So I've done some searching and haven't come up with anything conclusive. I am putting together an S14 SR20DET and also have an S13 SR20DET laying around. As I've found out, the S14 has a smaller 50mm TB and the S13 has a 60mm TB. The SR20DE TB is a popular swap because it bolts right up. Is there some reason people don't use the S13 SR TB on the S14 SR?

From inspection, the S13 SR TB looks like it will bolt up to the S14 and even the TPS sensors look like they'll plug and play. Is there anything I need to know before I go ahead and swap these around? Am I going to have to put the S14 TPS on the S13 TB because the signals are different? That's about the only reason I can think that this might now work. I also think I'll lose the cold start idle controller, but I don't plan on using this in the cold too much.

I don't want to waste the time and gaskets to find out it won't work if someone has all ready done this. That being said, if I don't see any replies before I'm done cleaning the shop, I might get impatient and just go for it and see what happens.

I went ahead and pulled both throttle bodies. I took some pictures for comparison.

In the first picture, you can see the similarities between the throttle position sensors. They're the same plug with the same colored wires in the same order on the harness side.
S14 on left, S13 on right:


In this picture you can see the differences in the pulleys. You can also see the cold start control mechanism that is present only on the S14 TB - at least that's what I think it is. I didn't look it up because I don't really care.
S13 on left, S14 on right:


Here is a view of the bottom. You can notice that the S14 TB has two vac/boost ports coming from the TB. I don't recall what they went to - again, don't really care, just observing.
S13 on top,
S14 on bottom:


Here is the view from the front - this is when the differences are really apparent. You can easily notice the difference in size between the two throttle bodies. A 10mm difference doesn't seem like a lot, but it's noticeable and substantial. I'm not sure why Nissan went with such a tiny throttle body on the S14.
S13 on left, S14 on right:


This picture shows the back. I was surprised to see the notches cut out on the bottom of the S14 TB. When you look inside the intake manifold plenum, you can see that there is a pathway [for lack of a better term] from these notches to the #1 runner. I'd be interested to know why they did this and what the philosophy is behind it.
S13 on left, S14 on right:


I put the S13 TB on the S14 plenum to make further comparisons. The next picture is a side view. This shows the first few problems. For starters, you can't bolt it up because the coolant line hits the #1 runner. Also, where the throttle cable would attach to the S13 TB in this orientation would be near the 7 o'clock position which might be too far for the cable to reach.


The view from the top illustrates the other problem. The bracket that holds the throttle cable is not in line with the correct pulley. This could potentially cause some binding issues with the cable if adjustments aren't made. I suspect that the bracket will need to be hogged out to allow it to better angle to the pulley.


So my conclusion right now is that the SR20DE throttle body would indeed be the better option. I might try to find one so I don't have to ruin a perfectly good S13 TB. After all, I do have intentions of using the S13 SR at some point in the future.

Hopefully others will find this comparison useful.

i was told it isn't a direct bolt up as it seems. if you want the simple bolt on TB the n/a s14/s15 sr20de came with the 60mm TB while the s14/s15 sr20det came with the 50MM, which makes it a direct bolt on affair and you don't lose the s14 cold start hardware. i got a hold of a 60mm n/a TB couple years back from a company i am friends with. doing the n/a s14 sr TB swap is the easiest. i was told the s13 sr won't fit. i believe the g20 TB are closer than the s13 ones. but the g20 as well will require work as well. if you'd like to see pics of the TB swap PM me i can help you out. or if you're looking for the n/a TB i can get the company to contact you to sell you the n/a TB.

As far as the TPS sensors are concerned, they should be the same. FSM confirms that their voltage outputs are the same. To be honest, looking at your side by side comparison of the bore, they look to be the same to me. The height difference seems to be coming from the throttle pulley. That could just be the picture playing an optical trick on me as a ruler on my monitor is only so useful/less. You could always try a spacer to step the TB away from the plenum to find the clearances, but that would have to be custom.

And as for why Nissan would choose a smaller bore TB would probably have to do with the VCT setup.

Throttle throat size is less important on forced induction.

TPS is the same though, and the warmup high idle cam is fairly important, the S13 TB doesn't have it because those motors have that in the idle air control.

I wouldn't waste your time with a larger TB, you aren't going to gain anything unless you're pushing 400+ BHP or find a really good deal on an S14/S15 SR20DE TB.

I agree that it is less important on FI than NA, but it is going to be the bottleneck on my setup as it will be for anyone with upgraded intercooler and charge pipes. I would speculate that anything over stock boost levels with upgraded intercooling (as in larger diameters) would benefit from a slightly larger TB. I will probably try to find a G20 TB.

Anyway, here is another shot for Bart. Hopefully this looks better.

the 50mm doesn't start choking air until you get camshafts and start exceeding 350hp. so if you're not making over that i'd stay with the 50mm. the g20 will require some extra work too. for TPS you can swap your sensor in or wire in the new one. i'd really recommend getting the s14 sr20de though. it'll save you lots of time doing extra work for something that just moves the powerband.
i love having the 60mm throttle body though. it was a night and day feeling. my top end felt a lot smoother and pulled a lot harder.

here are some comparison pics of the sr20det vs sr20de





and it all bolted up: