2.5 V6 24V engine questions - Alfa Romeo Forum
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mudhut
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2.5 V6 24V engine questions

Does anybody know:

1. Rpm that the ecu cuts in at for this engine?
2. Max safe rpm for this engine?
3. What fails first if over-revved (I believe it's the con rods but anybody know for sure)?
4. How fast can hydraulic valve lifters go before it's necessary to use solid shimmed items?
5. How fast can the valve springs go before they float?
6. How much scope for improvement in cylinder head flow is available using standard pistons and valves? I'd have imagined that it is already pretty good in this respect. Anybody tried and measured it?
7. Any scope on this head for increase in inlet valve size?
8. Anybody know of a conversion to coil/distributor - possibly off the rear cam?

Ta.
 
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Stock ECU cuts at 6800 RPM. I set my cut-off at 7600 RPM and both my 2.5 and 3.0 haven't had any problems with that. Once during testing I've even revved over 8000 RPM, nothing has broken.

What RPM do you have in mind?
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Thank you.

What I'm considering is fitting the Alfa 2.5 engine into my Hawk Stratos. I want the engine to replicate the rev range of the original 2.4 Dino engine. On the Dino, the tachometer is marked yellow at about 7200 and red begins at about 8000.

The Alfa engine reaches max torque at 5000 rpm and max power at 6300. There is no point in me trying to increase the rev limit on the engine if the cylinder head does not breathe well enough to maintain reasonable torque at higher rpm which is why I want to know if the head can be improved very much.

I have three Weber 40 DCNF carburettors but I think that they may not be big enough for a rev limit much higher than 6500 with a cylinder volume of 415 cm.
 
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I've built a 3.0 24v with GTA cams for a mate.. after remapping the redline was set to 7200 rpm but if I had been there the limit would've been set higher as the power isn't dropping off yet... from about 6800 rpm to 7100 rpm the power level stays the same (240-ish bhp) but it seems just before cut off the power rises slightly...

that is with the stock injection system and 3.0 injectors though... doubt the stock 2.5 injectors could deliver enough fuel at those rpm
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@ Cuore_Sportivo_155:
Interesting info. So the torque is dropping off at the same rate that the revs increase from 6800 to 7100. I can't imagine why the power would rise right at the end. I presume there would have to be better cylinder filling - perhaps a lucky consequence of the inlet and exhaust designs at that rpm.

The grand plan that is under consideration here is that I want to replicate the look and feel of the Dino engine. Interestingly, although the 12V Dino engine is very oversquare and delivers max power (about 190 bhp) at 7200 (the start of the yellow area on the tacho), it makes maximum torque at only 4000 rpm. This is 1000 rpm less than the Alfa 24V which produces almost exactly the same power as the Dino but at less revs. I presume this is a characteristic of it being a 24V engine, amongst other things.

I'm considering making an inlet manifold to mount carburettors and also would need to look for a way to mount a distributor. There would then be no modern electronics to act as a rev limiter unless I add something electronic on for safety. In the first place I could just go to carbs and leave the ecu connected to control ignition. My kit car was registered long ago enough for a replacement engine to be able to run without catalytic converters and it also has very relaxed emissions requirements (either no dense smoke visible or less than 4.5% CO and 1200 ppm HC, depending on the person who tests it!).
 
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4.5% CO runs like ****e anyway, so you basically can do what you want....
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Hello MudHut !

I too, am looking at going down this road ... but not by choice !

I'm hoping to rally a Stratos replica but the "Authorities" are insisting I use the 2.5L V6 and downdraught Webers, for the sake of authenticity. I agree with the Webers but here's the problem ... in competition, the factory Stratos' produced 265 bhp. A few Alfa experts I've talked to say there's NO WAY you're going to get that sort of power out of a std bore Alfa engine running Webers. It would make much more sense to use the 3.0L engine but the authorities have flatly refused.

I'd be competing against Cosworth Escorts and Fiat 131 Abarths, so the bhp will be needed !

so ... please keep us informed of how you're going with it !

Thanks
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Quote:
Originally Posted by Cuore_Sportivo_155 View Post
I've built a 3.0 24v with GTA cams for a mate.. after remapping the redline was set to 7200 rpm but if I had been there the limit would've been set higher as the power isn't dropping off yet... from about 6800 rpm to 7100 rpm the power level stays the same (240-ish bhp) but it seems just before cut off the power rises slightly...

that is with the stock injection system and 3.0 injectors though... doubt the stock 2.5 injectors could deliver enough fuel at those rpm
Sorry for this off topic.......
Currently running my 2.5 with GTA cams and intake plates/runners, rebuilding 3.0V6 from 166, and my plan is to change engines in a month or two......AFAIK maf and all electronic is same(injectors are different) and 3.0 use same ECU as 2.5V6 - i mean CF2 engines for both......
Is it possible in your opinion just to remap my 2.5 ecu with modified 3.0 remap file, or i need to find 166's ecu???
Thanks.
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we used a remapped 2.5 ecu
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Great, very useful info for me.
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mudhut
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Quote:
Originally Posted by StratosHopeful View Post
Hello MudHut !

I too, am looking at going down this road ... but not by choice !

I'm hoping to rally a Stratos replica but the "Authorities" are insisting I use the 2.5L V6 and downdraught Webers, for the sake of authenticity. I agree with the Webers but here's the problem ... in competition, the factory Stratos' produced 265 bhp. A few Alfa experts I've talked to say there's NO WAY you're going to get that sort of power out of a std bore Alfa engine running Webers. It would make much more sense to use the 3.0L engine but the authorities have flatly refused.

I'd be competing against Cosworth Escorts and Fiat 131 Abarths, so the bhp will be needed !

so ... please keep us informed of how you're going with it !

Thanks
Hi and welcome. You really need to get yourself over to the gang at the Stratos Enthusiasts Club website here. I'm there too, same username.

I don't think you'll get 265 bhp out of the 2.5 engine either with the standard camshafts. To make this kind of power, you will likely need to raise the rev limit but I think it's that the head will have to breathe better too. Going to be expensive to make more than 100 bhp/litre but at least you can live with a cammy engine for competition use. My requirements are more modest, I'm relieved to say.

Don't expect rapid progress on the carburettor front. I'm not terribly happy with the DCNF carbs I bought and might have to bin them - was trying to do it on the cheap and should have known better. Too much else going on at home right now anyway.
 
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Thanks MudHut, will check out SEC !
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Quote:
Originally Posted by StratosHopeful View Post
...It would make much more sense to use the 3.0L engine but the authorities have flatly refused.
Will they actually be measuring the engine capacity...?

I know there are historic 105 series GTV running over 2L...
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