Tech Area

4 to 6/86 to 88

Question: I found a used Fiero v6 with 90,000 miles on it on eBay. I won the auction with $200.00 before I learned that the engine came out of a 1986 Fiero, but I want to replace the ailing 4-banger in my '88 Fiero with it, and the guys at the shop are excited to do the work.

I want to mount the motor using typical '88 Formula design instead of the '86 way. I've NEVER seen the mounts in the '88, and I don't know what I need to eliminate the driveline mini-shock absorber thingy. Do you have time to describe the difference so I can get the right mounting hardware? Got pictures depicting the typical installation or mounts? Can you direct me to a website displaying such pictures??

Also, I want to use a '88 Formula ECM, instead of the original '86 ECM. Do you have an 88 formula ECM on hand? Do you have a backlit '88 Formula instrument cluster handy? How much would/will you charge for these components? I know the motor is coming with the original dogbone, and the driveline absorber appears to be attached in the photos from EBay. How difficult is the mount reconfiguration?

Why am I doing it this way (e.g., piecemeal)? Mostly lack-of-funds; it's cheaper to rebuild the car in fits and starts based on my payday income. I'm considering having the garage mount the V6 and recradle it to the chassis, then I'll have the car towed home where I can add cooling system modifications, upgrade the fuel pump, install the ECM and throttle cable myself. Then I'll have the car towed to PepBoys for the exhaust system install in a few paydays. But I've got to get this going, because I'm tired of driving my adequate but clunky old VW Passat to work.

Answer: The correct '88 parts may cost more then the engine!! There are quite a few differences. Front V6 engine mounting bracket is scarce.....$70. Front mount expensive new....used is $25. Lower a/c compressor bracket is $15. Then to be correct, different exhaust crossover pipe....$90, and EGR pipe...$90, different oil pressure sensor which requires different engine wiring harness ...$275. Timing cover and oil pan are also different. $140. Engraved pleneum is $75. However, the crossover/w tin heat shields, EGR pipe, oil sensor/wiring harness, timing cover and pan, and pleneum can be used from the '86 engine.

Don't forget you also need the V6 air cleaner assembly and "S" intake tube, molded heat hose to thermostat housing, and forward and rear vacuum lines in addition to the throttle cable. Then you will have to really squeeze the brake booster rubber line to the smaller size of the '86 vacuum tube (unless you find the engraved pleneum with that tube). You will have to cut off about the last 3-4" of drs side coolant tube to use a stock V6 hose, and remove and plug the waterpump nipple for the heater hose that is not on the '88's.. '86 ECM/chip is actually better by 5 hp then '88. Complete Formula instrument and aux gauge pack is $150, but you really only need an '85 V6 tach. We don't have or know where pictures may be. Sorry. May have forgotten something, but this is most of what needs to be changed/added/removed.

Actually '85-86 timing covers and oil pans are the same and '87-88's are the same. Cannot be mismatched, but will interchange as a set.

We don't know about online, but expect that must folks would not know this stuff, or care, unless in a similar situation as you. Another difference that we forgot. 1988's used a smaller size alternator (fits same bracket as '85-87) without a heat shield on the back. The '88 used a heat shield attached to the exhaust manifold.

BTW, the '87-88 oil pan is several gauges of metal thinner then '85-86 (consequently rust through from the outside in salty environments), and their 1 piece rubber gasket is about 5 times more expensive (but seals better then the cork of the '85-86). Sorta "damned if you do, damned if you don't".

Only '87-88 engines came with engraved plenums, but they have been added to many '85-86 decaled engines. You may have an '87-88 engine, but most folks won't go to the trouble of changing timing covers and oil pans. '87-88 had the bottom of the timing cover on a flat plane even with the bottom of the block. Oil pan was also completely flat. That combo uses a 1 piece rubber gasket. '85-86 timing cover slanted approx 45 degrees down and away from the edge of the block and so does the pan. This combo uses 2 side and 1 front cork gaskets and RTV at the rear. 1988's used a foil wrapped crossover that was shorter toward the convertor down pipe by 3-4" as the '85-87. Requires a matching (also scarce) down pipe to keep exhaust even under the car. It also mounts the EGR valve at a different angle so that a longer EGR valve pipe is necessary.

