Well, I completed the head conversion on the 258 with a 4.0 HO head
The head I used was a 0630 re-done by clearwater. It is a bit more expensive but they flux weld the 'extra' coolant passages. I figured that would be better than messing with peanuts and epoxy's. I am still wondering though if it is necessary to do that, because if you look at the head gasket for a 258 and/or a 4.0, you'll see that those passages are not even in the gasket. But since everyone says they need to be plugged, I might as well... better safe than sorry. Clearwater says that the 0630 is a stronger head than the 7120 is. The
7120 flows a bit better (according to some internet rumors) but the difference, according to clearwater is minimal. Since the engine will have a lot higher compression, I opted for the stronger head.The performance gain is pretty much based on a higher compression ratio, fuel mixture and exhaust flow a lot better through a 4.0 HO head than it will through a 258 head. I talked with clearwater (and a little with hesco) about having the head ported. You could gain between 5 and 40 HP by porting the head. BUT (according to both) porting is expensive and it pretty much is a crap shoot wether you gain the 40. They both made the remark "if you want to have a high probability of success it means you have to have it ported by someone that REALLY knows what he is doing. That is expensive... and do you really want to pay 1000-1500 for 20HP or maybe in worse case scenario
5 ?" The standard head gives you a gain of around 40HP already and choosing a good setup will give you more gain than just porting it. (their words, not mine)I also go the clifford performance intake manifold (it is one that is heated by splicing it into the heater core 'circuit'. I also bought the clifford exhaust header. Fitting the exhaust header and intake manifold works really well (on my 0630, I don't know if it would on the 7120 head). No mods are needed it bolts right on. No clearance issues with motor mounts etc (however it is pretty close to the driver side motormount). According to clifford, that exhaust header and intake are especially designed for this swap. (I almost regretted choosing clifford though, I had to wait for more than two months on a prepaid/ordered intake manifold.)
According to Clifford (of course they sell them too) but also others, using a good header and intake will give you some extra horses, especially if the header, intake manifold and head are a 'match'.
The exhaust: clifford recommended using an X-pipe. That was pretty much confirmed by others. You gain some low end torque doing that (about 12% according to the specs). Clifford also recommends using
2-1/4" exhaust pipe.Carburator: I used a 4 barrel Holley 390CFM. Again clifford, and others, say that it is a really good choice to make with this conversion. They sell a 'pre jetted' one for $150 more. However I got a really good deal on my holley from Jeggs so I didn't get the clifford re-jetted one.
Other things: nice air filter from Mopar, new lifters, 4.0 valve cover, universal accelerator link/cable and of course you need a bunch of hoses etc etc etc;
My engine was rebuilt about 10 years ago. I had a machine shop take a look at it. Their comment "this block was rebuilt less than 5,000 miles ago", sounds about right, I don't drive it much. The crosses from honing are still in there. No carbon deposits, no sludge. Their advice, put new lifters in and you are good to go.
Why I did this ? My exhaust manifold had a crack in it and a piece of the flange, where the exhaust pipe attaches, broke off. Also, I ALWAYS had that exhaust manifold leak. (coincidence?: a crack developed in the head exactly where the exhaust leak was) So I needed a new head and exhaust manifold anyway. So I opted for a "do over"
The machine shop told me that you do not want to do this with a tired or even somewhat tired engine. According to them, for one it makes no senses and second; you'll bust your engine, it will leak oil in all kinds of places, and more than likely throw rods.
The conversion cost me about $2,500 in parts (it adds up real quick). 425 head, 760 for header and intake manifold, 575 carb, headbolds $150, valvecover 175, etc etc
Other than stock, I already had the HEI conversion (that one helps a lot, it makes the powerplant run a lot smoother). If you do this conversion you also want to do the HEI ignition. (The HEI ignition makes the standard 258 run a lot smoother already)
I did this conversion because it looked good on paper. I already had the HEI setup. I also have the onboard air (with york compressor) that I didn't really want to mess with relocating etc. I already did the T18 transmission swap. So moving to another engine and doing a complete swap might have been cheaper on the engine, but than I had to do all these other things (bellhousing, flywheel, clutch, brackets for air compressor etc, etc, etc). Besides, a new/rebuilt complete other engine is probably more expensive.)
Yesterday I took it out for it's first run, it doesn't only sound good on paper. I actually heard squeeling noises from my rear tires (33 swampers) because I took off like I was used to in my 258 powered CJ. I drove it up 'the hill', I used to be glad starting it with 65mph and still doing 50mph on top. But it kept accelerating all the way up hill this time (I had to back off even because there's always a cop sitting on top of the hill.)
Oh btw, I have a flowmaster muffler, it makes a nice deep 'get out of the way' rumbling kinda sound.
here's a checklist of what I did to my toy so far (hope I didn't forget anything): '79 CJ5:
- 258 4.0L HO head conversion.
- 390 CFM holley
- Clifford intake manifold
- Clifford exhaust header
- HEI ignition (custom built from a chevy HEI distributor)
- T18 transmission out of a ford pickup (granny 1st and reverse)
- Dana 300 out of a scout (I believe)
- custom built skidplate to keep it all up.
- Moser one piece axles for my dana 20 rearend
- 23 Gallon fueltank from a scrambler instead of the 15 gallon standard tank
- nice rear rock crawling bumper (forgot the brand name)
- Dual Optima battery setup (redtop for 'car' stuff, yellow top for winching) with battery seperator etc.
- Warn 9000lbs winch
- KC daylighters.
- 2.5 inch rancho suspension lift
- 2 inch body lift
- 33" TSL super swampers.
- York air compressor with 5 gallon tank.
- Tuffy (?) console and rear toolbox.
- Bestop seats. (I still wonder why I got the slide brackets, in a CJ5 there's no room to slide the seats)
- sway bar disconnects
Some other plans I have:
- clock the dana 300 for more clearance.
- better front locking hubs
- brake booster (if there's room) in stead of the regular master break cylinder.