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Discussion Starter #1 (Edited)
'86 2.5 gtv6 - To swap to a 3.0 24v engine or supercharge - that is the question

I was wondering if anyone had experience with boring out one of these engines. My initial thought was to replace the existing engine with a 3.0 from a verde, but after some thought, boring the stock one out to a 3.2 (if it's possible) seems more up my alley.

Does anyone have any experience doing this? Or even know if it's possible to bore the engine out to 3.2 liters?

I don't know much about these procedures, so anything would be great.

Thanks in advance for any advice, tips, facts, or general info on the topic.

Oh, and if anyone has any photos, of either boring their engine out or replacing it with a 3.0 they're more than welcome!
 

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you can do a 2.8 conversion, but 3.2 is fairly pointless, since there is a kit to take the 3.0 to 3.5. already
 

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Discussion Starter #4
wow, 3.5? not bad. Do you have any info on who makes such a kit? how much one would cost? and the difference in power over the 2.5 and 3.0 engines?

I didn't know something like that existed. Because cost is an issue, I'd like to keep things around 4 or 5 thousand dollars.

If it would be around the same price range, or just a bit more, I might make the jump to the 3.5

thanks in advance!
 

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Im not sure if the 3.5 kit is available in america, I think the 24valve conversion is more common in the USA. it involves machining the block to take new liners. several suppliers do it in the UK. power wise, there is a big difference between the 2.5 and standard 3.0, 30odd hp. the 3.0 has bags more torque over the 2.5, but in my opinion isn't such a sweet engine. the 3.0 is more bruteish than the 2.5. The 2.8 conversion can be done in much the same way, but still involves machining the block to do it right. The 3.5 conversion yields over 200hp.

Personally for £4-5k, I cant see you getting much more than a good head job, and some nice cams, and headers for the 3.0 or 2.5. 2.5 might yield you about 175-180hp, while the 3.0 will get you about 200odd hp. Personaly for that money, I would go for supercharging the 2.5l. best speak to Greg Gordon, but I would guess that $5k should get you a reliable 2.5 on Ljet, putting out 220-230hp without too much bother, and will produce way more torque than the standard 3.0l..

HI Performance Store, Inc
 

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You can't get there from here on a 2.5 engine. If you machine 2.5 block out to take 3.0 liners you can get 2.8 with stock crankshaft.

These are wet sleeve aluminum engines not really a boring thing like a cast iron block.
 

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Discussion Starter #7
just to be clear, the 3.5L kit is for the milano engine, and would not work on the 2.5 gtv6 engine that I have in there right now - right?

also, does the kit include bumping up the number of valves per cylinder?

I'd like to get 24v if possible, like the 164 engine, without having to deal with actually putting a 164 engine in my car (I think it's above my price range, and I hear it's a TON of work regardless).
 

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just to be clear, the 3.5L kit is for the milano engine, and would not work on the 2.5 gtv6 engine that I have in there right now - right?

also, does the kit include bumping up the number of valves per cylinder?

I'd like to get 24v if possible, like the 164 engine, without having to deal with actually putting a 164 engine in my car (I think it's above my price range, and I hear it's a TON of work regardless).
It is my understanding the 3.2 or 3.5 conversion is for 3.0 24v engine not 12v 2.5 or 3.0 engines.
 

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just to be clear, the 3.5L kit is for the milano engine, and would not work on the 2.5 gtv6 engine that I have in there right now - right?

also, does the kit include bumping up the number of valves per cylinder?

I'd like to get 24v if possible, like the 164 engine, without having to deal with actually putting a 164 engine in my car (I think it's above my price range, and I hear it's a TON of work regardless).
You won't be putting 24V heads on a 12V block, like Steve says "Can't get there from here" :D
 

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As pointed out 2 options with the 2.5.; convert to 2.8, or supercharge. no competition , the SC wins hands down. The 2.8 conversion, gives around 185hp, with some minor head work. Yes ,The 3.5 kit is only available on the 3.0 12 and 24valve, with block machining and new liners. With head work and ITBs the 3.512v can give you 240-250hp. As I said, I'm not sure anyone does this in the USA. AH motorsports do it in the UK. If you want a 24valve, you will have to go with the 24valve 3.0 or 3.2, you can't covert the 3.0 12v to 24valve, its totally different.

The 164 24v is really your cheapest option for a 24v conversion, but isn't a straight swap, there's plenty of work that needs to be done. dont think you can do it for 5k though. Personally if you are not supercharging the 2.5, don't bother with it, because it will cost you a lot more than 5k, to get 200hp from the 2.5. Go with the Milano 12v 3.0 if you want low cost. find a good low mileage engine, buy it, and spend your money, having a nice job done on the heads. No reason you cant get over 200hp from a 12v3.0 with $5k. Others will no doubt comment, but I believe the 24v is tough to get hold of in the USA too.
 

