Hi, I have a 650 cc engine in my 72 500 L and I was wondering what is the maxiumum safe rev s on a standard engine.Also why is the tailpipe on standard exhausts always flattened at the end . ( To increase back pressure maybe ).

phoenix1 said:

Hi, I have a 650 cc engine in my 72 500 L and I was wondering what is the maxiumum safe rev s on a standard engine.Also why is the tailpipe on standard exhausts always flattened at the end . ( To increase back pressure maybe ).

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Hi Phoenix, Unless your engine is fully balanced, has top quality bearings and no worn parts and has been carefully built, I would not go beyond 5500 rpm - the odd excursion to 6000 maybe ok, going to 6500 rpm will in all probability result in a broken crankshaft and resulting mayhem internally (you will trash the engine completely) one item of note is that you should be confident that any tacho in your car is accurate

Ian.

I also have a standard 650 engine and although I'm conscious of the rpm. I judge the safety margin according to road speed and the noise. Hence I'm out of my comfort zone at 70mph although the car will go faster. With the 500 engine that zone ended at 60mph. Anecdotally I think that for longevity of the engine and my own peace of mind, cruising at between 55 and 60mph is safe to do all day.... I've tested that assertion recently with a continuous 4 hour slog at just under 60mph. To modify a saying from the retail industry, rpm and top speed is vanity, mileage and reliability is sanity.