For 2.0 litre limit and no turbo, SR will beat CA

SR20DE (2000-2002 Infiniti G20) 145hp roller rocker motor
CA18DE (1988-1989 Nissan Sentra) 125hp
SR20VE import engine (FWD) 190-205hp

Of course both engines can be built with aftermarket parts to make more HP, these are the factory output

Lampy in wa Oz runs an L series with Ka head making 286hp ate
in a heavy 510 so that could also be your last option if nothing
else is allowed by Peter on your side of the pond has a ga16
ready for what I thought was up to 1.6class but if its 2L then
better go for the full cubes! sr20ve is hard to ignore if allowed.

https://www.youtube.com/watch?v=ut0hQc8pWOw

The guys over here use CA18 and SR20 motors in our upto 2000cc improved production class. Most fit into 1200s quite easily or the silvia which cams has ok'd to run in the class

Here is the scoop; for the class I'm currently running I'm allowed up to 2.0 liters. The only hitch is the motor had to be legal in a sanctioned series pre 2000.

So I can show L series having been run in Japan.

Improved Production allows A12 turbo (That's what Simon runs correct?)

Here in the USA SCCA allowed A15, which is what I run.

This all stems from my wife's. "Can't you just put a bigger motor in it" comment. I do love the A-series motor and a L-series is a pretty easy swap but I'd like to see if there are other options.