I have access to some '92 4.9 heads and was wondering how they would work on my stock '89 4.5 deville motor? Would it be good for some more power and how would effect drivability?

You do NOT want to do that.


The intake ports are very different. The 89 4.5 had cylinder heads with very high swirl ports that worked well with the TBI. Changing to the 4.9 heads would get a little more flow...but loose much of the swirl resulting in poor driveablity. The spark advance requirements are totally different between the 4.9 port fuel injection system heads and the 89 TBI heads. Since changing that would require a custom reprogramming of the PCM you really cannot compensate adequately for the change. Besides, there will be precious little difference in performance between the two different heads on your engine so it would not be worth the change even if you could reprogram the PCM and correct for the mismatch in parts.

Thank You bbob - I figured you would be the one to provide info! I didn't realize the impact on the spark advance just changing the heads would create. The engine provides tons of torque as is but the quest for more power is addicting.