How to get more power from 2.5 v6 - Alfa Romeo Forum
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(Post Link) post #1 of 18 Old 3 Weeks Ago Thread Starter
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How to get more power from 2.5 v6

I've done the usual breathing and exhaust mods including straight pipe and a remap. Trying to get more power out of my engine without a supercharger or turbo. My question is what is the limiting point in our engines. In other words. I've seen 2.5 v6 engines N/A pushing out up to 100hp more than ours. Why is that and what can I do to achieve this. I was thinking of raising compression with high compression pistons but my mechanic recommended not to for the poor fuel quality where I live.

Mods:
3.2 intake
Straight pipe exhaust 2.5 inches+ one rear muffler
Eibach pro springs and blistien b8 shocks
Remap by independent tuner
Copper spark plugs
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(Post Link) post #2 of 18 Old 3 Weeks Ago
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I think you possibly answered your own question- fuel quality.

If you look at all the petrol engines fitted to the 156, you'll see they all have approximately the same specific output (power/engine size). I've looked through this and noted all the Alfa engine have generous valve sizes for the respective capacity. If we look at 4 cylinder engines for a moment, 2.0 TS valves are larger than the old Focus ST170 or even the 16v Vauxhall/Opel red top. Strangely, the ST170 can be easily tuned (induction kit, de-cat and remap) to make 200BHP. (Also remember Renaultsport 197) Similarly, Anderson Racing Engines can extract almost 300Bhp from the red top without changing the camshafts but it does need to rev to around 9000rpm to achieve that. It isn't cheap to make that power though but it does out-perform a Honda S2000 everywhere in the rev range without trick cam timing, variable inlet manifold but simply uses Jenvey throttle bodies instead.

I can only think that in the scale of things, larger companies can divert more resources to development and that as there are many more engineers modifying more common engines, I think there is just more chance that someone stumbles upon the exact formula to make the respective engine really work.

I think that is largely what it comes down to. If enough people spend long enough, someone will 'get lucky' through experience and dedication. I just don't think there is enough collective knowledge to better develop Alfa engines. I don't mean to demean any tuners but their time and resources are not limitless and there is comparatively little competition to move things on.

Perhaps one day, before cars become electric, there will be equipment available to scan engine components and have sufficiently developed programming of thermodynamics to be able to calculate and machine the optimum configurations so the Alfa engines perform competitively.

As for the Busso, until such time someone makes a shielded carbon plenum chamber and better engine bay ventilation to lower induction gas temperature significantly, I think efficiency will remain quite compromised.

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How to get more power from 2.5 v6?
Take it out and replace it with a 3.0
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Almost no parts are available for the 3.0 let alone the engine itself I will have to source from another country making supercharging a cheaper option
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Fruity I've been thinking the exact same thing in terms of under development. What if I ceramic plate the intake system and add an intercooler or maybe a water methanol system. Do u think it would be worth trying
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Fruity I've been thinking the exact same thing in terms of under development. What if I ceramic plate the intake system and add an intercooler or maybe a water methanol system. Do u think it would be worth trying
Dont waste your time and money on stuff like that, it's useless for in your case.
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Do u have any suggestions mate
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Yep - stick a 3.0 in. Or a 3.2.

Modifying engines is very expensive. If an engine exists with a bigger capacity, and is a drop in replacement, then that is the cheapest way. You only need a short engine, in theory you only need crank, pistons and liners - all of the rest of the parts are common. A 2.5 ECU and MAF will certainly run a 3.0 and probably a 3.2. You can then fiddle around with throttle bodies and plenum mods if you want to.

You could stick some GTA exhaust cams in, but they're rare and expensive, and you might as well stick the whole engine in.
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(Post Link) post #9 of 18 Old 3 Weeks Ago
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Yep - stick a 3.0 in. Or a 3.2.

Modifying engines is very expensive. If an engine exists with a bigger capacity, and is a drop in replacement, then that is the cheapest way. You only need a short engine, in theory you only need crank, pistons and liners - all of the rest of the parts are common.
Yep, many years ago on another forum, I'm sure someone used the internals from a 164 3.0 in their 156 2.5 crankcase.
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Unless you go the route of supercharging, any work on the 2.5 will give fairly limited results. I don't know anyone who does an off the shelf 2.5 supercharger kit.

The 3.0 has a much better torque curve so a larger capacity engine makes for much less need for gear changes as the 2.5 is very short on low and mid range torque.
Also, strangely the 2.5 torque drops off very sharply near the top of the rev limit. The 3.0 isn't nearly as bad and has a far more usable torque band. A 3 litre makes much more sense. Remap it afterwards and you'll have 230bhp. It is tried and trusted and requires no specialist parts. It is easily the best and cheapest route to significant gains. You would spend lots of money and time to achieve that with the 2.5 and you probably wouldn't like the result.

Start looking at breakers or eBay in Italy, France, Greece etc

South Africa did a 3.0 156 so you could get everything from a single car but they are no doubt quite rare.
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A 3.0 in basically stock form is going to be a lot more reliable than a 2.5 tuned for a similar power output.
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(Post Link) post #13 of 18 Old 2 Weeks Ago
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Autodelta do a SC kit for the 3.2 GT and 3.0 GTV, maybe they could be of help putting an SC on the 2.5? They also do 3.3L conversions for the 2.5 (looks like different sleeves/pistons).

All of that is serious money though, 5-6K.

One other option i can think off is cams, you seem to already have tackled the other bits to make it breathe well, might as well give it a more agressive cam. Not a cheap option either though, C&B ask nearly 2K for a set of 24v cams, plus fitting and remap.... Does anyone know if a set of 3.0/3.2/GTA cams would be an improvement over the 2.5?
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Autodelta do a SC kit for the 3.2 GT and 3.0 GTV, maybe they could be of help putting an SC on the 2.5? They also do 3.3L conversions for the 2.5 (looks like different sleeves/pistons).

All of that is serious money though, 5-6K.

One other option i can think off is cams, you seem to already have tackled the other bits to make it breathe well, might as well give it a more agressive cam. Not a cheap option either though, C&B ask nearly 2K for a set of 24v cams, plus fitting and remap.... Does anyone know if a set of 3.0/3.2/GTA cams would be an improvement over the 2.5?
3.0 cams are the same as 2.5 and all busso engines have the same cam profile for exhaust. It's only the intake cams that differ in the GTA
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After much research I guess everyone is right, the 3.0 is my best option, I don't think I can reliably take a 2.5 much further without sacrificing reliability of my daily. I'll start looking around for one, I found good examples for around 530 euros with 80ish thousand km on the clock. Should still have some life in them.
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Supercharging is dangerous in my opinion unless supporting internal mods are done which need very deep pockets. Besides I'm not looking for much just a bit more torque and a wider powerband
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I'm uploading this image for the sake of future reference to
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3.0 Vs 2.5
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