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TBI to Z31 MPFI swap


Kingman
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Well, some background info first. I spun a rod bearing on the stock motor at 194K, and swapped in a motor from an '84 Z31 (300ZX) with only 102K. The bare minimum to get the truck back on the road was to keep the factory TBI set up, which is being a little problematic. I've always wanted to swap in a Z31 intake set up even before I blew the motor, so this worked out perfectly. I found the 300ZX on Craigslist for parts, and the guy said he'd take $100 for the motor. However, since his job schedule kept changing he wasn't able to work on the car to pull the motor out for me, so he said that if I came and yanked it I could have the motor for free.

 

I've got a TON of wiring to sort through yet, but it'll be easier once the manifold and stuff is on so the placement will all be correct, to help figure out what goes where. At the moment I'm having an issue with the rear hard line coolant hoses hitting the firewall. I can use the other factory lines if I bypass the coolant lines going through the throttle body. I've heard of a lot of people doing this without any problems.... There's also an issue of fuel pump wiring and some wiring for the gauge cluster that I'll need to sort through and remove from the TBI harness as I slowly work it out of the equation. I've done a lot of research on Z31performance.com, mostly for wiring harness diagrams, pin outs, and what other people have removed/changed to make these intakes work with other vehicles. There's going to be an issue with the air intake tubing as well, the factory Z31 uses some extreme angles that just will not work on a Pathfinder. I'll figure something out, but likely my truck won't be back on the road for a while now.

 

So far:

Original TBI set up.

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Entire intake removed.

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The Z31 intake prepped to go on.

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I'll keep posting pictures and updates as the project goes on. I'm hoping someone who's maybe planning on doing the same thing can learn something from my mistakes and I'll try my best to post specific changes needed for it all to work. :crossedwires:

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I may have to. The guy I've been talking with that's done it before said there was about 1-2" of clearance between the firewall and the heater core, and the heater core is below where the firewall needs to me "massaged."

 

A problem with running Z31 wiring and a Pathfinder plenum is that some of the sensors are different, and I'd have to rewire even more stuff...

 

Plus, I don't have any money to buy a new plenum...

Edited by Kingman
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Don't have a sledgehammer at the house, a friend is bringing me one tomorrow to start notching out the firewall. That should be the exciting part...

 

I've got a coolant elbow to work out for the heater core, nothing too major. Nismopu is going to stop by tomorrow and take a look at things, since he's done two Hardbody-Z31 swaps before.

 

0911101737.jpg

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Yes, the Pathfinder intake does flow a little more in the bottom end due to the longer runners. However it doesn't distribute the air as evenly as the factory Z31 intake to all the cylinders so it almost evens out. A gutted intake flows way more, and using a 200SXSE 60MM throttle body with a gutted intake gives a pretty decent performance gain, and better throttle response. With the intake I'll probably be moving more towards 300ZX mods, rather than Pathfinder engine mods. Especially a turbo... :crossedwires:

 

Another thing I'll be doing is moving the MAF sensor to within 6" from the throttle body opening. Much better throttle response and more accurate measurements from the sensor. When you stomp on the gas it'll instantly recognize it and compensate, rather than waiting for the air inside the entire intake to be sucked in, expanded, and then the outside air from the filter being sucked in and then reading that.

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Another thing I'll be doing is moving the MAF sensor to within 6" from the throttle body opening. Much better throttle response and more accurate measurements from the sensor. When you stomp on the gas it'll instantly recognize it and compensate, rather than waiting for the air inside the entire intake to be sucked in, expanded, and then the outside air from the filter being sucked in and then reading that.

 

That's not how it works with the MAF sensor and the distance is short enough already.

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That's not how it works with the MAF sensor and the distance is short enough already.

 

Yes, it is how it works. The MAF measure how much air is flowing past it. When the sensor is at the end of the intake, there is lag time between when you stomp on the gas and the air actually being sucked in from the outside. The sensor cannot measure anything until air is flowing past it. Like I said, when the vacuum inside the engine decreases (variable vacuum through the throttle plate) the air inside of the intake tube expands and thins out as it's being sucked in, when when the air expands all the way out and the vacuum reaches the outside of the intake it then sucks fresh air in and flows past the MAF sensor. Moving the sensor as close as you can to the TB opening will increase throttle response, because the time it takes for the air to be expanded and sucked in is a lot less. The sensor registers it much faster that way. It's physics, there are MANY books and manuals about this kind of stuff to back up what I'm saying.

Edited by Kingman
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There is a vacuum inside the boot already. It would not make a difference if the sensor is 3 inches away or 6 inches away as long as there is no leak between the sensor and the throttle plate. Nissan would integrate the MAF grid into the throttle body if that were the case.

