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just to put this question into perspective, the car I'm talking about is a 2007 Alfa Romeo 159 1.9l jtdm turbodiesel.

So, I was driving it and I needed a bit of life out of the engine, so to get the turbo to kick in I revved the engine to around 3500 rpm before shifting into 2nd and 3rd gear (I was merging into the highway). That's when my brother scolded me, saying to never high rev (remember, 3500 rpm max) a diesel engine in 1st and 2nd gear, even if it's in temperature.

I say it's bonkers, and you can "high" rev a diesel in low gears as much as you can in high gears. Otherwise, how can you get the turbo to kick in when launching?

Who would be right here? If you have any sources for your answer that would be great, so I can show my brother proof of whether he's right or wrong.

  • Apparently, the power output for that engine is quoted at 4000rpm for 207bhp, so 3500 cannot be the max rpm... It may well be a limit you wish to use... – Solar Mike Jul 5 at 8:26
  • @solar Mike yes it's not the max rpm the engine can reach, it was the rpm at which I shifted gears. I think it can safely reach 4500 rpm for brief periods of time that engine. – vale.maio2 Jul 6 at 10:19
  • You clearly state “remember 3500 rpm max”.... so what do you think you meant and what might we have understood? – Solar Mike Jul 6 at 10:22
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The gear doesn't matter, the engine temperature does.

From the engine's perspective, it doesn't see what gear you use. It just sees some resistance at the output shaft.

It doesn't matter if you rev to 3500 RPM on first or top gear. At the first gear, the revs rise higher so it may be easier to overrev accidentally, but fortunately, modern engines have computers preventing you from overrevving.

What you shouldn't do is to rev to over 3500 RPM with the engine cold.

I'd say from a practical perspective, revving to over 3500 RPM on first gear is usually pointless, but on second gear you may want to rev to max RPM when merging to a highway.

  • That was exactly my theory. The engine doesn't care about the gear ratio, all it cares about is being in temperature (and it was) and not being revved too high (3500 rpmm is quite ok even for a diesel engine). – vale.maio2 Jul 5 at 7:55
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This may well be closed as it is about driving techniques more than maintenance or repair...

You can rev the engine up to the governed limit for a small amount of time. So acceleration is fine, then change up.

What is not good is to hold it at that limit for extended periods of time, ie cruising at max speed at max rpm in second for extended periods...

Just for info, when I pull away I tend to limit the time of slipping the clutch to a minimum and use the torque of the engine to accelerate.

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