In getting ready to put a smaller motor into our race car, we needed a way to get the turbo plenum into the fuel injectors. Two motors ago, we had a 1300cc Hayabusa, and had spent considerable time making the plenum fit those injectors. The motor we've run the last two years was a Suzuki GSXR 750, but as it turned out, the intake spacing was exactly the same as the Hayabusa, so we continued to use those injectors. And in case anyone thought that was too much injector for that approximately half sized engine, we eventually had so much boost that the injectors were over 90% duty-cycle. We wound up having to increase them significantly.
The motor we're working with now is a Honda 600 de-stroked to 500cc. But since everything else was already set up for the Hayabusa injectors, we thought it might be the best approach to keep using them. But this time, the cylinder spacing is much too close. What we would need to make it work would be an adapter plate that changed from the Suzuki Hayabusa spacing to the Honda spacing. And as long as we're adding a plate to the intake, we might as well make it big enough to put NOX nozzles in, (we aren't likely to do that, but better to design the option in now). The results would look like the cross section below.
Before going to all the expense and effort of making one in aluminium, I decided to machine a test piece using machining plastic called red board. That would let us test everything, and redesign any changes before actually cutting metal.
I decided to machine it in four steps. I programmed the outer profiles of the top side using D2NC, a 2.5 dimension G-code program, that gave me lots of control for for a few tricky cuts. Then the upper insides using Fusion 360 to get the smooth curves. Then I flipped it over, and machined the bottom, using the same two step process.
I discovered a couple of problems. The red board is brittle, and I put some cosmetic nicks into it when chips broke off near the end of the cut. Next time I'll spiral in to leave everything supported. Also, I set the fusion 360 machining profile too big. It cut the insides pretty well, but spent way too much time working over the outer profile that was already complete. Also, I need to get the bit to run down a little lower into the holes next time. I had to file out the last couple of mm on a couple of holes.
That's the results. I like them, and I know how to make the next one even better. We'll need to make a specialty cutter to under cut the notches. We'll try fitting it to the motor next weekend.