Info on 425 motor and 400 transmission

fleethood · #1 (**permalink**) 01-31-07, 01:23 AM

Hey guys Im new to the forums. I wanted to get feedback and info on the 425 motor and 400 transmission. There is this 1983 Fleetwood Im really interested in and the guy sas that he put in a 425 motor and 400 transmission. I never heard of the engines so I wanted to know some basic info and your input on this engine and tranny, thanks!

davesdeville · #2 (**permalink**) 01-31-07, 05:37 AM

The 425 combo is more powerful stock, has way more power potential, and is more reliable by a wide margin than the original 4.1 motor. The TH400 is the transmission used in 5200lb cars that make well over 400ft.lbs., it's pretty bulletproof. The downside of the swap is poorer fuel economy.

fleethood · #3 (**permalink**) 01-31-07, 01:20 PM

What do you mean by poorer fuel economy?

thanks for the info davesdeville. any more info would be appreciated guys, thanks!

eldorado99 · #4 (**permalink**) 01-31-07, 04:05 PM

He means that the 425 with a TH400 tranny will use more gas because the engine is larger than the stock 4.1 litre, and because a TH-400 is a 3 speed and doesn't have overdrive. I suspect the usage of the 425 with TH400 would be a somewhat minimal drop in mileage (Though definitely noticeable) compared to the amount of power and reliability you would gain by having the 425 in there.