Bronco II 2.9 to 4.0

Rustbucket350 · Jun 17, 2016

I'm getting ready to pick up an engine to rebuild or refresh for when my 2.9 eventually gives out. I know the OHV 4.0 is basically a direct swap but what about the SOHC? I'd rather have the extra power if it'll fit under the hood. I have the TK5 manual trans which I'm confident will hold an OHV but maybe not the SOHC. Right now though, I'm mainly concerned with whether or not the SOHC will physically fit since they're all over the place and I can pick one that doesn't need a whole lot of work. I don't drive it hard so I'm not worried about the 7.5 axle.

adsm08 · Jun 17, 2016

I am working on a SOHC swap right now. I am doing this on a vehicle that I am building from the ground up, and I have a running OHV to throw in if it doesn't work. There are several issues that I know of at this moment.

1) The SOHC was predominantly a returnless fuel system. You pretty much need the fuel rail from a 97 Explorer to make it return style. I believe the returnless fuel system could be done by replacing the current FG-800-A fuel filter with an FG-1036 and modifying the return line in front of the filter.

2) A cam sensor that will work with the SOHC engine and an EEV-IV computer doesn't exist. SnoRanger had a piece custom milled that he thought might work, but never got a chance to try it before blowing his transmission up and deciding to put a 4BT in. I plan to get around this by using early stuff that will be batch-fire, thus eliminating the need for a cam sensor at all. This also means a custom built injector harness.

3) The SOHC engine is wide. If you have AC you might have clearance issues to the valve cover.

4) The SOHC mounting brackets don't work with TTB mounts. They are too wide for the cross member and the hole spacing is wrong for the mounts. I am hoping to overcome this by just bolting the OHV brackets tot he SOHC block.

5) You will need to run 89 octane to keep the SOHC from knocking with an EEC-IV computer.

Rustbucket350 · Jun 17, 2016

That does seem a bit more involved than I was hoping. The SOHC heads are huge compared to the OHV and it has a lot more sensors on it. This is my driver so it'll have to be an easier swap that I can do in under two weeks. I suppose I can pick up a regular OHV and do the best I can with it. I think a set of flat top pistons, some head work, one of the comp cams, and headers would make decent power. I wish I could find actual dyno numbers or somebody that has run a similar setup in the quarter to see if the expense is worth it. If it'll only gain 20 hp or so I'll just leave it stock and put the money in the gas tank.

adsm08 · Jun 17, 2016

Honestly I don't think the SOHC is going to be much more involved.

When I did my first 4.0 swap on my 87 I spent a week dropping the engine in and another month working on wires.

Rustbucket350 · Jul 6, 2016

Well I ended up scoring a low mileage OHV 4.0 for almost nothing. How does the 4.0 compare to the 2.9 as far as torque in the Bronco II? Its a pretty light vehicle so I'm hoping it'll be a noticeable improvement. I'm debating getting a set of headers but I'll leave the rest stock since the only two cams aren't very exciting for the money and the heads look like they'd need a lot of work to get a noticeable gain from a cam swap.

adsm08 · Jul 7, 2016

Headers aren't worth the headache IMO.

As far a power gains it is noticeable. I have trouble holding mine at 25 on the back roads.

Rustbucket350 · Jul 7, 2016

Well that sounds good to me. I'd really just like to be able to get on the highway without people honking at me to be honest. A V8 would have been my first choice but then I'd have to change the entire drivetrain.

AllanD · Jul 16, 2016

Frankly at the time I did my 4.0OHV swap back in the summer of '07
I physically had a pair of 4.0SOHC engines...

But I had little interest in fighting with a Returnless fuel system
or dealing with any of the other issues mentioned

Added to that the SOHC engines available at the time didn't have a great reputation
for reliability... not to mention a well deserved reputation for being piggy on fuel

Frankly if a 4.0OHV is ever "Not enough" I will go 5.0, and then I will also deal
with whatever is needed to either adapt EDIS-8 to EEC4 or bite the bullet and deal with EEC5

As for your question on torque in the 4.0OHV?

The 4.0OHV engine makes more torque before 1300rpm than the 2.9 makes EVER...

The only things the 2.9 does better is cruise at higher rpm, I've had a 2.9 at 3100rpm for several tanks of fuel
and it just didn't care... the other thing a 2.9 can do IF perfectly tuned is get good mileage...

In my 4.10 geared 2wd Supercab cruising in 5th in July/August weather westward bound across Pennsylvania on I-80 my 2.9 would consistently get 25-26mpg. with the AC on full blast and cruising at a consistant 70mpg

The best I've ever done with a 4.0 in the same truck (converted to 4x4) is 22.1mpg

rev your 4.0 above 2300rpm cruising speed and it will wolf fuel like an oil well fire...

Which is why I've wanted to re-gear my truck to 3.73's...

AD

adsm08 · Jul 16, 2016

AllanD said:
But I had little interest in fighting with a Returnless fuel system
or dealing with any of the other issues mentioned

I'm keeping it return type fuel system. 97 fuel rail is return.

Also, since the SOHC Rangers were mechanical returnless, meaning fuel returns from the filter instead of the engine, it should be fairly straight forward to make a MRFS setup on an older truck.

holyford86 · Jul 18, 2016

Another issue with them is the two piece pan, it won't clear the ttb crossmember without major trimming, a good workaround is to stick the ohv pan on the sohc, along with all the main bolts

Sent from my SM-G900P using Tapatalk

AllanD · Jul 19, 2016

The one other issue I had at the time was the unavailability (to me) of an 8-bolt flywheel to match the 97-1/2 4.0 crankshafts.

I did not acquire my first 8-bolt flywheel until the late summer of 2012.

I removed it from a Ranger with a 4.0SOHC engine that was in the junkyard...

One where the timing chain for the drivers side head had sawn it's way out through the head to "Daylight"...taking pieces out of both the head and the timing cover on the way...

I'm still not thrilled with the idea of owning an engine that can self-destruct itself that way

As I've said, for me when a 4.0 proves to be "not enough" I'll build a Ranger with a 5.0.

I'm not sure I really want to fight with EEC5, but I'm sure I can make EDIS8 work with EEC4.

AD

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AllanD · Jul 19, 2016

The one issue with switching to the "one-piece" oil pan is that the upper half of the two piece oil-pan is in fact the main bearing cap "stud girdle"

Worse your donor motor MAY include a balance-shaft assembly
located there as well.

AD

Bronco II 2.9 to 4.0

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