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97 4.0ohv in place of 93 4.0ohv...aren't       #: 1481
 Moderated by: Mike69, MaDMaXX,
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 Posted: Sat Jan 19th, 2019 11:37 pm
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Joined: Sat Oct 27th, 2018
Location: Olympia WashingtonUSA
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Name: Vincent Henning
Occupation: Retired USAF MSgt & Retired Aircraft Maintenance Technician
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Hey all,

I just did a lot of major work on my 93 Ranger 4.0 4x4 XLT 5 speed.

I took the rattling valve train original 93 4.0 OHV motor out and swapped a low mile 97 4.0 OHV in its place.

I used my aluminum upper intake, the 97 lower intake, new 8 bolt flywheel, my 93 harness, 93 computer, blocked off EGR port on left exhaust manifold.

It fired right up and runs great but I notice some detonation pinging under light load when going around some corners in 3rd gear, or other situations, easing into the throttle....but I can usually get it right out of it right away.

The pinging is easy enough to get out of, but I know my wife certainly wont notice this trait when she drives it.

This got me wondering if the compression ratio was different between the years?

Turns out they're not, but they did have different shaped heads and dished piston combos over the years.

When I was reading about compression ratios, I came across this article:

It states under the rebuilding paragraph:

Rebuilders should not install an engine with the 95TM heads and deep-dish pistons in a ’95 or ’96 Aerostar. All of these engines had the same compression ratio whether they came with the original heads with the open chambers or the newer ones with the heart-shaped chambers, so they would seem to be interchangeable, but the computer calibration that was used for the old-style heads with the open chambers will not work with the newer heads with the fast-burn chambers. In fact, "It will burn the engine down in a few thousand miles," according to a Ford engineer who worked on this engine program. Ford continued to use the early heads on the ’95 and ‘96 Aerostar because they still came with the early calibration, so rebuilders must do the same.

Am I reading that correctly...that my 93 computer is going to have a different timing curve that will not accommodate the newer combustion chamber shape??

If that's the case perhaps I've made a major blunder??!

I really don't want to yank all that back out to throw an older 4.0 back in it!!

1993 Ford Ranger XLT Supercab
4.0 OHV V6 4x4
Converted it to 5 Speed and Manual Transfer Case!
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