DeTomaso Mailing List: March 2000, Message #145

Greetings from Downunder.
There is a very fine balance when setting the timing on an engine, I do
"in-cylinder" measurements on a large variety of engines (mainly diesel)
from 500 hp to 100,000 hp (officially the most powerful Diesel engine built
so far), we read the pressures inside the combustion chamber at a rate of
1440 times per revolution, then plot this against the crankangle, this
enables us to set the timing to within 0.1 degree of crankangle for maximum
power or efficiency.
What we find is that an engine too far advanced, produces a lot of pressure
while the piston is still on the upstroke, actually producing "negative
power", this then has to be compensated for by feeding in more fuel later in
the cycle (on an engine with computer controlled fuel injection), the early
ignition also means much higher peak pressures putting enormous loads on
pistons, rings and bearings, resulting in a highly stressed and inefficient
engine, this is why many times power can be gained actually retarding some
engines, of course keeping a close eye on exhaust temperatures.

Lars
Longchamp GTS #3215

----- Original Message -----
From: <RLG1973DT@cs.com>
To: Multiple recipients of list <detomaso@realbig.com>
Sent: Monday, 6 March 2000 6:04
Subject: 45 deg spark advance?


> An article written many years ago in Hot Rod on the 351C quoted Bob
Glidden
> as saying that the Cleveland "will like 44-46 deg of spark advance, even
more
> if using the open chamber heads."  Nowhere else I've seen recommended more
> than 42.  Of course, not many people were beating Glidden back then
either.
> There are some very experienced engine builders and dyno labrats on the
list.
>  What do you think about this, particularly with open chamber heads?
>
> ron
>
>