I bought a 2000 nord engine (standard pistons and rods, just balanced and with balanced bottom end) from a respected Alfa engine builder and asked for a safe limit, his answer was 6,500 with occasional 7000. I assumed this was in a race application where limited life might be acceptable and have kept it under 6100 on road use (and that only momentarily).
Well worth checking the accuracy of your tacho. For several years I always felt a previous engine had more to give but kept to the redline, only to find later that the tacho was over reading by more than 20% and so I'd never got much above 4700in reality - what a waste. Now I go to 7500 on the tacho knowing it's just on 6000 true RPM
I fitted a bluetooth 123 dizzy which gives a true RPM reading. It helped considerably.
If you hold to the generally accepted principle that a standard road engine (cast pistons etc) should not exceed a piston speed of 3,500 feet per minute, then you should be careful above 6,000 rpm. At 6,000 rpm, with a standard stroke of 88.5mm, the piston speed is ~3,484 FPM.
MANY (too many) years ago, I built a 101-1300 Veloce race only engine with (terrifying) Isky , by- guess-and-by-gosh cams with so much low end overlap people lined up to watch me start it. Flames jumped out the velocity stacks below 15-1800 rpm cold. This engine had cast Alfa Veloce pistons with offset wrist pins. At the time, we used 4000 F/M as a reasonable piston speed.
Those 74 mm Alfa race pistons were no doubt lighter than todays cast 2L versions. I agree with the above by horsewidower that maybe 6,000 is enough.
I would be more concerned about rod bearings than pistons at high rpm. I have been using forged pistons for the past 6 years but prior to that I ran my motors with "motronic" cast pistons to 7000 rpm with no problems.
This is one of the many reasons I wish I got the bluetooth (not switched) 123 dizz: accurate tach. I've checked mine with a good digital timing light but even then, its an imprecise science and the tach is liable to drift with use and age.
Install a HIGH quality rev limiter module available from Pegasus Racing in Wisconsin. These are set up by programing them at 1/2 the shut down engine speed. In your case, 3000 rpm. Then the tach, ANY tach, just becomes an indicator of what's happening. With aggressive or track driving, you should NOT be staring at any instrument anyway. A 500 rpm inaccuracy is not a big deal
Yes the fancier 123 has the rev limit and accurate tach. The switched unit has neither. Personally, I am on the street not track and if I were spending more coins it'd be on upgrading the 123 rather than a stand alone, but everyone's application will differ.
My tach reads 10% high and I have a red line - A narrow slice of red electrical tape stuck on the glass at 7700 rpm. I find it easy to stay within that limit except when I am doing tuning runs and then I often let it run to indicated 8000 rpm. The bottom end of the motor is stock except for a windage tray. I have about 15000 miles on that short block and no problems.
Ed, I'd certainly be interested in any power curve plots that you might have. I'll go back and see if you have that in one of your threads. If I read your statement correctly with a 10% error, at an indicated 8,000 you're at a real 7,200.
Where does it tip over the curve and start declining in power?
It is almost 5 years since I started https://www.alfabb.com/bb/forums/spider-105-115-series-1966-1994/304825-79-spider-dyno.html I just got home from 2 days with Al Mitchell and his dyno in Smithfield Virginia where we tested my rebuilt 2L engine. I am pleased with the results - 155.1 RWHP and...
I did a lot of bouncing off a 6,500 redline (software controlled with megasquirt) under boost on my first motor. That eventually resulted in a blown head gasket, but everything else held together. I believe it did have stiffer valve springs, but was otherwise stock.
Motors often let you know when they are unhappy at high RPM with the power band. No point of revving high when you aren’t making power up there.
Our Grassroots Motorsports Challenge Alfa was all stock ... including valve springs ... except for the addition of a turbo. In order to avoid an extra shift during the autocross, the engine was run to 8000 RPM ... at 18 psi boost ... and recorded FTD. I don't recommend it on a regular basis, but it's a real testament to the robustness of the 115 engine.