Hi all,
Can someone out there give me a detailed dissertation on Valve Spring
pressures, Valve installed height and how they affect performance etc?
Why? I got my MGA cyl head back from the shop. It's had new unleaded exhaust
seats, new springs, ported & polished (not extreme - mainly exhausts) and
I'll be using my new 1.6 ratio Roller Rockers on it with the std cam, std H4
carbs, K&N type filters. The shop originally adjusted the spring pressures
to all be around 95-105lbs opening pressure. The shop had to fit some
spacers to the springs to bring the inlets up to the same pressures as the
exhausts - I figure this is related to the valve installed height - ie the
seats 'depth'?. Can someone when they get the time explain the importance of
the installed height, open pressure, max pressure etc etc.
I realise the following things. 1) Pressure affects performance, the harder
the spring the greater the force required to open the spring and keep it
open therefore the more loss of HP. 2) Stiffer springs are required to allow
higher RPM's to avoid valve bounce. 3) Higher lift cams, High lift rockers
may require different springs to avoid coil bind. 4) Too high rpms, too soft
a spring can induce valve bounce at high rpms.
If this is too much of an issue to go over in an Email, can someone
recommend a good book? I have three so called blue printing books, the Peter
Burgess books etc and they all just kind of skip around these issues and
expect you to just 'know it'.
The reason I'm asking is I have to take the head back, because the seats
were recut after the port work, and when they reassembled the head, they
didn't recheck the pressures - and also forgot to reinstall the spacers. I
noticed the spacers weren't there and asked why. The guy at the shop thinks
it's best to recheck them again and see whats required to quote unquote "get
max perf from the head". This is the bit I don't understand and I guess it's
all related to the springs... For instance how does different spring
pressures valve to valve or exhausts to inlet affect the performance? Smooth
running? OK so anyone care to go over these principals??? <G> It's all a bit
too confusing without all the facts. :)
Xmas Cheers to everyone,
Neil.
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