Inliners International Forums General Discussion Engines chevy 250 and iron duke swap

Was thinking of swaping my 250 inline in my 1980 truck with a 151 iron duke. I get 18 to 19 mpg now will swaping get me 1/3 mor mpg or 25-26 mpg. It's a fullsize chevy pickup. will my 3 speed transmission mount to the 151 engine? What doIneed to do with motor mounts?

If the 151 is out of a rwd car or S10 it should bolt up to your bell housing. You will need to fabricate motor mounts and use one heck of a fan extension, move the radiator back or go to an electric fan

I really doubt you will see improved mileage as the poor little 151 will be working its tail off moving the mass of a full sized truck, especially with a three speed.

I'm not sure you are going to be happy with the improvement overall. The 4 cyl will be working a lot more and the truck will feel that much heavier, probably without gaining that much in mileage. If you want to improve mileage think seriously about getting rid of the 3 speed. a 4 speed auto with overdrive or better yet a manual with over drive will make all the difference. Same driving experience, but better mileage.

I have to agree with Greg, the iron duke is going to have its tounge hanging out to move the truck. Perhaps a better approach is to install an overdrive transmission, also replacing the mono-jet carb with something else will help a lot. A TBI system off of a 4.3 V6 will do wonders for fuel economy with the OD trans. Also a better exhaust system will help.

The guys are telling you right. A small engine working itself to death will get worse mileage than a larger one working within its' power and torque range. But just in case it works out I have an extra .049 cu in model airplane engine to stick in one of my rides. ( joking of course )