mgs
[Top] [All Lists]

Re: cooling

To: MG Mailing List <mgs@autox.team.net>
Subject: Re: cooling
From: Aaron Whiteman <awhitema@panix.com>
Date: Sat, 3 Feb 2007 17:46:49 -0800
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?

[demime 1.01d removed an attachment of type application/pkcs7-signature which 
had a name of smime.p7s]




<Prev in Thread] Current Thread [Next in Thread>