91 Firebird 305 Replacement (Page 2/2) rogergarrison MAR 23, 12:00 PM Same thing with Mopar LX platforms. My Magnum with 5.7 Hemi got 8 more mpg than a friends identical Magnum with a 3.5. V6 imabuzzkill MAR 24, 07:58 AM If you swap in another 305, it has to have the correct TBI heads (the center 4 bolts are at a different angle) (I didn't read everyone's responses so if it was said ignore me.....) If you build a motor, I recommend doing a 334 (stroked 305). Good power increase and if you keep it sane, you won't have to change to much as far as ECM wise. I have had good luck with 305's in the past and got great MPG's out of my carbed 84 TA. Good luck Erik JUN 08, 12:00 PM I have a 92 RSconvertible and it has a 350 in it from a 1970s pick up. Someone mentioned the four center bolt holes being out a different angle and that is correct what you do is you ream out the 4 center holes on the intake manifold to the correct angle. That will let the bolts grab onto the threaded holes on the head Then get beveled washers so that the bolt can grab it correctly. You'll also have to get slightly longer bolts too. That is a great idea using the truck computer and injectors although I am running the stock 305 injectors and computer it runs really good and it doesn't lean out or getting any KR. I did have to bump up toa R45TS spark plug though. Also you have to get an adapter to get the coolant fan switch to thread into the earlier head. 305 and 350s are internally balanced have the same crankshaft a 3.48 inch stroke. Lou6t4gto AUG 14, 07:45 PM what will "BOLT IN" as a" Direct swap" in place of a 305,(minus the throttle body manifold that will bolt right on off the old engine). The "List" starts in 1955 ! 265, 262, 283, 305, 307 327, 350, or sb400. ( also "stroker" 377, 383,406, 427SB) Probably the worst of all of them was the 305 and sb400. FFIEROFRED AUG 30, 10:34 AM Early was internal. For sbc's the 350 is the gold standered. the 305 is the weak little brother. Never mind the HP ratings. You very rarly need to rev it to red line. The 350 makes for a much better driving car because it has so much more low speed power. With the 350 you don't have to put your foot so far in to the pedal to make it move.