6 blue injectors aswell.


im going to port + polish the cylinder heads, and have them reconditioned.
i will also be replacing the cambelt , tensioners, water pump, all top 1/2 gaskets, sump gasket, might change oil pump, big end shells, crank regrind if it needs it, etc etc.

should be quite a powerful and sweet motor when its finished

[cav_2.0_gli]

so at the end of this, i shall have:

3 Litre crankshaft
3 litre G camshafts
3.8 bar FPR
Blue injectors
ported + polished cylinder heads x2
ported + polished inlet manifold
ported + polished throttle body
both cylinder heads reconditioned
custom made S/S exhaust manifolds + exhaust system
ECU remap
performance HT leads + spark plugs
all new gaskets (valve stem, , full service, new cambelt + tensioners + water pump
new bigend shells, piston rings
if it needs a crank regrind
Ramair induction kit
oval sports backbox
and goes know what else

wonder what power she'l push out after that?

[Squig]

what difference, if any, will the 3.0 crank make... i was under the impression that the x30xe and the c/x25xe had the same stroke?

[HAIRIBO]

The 3.0 crank is heaveir than the 2.5's if anything I would have thought that this would hinder your performance. as if you lighten the crank you realise more power. Putting a heavier crank in will just slow it down. (Just think flywheels) No body puts a heavy flywheel on. they lighten and balance them! If you going to be spending all that money re shelling a 2.5 block and flowing the heads, why not use a 3.0 engine. do all the work to that! I bought my 3.0 block for £50. the piston rings/ shells and new bolts cost more than 3times that. over £65 on bottom end bolts alone. Seriously mate. Think long and hard before you take your healthy 2.5 out. as it gets stupidly expensive rebuilding an engine. If i was you, buy an old 3litre and work on that when you get the money, over time you'll have built a top engine, then swap them over. other wise you might take your cav off the road only to find you cant afford to finsih!

[cav_2.0_gli]

hmm,

ive been thinking about this for a few days now, and i think your right. its best to leave her as she is, and just get a different engine at some point, and do it that way.

think im gona leave my old girl as she is for the time being, and just change her gearbox+clutch+flywheel instead.

im gona fit some new Blue V6 injectors to her aswell, and racing HT leads + plugs, and give it a proper service while ive got it off the road.

can't wait to get her back on the road!!!!

gona get her some new arches + resprayed + windows tinted aswell.

plus gona start refurbing her new alloys too.

[HAIRIBO]

Makes sense, unless you have plenty of spare cash or another car to use day to day.