Bruce:
For these kinds of questions, you will get lots of opinions. Instead,
why not pop $40 and get Dyno 2000 engine simulation software? You can set it up
to match your existing engine (stock) and then try tweaking compression,
camshaft duration and lift, etc.
What I found on the simulator is (surprise!) is that the answer
is "none of the above". Changing the camshaft and cam lift yield
disappointing results. The reason is the low static compression ratio
of the stock motor.
If you are going to spend money, the best thing you can do is
raise the compression ratio to about 9.5:1. This is good for almost
15HP, and will give you a nice pop in fuel economy too.
After you have done this, *THEN* all the other things start to
work as you might expect; Changing the camshaft gives you decent
improvements, changing the cam lift gives you more power, etc. Until
you raise the compression, anything I tried gave very small improvements
in power.
I should state for the record that this package is not terribly good
to predict power unless you have a known baseline that you can calibrate
the setup to. For example, you need to play with the intake manifold and
exhaust manifold parameters to match the power output of a stock engine.
If you didn't already know the output of a stock engine, simply plugging
in some guesses would not get you very close to the correct engine output.
Just my $0.00000000002,
Vance
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The most likely way for the world to be destroyed, most experts agree, is
by accident. That's where we come in; we're computer professionals. We
cause accidents. - Nathaniel Borenstein
-----Original Message-----
From: Simms, Bruce CIC [mailto:BSimms@cicorp.sk.ca]
Sent: Wednesday, May 21, 2003 2:48 PM
To: '6pack@autox.team.net'
Subject: Performance camshaft vs. roller rockers?
The head is off my 73 and at the machine shop for repair and upgrade. Will
get hot tanked, crack tested, shaved to 9.0 compression, port matching and
relief of valve shrouding as recommended by various listers. Mechanic
reported several bad exhaust valves and valve seats. Bottom end looks good
as examined with head off. 69-73 (CF12500) camshaft is not ideal for
performance, so something needs to be done. Dyno test curves in Comp Prep
Manual indicate that camshaft upgrade is crucial. With head off, it's
probably what, an additional 3 hours for my mechanic to change the cam.
Would send my old cam and lifters to be re-ground at a cam specialist such
as Colt Cams in British Columbia. (I'm in Canada). Also have HS6s, header
and custom dual exhaust.
The other option may be roller rockers. Would roller rockers such as Jim
Swarthout's 1.75 ratio give me an upgrade in performance similar to a street
profile cam of say 270 degrees duration? Would likely do the roller rocker
conversion myself. Mechanic says my rockers appear to be in good
condition. The roller rocker benefits of added efficiency and decreased
wear are likely nice things by themselves.
All advice and opinions much appreciated. The list is a tremendous
resource. NFI in any auto related business, just trying to get a nicely
upgraded road engine at reasonable cost.
Regards, Bruce Simms CF1941UO
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