You can use the '88 4 cyl auto, but performance will be a bit sluggish (2.84 final drive ratio). You will have to change the kickdown cable to that of a V6. Only change necessary, but it would be wise to use '85-86 trans mounts/brackets (1 front, 1 rear) instead of the single one in the center. Holes are already in the engine cradle.

Updated/Additional info:
V6 fuel pump, a complete ready to start/running V6 engine w/correct (to your car, auto or manual trans) wiring harness, V6 alternator, V6 a/c compressor, V6 dogbone, V6 flywheel/flexplate, water crossover pipe, V6 ECM + it's plastic holding tray (holder does not apply to 85-86 4 cyl), complete V6 air filter assembly, V6 throttle cable, and V6 engine compartment hoses/lines. V6 trunk bulkhead vacuum lines and front bulkhead EGR solenoid metal line are needed and should be added when engine is out. VERY few parts interchange between the 4 cyl and V6 engines, so make sure the engine is complete and ready to start/run. We would be happy to purchase the 87-88 4 cyl throttle cables and ECM holding trays, or to swap those for V6 parts.

Changing spark plugs and water pump at this time would also be a good idea. Water pump MUST have a cast iron impeller (vanes seen only from the side).

Concerning installation:

You will have a problem with the exhaust and front engine mounting. Both systems are made differently on 88's and 87 parts will NOT fit the 88 engine cradle nor vice/versa. Inspect/replace, if cracked, the V6 forward manifold.....NOW.

The cross car (pass side to drs side) brake line across the trunk bulkhead is different between 4 cy and V6 cars, but will not interfere with the V6 installation and should not have a heat problem due to close proximity to the V6 exhaust manifold. However, if "spongyness" in brakes is observed after long periods of driving, replace this line with a V6 one.

Would suggest having a 2" extension welded to the "foot" (going toward front of car) of the 87 mounting bracket.Then, redrilling the holes in the modified bracket AND the engine cradle mount tray to accept a solid 87 engine mount instead of trying to use the viscous filled 88 mount. This will save finding an 88 V6 mounting bracket/mount and a/c compressor adjusting bracket. There will NOT be a V6 engine shock mount bracket (or a place to put it) on the 88 cradle.....don't worry about that....it is not really needed. Discard the shock but leave the engine side shock bracket in place. None of this is appropriate to 85-87 cars. 88 V6 engines going into earlier cars must use the earlier mount bracket and will not have the engine side shock mount bracket (again, don't worry about having a shock), just remove the 88 engine mount bracket and use one from an 85-87 V6.

Drs side 4 cyl coolant tube will need to be shortened 3-4" in the engine compartment and hose double clamped. Attaching the heater outlet hose will require adding a nipple to the V6 water pump (87-88 V6's have a pipe plug) and you will have to cut off the "quick disconnect" of the 87-88 4 cyl heater outlet hose to extend the hose to the nipple.

A competent muffler shop should be able to make a down pipe between the V6 exhaust crossover pipe and your catalytic converter. You will need to cut the 4 cyl head pipe just above the drs side springs to make room for the engine. If dual outlet exhaust is wanted, remember that only an 88 exhaust system (including muffler) will fit under the 88 engine cradle. The V6 should not be too loud to drive there. 85-87 cars can use a complete V6 exhaust system from one of those years. If it is an 88 engine, an 85-87 exhaust crossover pipe is necessary to avoid cutting/welding.

If your car is a manual trans, there will be interference between the shifting cables and the V6 air inlet ("S") tube. Simply twisting the "S" tube should allow clearance. If running a shifting cable across the V6 throttle valve body, make sure the cable does not interfere with the throttle action. The 4 cyl clutch assembly can be used, but a 6 cyl clutch (with 4 cyl release bearing) would be better. Water crossover pipes' lower bracket will not work, but hose (remember to double clamp) will hold it in place as long as upper bracket is attached.

Radiator should be OK in your locale, but may need changing to V6 if car is moved to warmer climates.

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