Thread: Convert 350 heads to fit 305 engine?

Tweet

Will 350 stock head bolt onto a 305 stock engine without any modifications? If not, how much work would be involved to make it fit? Thanks

The heads will physically bolt onto the block with no mods.
There are at least 2 potential problems though. First, the chambers on the 350 heads are larger than the 305 chambers, so with all else being equal, you'll lower the static compression ratio considerably. Also, the ports in the 350 heads are larger than the 305 heads, so at low rpm's, you may have insufficient vacuum to facilitate good cylinder filling. Secondly, the 305 cylinder bore is 3.736" as compared with 4.000" for the 350 bore, so the valves will be severely shrouded, preventing a good "kernel" formation coming past the valves and resulting in insufficient cylinder filling. If the 350 heads have large valves, it may also be possible to crash a valve into the block deck with a fairly high lift cam. maybe not likely, but possible.

I would only do this if I were absolutely flat broke and needed to get a motor running to have a ride to work. I'd mount the bare block up on an engine stand and mount a head on with a couple of bolts. Then I'd swing the motor around with the main caps up so I could see down the bore and look at the valves. I'd have a buddy push down on the valve stems with a block of wood while I eyeballed the valve/deck interface with a flashlight to check for interference. If all the valves cleared, I'd screw the thing together and run it until I could do better.

Txchevy,
I agree with Techinspector mostly. He mentioned compression ratio and that is the biggest prob. Most 350 heads have have a 70+ cc chamber volume while 305 have about 55 cc chamber. I don't know if the motor will even crank with that much of drop. 305'd had about 8.25 to 1 or so c.r. and you would end up with around 6.0 to 1. The other problem he mentioned is valves. The 350 valves have a different angle to cylinder and even if they clear the top of the bore, they may hit cylinder wall. If the problem is $, you would have better luck haveing the 350 valves put in 305 heads (if they are not to big). Other wise World Products make an excellent 305 replacement head that with a cam, intake and headers wakes up the 305. Just my two cents worth.