QUOTE(r_towle @ Oct 21 2011, 11:33 AM)
So, if you are going out on a short trip...50 miles or so, you would be best advised by SDS to pull over three times and turn off the motor, then start it again to reset the ECU for a proper mixture?
I suspect most of the world does not have your specific regional elevation changes.....so that may be true.
If I used SDS, I would never have to deal with that issue...its all within 1000 feet difference around here...unless I decide to drive up a mountain...but then I can stop and start I suppose.
Sounds like a PITA....put a big red sign on the rearview mirror to remind you to do that once in a while...dang.
Rich
Hey Gang....I posted this thread to Ross Farnham at Racetech/SDS to get his comments on how the system works with altitude changes. Here's his information:
"The engine does not care what the baro is to any great degree when
starting within the normal realm of say sea level to 5000 feet MSL if
the start and ET values are set to some mean level as we recommend in
the manual. We apply no baro correction for altitude because the engine
only cares about MAP when running and this is an absolute sensor we use
so assuming the MAP values are essentially linear as we recommend, the
engine will lean automatically with altitude increase and richen when
going down. The fact that we have many hundreds of systems flying in
aircraft and UAVs to over 25,000 feet over the last 17 years shows that
the system works well over a very wide range of altitudes. Our system
does not "learn" a new map like OEM systems today or do anything
different when you turn power off and on again.
Generally the start and ET values have no effect on anything when the ET
is over about 130F as no enrichment is required above that point.
If closed loop is used in cruise conditions, the ECU automatically keeps
the AFR around 14.7 to 1 regardless of the open loop values.
With regards to merging TP and MAP, the first thing I'd say is, it is
usually inappropriate to use a hot cam and ITBs on a street engine
simply because there is no vacuum as soon as the throttle plates are
cracked open so there is no vacuum signal for the MAP sensor to measure
and send to the ECU- garbage in = garbage out. Also, even at idle, the
vacuum is so low you are only using half of the sensor resolution. We
can use TP for idle fueling only with warm cams to help stabilize it and
MAP above the closed throttle TP value but with high overlap cams, idle
vacuum actually increases at slightly high rpms and this inverts the
logical fueling that "normally cammed" engines have and need. We see
many people disregard our advice on this and end up with poor
driveability. You don't see OEMs use ITBs and high overlap fixed cams
(usually VVT with mild cam timing down low). They also use MAF which is
not affected by idle vacuum values. 3D systems would have an advantage
here over a 2D system but MAF is is much better idea than MAP when using
hot cams and ITBs and I believe any programmable system able to use MAF
will be superior in this application. MAF is messy though with ITBs as
the ITB inlets need to be merged into an airtight airbox with MAF sensor
attached to the front.
You can switch SDS to TP but then you have no altitude compensation and
TP setups are usually harder to tune because people don't grasp the
concepts well.
Well executed plenum style manifolds and single throttle bodies
generally work much better on street engines. ITBs have their place on
race engine where revs are high, throttles are generally half to wide
open and low end cruise and driveability are not very important factors.
The ECUs simply respond to their programming- they don't know any
better if it is good or bad for the most part although we have an auto
enrich function if a WB is fitted to help save the engine from really
bad programming."
So, my understanding is: If you're on MAP sensing, it compensates automatically--they use these systems on aircraft for heavens sake! If you're on TP sensing but in "Closed Loop" mode, the system will strive for 14.7:1 AFR regardless of altitude, which covers any cruising type of street driving. If you're racing at an altitude markedly different from where you developed the fueling values, you'll need to lean or enrich your whole table--which really only takes 5 minutes once you've done the homework. My 2316 on SDS with TP sensing with Jake's 9560 cam works wonderfully for me in street driving and DE's at VIR & Summit Point--elevation changes less than 1500 feet total.