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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