The 89s and up recieved extensive head work and a less restrictive exhaust NormAllante North * said:Hello DeVillish,
It appears that the difference in the two 4.5 engines is in the crank and pistons/rods. The Allante had Port Fuel Injection and earlier model 4.5's had throttle bodies. Which does yours have? Some of the earlier Allante's may have had different heads than the other 4.5's, but I may be wrong on that as I remember reading something on the Allantenet site about it. You may want to try the Allantenet.org site and do a search to see if you can find more information on the 4.5 engines.