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Discussion Starter #1
I have a 99t 2.5 156 v6 which I wish to turn into a track day car. The engine is currently in bits soon to be rebuilt. Now before I start rebuilding it I want to do it in such a way as to get as much power as possible.
The question is. Are the 2.5 24v and 3.0 24v blocks the same therefore enabling me to fit 3.0 pistons and liners to my 2.5 block turning it into a 3.0? And if that is the case, are the heads the same? Or would I be better off just buying a 3.0 engine complete?
Any help or suggestions would be greatly appreiciated.
 

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Fit a 3 litre.

No question about it. I have a 156 2.5 race car and a 156 with a gtv 3 litre engine. Had both cars nose to tail on a race track and the 3 litre romps away. Loads more torque.

These are also pretty expensive engines to rebuild, so the easy option is 3 litre. Many parts between 2.5 and 3 litre are diferent.

Beware of anything people tell you about BHP figures, the only true indication is a rolling road.
 

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Discussion Starter #3
Thanks trackstar. Was fitting the GTV 3.0 to the 156 pretty straight forward? Theres a lot of conflicting advice about and most from people who haven't attempted the 3.0 upgrade. I don't want to spend a small fortune on an engine and then spend the weekends pulling out my hair trying to make it fit.
 

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Relatively straightforward.

You can swop the 2.5 water/oil cooler onto the 3.0 or move the power steering cooling pipes which run accross the front of the car and fit the nice GTV oil cooler.

Use the 3 litre injectors and standard 2.5 MAF etc.

The GTV's do however have a dual mass flywheel (weighs 13kg against 8kg for the 2.5) and these V6 engines are balanced as a complete unit, so transfering the 2.5 flywheel could unbalance the engine, noticably ay high revs. I know experiened Alfa independants who do this though and have no problems.

The 3 litre car I have has the 2.5 flywheel and runs the standard 2.5 injection system 'in theory' the MAF and modern ecu will adapt the fuel#air needs and mine makes 218 bhp with a nice power curve, no flat spots and no dip in power up to 6,800 rpm.

I have just built a production race GTV 3.0 engine for my brother to shoe horn into a 155 and I did use the 2.5 flywheel but had the whole lot (pistons, conrods, rings, crank, pulleys, flywheel etc) all balanced to 8,000rpm so no worries there.

Quite dificult to get that sort of power from the 2.5 without sacrifice.
Although the 2.5 jus loves revs!
 

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Discussion Starter #5
That's really helpful trackstar, thankyou. I am leaning towards buying a 3.0 lump rather than upgrading the 2.5 I have. It was suggested to me on another site to install GTA inlet cams as the profile allows the inlet valves to stay open longer. If I did this I would also fit the bigger crome intake pipes and bigger injectors.

Is it the 24v engine you are putting into the 155. This is of interest to me as I will no doubt start fettling with my 155 once the 156 is done. Mind you, I think the wifes motor will get looked at before then. She has expressed a wish to go faster.

Thanks again.
 

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GTA inlet cams are a better profile and not that dear (circa £120 ea) so yes thats a good move

The inlet tubes on the GTV are the larger diameter so stick with them, the white 3 litre injectors give plenty of flow (you would get away with the 2.5 ones though).

The later GTV's and GTA have a red 4 hole injector which are not really an improvement and are matched to the newer type ecu (on the plenum)

I would definetly advise rolling road mapping for ultimate fueling/timing, although I know of a number running fine on the 2.5 setup.

Yes the 3.0 we are planing to shoehorn into a 155 is a 24v....... and yes.... we are brave!
 
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Yeah, I'm blowing my own trumpet
but:

http://forum.alfa156.net/forum/forum_posts.asp?TID=26334&KW=gta&TPN=1

Trackstar: I live in Chester, If you want maybe we could meet sometime? Sounds like you have a lot of experience in these things.... :D

With regard to the oil cooler / heatexchanger - I couldn't use the heat exchanger on mine as you need a collant feed from it back into the block. That doesn't exist on the GTA lump.
 
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I have a 99t 2.5 156 v6 which I wish to turn into a track day car. The engine is currently in bits soon to be rebuilt. Now before I start rebuilding it I want to do it in such a way as to get as much power as possible.
The question is. Are the 2.5 24v and 3.0 24v blocks the same therefore enabling me to fit 3.0 pistons and liners to my 2.5 block turning it into a 3.0? And if that is the case, are the heads the same? Or would I be better off just buying a 3.0 engine complete?
Any help or suggestions would be greatly appreiciated.
The blocks are different. You have to machine the 2.5 block to fit the 3.0 liners. I think a 3.0 crank will drop straight in and give you a 2.7/2.8...... Its been done before.
 

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You can use the internals from a 164 3.0 24v in a 156 2.5v6 block too.
Obviously machined as mentioned above.

Redd has done that with his 156 Q-System..
 
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