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There is a vacuum inside the boot already. It would not make a difference if the sensor is 3 inches away or 6 inches away as long as there is no leak between the sensor and the throttle plate. Nissan would integrate the MAF grid into the throttle body if that were the case.

 

6" away compared to almost 2.5' away for the factory Z31 location is a major difference.

 

But the project is on hold, my mom had a cow about me even working on it at the house so I have to tow it somewhere else to finish it up. She said she doesn't want to look bad around the neighbors, but we're at the very end of a gravel road in the woods. :scratchhead: Oh well, she pays the bills so whatever she says goes...

Edited by Kingman
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Thanks man. All the lower end parts were practically the same besides the oil pan, nothing else needed to be changed besides that and some custom motor mounts made.

 

I've had the motor it's self in for about 4K miles now.

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There is a vacuum inside the boot already. It would not make a difference if the sensor is 3 inches away or 6 inches away as long as there is no leak between the sensor and the throttle plate. Nissan would integrate the MAF grid into the throttle body if that were the case.

 

 

And some Companies do exactly that for the very reason kingman explained.

There's allot of things nissan coulda done but they didn't, the same goes for any car and there often doesn't seem to be allot of rhyme or reason aound any of it.

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Thanks man. All the lower end parts were practically the same besides the oil pan, nothing else needed to be changed besides that and some custom motor mounts made.

 

I've had the motor it's self in for about 4K miles now.

 

 

hmm you should have been able to unbolt the pathfinder motor mounts and bolt them straight to this block and then reinstall it in the pathy....I was able to do that on the maxima/altima engine...I believe all the VG engine blocks are the same as far as threaded bosses and mounting but depending on application they use different ones

 

Maxima Engine:

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Here's a pic of the engine almost ready to go in the pathy (as TBI):

DSCN2572.jpg

 

DSCN2884.jpg

 

I thought I actually had the bracket mountings but i can't find those

Edited by unccpathfinder
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hmm you should have been able to unbolt the pathfinder motor mounts and bolt them straight to this block and then reinstall it in the pathy....I was able to do that on the maxima/altima engine...I believe all the VG engine blocks are the same as far as threaded bosses and mounting but depending on application they use different ones

 

All VG blocks are not the same. The pre-'86 Z31 blocks had different mounting bosses for the motor mounts. After that, they were all unified so they would work. The Pathfinder motor mounts lined up somewhat closely on one side, but not enough to work and the other side wasn't close enough to be safe. Comparing the two blocks next to each other showed how different the bosses really were.

 

The modifications made to the mounts. Holes were drilled at the end of each added piece to fit the nearest boss in the block. It was a pain in the ass...

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Instead of hammering out the firewall I decided to take a little harder but probably safer and better looking route. I need to build a sheet metal box to fit inside the firewall after a square hole is cut in it to fit the back of the intake. The box will need to be 11" wide, 1.5" deep (giving room in back), and 6" tall. After the box is made I'll put some rubber insulator behind the box flanges and screw it in to the firewall.

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Ok so suppose air is compressible but would there really be a benefit on moving it closer? How about all the drawbacks like making the sensor run hotter?

 

Yes, for the reasons I said above. Twice.

 

The sensor will not run a significant amount hotter being moved closer to the intake. Z31 sensors are already heated and self cleaning, getting way hotter than being a little closer to the engine. They do not measure intake air temperature anyway, it makes no difference to it.

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Interesting...that was an 86 engine so I can't say I looked at anything pre86

 

Ah. When I first ran in to troubles with the mounts I was pretty damn confused myself, as I too thought every block was the same. Then after some poking and prodding around I found out the differences. I wish the motor that I got was from an '87-'89 car since they use a much faster ECU and high impedance injectors. Makes them a lot more accepting to serious mods. That, and the motor mounts would interchange. But I can't complain, like I said the motor was free...

Edited by Kingman
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Yes, for the reasons I said above. Twice.

 

The sensor will not run a significant amount hotter being moved closer to the intake. Z31 sensors are already heated and self cleaning, getting way hotter than being a little closer to the engine. They do not measure intake air temperature anyway, it makes no difference to it.

 

I still think it will be a wasted effort and won't do anything to the throttle response or at least not enough to feel the difference. :tongue:

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I still think it will be a wasted effort and won't do anything to the throttle response or at least not enough to feel the difference. :tongue:

 

That's fine. Placing the MAF sensor right next to the throttle body will be way easier than trying to stick it somewhere else, anyways.

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