If you had a running 258 and wanted more power and had around $1500 to spend to get more power what would you do?

Dyno it with the EFI. If the numbers are still low,
Check your cylinder compression.
Check your timing.
Check your valve timing.
Original cam?

Check your differential gearing to tire size.

 

More displacement is my suggestion. It’s glorious.

 

Since you don't mention it I'm assuming you still have the stock distributor?

The only real change I did to my 258 was timing. I put a lighter advance spring in the distributor, and bumped the initial advance also.

Otherwise bone stock, still 1bbl carb. The 1970's emissions timing curve is terrible.

It's very snappy and will happily hold second to 3500 rpm or so. Has plenty of power. Before it really felt like it was running out of breath at much lower rpm.

Best part is the springs are cheap. Spent maybe $15

 

I fully rebuilt my 258 quite a while ago...
.030 over bore, reground crank, main bearings, rod bearings, cam bearings.
Hedman headers, all 2-1/4" exhaust with Flowmaster 40 series muffler, Clifford intake, GM TBI fuel injection, HEI distributor, SPAL electric fan, Comp Cams 252H camshaft.
I have more than enough power (torque, HP doesn't matter) for effortless highway travel and plenty of off idle torque.

You already have the same as me, even a little better, you just need a littler hotter camshaft to wake up your engine. That 4.0 head should be a big improvement, especially with a higher performance camshaft. Last I looked, camshafts were cheap...

BTW, I'm on 35's with 4.56 gearing and a T5.

 

If you had a running 258 and wanted more power and had around $1500 to spend to get more power what would you do?
It has the offy 4bbl intake, holley sniper EFI, Clifford dual headers. It currently has the 4.2L head and I bought a 4.0L head to put in it but haven't yet. I had it dyno'd when it had an edelbrock 500 cfm and it was putting out 109 hp.

Put the 4.0L head on it w/the 4.0L ECU/engine wiring and an Erson RV cam in it (of course new timing chain/gears while you're at it) and you will be good to go. If that's not enough power for you (assuming you have the appropriate axle gearing) then you should go the 360, or LS route.

 

Its got the HEI distributor on it, 3:73 gears 33x12.50 Truxus STS.
Had 35's on it and it bogged in 4th gear at highway speed. Im considering changing the cam with the 252 comp cams. I want to have the dyno shop tune my Sniper system.

 

There are always peripherals that make a package ideal, but I have found that the 258 crank and 4.0 head are an awesome baseline to build a package on.; whether it's a 258 engine with a 4.0 head, or a 4.0 engine with a 258 crank. I've built 2 engines with this platform; '89 YJ 258 with the 4.0 head (mildly ported), and '95 ZJ 4.6 stroker (4.0 block, TUPY head and 258 crank). One package involved a 258 with a 4.0 head, while the other one used a 4.0 baseline with the 258 crank. Since you already have the 4.0 head, my recommendation is to get it installed and then go from there.

 

I gotta 258 Hornet

With a Offy and a Holley 390

Once on my way to Lake City S.C. I passed a whole squadron of F-16s,

left them in my rear view mirror !!!!

They were sitting on the airfield at Shaw Air Force Base.

In the early '70s when my Dad was stationed there,

I passed F-4 Phantoms all the time on my bicycle!

------JEEPFELLER

 

Lots of good suggestions here,
but,
I would start with insuring my bottom end is solid before doing anything more.
It doesn't matter what you bolt on if the compression is 110LBS, the cam is worn, or the timing chain is sloppy, you're only half stepping your upgrade.

While on the outside edge of performance, 3.73's and 33's should run pretty well on the highway.

 

If you had a running 258 and wanted more power and had around $1500 to spend to get more power what would you do?
It has the offy 4bbl intake, holley sniper EFI, Clifford dual headers. It currently has the 4.2L head and I bought a 4.0L head to put in it but haven't yet. I had it dyno'd when it had an edelbrock 500 cfm and it was putting out 109 hp.

To quote a very knowledgeable fellow named JeepHammer, the Jeep 4.2L 6 cylinder engine is essentially a tractor motor designed to yield low end torque, and it does so beautifully. You will spend a lot of money on all the engine upgrade suggestions here and it will yield only small improvements in HP. Matt1981CJ7 provided the correct answer. If you want the Jeep to be all Jeep and have real power, install a 360 cu in Jeep V8. That won't be cheap, but displacement and horsepower ain't cheap. If you want the most economical path to V8 power install a small block chevy engine.

JS