95-97 head swap on a 92?

[twoll86]

so from wat ive read on the tech page and searched it looks like you could swap the heads from the 95-97 to a earlier 4.0. my ? is is it possible or would the valves hit the pistons. im asking cause it looks like a cheep way 2 up the compression and get more hp. any one now 4 sure or what needs 2 be done?

 

[twoll86]

anyone know?

 

[Yellowsplash]

Yes, Its possible and should raise your compression to around 10:1...the problem is that when raising compression, your engine is much more prone to knock/detonation. While this can be tuned around, your vehicle is OBD I and is much harder to tune. You cant use a programmer like OBD II, but actually have to get a chip that plugs into the back of the ecu much like a jet chip would. What makes it even worse is its very hard to get a mail order tune that works correctly without some dyno time. If you do go this route, you might want to get ahold of doug at bamachips. Hes the man when it comes to tuning rbvs.

 

[twoll86]

sweet thanks for the info

 

[AllanD]

I made a post in this subject but it appears to be GONE
(or was that an identical discussion?)

The main difference in the later heads is that the combustion chamber shape
to generate more swirl.

the later (95up) engines had a larger dish in the piston to compensate.

 

[Bird]

It's an 'easy' way to pick up 15+ rwhp, but, as said, spark knock can rear it's ugly head - running premium fuel (in higher elevations you can get away with 89 octane) is one method of reducing spark knock - most other methods involve reducing timing which negates the hp gain from the compression increase and some additional fueling at WOT which increases the $ per hp costs..

Another thing to watch out for is the increased risk of pre-ignition due to hot spots forming on the edges of the combustion chamber under the higher compression / combustion pressures - easily alleviated with some minor chamber cleanup.

Bird

 

[dzk007]

Allan, that was my pm you were responding to.

I'm about to replace the motor in the '91 exploder I just bought and I'm hoping to figure out which parts too go with. I'm curious as to wether the '95+ ports will line up with my engines original manifolds. Would there be any other bolt up issues with accessory items?

I live at higher altitude (5500 ft) so spark ping isn't as much of a problem here.... but I would do a good job cleaning up the chambers anyway.

 

[AllanD]

If I were personally moving to a mountain state to live I'd put the '95 heads on my 93 engine.

But as I told you in the PM, "porting" is most beneficial to an engine that revs.
the 4.0OHV CAN'T rev (dynamic balance issues)

If you were to build a completely custom engine around an engine with
an 8-bolt crank you can make it rev, but that becomes a purely custom proposition because the factory ppistons for the "lightweight" rotating assembly were semi-famous for skirt slap.

I think it best to use a stock '93-94 short block, preferably on 1993 engine
management. Not a 1994, or a Cali '93, IMO SEFI is overrated because of
the propensity for the synchronizers to fail in service.

It has been my longstanding position that parts you don't install cannot
break and leave you stuck alongside the road.

THE thing to do to "wake up" a 4.0OHV is put a set of Borla
or JBA headers on it.

Granted my first experience with my ranger at high altitude was when
I had JUST installed my 4.0 engine and TOWED my ranger to wyoming
(it was my "Lifeboat" and my trip home) with ~100 miles on the new
engine install.

My ranger literally aquired 1900 of it's first 2000miles bolted to the
back of an F-250 via a towbar.

and even though I had a full load of fuel (this has special meaning on my truck)
onboard and I was at high altitude even climbing the hill getting onto I-25 North
out of casper heading towards Barr Nunn, there was no mistaking that this truck
was faster than it had ever been with a 2.9 and my only basis of comparison
was running that 2.9 at the ~500-1000ft elevation at home.
How strong the 4.0 is really became noticeable climbing up to the overlook
just on the north side of casper mountain on the road up to the Hogodon
ski slopes. Climbing that hill and going from 6000-10,000 ft with a full collection
of spare parts and ~600lb of fuel and the A/C running full blast in the 106degree
heat was eye opening.

the 2.9 has to be spun to 2200-2400 before you start to feel it get into
the torque.

a 3.0 feels "worthless and weak" to most people because they really never
go looking up at 2900-3400rpm where it is found and it isn't real distinct
when you find it.

The 4.0OHV is torque RIGHT F'IN NOW! from 1250rpm on up.

Anything a 4.0 powered truck won't do is probably due to gears that
are too tall.

Dave on your Explorer I have one thing to add: 3.73 gears.

Your '91 explorer probably has 3.27's or 3.55's, change them out.

And Dave, while I did reply to your PM's I posted in this topic before
I had about a dozen replies vanish and I had to repost some of them.

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