350 swap with a 305??????


Senior Member
Had the top end rebuilt this past March in my 305 TBI in my 87 Silverado. Didn't know you should rebuild the bottom end too, until now. Rods are a knockin', & have heard schools of thought from both ends. Here is my dilemma.......
Was going to rip the 305 out & put a carb. 350 in it. Then the guy who's doing the rebuild suggested my earlier plans of putting a 350 block in it with my 305 top end on it, since it was fresh & I had already spent all that $$ on the top end. Now guys at the parts house are telling me you can't put centerbolt TBI 305 heads on a carb.'d 350 block. It'll up the compression (which is a bit of a plus), but they also said problems with dependability, head gaskets not matching, timing adjustment difficulty, detonation problems, etc etc etc. The donor motor is a 350 from a 76 Vette.
If I went with a totally carb'd engine, I'd have to bypass the computer (is it hard or easy?), pull the new sending unit out of the gas tank & put a carb style fuel pump on, etc etc etc.
I've already spent more than I wanted to on this motor & the TBI runs like a dog compared to my 84 with a 305 4bbl.
Any suggestions? Motor will be swapped at the end of this week. PLEASE HELP!!!!!!!


Junior Member
The 305 top half will work on a 350. However your compression will be way up. I don't know what the specs on the two motors you have are, but if the heads have the 58cc chambers your comp. could be too high to use pump gas. This will cause detonation and possibly make it difficult to time. You will want to use 350 head gaskets to match 350 bore. You could also use dished pistons in the 350 to get a usable comp. ratio.


PlowSite.com Veteran
check your local hot rod shops they will be able to help a little i would swap in the whole thing cleaner to oil pan will all fit,to power up the electric pump a place like summit racing may be able to help

of course on the other hand you could rebuild the bottom for a lot cheaper and quicker turnaround than the other swap in my humble opinion


Senior Member
Talked to a few more guys today, & figured out a plan.
Easiest thing is an entire engine swap, & with my situation I need a TBI motor/block put back in.
Called around & found a '95 350 with TBI & 55k miles for $950, & NO core charge (I get to keep my 305 with new top end). Guy will install it for about $350 plus any add'l. parts. So this is the route I'm planning on taking. Thanks for your info!
Not so fast! Just a couple things to check to make your transfer a nice one. Make sure the motor your getting comes with the harmonic balancer (and timing cover).The 350 balancer is larger in diameter, and is balanced slighty different. Next make sure if its an automatic that your flexplate is the same diameter as the 305. Some 305 came with a smaller flexplate and used a different nose on the starter.


PlowSite.com Veteran
just a little info...

As far as SBC harmonic balancers are concerned, There are ONLY 3.
1)6.75" (small diameter)
2)8" (large diameter)
3)the 400ci motors -externally balanced.

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