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I'm getting ready to purchase a throttle body plenum combo, but as far as size which is better the 70mm or the 75mm? I have no plans for any FI. Just sticking to bolt ons. Current mods consist of, SCT 4-bank chip, BBK CAI, Exhaust(2.5 O/R H w/ Super 44's) 3.73 gears, Auto w/ shift kit, and accel super coils.
 

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I'm getting ready to purchase a throttle body plenum combo, but as far as size which is better the 70mm or the 75mm? I have no plans for any FI. Just sticking to bolt ons. Current mods consist of, SCT 4-bank chip, BBK CAI, Exhaust(2.5 O/R H w/ Super 44's) 3.73 gears, Auto w/ shift kit, and accel super coils.
Stick to the 70mm if Forced induction is not in your plans. I'm running a trickflow 70mm throttle body and upper plenum and love it!!
 

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i got a bone stock gt....lookin to upgrade my babys breathing apparatus (plenum specifically)...anyone here got something they want to get rid of?? (pm me and lemme know)
 

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The only difference you'll notice between the 70mm vs. the 75mm is throttle response and at what percentage of throttle you'll hit WOT. Remember, although the TB doesn't "add" power, it lets more air in than stock, but has a diminishing point. Your normal TB is calibrated with your TPS to tell the computer that when the pedal hits the floor, you're at 100% or WOT. When you go with a larger TB, you'll hit WOT earlier than when the pedal hits the floor, and you'll have a much snappier engine response from idle. Anything beyond WOT even if you're pedal is only 3/4 pressed is just dead pedal and doesn't do anything. Personally, the 70mm is your best bet if you have no plans of ever using forced induction, nitrous, or fuel upgrades. If this is ever a possibility in the future, save yourself some money and just go 75mm. This way you're ready in the future for bigger upgrades. Hope this helps, take care!
 

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The TPS reports the angular opening of the TB to the PCM, something which remains the same regardless of what diameter TB is installed--it's just that for any given angular opening a larger hole is opened up. That is why a larger TB gives the impression of "snappier" response.

In a stock 2V tune any TPS output in excess of 2.71 V is considered WOT (in the tune's TP for WOT function). This is at about 55% open per this graph from the shop manual:



It is also important to realise that a larger TB has no effect until area of the "hole" opened up by the throttle plate becomes larger than the area of the "hole" in the smaller TB--when fully opened. This is why the effect of the larger TB only shows up on dyno charts at 5500+ rpm; below that the stock TB can flow enough air. The larger TB does not make the engine take in more air, but instead allows the engine to breath more easily when it needs more air after 5000 rpm...
 

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The TPS reports the angular opening of the TB to the PCM, something which remains the same regardless of what diameter TB is installed--it's just that for any given angular opening a larger hole is opened up. That is why a larger TB gives the impression of "snappier" response.

In a stock 2V tune any TPS output in excess of 2.71 V is considered WOT (in the tune's TP for WOT function). This is at about 55% open per this graph from the shop manual:

It is also important to realise that a larger TB has no effect until area of the "hole" opened up by the throttle plate becomes larger than the area of the "hole" in the smaller TB--when fully opened. This is why the effect of the larger TB only shows up on dyno charts at 5500+ rpm; below that the stock TB can flow enough air. The larger TB does not make the engine take in more air, but instead allows the engine to breath more easily when it needs more air after 5000 rpm...
This is a plus one for you. +1
 
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