inducer size and fuel restricted class

hi

How can i gain more horsepower if the turbo inducer size is restricted and oxygenated fuel and NOS are prohibited.

My 5c worth.

There are at least three ways to improve your vehicle's performance, it's going to depend on how much work and money you're prepared to invest.

a/ breathing. This is the fundamental limitation, and you want to get as much air through that orifice as possible, which is dependent on the area AND the pressure drop. Optimising the airflow through the entine intake and exhaust system to minimise the pressure drops - starting from the intake position being in a cool, preferably high pressure (at speed there is a pressure head developed) area, through a well designed, low restriction airbox/filter to a correctly sized turbo' that is sized to the power expected using smooth, sweeping pipework. If you minimise the restriction through to the engine, using a well designed charge cooler, you should be able to make a small improvement in charge density and temperature, which should allow more timing to be used and so impoved torque. Same for the exhaust side, you're looking to reduce exhaust manifold back pressure and exhaust sytem pressure while maintaining the required pressure/volume to drive the turbine efficiently.

b/ engine. Depending on the mechanical RPM limits, you may find that you can maximise power well below that, and that's the important part - more rpm means more friction/parasitic losses! Depending on what you have, you may find playing with the camshaft(s) timing(s) gives some benefit, as it may allow the engine to work better and ultimately 'suck' the air through the turbo' more efficiently. A bit more involved is to use higher compression pistons - this is going to depend on where the OEM CR is, and if it's a limitation or not - even then, it may be a slight compromise if it allows more power/torque to be gained above and below the power/torque peak, even if the timing has to be compromised AT peak torque! You may also find advantages in careful reworking of the cylinder head/manifold while keeping the ports small for velocity, and coating to the piston, chamber, etc, to reduce heat/thermal energy loss to the coolant and oil. Some might run a slightly thinner oil, but that can be risky if done correctly. Some might run a higher coolant temp'to reduce heat loss to the coolant.

c/ weight - if you can't use power to improve the power/weight, you need to minimise weight. Depending on your rules, you may have to run mostly OEM parts, but sometimes there are areas where you CAN make significant improvements - aftermarket discs and calipers can both improve braking and save unsprung (the best) mass AND reduce the "flywheel" affect of rotatuinal inertia. Along the latter lines, wheels may be free, and a substantial mass reduction can be made with proper race wheels - total, unsprung and rotational inertia - as can tyres (but there is usually a spec' tyre). Again, depending on the rules, there may be an option of different wheel/tyres sizes from different variants of the vehicle, that are legal.

d/ drag. The air resistance can have BIG affect at higher speeds - depending on what you're doing, you may be able to significantly reduce the drag by simple things, like taping over body gaps, reducing the grill opening to just what's needed for the various coolers, using a simple 'belly pan'under the engine compartment/full underbody - being aware that the exhaust needs to be cooled, etc.

There'll be a lot more that more experienced people can suggest, that will allow you to fully utilise what you have.

You may find targeting a compressor speed rather than just a boost target allows a bit more top end not trying to drive it further into choke flow with unnecessary exhaust manifold pressure.