Taking out the 400, putting a 318?

[elanmars]

Would a sane man do this? How much of an improvement in gas mileage would it be? I wouldn't be selling the 400, it's just that lately the Charger has become my daily driver while my other has started to have issues here and there. And I really don't need that much power since I don't race it and I'm more of a cruiser.

So I'm curious if it's something I should do or not, need to hear from the experts! How big of a job is it and how much would something like that cost to pay someone to do? Would the transmission need adjusting? Anything else?

[Ghoste]

You would need a different transmission ( one with a smallblock bolt pattern) for starters.  It could be done quite easily but for me personally, I think I would first see if I could supertune the 400 for efficiency.  I'm not sure the difference in mileage would be enough to warrant changing to a smaller engine for me but everyone has a different opinion on something like this and yours is the only right one for you.

[RallyeMike]

Would a sane man do this?

No.

[acelondon]

i get about 10mpg in the city, and 20mpg on the highway with a 318 2bbl, no mods, 727 auto.

and i am not nice to my gas pedal. i make it work hard. 

now, if only my busted unrebuilt motor could do a burn out....

[chargerbr549]

Sometimes 400's can do pretty decent for fuel economy, for a while I had a stock 77 400 with TQ carb  that came out a royal monaco that  I put in my 69 Charger R/T auto, with 323 gears and 225 70R 14 tires and I could get 17-18 MPG consistantly on the highway around 60mph. Later on I rebuilt the original 440 and kept the TQ carb and I was getting 15 MPG and then later put on a 750 Holley and it dropped down to 12 MPG but throttle response and power definately improved. Some other things to consider is to put in a tall gear ratio around 2.76's and put in a lock-up converter tranny and a good dual exhaust system.

Kevin

[Steve P.]

There are many things to consider here. Mileage is not everything. It will be costly to change everything to small block. Motor, tranny, exhaust, mounts, drive shaft, tuning and wiring.

If you are driving very many miles it may be worth the change in the long run. With the price of gas today it may not take years to pay you back. On the other hand I have seen some good running 318" motors that get lousy mileage.  Some pretty good.  If you are very good at tuning you can get pretty good mileage from either motor. Most cases it depends on tuning and your style of driving. Also you have to think about worth of original VS. motor change when it comes time to sell the car if that happens.