The factory 50mm throttlebodies were designed for an induction system flowing ~150HP per side. Keeping this in mind, it is of no doubt that this component in a powerplant system will become a significant source of restriction as you increase the power the engine produces. It is not uncommon to find some Z32s that are making at least 2X this much power at the crankshaft (~500RWHP).
Consideration in the induction system's piping must also be taken into account as well. If you put a larger throttlebody on the plenum and use the factory intake piping, you aren't really doing all that much for the system as a whole, so if you do decide to go to 60mm throttlebodies, it would be strongly suggested to also go to larger intake plumbing as well. This, of course, will make your work to make this a complete mod more time consuming and expensive, but if you aren't upgrading the pipes, this mod will have little effect.
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The throttlebodies used for my mod were acquired from a local junkyard. I hit up the Nissan section to find two Nissan vehicles that have a 60mm TB that can be used for this mod. The 1st is the 240SX and the 2nd is the Nissan Stanza 2.4L. I have found that the Stanza TB is a much better suit for this mod than the 240SX TB and this writeup will be based on the modifications necessary to fit the Stanza TB. I acquired these for $30 a piece (if memory serves) - you should be able to also get them for somewhere around this price range.
Here is a comparison picture of the Stanza TB next to the stock TB. You can see an obvious difference in the plate diameter as well as the positioning of the attaching bolts. The linkages are also quite a bit different as well.
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Step 1. Remove the linkage securing nut. The assembly will come apart as shown.
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Loosen the two phillips-head screws that hold the plate in position. Once these screws are removed, you can rotate the shaft and slide the plate out of the shaft.
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The Stanza TBs also have an internal water jacket just like the Z32's OEM TBs. The pipes leading to this jacket can be removed to help clean up the appearance of the unit. There are two locking pins that hold these pipes in place; one per pipe. Drill both of these out using a 1/8" drill bit.
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Once you have drilled the pins out, you can twist the pipes free from the TB. They are not threaded into the TB housing though - they are pressed into place and you will have to rock them about while pulling and you can work them out of position.
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The shaft is pressed into ball bearings housed with the TB and in order to remove this shaft, you will need to drive it out. Find a suitable tool; a punch works pretty well - here I am using a 1/4" driver extension and a hammer to drive it out.
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Once you have removed the shafts from the TBs, it would be a good time to clean your parts.
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In order to modify the linkage to work with the Z32 plenum, there are several parts of which you will need to use from the stock TBs in order to make the proper mod.
You can see in the picture that we have two mirror image linkage sets, but the Stanza TBs are only for one side. These issues are addressed in short time. At the moment, disassemble both linkage sets on the Z32 TBs and set them aside.
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When I did this conversion, I intentionally swapped the shaft stop on one TB so that I could install the throttle position sensor pointing backward rather than forward. This cleans up the area since the wiring harness connector will be pointing back towards the firewall rather than towards the front of the car. This connector gets in the way of the hoseclamps that hold the silicon coupler on the driver's TB. There is no problem with doing this - the TPS will still operate without any issues when you do this. In order to do this, you must remove the shaft stop and install it 180 degrees from its normal position. You only need to do this to one shaft, and this shaft should be used on the driver's side TB. You can see in this picture what I mean. Once you have done this, mark the shaft with the swapped stop plate as "D". You will then need to remove the stop completely on the passenger side shaft.
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Now that you have your stop plate swapped for the driver's side and the plate removed for the passenger side, it is time to install the shafts. You will need to drive them back into the bearings and be sure to install the shafts properly with respect to the driver's and passenger side orientation. The threaded end of the shafts need to point towards each other! Once the shafts have been installed, install the plates as well, using blue threadlocker on the screws. Be sure to properly center the plate before tightening the screws!
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There is a catch with the 60mm TB's shafts as the Stanza linkage has more components and the shafts are longer than the Z32 TB shafts. You must cut them down in length so that the Z32 linkage will properly fit. But before you cut the shaft, you must add additional threads to it so that you can thread the linkage nut on. The thread pattern is an M8X1.0. You will need to thread the shaft until the bottom of the threads are 1.4" from the shaft stop plate. You will need to do this to both TB shafts.
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Once the threads have been applied to the shaft, you will need to cut the shaft to proper length. The shaft needs to be cut 1.7" from the shaft stop plate. A hacksaw, bandsaw, or cut-off wheel will work. Both shafts must be cut like this.
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The TB is designed to have the linkage attached on the left side and there is a stud coming out of the side of the unit of which the linkage return springs loop around. This shaft needs to be cut down to length for the driver's side TB so that it does not interfere with the Z32 linkage. Cut it down to 7/8" long.
The passenger TB poses a bit more of a complicated issue since the spring shaft is going to be on the wrong side of the unit. The shaft will need to be removed from the passenger TB, a new hole will need to be drilled on the opposing side, and the shaft has to be inserted. I used a drill bit of slightly smaller diameter than the spring shaft and I press-fit it into place and cut it to the same length as the driver's side spring shaft. Once you have done this, you can now install the linkages.
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The passenger side TB will need a stop installed on the end of the shaft. You cannot go without a stop on a TB or else you will experience 'sticking' of the throttle pedal. I built the stop from left-over hardware out of the Stanza linkage. I used the stop plate that was removed from the passenger shaft and tack welded it to a collared bushing that fits over the shaft. You have to drill the stop plate hole into a circular bore (~0.310") to allow it to slip onto the shaft. I used the same drillbit to hold the assembly together for tack welding in the vice.
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Now you can slip this new stop onto the shaft and drill a hole for a roll-pin to be installed to hold the stop in position. Be sure to have the TB closed and the stop in proper position before drilling the hole - you dont want to mess this up.
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Now you will clearly note that the bore size of the new TB does not match the entrance port of the plenum.. The plenum will have to be opened up in order to take advantage of the larger TB. You can trace the bore with the two top TB bolts in place and open the bore up with a die grinder.
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Once you have opened the plenum ports, you are ready to go to the next step: adding material to the plenum to fill in the two lower bolt-holes for the original TBs as well as add more material to allow new holes to be drilled and tapped for the new TBs. I used a Lincoln Electric HD3200 MIG setup with pure argon gas flowing at 20cfm. The MIG power was set to "D" and spool-speed set to 10. I used 5356 0.030" aluminum spool wire with a 0.035" welding tip. Material was added in several passes and then sculpted to shape using a 10KRPM Makita with a 6" sanding disc.
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One both sides have been filled in and shaped, the TBs can be placed back onto the plenum using the two upper bolts and center the TB to the opening of the plenum.
- Using a scribe, mark the locations of the two lower holes.
- Remove the TBs
- Drill for an 8X1.25mm hole
- Tap hole.
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Once both sides are drilled and tapped, you are ready to install the throttlebodies.
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Since the thhrottlebodies are larger than stock, the centerline of the TB shafts are slightly lower in position. This means that the center throttle linkage assembly will need to be mounted slightly lower than the stock setup. To achieve this, the holes in the control linkage mounting bracket were bored out to 1/2" using a drillpress and bit.
The center linkage assembly MUST be installed prior to installing the TBs or else you will have no way of slipping the control linkage into place. Leave the three attaching bolts loose to provide a bit of slack until the TBs are installed.
Install the TBs on both sides and secure them down, using a new TB gasket. The part number for the gasket is 16175-SR20T through courtesyparts.com.
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Here it is: The 60mm throttlebody conversion writeup!>>> - 
