----------
From: Chip Bond[SMTP:spirals@esinet.net]
Sent: Sunday, September 14, 1997 9:11 PM
Subject: RE: Compression check
>Actual, or effective? I believe the effective compression ratio is
the important factor in determining HP output, octane required, etc.
Speaking of HP engines, there are a number of articles stating that
putting a HP cam in an engine will effectively lower the effective
compression ratio and hence allow running on pump gas... an alternative
if you milled the head too much!
Lower octane contains more BTU than High Octane gas. The additives help
slow the burn, which is good for a tractor motor. A high overlap cam will
reduce the CR at low RPM (all else remaining the same). It will actually
spit at you from the carbs at low RPM. The question is what really happens
at, say 5500 RPM??...... At that speed the MASS of air (Mixture) has a lot
of inertia. Or, the column of air is moving very fast through the induction
tract. At this speed, if the exhaust valve is still open a little, the NEW
air has an opportunity to displace the the burnt air. Thus a better charge.
>At low RPM, with a HP cam, a lot of the new charge just goes through the
exhaust, less compression, less need for slow burn, lower Octane.
>I am certain the wait will be short! Equally certain is my fate in sharing
the "idiot" suit with you... Been there, burnt the book.
Rog, we are just a bunch of guys, that for some reason on another, wish to
HOT ROD Triumphs. Nick has been doing it as well, if not better, that the
rest of us. Look at the true absurdity of creating a HOT tractor motor,
then just grin :>) a little.
{I hope to have factory support for the next season :-}
>So, you guys with the letters after their name, this is SERIOUS stuff:
I agree, a three main crankshaft, cam cores that do not hve enough meat
left to grind to the desired new profiles, rocker gear that breaks when you
look at it. Aerodynamics that make a sheet of plywood look good. A 40 #
flywheel. This is serious.
>Assuming 92 high octane pump gas, how much do I mill the head to maximize
HP?
(is the psi reading at 1500 RPM of any importance? Can we determine the
maximum ideal HP? Is "physics" a science or art?)
92 Octane: It's fine. Use a "calculated" CR somewhere arounf 9.5/1 to 10/1.
You will be fine. If the engine knocks (and you can hear it) back the
ignition timing down a little. To get there, check your head. If it
measures 3.330", cut it .060"- 090". Then radius the combustion chamber.
Get a cam with total lift around .0300 or less. (valve lift would be a
multiplier or 1.5).
I'm proud that I can pull my Ford tractor out of the barnyard muck with my
Tr-3. Really!!....Long chain,
Bye for now.
Chip
|