Shiv's fuel rail yields 265 hp

Shiv's fuel rail yields 265 hp

Shiv developed a fuel rail for FI Miatas.

Here is a dyno comparison plot. He first installed the rail in Scott McLean's car, then did a baseline run. Shiv then advanced the timing bit by bit and ended up with 12 degrees advance over the initial settings, and leaned out the fuelling slightly. From 10-12 degrees advance there was very little improvement, which means timing was optimal (this is called "MBT" for mean best timing). Resulting timing was in the mid 20's, which is pretty amazing.

The orignal mapping was with the turbo defaults in the FM ECU . The default mapping is fairly conservative, to prevent knock in some susceptible engines with gas available in some places that isn't so good. In the baseline run with the fuel rail the roughness in the torque curve that is so common in hi-boost Miatas was gone. The 2nd plot on the dyno sheet was with an additional 12 degrees timing and slight leaning. Further fine tuning, rpm by rpm, was not done because of lack of time.

Car is an M1 1.8, 1994, with a 1996 boneyard stock motor, unopened, with an FM3 turbo kit.

The results are phenomenal:

That's close to a 20% increase from 4500 rpm up, nearly the same increase you get with a basic JR supercharger install.

My guess as to what's going on is that when an injector opens, it produces a localized pressure drop. The injectors open in a cadence, and that produces standing waves (resonances). The standing waves produce large variations in pressure up and down the fuel rail.

So, some cylinders run lean at some rpms, and the entire map has to be detuned to take care of the lean cylinders. Lots of lost power, higher temperature exhaust gas, more detonation. This seems to cure all that. Wow, talk about having your cake and eating it too.

Large injectors would produce a larger localized pressure drop..