need ideas on 91 4.0 engine build up or swap

[N2FORD]

I have a 91 2dr sport 4wd 5spd that the engine is sounding kinda rough in. Looking to get a core and do a mild build, cam, headers and other non overkill items. I want to keep driving mine while I do this build. What years will work for cores? I want to keep it very reliable and trail or street ready. I would like to build it for more bottom end grunt than top end speed. Any ideas or opions are greatly apprectiated.

 

[redmudder]

screw 4.0, swap 5.0 and youll never have to worry about it any more. but the swaps a *****. search arround, i have plenty of backing on that one.

 

[N2FORD]

Really don't want to have to do a major pain engine swap. I am o.k. with the power of the 4.0 just wanted a little more low end grunt. I want everything to still work correctly (fuel injection, computer, etc.) so i don't run into tons of problems. I could get a 302 out of an 00 Mountaineer, but then all the mounting, trans, OBD II and more issues are to much to deal with for me.

 

[Rhett]

Really don't want to have to do a major pain engine swap. I am o.k. with the power of the 4.0 just wanted a little more low end grunt. I want everything to still work correctly (fuel injection, computer, etc.) so i don't run into tons of problems.

You said you may want a mild cam. If you do that, you'll likely need computer work to get it to run to its potential. You might consider building the engine to handle a supercharger (i.e. put in high quality rods, etc.) so you can add that in later if you want. At least it gives you the option.

I hear ya on the swap. Lot of wiring and pain. If you just want a little more power, it's probably best to just re-do the 4.0.

What gear ratio does the truck have? Along with your rebuild, if it were me I would get 4.10's under there at least. Depends on your tire size, but even with stock tires, if it's low end you seek, go with 4.10.

You say you wonder which "cores" you can use. If you mean, which 4.0 engine blocks will work, The blocks are the same all the way through all years they made the 4.0 OHV Explorer (91-01 I believe).; you could even get a 4.0 OHV block from an Aerostar. The HEADS are what is different. If you need new heads, be careful what year you get them from because they're not all the same. Is the block cracked out on your 91?

And one other thing, if it were me I would probably get the heads and intake ported and polished while I was at it; and again, this will probably mean that you'll have to get the computer programmed to take full advantage of this. Then put all the bolt ons (TB, MAF, intake, exhaust, headers) on your truck and it will pull 190+ hp on the crank. That's pretty good for a normally-aspirated 4.0 OHV. With 4.10s, Explorer Sport 2wd 5 speed, 29-30 inch tires and 190-200 hp you'll be sitting pretty strong there.

 

[N2FORD]

I am running 4.10's with 33x12.5 BFG mudders. I do not know if my block is good or not. It is still running but it backfires some under a strain, has rocker/valve type noise and main bearing type noise when it gets warmed up. I was planning on getting a core from a junkyard and building it. Does anyone know what heads will interchange without problems? I was planning on trying to get a chip done when I get it built. Thanks for your input.

 

[tweakedlogic]

try doing a major tune up. sensors, plug wires, plugs, timing, airfilter, pcv valve, disable your egr valve. see if that helps.
I am starting the same project for the same reasons though. I just want as much power as possible from the 4.0.
I have heard that there is a stroker kit out for the 4.0. look into that. don't get the pacesetter headers, they are trash. There might still be aluminum heads available, not sure. MSD is really good, helps mileage too.
One thing I am looking into seriously is Extrude hone on the intake manifold and slightly larger injectors. with the tb and maf and cam

 

[Brain]

http://www.therangerstation.com/tech_library/40rebuild.htm
Hope this helps.

 

[MustangShane]

I'm right there with ya n2Ford. I like the power I have just a little more would help. I've been toying with the idea of going 302 with a manual trans. instead of buying a stang in the spring. I just dont know if it'll be worth it. With all the wiring and getting this little part and that little hard to find part. So I've considered redoing the upper half and getting a programmed chip. It sounds the most reasonable to me. Plus I have an extra block sitting around I can toy with if need be, so little down time.

 

[N2FORD]

Thanks for the link, that is almost mind overload. I will refer to that often as I try this build. Thanks to all that have replied. I was looking at some other info and headers seem to be not worth it. They will make you lose some bottom end, that defeats what I want. I want low and mid range. That is some thing that could be done later.

 

[tweakedlogic]

use the exhaust manifolds form a second gen or later. they flow much better than a first gen

 

[N2FORD]

So how late model can I go on the engine I get? If I used a later model (95-2000) what problems would I have. I realize I may have to change exhaust and intake. What about sensors and wiring?

 

[Brain]

The '91 doesn't have EGR and only has one O2 sensor, so if you go with a later model you would have to get the computer to go with it. I think they started using the EGR valves/sensors on the '93, but you'd have to check on that (I know my '91 and '92 don't have them).