Re: Old car, new engine. Spanking...

In article <9_1Xh.716$zI1.488@xxxxxxxxxxxxxxxxxxxx>,
burgerman@xxxxxxxxxxxx says...


Hes probably got most of the extra power purely from daft compression
ratios. Try it it works! But you need higher octane fuels to stop it eating
itself.



Sorry but that is provable wrong: the extra compression raises the
theoretical efficiency but it contributes but marinal to extra power.

The formula is n = 1- 1 /(L^(k-1))

L= compression ratio
k is a ration which defines if the burning goes on under constant
pressure (=piston moving down) compared to burning under constant
volume (piston in TDP)

IRL k equals around 1.4.

The *theoretical* efficiency for L = 10 is 60% , for L =17 it is 67.8%

So if you take an engine and you change nothing but the compression and
supposing that the mixture doesn't detonate unwanted, the gain is power
would be 13% ( 67,8 /60)

Petrol engines are not build for the extra stresses that the compression
raise that high introduces, diesels are. NA-engines can not
"intercool" or liquidate the heat interduced by the compression.

IRL our Greek will get close to nothing on raising the compression ratio
that high because ignition will have to be retarded too. He has a nice
engine which in the escort Mk2 will be a blast to drive but it hasn't
400 Hp not by a long way.

Hp-figures sell, just like topspeed-figures and "race"-parts anodised in
fancy colors but weaker then OEM-parts. How often have we passed a
competitor who claimed he was above 200 kph when our datalogging showed
170 kph... Most of the time they went on complaining that our engine was
modified beyond the rules "cause he was over 200 kph"...

Tom De Moor



Tom De Moor
.

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