[s-cars] Good read on cylinder pressure, engine balance, mep bmep etc..

Thu Mar 11 13:07:51 EST 2004

http://www.ceconet.com/actt/actt_main/downloads/Engine%20Balance%20-%20T
he%20Thinking%20Has%20Changed.pdf

Ok this is a really good read on the subject and more to the point that
I was looking at, cylinder pressures, mep timing etc and how they
relate.

-----Original Message-----
From: MLP [mailto:mlped at qwest.net]
Sent: Thursday, March 11, 2004 7:50 AM
To: s-car-list at audifans.com; CaptMagu at aol.com; richard at tanimuras.com;
Audi20V_Kruemmer at yahoogroups.com
Subject: [Audi20V_Kruemmer] FW: [s-cars] I don't understand lowering CR
for boost

Well, Ok, this ought to expose my ignorance in trying to work
ass-backwards
to justify the faith / conventional wisdom for arguing on should
consider
dropping stock CR's slightly for added boosted engine performance.  What
do
you think of this approach:

                CR                MaxBoost           Effective CR (the
java
applets say)
Stock        9.3 to 1          20.0  psi   ~~~>  @ 21.95 to 1

I know everyone is/wants to run more, in fact a lot more than a paltry
20psi, but just for arguments sake, lets suppose the above represented
the
practically knock/no-knock limits of your fuel/motor.  Can one then
assume
that, to get to the same CR limit if you started off with, oh for
example,
an

               8.0 to 1          20.0 psi   ~~~>   @ 18.88 to 1
               8.0   "            25.6 psi   ~~~>    @ 21.93 to 1

So, with an 8.0 CR, and an assumed VE of say @ 85% "fill" and ignoring
for
the moment (lets say you just have an awesomely powerfully efficient
FMIC)
any significant temperature differences at the intake manifold in the
arriving 20psi in the 9.3 CR motor vs. temperature of the arriving 25.6
psi
for the 8 to 1 CR motor, then

in Case #1, for the 9.3 to 1 engine, you get to jam some 378 cc's (being
@
85% of a swept cylinder volume of 445 cc's) of 20 psi charge vs. Case
#2's
378 cc's of 25.6 psi air/fuel in the 8 to 1 motor.  Somewhere there's
got to
be a conversion for psi of air to mass or lbs/air, and assuming the
temperatures are roughly equivalent, there's got to be a lot more
combustible O2 in the 26psi air charge vs. the 20psi charge on a cc for
cc
basis.

Alternatively, one could play with and compare the Ray Hall boost applet
results at http://www.turbofast.com.au/TFcompB.html  which suggests that
to
run 20 psi of boost in a motor with a standard CR of 9.3 to one (81mm
bore,
86.4mm stroke & a VE of 85%) the applet suggests one should be using
118.4
octane gas.  With a standard CR of 8 to one, at 20 psi the octane
recommendation drops to 110 gas.  One has to push the boost up to 26+
psi in
the 8 to 1 Cr motor to get the anti detonation gas requirement back up
to
the 9.3 to 1 @ 20 psi's 118 recommendation.   Isn't 110 octane vs. 118
another way of looking at ignition advance?   So again, with the 8 to 1
CR
one gets to run an additional 6psi of boost vs. the stock 9.3 to 1 CR
motor.

So, assuming you get your chip map(s) adjusted to your revised base CR,
you
get to run a lot more boost, with perhaps a bit more advance to make up
for
power lost in off boost, naturally aspirated mode by dropping the
compression ratio?  My guess is the major re-mapping must be in the
ignition
timing area of the ECU's triumvirate, boost v. timing v fuel at
rpm/load? 

Minhea? 
Bob P.?
QShipQ? 
Anyone else got an opinion?

mlp

-----Original Message-----
From: CaptMagu at aol.com [mailto:CaptMagu at aol.com]
Sent: Tuesday, March 09, 2004 8:11 PM
To: mlped at qwest.net; richard at tanimuras.com; s-car-list at audifans.com
Subject: Re: [s-cars] I don't understand

Mike  

I want the reeeeaaaallllyyyy long answer.

Hap, dreamin in Evahboost, Maguire

[Non-text portions of this message have been removed]

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