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Re: Engine Swap from 325 Poly to 354 HEMI in 58 Dodge

From: Tim
Remote Name:
Date: January 15, 2004


I just finished putting a 392 into my 57 desoto firesweep this past summer. The firsweep is basically a dodge under the desoto sheet metal. It has the same 325 motor and mounts, frame, etc. I have heard that the 354/392 will bolt in with original 325 mounts. My mounts were shot anyway, and i wanted something a little beefier to hold down the bigger motor. I used the mounts from hot heads and had to have some channel iron of 3/16 thickness cut, and i welded it in so the motor would have a flat perch on each mount to bolt to. I know it sounds complicated, but it was farily simple once everything was planned out. The motor itself was a tight fit. I used an AAJ brake kit and the new dual mastercylinder did not clear the valve cover, so i was forced to keep the original smaller master cylinder with my disk brakes, which by the way seems to work great anyway. The motor will bolt to the trans you have, but you might need to get the proper trans spacer that bolts to the hemi motor, although i seem to remeber that my 325 trans plate did fit the 392. Either way, trans plates aren't hard to get, and i might have an extra. i used the stock exhaust manifolds for the hemi motor wich are small and fit no problem. The clearance of the fan to the radiator is close but should work. It took me a while to figure out the proper pulley combination and spacing, and i still dont have it perfect, but my motor didn't come with the original hemi pulleys and so i had to use the ones off the 325 and what i could find lying in the attic. I had to eliminate any spacers that moved the fan pulley closer toward the radiator in order to make it fit. You might have to play with the drivline alignment also. I had to move the motor and trans about 1/2 inch toward the pass side to make it all fit and line up and just barely clear the little master cylinder. It's not a terribley difficult project but it will take a lot of time and planning to do it properly. I can tell you that it would be a lot easier and cheaper to rebuild your 325, or convert it to a hemi if you can find the proper heads. I don't know what you have planned for the car or how you intend to use it. My oninion is, unless you really want/need the extra power, you should keep your 325. Personally, i wanted the car to move a little quicker, and i was pleased witht he results. It had been running 17's in the quarter with the stock 325 and a holley 2-barrel, and the stock 392 got it into the high 14's with the stock TF, open rear, etc. Email if you want more info or some pics. I live in the philadelphia area in NJ if you want to come see how i did it. Hope this helped you out in some way. -Tim


Last changed: July 19, 2018