EA SW and TC vs SC
Todd King
Todd_King at ccm.co.intel.com
Mon Mar 24 20:19:34 GMT 1997
<<<
When I run my "Engine Analyzer" software and plug in turbo
or super charging, both definitely kick the hp and torque
up, but the SC is smoother and earlier. It also produces
larger numbers of both torque and hp. TC produces a 'squiggley'
graph, whereas SC produces a smoother, though peaky, graph.
Judging from the graphs, I wouldn't want TC on my truck
(4WD Bronco) app, as it actually hurts low-end torque a
little (below 2000).
>>>
Well Tom I run the EA SW too; you have to be careful with it on the forced
induction aspects. That torque peak you see corresponds to the simulated boost
finally getting up to what you entered, right? The SW has to "guess" as to
when full boost comes in. Having run turbo for a while now I can do sanity
checks on the results. Anyway, then the torque curve is monstrously high and
flat (definitely not "sqiggley"). For example, I use the medium (there are
only 3 choices) turbo size with a 55% percent efficient intercooler choice.
This (along with the rest of the engine specs) gives pretty darn good sim
results that closely match track results. It shows nearly 600 pounds of torque
at 3000 rpm from the 231" v6 on 50" hg (about the realistic max for the
production based motors), with ported factory iron heads and a 200'ish
duration/ .400'ish lift cam; I don't know how much torque you are after with
the 351 but I believe you can easily get what you need here :-) I'd have to
disagree with the assertion of larger SC hp numbers, unless you did not
include an intercooler in the sim. SC has been historically more glamorous
than TC but the facts are really just now coming into wide, general acceptance
on the TC issues and the limits are still being "pioneered". BTW Tom, I may be
moving to Austin soon- let's talk turbo at the Saturday night Round Rock
cruise or somethin'!
<<<
Now I don't want to start a flame, but you aren't getting something for
totally free here. A turbo raises your exhaust back pressure (by as much
as the boost I seem to remember someone saying - or close enough;) and the
power your engine has to use to fight that back pressure is volume*dP. And
guess what, the power reqd to compress the air at the intake is volume*dP.
>>>
Yep; BUT don't forget that most of that pumping loss is recovered by the
corresponding higher pressure on the intake stroke side, something most people
fail to consider!!! I don't want a flame war either so I'll have my say here
and then (hopefully) be quiet about it :-)
<<<
A SC takes it from the crank directly and a TC from the exhaust pressure.
Granted, the ~20 horses you lose will get you another 200+, so the net gain
is worth it;)
>>>
Yes, but since that crank drive is in no way harnessing any energy that is
normally just totally lost out the tailpipe then you are describing a true
parasitic loss! And BTW that 20 hp figure is WAY conservative to pressurize a
big motor at high boost.
<<<
The supposed in-efficiency compared to a turbo is there - but how
significant is it? Disconnect the belt and drive home at 80 anyway, the
>>>
Very! The Roots charger is typically about 45% or less efficient if I remember
correctly. More than half the input power is just going into heating up the
charge!!! Turbo compressors typically peak in the 70+% range.
<<<
street and other racing. Turbos can be taken to extremes that are beyond
the roots, but they are an order of magnitude more tricky, expensive and
complicated than the old fashioned roots and depending on what you want,
not offer that much more. Read all the posts about tweaking and peaking
>>>
Been living it for nearly ten years now; I have to respectfully disagree with
the above.
<<<
Either way, positive pressure makes much more power and thats all that
counts.
Robert Harris <bob at bobthecomputerguy.com>
>>>
You summed it up well Robert; totally agree here!
Todd_King at ccm.co.intel.com
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