Reply: <tech> DOHC vs. SOHC

[SMILLER@xxxxxxxxxxxxxx]

Chris, knowing probably about as much about cams and valve as I do,
asks:

>Date: Fri, 13 Nov 1998 09:43:57 -0500
>From: Christopher Pawlowicz <chrisp@domain.elided>
>Subject: <tech> DOHC vs. SOHC
>
>KC asks
>>What's the advantage of having two cams versus one?  I can see an
>>advantage with VANOS on one or both (more leeway for adjustment). 
>>Is there anything else that two cams do better than one?
>
>don't you *have* to have 2 cams to work a multi valve engine ?
>
>if you have 2 valves per cylinder they can be side by side (in the same
>direction as cylinders) and 1 cam can operate both valves..
>
>but if you want 3 or 4 (or more?) valves per cylinder you have 
>a cluster of 4, and 2 can be operated from one side, but the other
>two have to be operated from the other side of the bank of cylinders
>which means another cam
>
>is there such a thing as a sohc multivalve engine ?
>
>chris pawlowicz

Well, Chris, that's what I thought at first, too, but...

My wife's last car was a 1992 Acura Legend with a 3.2 liter V6.  It had 4
valves per cylinder, but only single overhead cams.  I think they could
make this work because the valves were relatively small, so maybe the
cam lobes could be narrower?  I'm pretty sure the shape of the
combustion chamber must have something to do with this, too.

On the other hand, my 1970 Fiat (my first car) had a 1.4 liter 4 cylinder
engine with double overhead cams but only 2 valves per cylinder.  Why
2 cams for so few valves?

So, the cam/valve mystery remains a mystery.  To me, anyway.

Scott Miller
Golden Gate Chapter
BMW CCA #44977

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