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Location:
Kita-Ku, Sapporo, Japan
Registered:
January 2003
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Re: fuel tuning question
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Tue, 13 September 2005 13:31
 
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ahh, i mean, for each complete engine cycle (ie two engine revolutions), how many times does a particular injector fire?
and the reason i ask is because you say you have 7.3-7.8ms PW..
assuming the injectors fire twice per cycle (once per engine rev) at 6000rpm, you have 16ms in which to inject, and still be 80% duty cycle... 7.8ms x 2 = 15.6ms = 80% duty.
at 8000rpm, you have 12ms to inject, so 7.8ms = nearly 100% duty, which might have weird things happening.. which would begin around 6500-7000rpm perhaps..
wait, Wolf reports duty cycle no? what does it say?
umm umm.... VE is basically how much air is getting in as a percentage of 100% being the actual swept volume of the engine
the calculation would go something like this...
fuel injected = max flow of injector X duty cycle (probably in cc's).
convert cc's of fuel into mass then into Moles of fuel (approximate as octane for data).
work out how many moles of oxygen are required for nominal combustion, turn that into litres of air (24.47 per mole at 25C),
then divide by 0.21 to get moles of air. (or 0.06 for tokyo  )
that tells you roughly how much air the engine is pumping thru for stoichiometric AFR..
to convert air used to a certain measured AFR, divide air volume by 14.7, then multiply by the measured AFR (ie 11).
that gives you amount of air used for given AFR..
from there, you can easily work ut the VE, as you can calculate how much air the engine would use if 100% efficient (ie half swept volume X (1 + boost in BAR), x RPM. then divide the air vlume calculated before, by this 100% VE number, and you get the VE at a given RPM...
since the only variables are injector duty cycle, AFR, boost and RPM, you can probably just make it into an excel calc sheet and plug in the numbers...
maybe this doesn't help the original problem much.. 
i guess my vote is for intake tract restriction (taking a very simplistic view of the situation), or cam timing not allowing as complete cylinder filling.
on the dyno this will show up as a decrease in torque (before power tapers off), and since torque is directly proportional to VE.. it sorta makes sense....
hmm, you could read the megaquirt Megamanual  .. the MS is tuned by using nominal VE% which is multiplied by the "required fuel" for 100% VE.. making it intuitive to tune as far as the numbers go..
Cya, Stewart
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