This is how it all starts, '04 Suzuki GSXR600 throttle bodies bought off of eBay for 50$ in Nov '05. I became infatuated with individual throttle bodies many months earlier after reading about them at the TWM and Jenvey websites. I came across the HomeMadeTurbo article where they took GSXR throttle bodies and put them on a Honda, then I thought to myself this would be a lot of fun putting together a kit of my own, then slapping it on my Miata. I'd get a lot of hands-on work, plus I'd learn a lot about engine management and tuning. And what better way to learn about engine management and tuning then to get a MegaSquirt :). I ended up going with the MS1 V2.2 board with Megasquirt N Spark Extra because it was the cheapest alternative while providing everything I needed from an EMS, and for 120$, you can't go wrong! More details on the Megasquirt can be found on its own page. Let's get on with the build!
Here's some shots of how the throttle bodies come from the factory. My set came with the injectors and fuel rail; however, the fuel rail is a dead-head supply system unlike the NA miata which uses a fuel pressure regulator and a return line. The flow rate of the injectors is unknown, and I don't have the money to send them off to be benchmarked, so in the mean time I won't think about fuel supply. Note that these throttle bodies have secondary throttle butterflies. I don't know how they work or operate, but either way, they're coming off :). The top right picture shows the throttle linkage side. You can see the black throttle stop screw at the top middle near the 1:00 position, this will be very important later on as it will control the idle speed of the engine. On the opposite side are two throttle position sensors (TPS), one for the primary butterflies, one for the secondary butterflies. There's also the large controller motor for the secondaries, this and the secondary TPS are coming off.
We'll begin by removing the fuel rail and injectors from the throttle bodies. The fuel rail is held on by 4 phillips screws which were extremely tight and stripped very easily. Some quick work with a dremel and I was able to use a large flathead screwdriver and they came off easily.
The primary TPS will remain on the throttle bodies and will be used for the Megasquirt EMS. So up next is the secondary TPS and controller. These two come off as one unit on the large base, as seen in the bottom right picture. They're held on by two long phillips screws, which came off without a problem. After that it was simply tugging at the base and carefully prying it off with a screwdriver to remove the entire piece from the secondary butterfly shaft.
Now we turn to the secondary butterfly plates which need to be removed so that we can pull the shaft out. Each of the secondary butterfly plates is secured by two very small phillips screws which also...strip very easily. These are a bit harder, so be careful and take your time. I only managed to get four of the eight screws out without stripping them, so out came the drill and a small bit, I can't remember the exact size, and a can of WD40. With some persuasion the last four bolts were removed and it was time to pull out the secondary plates.
The plates were removed by simply turning the shaft sideways and sliding them out. Nothing complicated here. The shaft on the other hand was something else...The shaft is held on by multiple C-clips. If I remember correctly, there are three, one on each side of the throttle bodies and one in the middle under the rubber protector. Unclip these and the shaft will slide right out.
This is what you get when all is said and done, four runners with 38mm butterfly plates. There's already four vacuum ports all tee-d together, and depending on the fuel injector setup, the GSXR injector port can also be used for a vacuum source, otherwise it'll be plugged up with some epoxy. The holes for the secondary butterfly shaft will need to be plugged up. I used some epoxy putty from the local Home Depot. That stuff is pretty good, all you do is knead it, jam it in the hole, and form it so it's smooth. If you mess up, it can always be sanded down, drilled, etc.
Next we'll need to find some velocity stacks for these bad boys. Here comes eBay to the rescue! After weeks of searching and watching, I picked up these velocity stacks for only 20$ and they're the perfect size. The v-stack side of the throttle bodies have a 2'' outer diameter and a ~1 7/8'' inner diameter, both of which lined up with the velocity stacks. All that's needed to connect them are some 2'' inner diameter couplers. The head-side of the throttle bodies have a ~ 1 7/8'' outer diameter so some smaller couplers will be needed there to connect them to a manifold. For couplers, I used the same thing as my intercooler couplers, marine exhaust hose. It's extremely cheap compared to (overpriced) silicone couplers, and it comes in practically every size. The only drawback to these is how thick they are, so I may pick up some skinner couplers later on down the line to "finalize" the project and clean everything up.
I also managed to pick up some GSXR750 throttle bodies with injectors, fuel rail, fuel pressure regulator, and wiring for extremely cheap (30$), cheaper than the GSXR600s actually. These will be used as a backup or a second pair, depending on how I feel. These have a larger throttle butterfly diameter at 42mm. The 38mm GSXR600 throttles should be fine for my '97 1.8l, supporting up to something like 250 HP, but just in case I have the larger set.