First Generation Firebird-L Mailing List
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Agreed.
There are a lot of variables not known here. What cc Edelbrock heads did he
put on there? What head gaskets? Any milling of the heads? You may need
more than 91 octane in your engine.
Use the Internet to help you. Google search is your friend. :) One 30
second search gave me this info....
"
The question "Is regular-grade gasoline as good as premium gas for your car"
is inadequate to encompass the role that octane plays in your car's engine.
Too much depends on your particular engine's design. But since most people
will be putting regular gas in cars that are just fine with it, and cars
designed to work best with premium can usually tolerate regular, the least
inaccurate answer is yes.
That's because most cars do not have a problem with pre-ignition, the
tendency of the fuel to start burning before the spark fires, when running
on regular gas. The fuel's octane number represents its resistance to that
pre-ignition, which could damage your engine, since the resulting explosion
would begin while the piston is still rising in the cylinder in the
compression stroke of the Otto cycle. That octane number is a percentage of
resistance to preiginition in comparison to a standard fuel, called
"octane." If the fuel resists pre-ignition 10% better (fires at 10% higher
pressure) than octane, it has an octane number of 110. If it's 10% worse
(fires at 10% lower pressure), its octane number is 90.
Engineers take advantage of that resistance to preignition to improve the
efficiency of their internal combustion engines by raising the compression
ratio. When they do that, at the beginning of the power stroke the engine's
fuel/air charge is squeezed into a smaller space, and the pressure at
ignition is therefore higher. At the end of that stroke, the volume in the
cylinders of otherwise identical engines is the same regardless of the
compression ratio, so the mean effective pressure in the cylinder is higher
in the higher compression engine. More pressure means more power.
That can't work if the octane number of the fuel won't support the added
pressure.
Raising the compression ratio not only improves power, but since it takes
the same amount of gas to cause a higher cylinder pressure, it also takes
less gas to give the same performance. So higher compression engines give
better fuel economy than low compression engines of the same power.
The result of all this is that while a modern high compression engine will
protect itself from damage caused by using a lower octane gas than the
manufacturer recommends, it does so by initiating the spark earlier in the
power stroke ("advancing the spark") and adding more gasoline into the
incoming charge ("richening" the fuel mixture). Both of these strategies
reduce efficiency, burn more gas, and lower performance.
So you won't necessarily save money by using lower octane gas in an engine
designed for premium. It actually lowers your gas mileage. To know for sure,
you'd have to do instrumented tests to figure out whether the lower cost of
regular (typically less than 5% here) justifies the loss in fuel mileage. If
you lost even 1 mpg, the math doesn't support the switch to the lower grade.
And if your engine predates computer controls (sixties muscle cars, for
instance), don't take a chance. You could end up with a blown head gasket, a
broken piston or rod, or even a hole in the cylinder wall.
"
Thomas
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Hugo Tafel
Sent: Sunday, January 24, 2010 11:52 AM
To: First Generation Firebird-L
Subject: Re: [FGF] Re: 87 Octane and Blown Head Gasket
First Generation Firebird-L Mailing List
.........................................................................
Anything is possible. A bad case of pre-ignition can blow a hole through the
piston so if all it did is blow a head gasket, then it's (relatively) easily
repairable.
Pre-ignition can also be caused by the timing being too far advanced (and
many other things).
Do you know what compression ratio he built your engine to?
Maybe he decked the engine for the new heads and now your compression is way
too high to where even 91 octane isn't good enough?
Do you have a temperature gauge? If so, did you notice the car running hot?
Make sure the guy stands behind his work and don't let him push you around.
Hugo
--- On Sun, 1/24/10, [email protected] <[email protected]> wrote:
From: [email protected] <[email protected]>
Subject: [FGF] Re: 87 Octane and Blown Head Gasket
To: [email protected]
Date: Sunday, January 24, 2010, 5:12 PM
First Generation Firebird-L Mailing List
.........................................................................
I am not well versed on mechanics but own a 69 Firebird Convertible that
recently had a 400 block rebuilt with Edelbrock heads. I pinging type sound
begin around Christmas. I took it in to the engine rebuilder and was just
told the head gasket was blown and the reason was due to regular gas being
put into the tank. I only use 91 octane. He admits there was sign of the
engine being overheated. Even so, has anyone ever heard of a head gasket
being blown by reason of bad gasoline or low grade gasoline? The car has
been driven less than 2,000 miles since the rebuild. Thanks...Al [Vntge60]
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