when revving a car or a motocycle engine to a high rpm its starts to make a sound like (dun dun dun dun dun dunn)

watch this video to understand what i mean( https://www.youtube.com/watch?v=Q7ZwJnaiEQE )

i want to know the name of that sound and if you know why engines make it tell us ?. Thank you in advance. :)

  • 2
    It’s the relaxation oscillation effect of a factory RPM limiter cut with hysteresis at 0 KPH well below redline to protect the engine. Smells like unburnt fuel to me. Sep 3 '20 at 15:30

That is the sound of the engine hitting the rev limiter and it prevents excessive rpm which can eventually destroy an engine,

Some engines, well the early ones, had rev limiters in the distributors and were easily removed / altered. I had to remove one for a customer as the "road" version was limited to 6000rpm, while the "rally" version of the same engine - which was identical - was up to 11500 rpm. We did warn the owner, but he got what he wanted.

Now, the rev limiters are not so easily altered, as the settings need to be changed in software and that means being able to write to the ecu.

  • You should also mention a 2-step, as it can produce the effect. Sep 3 '20 at 14:28
  • The rev limiter can exert electronic control over engine revs, but it can't do anything about mechanical over rev. If you are accelerating hard in third gear and slip it into second instead of 4th. You will absolutely over rev your engine, likely with unpleasant results. Electronic revlimiters are not a panacea.
    – Tim Nevins
    Sep 3 '20 at 18:07
  • @TimNevins collected a few cars that had done that xr2i needed nee valves for all cylinders.
    – Solar Mike
    Sep 3 '20 at 18:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.