Join Date: Sep 2005
Location: Geismar, LA, USA
Re: Help converting 1992 lx from 4cyl to 8 cyl
I actually recently picked up a 1986 GT myself, but mine has T-tops and was free!
The EFI system is the same from 1986-1988; it's called Speed Density and uses O2, water temp, air intake temp, manifold absolute pressure, and throttle position sensors to determine how much fuel is sprayed. However, in 1989 they switched to MAF (commonly known as mass air), which added a sensor to read the amount of air going into the engine to more appropriately determine how much fuel to spray. If you're leaving it mostly stock, don't bother with the MAF conversion. In fact, I know a guy first-hand who has a 500rwhp Mustang running on SD (speed density). It's not hard to manage a SD-based system.
The primary difference with the 1986 motor is the heads, upper intake, cam, and throttlebody. They're also flat top pistons, so you can't do most aftermarket cams or heads. However, you could switch to the E7TE heads, which are on the 1987-1993 HO motors.
Some cheap upgrades you can do:
Swap for a 1987+ throttlebody. The '86 is a 55mm, while the later models utilized a 60mm. You can even go with a 5.0 Explorer throttlebody- they're 65mm, but you'll need to swap the throttle lever from your stock unit to the Explorer piece. I know several guys who give away stock TBs and the Explorer pieces can be had for $50, max, on eBay.
Swap for a 1987+ upper intake. The later designs simply flow better. Avoid the 1994/5 models, because they had a neck that angled the throttlebody toward the front of the car and they're hard to deal with on the older models. I got my upper for free. Just gotta know who to call.
Swap for a 1987+ ECU. Slightly better fuel curves. Not that big of a deal. Local junk yard sells 'em for ~$20.
However, I know of people who pull 30mpg out of their stock '86 motors. The designs are so efficient that they get decent power and great mileage. Drive it around for a while before you really think about upgrading things.
Hope this helps- good luck!