so, you can spend tons of money if you want.
esslingerengineering.com
raceengineering.com
these little 2.3 motors have been used in usac midgets a full esslinger engine (esslinger aluminum block and head) makes 390hp and can turn 11,000rpm, something like 25,000$
they have the stuff to build something from stock all the way to 800+hp turbo stuff. and everything between, they also have iron blocks cast now too that can go to 3L.
there use to be a short course truck class that was dominated by iron esslinger motors, 2900cc deals with aluminum esslinger ARCA heads 300+hp with loads of torque for a 4 cylinder, expensive. that class sort of transitioned to sealed LS engines, which ended up cheaper, and roughly the same performance as the screamin 4 cylinders.
I have/use to race one between there ministock, 2.5L 260hp @ 7800rpm, would regularly see 8500 and as high as 9200rpm on occasion.
on the reasonable side of things, go get a 2.5L from the junk yard, the longer stroke heavier crank really moves the truck off idle MUCH better.
First thing you want to do is fix the valve float issue. The springs on the dual plug 2.3 and 2.5 engines are comically light. They float at like 4500rpm and the lifters pump up, so it looses all top end, and then is soft after you shift. these engines are stout, 8000rpm on the stock crankshaft in stock car use is childs play (the same cant be said for the rods the stock rods like to escape somewhere around 7800) the blocks are incredibly strong, There was a 2.3 with a volvo head making 830hp, with a stock block and 2.5 crank. These things want to be revved dont be afraid to
but first you gotta change the valve springs,
comp 26915 springs and chevy cavalier retainers can be used, but require grinding the rocker arms which sux....
boport.com has a really nice spring kit.
after this is done, youll feel like you have gained 20hp near the rev limiter because, you did, or rather, your no longer loosing 20 or likely way more hp up top, you can keep it pinned and it will rev on out....!
what else?
I had Delta cams in washington regrind one of the stock cams for me once, it added like 0.050" lift and a few degrees duration, the problem with cams for these is for roller cams you need good quality steel (slider or "FT" cams are cast iron) so you have a billet cam that ends up costing 400$, Ford cheaped out (well was ingenious really) and swaged hardened lobes onto a soft cam core which really brings the price of the roller cam down but for us this leaves little room for a regrind.
anyway delta can regrind something like a .390" lift 190* duration on the stock 118ish LSA, and it helps, DOES NOT SOUND LIKE ITS CAMMED or have any downsides to driveability, but you do have to shim the lifters to compensate for the reduced base circle.
going more extreme, Comp has some SHIT,
Schnider has cams with much more lift than comp, but the are 400$$$...... ok for this application youd want to ask them for their 0.525"/212, on something like a 114. Wont rump or anything, will make valve train noise though. this is not enough cam that any bottom end is eroded, only improved. will run much better on top.
I would highly reccomend never going solid lifter on your transportation vehicle ever
and on these, the rev limiter is 6250 anywhow.... with good springs the hydraulic would go to 7500, anyhow.
basically anything else is just way in excess.........
you know?
well i guess i can add if your going to take the head off to change springs, might as well get a nice 5 angle valve job done.
also the injector bungs block like 20% of the intake manifold which is the smallest part of the intake system, you can grind them mostly out and call it good.
the other option is turbocharging,
iv always thought a twin screw ihi1200 supercharger from a Mazda millinea would work well