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Re: MacBoost II
In a message dated 97-02-13 09:41:21 EST, you write:
<< Scott,
I realize a 272, 276, etc. are not turbo cams, I don't think I said
they were? They do however help North American ur-qs rev more quickly
past 4,500, a big problem in my opinion. I'm sure you can remember
RDH's posts on the problems he had when he installed a 272 and the way
he fixed it?
>>>>> The rev past 4500 is a lift issue, offset by the overlap
issue... Lift is the key, and something somebody needs to address...
Basically, you want the lobes more cone shaped with high lift, get the air
in quickly shut things down, then repeat... So if a 272 with overlap gives
more power, think of a correct turbo cam application... I don't remember
RDH posts, but overlap on idle would be a serious rocket science exercise,
and not sure that's where the address was. My guess would be to get less
fuel (or more ignition timing) at pre 4500 levels (since HC levels are high),
then more fuel (less ignition) past.. Cam timing might be a little
different, and I would guess that is what he addressed.... Anyone? Where is
that rdh guy anyhow? :)
>>>>>> Correct me if I'm wrong (need I ask), but while adjusting the CO
mixture can be used to supply more fuel at idle, it will also
supply a non-ideal mixture throughout the rev range?
>>>>>
Well, if you look at lambda, 1.05 (15.4:1)is the max for fuel economy, .86
(12.6:1) for power... What this would make me look at seriously is how to
set ALL/ANY adj to get as close to .86 at WOT. If your other parameters fall
anywhere in between, you still have a net gain, something between 1.00 lambda
(stoich) and .86 the rest of the time, ideal... So, a serious look at what
the CO screw does is the key... If WOT is a specific fixed lambda duty cycle
(audis), what would you want to do with baseline.....
>>>>>>>>>>
I don't agree that the MAC02 is a lost cause, all the functions except
knock control are available (within the constraints of CIS) and this
can be addressed by advancing the ignition timing in the EPROM and
using an additional knock sensor circuit to dial back the timing to
avoid detonation.
>>>> Not hardly saying a lost cause... Just that the 02 has a limited
function.... Why not convert to a Mac 11B/C if you are doing the above, it
is really what you are talking about making, and now you have WGFV function
as well, the boxes already built.... Mr. Lawson can help you here ... My
point is boost is the majority of a tweek regardless of box, the later boxes
just fine tune the boost equation, as do all the hacks.
I'll repeat this, I'm not "knocking" Paul's mod, it's a very cost
effective way of improving performance. Personally though I don't
like the resistive divider approach because all it does is change the
output signal from the pressure transducer. Now the ECU sees less
pressure at the inlet manifold, the timing is advanced because the
timing versus RPM look up tables are a function of boost and now the
ECU thinks the engine inlet manifold pressure is less than it actually
is and so you run more ignition advance because your operating on a
lower boost RPM versus ignition advance curve, it works, but it is
crude. The relationship between timing and RPM as a function of boost
is complex and in my opinion not well controlled by only changing the
slope of the output voltage from the pressure transducer. (Although I
know you need to either change the pressure transducer or modify it's
output in some way to go any where beyond 16psi boost).
Hmmmm.... Great summation, anyone out there with "stage II" boxes ought to
save that one (really! :). Look at any TAP or NED box, and reread the above,
not disagreeing, just looking hard at what you are saying, a 2.0PT will only
measure to 2.0 bar (that's 14psi at sea level), beyond that the output is
constant, actually, with the mods out there, BEFORE that output is constant
(and it should be, given what it's doing).... You are correct, and yet, as
long as you have proper fuel, not necessarily a bad thing... Creating tables
that will prolly do the same thing as what you describe here, doesn't sound
like a lot of fun... Modifying tables to do what you described is
different.....
Once I've BTDT I'll be sure to post. I really wish I had more time to
spend working on the car... oh well, in the mean time I'll keep trying
to learn and offer advice when someone makes a blanket statement that
I don't agree with, of course YMMV.
>>
I sense you are seeing this as a slam, it is not Mike.... I personally know
of a lot of folks that have spent a ton of time executing your exact
thoughts, and some of your statements need to be tempered based on btdt, the
definition of practical engineering. I am the last one to flame anyone who
is going at this computer thing. It IS the way to go, certainly based on
what is out there. I know what Mr. Paul has done, and understand where and
what needs to be addressed... I'm not sure Paul's mod, regardless of EPROM,
won't be still one of the answers, that's why the temper... Here in my
office, I have sitting 8 chips, 4 11B/C boxes, all with various EPROM and/or
hacks. And from my car tweeks, btdt, theories and eproms aside, I'm convinced
that Paul's mod will stay, regardless of EPROM... This is more magic than
science, and the easy stuff has been addressed. One of the main reasons I
posted to you. There are a lot of "rocket" scientists (some literally) on
this list that understand theories and EPROM programming, unfortunately,
putting that in the car and making it work or work "better" is where this
group is, PT included... What we are all looking for is really what is your
mileage based on what you did that may vary.... The definition of BTDT, I
suppose. Please feel free to post and disagree, I do all the time, and
hardly a personal thing.... Going forward faster is my only goal (cars and
tweeks and posts), ck the archives....
Respectfully
Scott