305 or 350

11-05-2006, 07:56 PM
Can someone tell me how you can tell the difference between a 305 and a 350 just by looking at it, or are they the same size block?

11-06-2006, 02:32 AM
Best bet is to use the casting number off the block. See http://www.mortec.com/castnum.htm


11-06-2006, 09:37 AM
yeah the only difference that might be there is the different bores. the 305 and the 350 use the same stroke crank (correct me if im wrong) and just use a smaller bore for the 305, i think its 3.7something or 3.8something, while a stock 350 is 4inch bore

11-06-2006, 02:55 PM
same stroke yes

there isno way to tell from the outsidebetween a 305 and 350, it is impossible, and no you cant tell by the harmonic dampner size contrary to popular myth, 305 used the same wide 7.25" one as alot of 350 engines did

86 was some changes though, but not any that could help determine a 305 from a 350 still

run stamping suffix letter code off front pad of block under alternator, or the casting codes off back top ledge of bellhousing to find out what it is


nastyz28.com for suffix stamping codes
mortec.com for block casting numbers

87 and up the liter size is cast on the bellhousing ledge too

11-06-2006, 05:35 PM
Any 350 previous to '87 is internally balanced and all 305s were externally balanced. If it's still got the flexplate on it look for weights, if it has any it's a 305 and also if there is a notch out of the inside of the harmonic dampener it's a 305, if it's smooth all the way around, it's a 350. Easiest way is to check the casting number on the rear of the driv. side of the block,(behind the head, in front of the bellhousing and check them against the last 3 (or sometimes 2) alphas on the pass. front of the block just below the head. As earlier posts suggest.

11-07-2006, 05:00 AM
How do these motors compare in power. I need a truck to tow about 6500 pounds including the trailer. Could I get by with the 305?

11-07-2006, 02:43 PM
well, if you dont need to go very fast, probably, but i would think if you were towing regularly, that you would need at least a 350 if not a 400 or a big block

11-07-2006, 02:45 PM
the worst 305 power output in the 80's was i think about 115 horsepower, while the worst 350 (probably wrong on this one) was about 160 or 180? you can easily hop up a 350 to over 400 horses though and a 305 likely is capable of 300 or so without a lot of cash. just dont loose all the torque down low with too big a cam the wrong type of intake. definately use a dual plane intake for towing or street use and long tube headers will help a little bit too

11-07-2006, 02:53 PM
Post-'85 blocks (blocks with one-piece rear seal) will typically have "5.0G" or "5.7G" cast on the upper left bellhousing flange. All one-piece blocks are externally balanced and all two-piece blocks are internally balanced. This goes for the 305 as well. The only SBC engine that was externally balanced from the start is the 400.

11-07-2006, 03:31 PM
My bad on the flywheel weight method. No wonder I keep thowing away 305s.

11-07-2006, 08:56 PM
nah, i would only tow with it once in a blue moon.

anyway I picked up a 99 Silverado LS today. 146K with towing package and lots of extras for only $4400. It has some minor body damage to the bed, but other than that the deal was too good to pass up. If it doesn't suit my needs I am sure I can sell it for more than what I paid for it.

11-08-2006, 06:00 PM
well, all the engines in those are more powerful than an 80's version of the 305, so youll be fine for any towing up to a certain point

Add your comment to this topic!