Contour Enthusiasts Group Archives Forums Modifications Duratec Performance Throttle Body

Just a consideration, but with such a large TB as a 65mm, I think you'd really kill off the bottom end of the motor. This may or may not be a concern, depending on your application, but 65mm's isn't going to generate as much velocity at the lower rpms as the smaller TB. I don't have enough experience with how TB size interacts with IMRC and the primaries vs. secondaries, perhaps it wouldn't be as bad as I think. I know on my 3.4 liter pushrod Grand Am, stock is 56mm, we have a 62mm avalible which helps quite a bit, but going beyond that is really detrimental for the bottom end, you just can't generate velocity in the intake system. Like I said though, this is just theory for me thus far on the Duratech, I don't know enough about how TB size interacts with multiple length runners.

Seeing as the low speed (long) intake runner diamters remain unchanged, and they are more of a restriction than the TB itself - the ONLY way you MAY see a low of low end torque is by opening the the TB 100% at low rpm's (mashing the gas pedal). There may be some inital hesitation but that should only be temporary.

I agree. When I tried to explain this before no one got it!
Without the secondary plates in then you have more than twice the diameter and the thottlebody once again becomes the restrictor, so your bottom end will SUCK with an even bigger TB when they are deleted.

I run the big 70mm TB baby ...with secondaries left in just for this reason. I don't suffer any low rpm driveability or powerloss from it and I get pretty much instant throttle response. Anything above 3000 rpm and I'm pushing positive pressure from the turbo so I don't notice any issues with it.

Turbo's solve everything!

Stazi: You're missing the basic math.... The further the cable attachment point is from the centre of the shaft, the larger the arc of movement. A larger arc will translate to less radial movement of the shaft for an equal amount of movement longitudinally at the cable. Therefore, unless the distance from the outer perimeter of the fulcrum to the centre of the shaft is the same radius of the arc will be different and the amount of travel will also be different.

I agree wholeheartedly that the TPS is attached to the shaft and the PCM only senses rotation of the TPS.

One other issue for consideration is at what point in the rotational movement of the TPS does the PCM see WOT? This is important as it is the transition point from closed to open loop. The PCM "should" be able to compensate for the larger t-body during closed loop. Open loop maps are a different story.

The only thing that the larger fulcrum will do is make it so that you have to push the pedal farther to get the same amount of TPS travel. The TPS will get the correct information because it does not care where the gas pedal is, it only cares where the throttle butterfly is. No math involved.

What might end up happening is that the butterfly does not open all of the way. The only way to know that is to install it and see what travel you get.

Just so we are all clear on this one, I'd like to assist in clarification and I hope you don't mind as I'm just trying to help here.

Originally posted by Bradness:

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... The further the cable attachment point is from the centre of the shaft, the larger the arc of movement. A larger arc will translate to less radial movement of the shaft for an equal amount of movement longitudinally at the cable....

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I agree. Basically, further out the attachment the more the pedal has to travel in order to move the throttle plate. This increases the precision that the foot(driver) can use to control the throttle.

Originally posted by Bradness:

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... Therefore, unless the distance from the outer perimeter of the fulcrum to the centre of the shaft is the same radius of the arc will be different and the amount of travel will also be different.

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Again, I concurr. This is just saying that if the fulcrum is oddly shaped, or not perfectly round, then as it opens the amount of foot pedal travel will change making the throttle plate move faster or slower.
This is used by the designer to tune the throttle response and sensitivity as the throttle plate begins to open.

Originally posted by Bradness:

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I agree wholeheartedly that the TPS is attached to the shaft and the PCM only senses rotation of the TPS.

One other issue for consideration is at what point in the rotational movement of the TPS does the PCM see WOT? This is important as it is the transition point from closed to open loop. The PCM "should" be able to compensate for the larger t-body during closed loop. Open loop maps are a different story.

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I can answer this. It is a fixed percentage of the range of motion that the TB has. It is mostly around 60% opening and calibration is automatic unless the mounting position of the TPS in relation to the shaft is altered.
It does however have the capability to learn the load associated with those throttle positions and it becomes more accurate that way. That's how it adapts to the different throttlebody size.

Heres how it works:
The pcm can determine the min and max voltages from the tps because it uses the 3-wire setup, even if you don't move the pedal.
It has the reference voltage applied on one wire that is essentially the potentiometer wiper contact. Then the other two wires are hooked to opposite ends of the potentiometer. Depending upon the position of the wiper determines how much Distance is between the wiper tip and both ends of the resistive surface. So at idle, the wire 2 is high voltage and wire 3 is low voltage. Max out the tps at WOT and that switches to the opposite where wire 3 is now low and 2 is high.
There is some deviation from each potentiometer but they are precise enough that the voltage is within a 1 volt range for min/max voltages.
The WOT throttle point is measured in counts, not volts. THe counts are based upon whatever voltage range the pcm sees. 1023 counts. So if it were a 1 volt sensor range, the pcm will see about 0.6 volts as WOT since between 600-700 counts is WOT.
If it were a 5 volt sensor range then about 3.0 volts is the WOT point.
The driver will notice a difference in sensitivity with the pedal travel depending upon Fulcrum position and shape.