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`90 Alfa Romeo 75 with 3.0V6 from 164
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Discussion Starter #1
Does somebody knows the real physical rev limit for 12-valve V6?
We had some discussion about max revs of 12-valve v6 in our local alfa-club. Some people asserts that rev limit is near 8k, but I think it is near 6000-6300 because of exhaust valves rockers construction.
 

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For the 2.5, if you remove the rev limiter, the valves float at about 7500, above 8000 you are in serious danger of losing a rod.

Greg
 

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I thought it was 6200, for the older ones. 2.5
 

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Richard Jemison
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RPM limits on V6 12 V

Without any rev limiter, and assuming the ability to get the engine to these RPM, you will find that the limiting issue truly is the exhaust rockers.
The early design (blade type) with the slow ramp rate of stock cam profiles is safe to around 7200 RPM extended but there is no reason to have it rev long at that point as there is no power there..

With race or performance exhaust lobe designs the safety drops below that even for short periods above 7000 RPM
The later design 164 type rockers (I-beam type) are far more durable although heavier and with those I really dont worry about short trips above 7500. But I am basing this on exhaust lobes with correct design. In particulat Cat-Cam lobes that I tried in the `90s were breakers and benders of rockers.
 

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Every time this comes up I have to wonder how the big V8 guys get the super weight valves to go to 8000+ and 7200 no problems. With there mile long pushrods and very large valves I would think the mass is easy 2x the alfas.
I know they like to use Ti. parts but even so.. but on the other hand you can get V8 Ti, parts for next to nothing. I have thought of getting a set of Ti V8 valves and turning them down to alfa size. as they are super cheap.
 

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I have thought of getting a set of Ti V8 valves and turning them down to alfa size. as they are super cheap.
That would be interesting to see as I've heard numerous times that Titanium is difficult to machine without the correct tooling.

The other thing that should be mentioned is that the old school V8 fraternity have roller rockers and cam followers to help keep things alive at high revs. Roller exhaust cam followers and rockers for the Alfa 12 valve should help reduce the stress on those parts. Add hollow larger diameter push rods and you're away :D
 

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I have hit 8K with a relatively stock 2.5 . At the top of it, it seemed to start to float the valves and not be pulling.
I did it with a slightly mod-ed 3.0 and it was still pulling at 8K , but I was scared
I was gonna throw a rod,,,,,
 

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`90 Alfa Romeo 75 with 3.0V6 from 164
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Discussion Starter #8
Thanks for your answers, guys!
 
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