Natural rev limiters

[C M Smith <cmsmith@domain.elided>]

And I'm not referring to those soft valve springs found in certain British 
pushrod engines which announced the approaching "redline" with a metallic 
ringing of valve bounce!

I would guess that the practical limit for redline on  a street engine is 
valve timing. There must be a rev range that works for a smooth idle at say 
800 rpm and an engine that still develops more power above 5,500 rpm, 
unless variable valve timing is available. After all, why have a redline 
much above 6,000 rpm if peak power is developed at 5,500 rpm? The money 
would be better spent adding a gear to the transmission. There are some 
engines that spring to mind such as VW and Mazda that have 7,000 rpm 
redlines but the journey up to the limit isn't worth it. The long stroke 
engines get short of breath rapidly after about 6,000 rpm.

Conversely, how many regular drivers would put up with a very lumpy idle 
cycling around 1,500rpm?

I note that Honda's newest engines with stratospheric redlines use variable 
valve timing and variable intake runners, and doesn't BMW actually use a 
variable exhaust as well?

My .02


Michael Smith
Calgary, Alberta
Canada
91 Alfa 164L, White, original owner

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