I'm going on what I remember, but I very well could be wrong below,
consider it opinion. Also, I've fixed your post so that it isn't top-
posted.
On Feb 3, 2007, at 11:12 AM, Bob Donahue wrote:
> On Jan 31, 2007, "riverside" wrote:
>
> I've always hear that high compression makes more HP by improving
> the efficiency of an engine. If that is so, shouldn't high
> compression also make less heat?
In all carburetor based engines, you are going to be drawing in a
fixed volume of fuel/air (the ratio will vary based on conditions in
the carb, but the total volume is fixed). You then compress this
mixture, and just before it is "as compressed as it is going to be",
you light it, which explosively expands. There is a delay between
the spark and the expansion, so by the time the mixture is really
burning, it is fully compressed; all the power of the expansion is
being used to push the piston down.
The more you compress it, the more energy you can pull from that
mixture, but no matter what, you burn the same amount of fuel.
Heat is going to come from three sources: friction in the engine,
heat generated by burning fuel, and heat from compressing the
mixture. Compressing the air/fuel mixture increases heat--this is
why higher compression engines are more likely to have pre-ignition
problems. If you compress things enough, you can incite the burn
without the spark, diesel engines take advantage of heat from
compression alone quite effectively.
> Why should the engine below be harder to cool than a standard B
> engine?
The engine, for reference:
>> up ( 1924cc, 270 deg cam, 9:0 compression, SU's,
>> minor head porting) B motor. I am not sure how much will be needed
The engine is bigger, so assuming the carbs are set up for the
1924cc, it will have more fuel, thus more charge to burn and more
heat. With the increased compression, you will heat the mixture more
before you apply spark. Both of these sources are going to increase
the heat in the block, which translates to more heat in the cooling
system, so the cooling system has to work harder to maintain the same
temperature vs a 1800cc engine.
--
A: Because it messes up the order in which people normally read text.
Q: Why is top-posting such a bad thing?
A: Top-posting.
Q: What is the most annoying thing on usenet?
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