[Diy_efi] RE: Diy_efi digest, Vol 1 #413 - 12 msgs

[Shannen Durphey]

Point taken.  I may yet be introduced to that situation.  But what we're
talking about now, tuning a car to run at Daytona, is a long ways removed
from what most of the guys on this list will ever do.  I could say that
your situation is not typical and isn't what the majority of chassis dyno
tuning involves. 

Not all shops with chassis dynos are tuning shops.  Some only offer a dyno
and their operator, rent out the tools so to speak.  Many of the DIY guys
here will get on a dyno for the first time to tune their own car or their
friend's car, and be blown away by all the stuff going on.  In the process
of tuning, they'll take a bunch of time to get dialed in.  I stand by my
warning that using a braking type dyno can give a less than optimum tune,
and I stand behind my reasoning why.

And the question wasn't even addressed, how do you decide "right?"  I'm not
asking about the actual tuning process.  I'm saying that you tune for
durability vs power.  It's pretty common for guys to give up some
durability to make more power on a short track.  If you've tuned the engine
to live longer, you're trading some power.  If you're getting passed
because of that decision, it was the wrong "right."  Yet again the tune for
the long, heavy load isn't optimum for the short, light load.

Gear and load corrections can be a good thing.  Understanding how or even
if these corrections are included in factory calibrations can be a
challenge.  I've been looking at modifying the code in my ecm to adjust
boost control based on engine acceleration rates and the boost rise time. 
It currently uses a table of fixed "duty cycle vs rpm" values to apply to
the boost control circuit.  Every change to the hardware requires a table
rework.  Using engine acceleration and the change in boost over time will
allow the ecm to do a better job of predicting where the boost will be at a
given rpm.

Shannen



Dave Dahlgren wrote:
> 
> I think you need to introduced to the long straight at Daytona up on the
> banking.. No matter how heavy or light your car is you hit the aero wall so to
> speak where it is on the floor and she won't go no faster... That is what a
> brake will give you and you better be correct at that point. The better after
> market stuff has tables and corrections for what gear you are in. You can and
> should change timing fueling and boost according what gear you are in as it
> compensates for the relative load on the engine.
> Dave
> 
> Shannen Durphey wrote:
> 
> > Using a braking type dyno to tune a car for WOT can produce misleading
> > results.  A lightweight car with a high power to weight ratio would
> > typically never see the same load and duration that can be applied with a
> > brake type dyno.  Running up to a specific rpm and holding that rpm while
> > fuel and spark are tuned in will tend to heat parts more than they would be
> > heated in "normal" operation.  The consequences can be more fuel/ less
> > spark than optimal get dialed into the final tune.  Power may be down, fuel
> > consumption may be up, or both can occur.  The inertial loads alone provide
> > more than enough resistance to provide an acceptable street and competition
> > tune for these vehicles.
> >
> 
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