SR20DE Throttle Body Conversion: Part One
By James Jurado
For those of you who want to upgrade your throttle body on your GA16DE powered cars, there are a couple of options out there that you can do. You can have the one on your bored out by a reputable machine shop (i.e. JG engine dynamics) or, if you can get your hands on one, bolt on the throttle body from an SR20DE.
What’s the difference in the two you ask? Well I’ll tell you the advantages and disadvantages in installing the two. The GA16DE’s throttle body’s anatomy compared to the SR20DE throttle body is almost identical. The bolt patterns, coolant hook-ups, and vacuum lines all match up the same. But the only differences lie with the bore size, and the TPS configuration. With the 1.6 throttle body bored out to its maximum specifications, overall bore size will still not be as large as the stock bore size of the 2.0 throttle body. Which also leaves us to consider how much more potential there can be had with the 2.0 throttle body! If you can get your greasy hands on one of these throttle bodies, I’ll let you guys know of some of the obstacles that will be encountered on making this modification work.
Necessary parts: There was not much needed here. You will need to purchase brand new throttle body gasket from the dealership. It only cost me about $4.50 with the Se-r discount at Puente Hills Nissan. Without the discount its about six bucks. You will also need to make sure that it is for an Se-r! Otherwise the bore size of the 1.6 gasket will not match the bore size of the throttle body.
You will also need to get an aftermarket intake setup, if you don?t already have one. The factory rubber intake tubing will not fit over the throttle body. If you have only the filter with the MAF adapter plate, you’ll need to go out and get the mandrel bent intake pipe with the proper sized couplers for the Se-r. You can also go out to Home Depot and make your own. If you do that you’ll need some 2″ abs pvc, 4 hose clamps and 2 2″ rubber couplers. The Home Depot couplers will be a very tight fit on the TB, but it will fit. You’ll just need to stretch it over the mouth of the TB. I also went out and bought a couple of brass fittings to tap into the side of the PVC for the necessary vacuum hoses. These can be purchased at a Pep Boys autoparts store for less than five bucks.
Installation: Everything matched up perfectly, with a few exceptions. There are two connections on the bottom of the TB for the coolant hoses. You will have to slightly bend these so that they pint straight down, otherwise they will be hitting against the manifold. I heated them up on my gas kitchen stove, but if you have access to a butane torch then good for you! Heat up the connections a little bit (NOT RED HOT!) , and use a shop hammer to gently tap the tubing straight. You should be tapping the base of the body as you are not trying to actually bend the tube, you just want it to rotate in its base.
The most challenging part of the throttle body mod will be with making the 1.6 TPS work on this unit. As I am still trying to figure out how to do this, I’ll tell you what I have encountered so far. On the 2.0, the TPS lever sits towards the front of the throttle body, rotating clockwise from the seven o’clock position to eleven o’clock. On the 1.6 the TPS lever rotates clockwise from the one o’clock position to about five o’clock. The same goes with the lever on the TB that moves the TPS switch. One thing I tried to do was flip the 1.6 TPS around and bolt it backwards, with the plug end facing the intake manifold. The levers made contact with each other to make the system operable, but I was questioning its inability to then be unable to be adjusted. This set up caused the TPS lever to be out of spec with its position slightly opened up, even though the throttle was completely closed. Installation on the car was slightly difficult as the TPS also got in the way of a few vacuum hoses and rested against the intake manifold. Not good if you begin to wonder if the heat would cook the plug in connector on the TPS. After starting up my car, I could immediately hear the difference in sound. It actually sounds a lot healthier with all the extra air going in the engine. Engine response was incredibly awesome as the RPM’s just shoot to redline without any delay. The only bad part was that the engine was idling way too high at about 2k. After taking a little test drive around the block, the increased power was second to none, as I was even able to get some 2nd gear peel out on my 16″s. Another bad part though, after the initial run down the street, engine idle was now at 3-4k!! My suspicions were of my poor, mis-calibrated TPS sensor. With the sensor mounted backwards, adjustability was not going to be possible. That little fraction of an inch that was needed to get the TPS sensor in the closed position caused the high engine idle. What to do now? My next idea was to shave down and bend back the lever on the TB so that it would let the TPS lever rest back a little more. This also proved ineffective as engine idle stayed the same.
The next idea I had was to spot weld a matching lever on the one o’clock position of the lever. Problem is I don?t have access to a gas welder at the moment so that idea was chucked out the door. Last but not least, my idea was to completley disassemble and reassemble the throttle body’s internals and make it so that its TPS lever was pointing towards the back. I managed to get the linkage assembly removed so far. Also another small detail I’d like to point out. On back of the throttle body, in the area where the TPS mounts on, there is a small tower that it rests on. You only need the two towers that the TPS bolts onto, so the third one that rests in the 3 o’clock position will have to be leveled off with a hacksaw. This is so that the TB’s throttle position lever will move freely on that side.
Well that?s all for now. As soon as I can figure out how to take apart the butterfly valve, and its related assembly parts, I’ll finish up part two. I’ll also include some more SOTP test results and also give my impressions of the port matching job that I’ll be getting from JG Engine Dynamics.