Too high a rearend gear and too little power. It takes big power to redline a Mustang in 5th gear. easily twice that of a stock engine if that little. I'd guess about 135-140 mph where your tach was in 4th. when the 89 was stock, it would register 140 topped out. Didn't matter if you were in 4th or 5th.
4th was pegged and fifth wouldn't pull any higher. FYI, Car Craft (in 1988) took a stock (albeit a factory "selected") 89 GT and ran it 147 mph on top.
__________________
1986 four-eyed LX coupe, 358 Cleveland, Tremec TKO600/centerforce clutch, dish cut Probe forged pistons, comp cams hyd.roller cam, .579/.588@224/230, Edel.performer, 670 holley street avenger, CPR custom built long tubes, ported and polished 4bbl heads, manley valves, beehive springs, MSD peo-billet dist/MSD6AL, fluidamper, 5 lug conv. with 17x8 bullits there's more but it's still not finished yet.
Oh, and the oldest boy is turning his 89 GT into a FFR cobra this next summer.
|