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Discussion Starter #11
ok, but assuming I dont go the route of buying a new engine, would it be possible to bore out the existing engine to 3.0 and then just take the headers off of a 164, and make it a 24 v?

that seems a lot easier - no?
 

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in short No. You cant get to 3.0 from the 2.5, (I may be wrong, but I think 2.8 is a big as you can go, due to the block design) and you can't make 24v heads work on the 12v block.
 

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Discussion Starter #13
Oh, I just wanted to say in addition to my post above, that I think I'd like to keep it naturally aspirated.

and do you think buying a new engine is better than boring the current one out? maybe I missed something, but I don't get why that would be...

I THINK its around the same price (although I'm not sure)...
 

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you can't bore out any of the alfa V6's, they are alloy wet liner engines. you can only machine the blocks, to take a larger liner. for the 2.5, I believe 2.8 is the largest you can go, without weakening the block. whilst for the 3.0. 3.5 and for the 3.2. 3.7.

you wont achieve any of the above options for 5k imo. a simple rebuild will cost close to that on its own. cheapest option is a good milano 3.0 12v verde, with cams, headers, ported runners etc.
 

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Discussion Starter #15
Oh, I just wanted to say in addition to my post above, that I think I'd like to keep it naturally aspirated.

and do you think buying a new engine is better than boring the current one out? maybe I missed something, but I don't get why that would be...

I THINK its around the same price (although I'm not sure)...
nevermind I got it - the reason being that you can't bore out a 2.5 to 3.0.

assuming you could however, or regardless of that fact altogether,

would it be possible to put the 164 headers on either of the two engines?

yes or no, anyone know why?
 

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NO. for a start, none of the oil and water galleries line up with the 12v blocks. the combustion chambers are a also a different design, you would end up with odd compression
 

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Discussion Starter #17
you can't bore out any of the alfa V6's, they are alloy wet liner engines. you can only machine the blocks, to take a larger liner. for the 2.5, I believe 2.8 is the largest you can go, without weakening the block. whilst for the 3.0. 3.5 and for the 3.2. 3.7.

you wont achieve any of the above options for 5k imo. a simple rebuild will cost close to that on its own. cheapest option is a good milano 3.0 12v verde, with cams, headers, ported runners etc.

got it. the milano engine is starting to look better and better. I suppose that down the road I could do the 3.5 conversion if I wanted to...

does anyone have info on who sells these kits, what they cost, and what kind of power they produce?
 

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I think what you missed is that a big bore kit could be more expensive than a complete bigger engine. The less expensive way is to put in a bigger engine with some minor changes as cams and headers, that will give very good results. Boring up a block and installing new liners and pistons is very expensive and then you never can use original parts any more, totally dependent that the supplyer company keeps alive to supply the right spare parts.
Big bore kits have been along since early nineties, supplied by Dieter Gleich, Germany and Sam van Lingen(SAVALI, Holland). Nowadays there is a company in UK that makes big bore kits for a price. But chances are you would be just as happy with a lightly tuned Alfa 75/164 3L 12V engine(200hp) or a 3L 24V 164 (210Hp), or even a 3,2 24V GTA engine with 250Hp.

Here the link to AHM Motorsports,

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yup agree with that too. just remember tho, if you go for a gta 3.2 or 164qv say, you will need the ecu with it. Ljet 2.5 ecu wont be up to the job for the 24valve. if you can find a 164 24v s or qv that doesnt need a rebuild, you could do it for 5k
 

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Discussion Starter #20 (Edited)
I think what you missed is that a big bore kit could be more expensive than a complete bigger engine. The less expensive way is to put in a bigger engine with some minor changes as cams and headers, that will give very good results. Boring up a block and installing new liners and pistons is very expensive and then you never can use original parts any more, totally dependent that the supplyer company keeps alive to supply the right spare parts.
Big bore kits have been along since early nineties, supplied by Dieter Gleich, Germany and Sam van Lingen(SAVALI, Holland). Nowadays there is a company in UK that makes big bore kits for a price. But chances are you would be just as happy with a lightly tuned Alfa 75/164 3L 12V engine(200hp) or a 3L 24V 164 (210Hp), or even a 3,2 24V GTA engine with 250Hp.

AHM Motorsports, UK

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Thanks, You're right, I didn't get that boring out the engine would be more expensive than just buying a new one. The only issue I had with putting the 24v 164 engine in was that I've heard you run into huge problems because the 164 engine is transversely mounted and the gtv6 needs a longitudinally mounted engine and it's probably closer to a $10k job.

Basically (the conclusion I've come to is) for the money I'm looking to spend I'd either want to put a milano engine in there, or supercharge the existing one.

any guesses on what the specs would look like on either setup? I like the idea of keeping it naturally aspirated, but if a supercharged 2.5 would blatantly be better than a 3.0, (or vice versa) - I'd go in that direction.

It was mentioned (mjr) that the 2.5 is favored over the 3.0. Are there many others that feel that way?
 
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