[s-cars] "... a vacuum cleaner on steroids..."

[MLP]

I think I missed the Friday afternoon laughs, but to start the week off
right, from this weeks 
issue of AutoSpeed, http://autospeed.com/cms/A_2063/article.html  we
have 

1.  the possibly serious contender, http://www.boosthead.com/product.php

2.  the not so serious, http://www.electricsupercharger.com/ and
3.  the laughable, http://www.autospeed.com/cms/article.html?&A=0237

also a Pribble alert, in the google advertisers box that pops up at the
end of AutoSpeed's on line articles, .... you guessed it, a current link
to a list favorite, the Noi Joisey tuning experts, http://motodyne.com/
who appear, still, to be alive and well not with standing the hit out on
Jimmy.  Let's hope for Jimmy's sake that the "hit" is coming from
motodyne's SL500 #1 employee, I guess her name is Mercedes? 

Finally, NAC but interesting none the less, especially for those who've
been playing around with their intake systems and / or head chambers, 
is the "Cylinder Specific Tuning" article at 

  http://autospeed.com/cms/A_2061/article.html 

".... Any variation in breathing between cylinders has significant
implications for causing a cylinder-to-cylinder power imbalance.
Randolph used in-cylinder pressure measurement to quantify the mass of
air being breathed. (These measurements were made with the engine being
driven by an external motor and measuring peak pressure during the
compression stroke.) He found that this pressure measurement provided
information that could significantly vary from the sort of data gained
on a flowbench. "
"A four-cylinder engine was tested in this way. The engine used an
intake manifold where Cylinders 1 and 4 had the same length intake
runners, and Cylinders 2 and 3 were the same length, but these were
shorter than 1 and 4. There was a measured dynamic compression pressure
difference between the cylinders at all engine speeds. Specifically, at
around 3000 rpm the short intake runner cylinders had more airflow
(which would cause them to run leaner in a multi-point EFI engine),
while the two different lengths of intake caused resonant tuning peaks
to occur at different rpm - for Cylinders 2 and 3 it occurred at 4000
rpm, while for Cylinders 1 and 4 it was at 3600 rpm. 
Unlike dynamic in-cylinder pressure measurements made with the engine
being externally driven, measuring variations in cylinder-to-cylinder
mixtures is easily carried out with multiple oxygen sensors. Many
workshops specialising in engine-dyno tuning use multiple wide-band
oxygen sensors in this way. (A cruder method is to measure individual
cylinder exhaust gas temperatures.) 
Cylinder to cylinder air/fuel ratio imbalance is likely to occur because
of a variation in flows (covered above) or the use of non-matched
injectors. 
Randolph tested a carburetted V8 race engine and found that the actual
cylinder-to-cylinder air/fuel ratios at peak power varied from 11.1:1 to
13.9:1! Importantly, the average air/fuel ratio was 12.5:1 - an AFR
usually employed to gain max power on a naturally-aspirated engine. (And
in this case, an air/fuel ratio analysis of the total exhaust gases
would have shown this 12.5:1 figure.)
Looking at the data in more detail, it was possible to work out how much
each cylinder was losing in power due to its leaner or richer mixtures.
This analysis indicated that Cylinder 5 (an AFR of 13.9:1) was down in
power by 2.1 per cent, while Cylinder 2 (AFR of 11.1:1) was down by 1.1
per cent. The overall average power loss through the
cylinder-to-cylinder AFR variation was 0.7 per cent.
However, Randolph suggests that the 0.7 per cent power loss is extremely
conservative because it doesn't take into account the flow-on effects,
eg that the ignition timing that will be able to be used will be in part
be dictated by the leanest cylinder, because detonation is more likely
with that cylinder's higher combustion temperatures. 
Burn Rates  ~ The variation that occurs between cylinders in their burn
rates and in-cylinder flows can be significant. This is especially the
case because these factors will affect the minimum ignition timing
advance for best torque.
....
Knock ~ Randolph performed some testing on a V6 engine. To reach the
same level of knock intensity in each of the cylinders, the variation in
ignition timing amounted to 8 degrees. That is, in the test engine
Cylinder 4 could tolerate only 4 degrees of advance while Cylinder 1
could tolerate 12 degrees! In this engine an increase in peak torque of
about 5 per cent was possible if each cylinder was optimised with
greatest ignition advance prior to the onset of knock. 
However, another test engine - this time a V8 - had only a 2-3 degree
spread across all cylinders. 

  :-)

mlp