Community Member Credit: Stephen Max
Here are the steps involved in converting to a 70mm Pathfinder throttle body:
1. Make or purchase adapter plate,
2. When you first do a trial fitting of the adapter plate to the intake manifold, you will see that the 70mm opening is considerably larger than the bore of the intake manifold. I got my high speed drill (cordless drills are too slow) and a bag of coarse grit 2” sanding drums and started opening up the intake to match. First scribe or mark the 70mm diameter of the adapter plate bore onto the mating surface of the intake. Then start removing material. I did it with the intake manifold removed from the engine. If you do it on the engine, stuff several rags down the throat to keep aluminum dust out of the engine and then use a shop vac to suck all the dust up. It’s a good idea to have the shop vac running with the nozzle fixed in place at the grinding area so that the dust immediately gets sucked away. Note that the outer surface of the intake necks down several millimeters just beyond the mating surface. For that reason I was not comfortable increasing the bore all the way out to 70mm in that region, rather I tapered down to a 68mm bore to keep from breaking through the wall of the intake. I removed material for about 3-4 inches into the intake, and followed up with a nice polishing job with a Dremel. I wish I had a picture to show you, it was very pretty.
3. If you bought a TB that had the Pathfinder IAC and coolant passageway attached, you will have to remove them because there is not enough space beneath the TB for the IAC stuff.
4. You will have to make a plate that bolts to the bottom of the TB to seal it off, otherwise you will have a massive vacuum leak. See the attached jpg below. You can reuse the fancy o-ring gasket if your TB came with it, otherwise you will have to buy a new one from the dealer. I drilled a hole in the bottom of the plate and attached a hose nipple for the EGR control valve solenoid vacuum hose.
5. Some people have left the TPS as is, with the connectors pointing away from the intake manifold. This really stretches the TPS harness and in my case there was not enough slack in the harness to reach, so I took the TPS off and rotated it 180 degrees so that the connectors point backward to the intake manifold. The harness connectors can now easily reach the TPS.
6. After you remove the Maxima TB you will have to connect together the two coolant lines that connect to the TB, since you removed the coolant passageway and IAC from the Pathfinder TB. But you’ve always wanted to do the useless TB coolant bypass, now, haven’t you? Admit it.
7. At this time you can bolt the adapter plate to the intake manifold (if you haven’t already) and then bolt the TB to the adapter plate with a new gasket. The Pathfinder TB gasket is a fancy metal one, similar to our IAC gasket. You may have to connect the TPS to its harness as you are mounting the TB.
8. Attach the throttle and cruise control cables. My .75” thick adapter plate allowed me to attach the throttle cable without having to reposition the throttle cable adjustment bracket, but the cruise control cable was just a hair too short. I don’t care since my cruise control hasn’t worked since I did the tranny conversion anyway, but if you want cruise control you will have to do some repositioning of the bracket. I’ll do it eventually since I don’t like the looks of a loose cable.
9. Attach the intake pipe to the TB and you’re done. On my setup, the TB sticks out about .25” further than the Maxima TB did. The Pathfinder TB is shorter axially than the Maxima TB, which helped make up for the .75” thick adapter plate. The extra .25” or so was not enough to cause any problem with the intake pipe.