Jon,
A lot of info here. You are right the TPS just measures throttle
position (generally a voltage from 1 to 4 or 5 volts, closed to open).
If you open up the
throttle bores, you are allowing additional air to flow to the engine
and the TPS is generally used to determine how far your foot is in it.
If you are in closed-loop,
(the engine is looking at the sensors and pulling values from the fuel
and ignition maps, you could end up with a lean condition or worse yet,
the values between
the sensors may be so mis-matched that you get a "Check Engine" light.
This is all based on the strategy the Powertrain programmers have
programmed into
the computer (and it is classified). The values in the "look up" tables
are all based the total powertrain package. The programmers generally
don't take into account
and individual installing a TB that flows 30% more air then the
original. They do take into account temperature and altitude variations.
My goal would be to provide
additional fuel for the additional air, throughout the entire RPM and
power range, not just a WOT. By looking at the exhaust before the Cat, I
can tell if I have a
lean condition. I wanted to take the easy way out (find someone who has
already performed the work and just copy the TB mods at a lot less
cost), but I haven't
found anyone who has done the dyno work. In regards to some type of
microprocessor, I suspect that something as simple as a resistor or
re-clock on the TPS
would be good enough if there is indeed a problem. Again I am looking
for driveability and power, I don't want to loose anything. Once I get
all of this resolved
in my mind and I sure the mods can pass emissions tests, I wouldn't mind
doing the work for other people. It is really a simple 15 minute task. I
did check
with Barry Grant (Barry Grant Carburetors) and they have NOT modified a
TB for the Magnum (misprint in some magazine). I guess this will be my
next project.
Frank
> -----Original Message-----
> From: Jon Steiger [SMTP:stei0302@cs.fredonia.edu]
> Sent: Tuesday, August 18, 1998 3:08 PM
> To: dakota-truck@buffnet.net
> Subject: RE: DML: RE: Throttle bodies again.. (was: 98 R/T power
> mod's que stions)
>
> On Tue, 18 Aug 1998, Holloway,Frank T wrote:
>
> > Bill,
> > Thanks for the info. Getting larger plates and boring out the TB is
> > actually the easiest part of the job. Once I make the hold-down
> plate
> > for the TB and
> > the fixture to hold the throttle shaft for modifications, the actual
> > time should be less than 15 minutes per throttle body. I'll find out
> > what year TB's are
> > interchangeable. Getting flow numbers both before and after will be
> > easy to. What concerns me more than anything is the relationship
> between
> > the Throttle
> > Position Sensor, Map Sensor, Engine Controller, and Air Temp.
> Sensor.
> > Wide Open Throttle will benefit from the Mod. because the engines
> run
> > rich at WOT.
> > Cruise won't be a problem because the Engine Controller is in
> > "closed-loop" and is looking at the O2 sensor and adjusting fuel
> based
> > on O2 readings. Part-
> > throttle acceleration could be a problem because the Engine
> Controller
> > is looking at the above sensors and making fuel and ignition
> adjustments
> > based on
> > these, with larger plates the TPS will have different inputs to the
> > Controller.
>
>
> The inputs from the TPS would be the same regardless of the plate
> size,
> wouldn't they? On my '96, the TPS appears to simply measure the
> rotation
> of the butterfly shaft (0-90 degrees) The only problem (as I see it)
> is:
> if the computer is calculating the air flow based on the butterfly
> position
> and the stock bore, it would think that there is less air flowing than
> there
> really is which might cause a slightly lean condition? I don't know
> anything about
> the function of the map sensor, so I can't comment on that.
>
> I suspect that the larger bores wouldn't cause a problem, but if
> they
> did, it shouldn't be too hard to burn a microcontroller which would
> read
> the TPS output (probably just a voltage?), calculate the amount of air
>
> flow, determine what the throttle position would be to create the same
> air flow in a stock throttle body, and transmit the corresponding
> voltage
> to the PCM. So, taking an exaggerated example, say the throttle is
> 1/2 open
> (butterflies at 45 degrees). Based on the new bore size, the
> microcontroller
> determines that the TB is flowing 350cfm. Then, it determines what
> throttle
> position would be required to flow 350cfm on the stock throttle body,
> which might be 3/4 (or about 68 degrees of butterfly travel). So, it
> sends
> the appropriate voltage for 68 degrees to the PCM. This could be
> greatly
> simplified by making all of the calculations beforehand and simply
> storing
> them in a lookup table. In this case, the microcontroller would see
> a voltage from the TPS, then look up the corresponding voltage to
> send.
> It all depends on what you want to do with it... A microcontroller
> running at 10MHz or even 4MHz should be more than adequate to do the
> job. The advantage of doing the calculation right on the chip is that
> it would allow the new bore size to be input, through a plug-in
> keypad,
> a dip switch, etc. That way, you could use the same module on a bunch
>
> of different throttle bodies.
>
>
> > What I really need to do after the mods, will be to run
> the
> > truck on a dyno and
> > measure exhaust before the Cat and see what I have (the mod may
> require
> > re-clocking the TPS sensor). I have yet to find anyone that has
> actually
> > spent the
> > time on the dyno to measure the results. The last thing that I want
> is a
> > "Check Engine" light after the mods.
> > Frank
>
>
> Yep, it should be interesting to see the dyno (as well as the
> flow) results.
>
>
> By the way, I don't know if I missed an earlier post or something,
> but
> were you offering to do this conversion for others or was this just
> personal experimentation? I noticed a post from Bill who said he
> might be interested in a bored out version. If you are indeed
> planning
> on doing this, I would be interested as well. (Depending on the price
>
> and my financial status at the time, of course.) :-)
>
>
> -Jon-
>
> .--- stei0302@cs.fredonia.edu
> ----------------------------------------.
> | Jon Steiger * AOPA, DoD, EAA, MP Race Team, NMA, SPA, USUA *
> RP-SEL |
> | '96 Dodge Dakota v8 SLT CC (14.85@90.72), '96 Kolb FireFly 447
> |
> `--------------------------- http://www.cs.fredonia.edu/~stei0302/
> ---'
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