305 heads vs. 350 heads

[bobboinge]

I have a '94 blazer w/ a 350 that needs the heads done over. A friend of mine has a set of just rebuilt 305 heads. Will the 305 heads fit and perform well on my 350?

[rlith]

They won't even fit on your 350 and the manifolds won't match up

[bobboinge]

Thanks for the info... I was curious...

[BlazerLT]

I have heard of people installing 305 head on a 350 for more compression.

I would look into it more, some 305 heads will indeed install properly.

You need to know the chamber size on the 305 heads and the piston type in the 350. If you have a flat top 350 and the small 57cc chamber 305 heads you will have detonation for days! Your compression would be near 11:1 and that is way too much for pump gas on the street.

Using dished pistons and 64cc chambers will yeild around 9.5-9.7:1 compression. 305 heads typicaly come with either 1.71 or 1.84" intake valves and 1.50" exhaust valves. More than likely your 350 heads have 1.94" intakes and 1.50" exhaust. Also the intake ports on most 305 heads are a tiny 141cc's and most 350 heads are 155 or larger intake runners.

To make a successful 305 head 350 you need to install 1.94 intake valves in a 64cc chambered head and port the heads paying close attention to the short side radius and the bowl throat area.

Your goal of 300-350 HP is easily obtainable with stock 350 heads with the same port work and thinner compressed thickness head gaskets and/or having the heads cut about .020"

This with a mild cam with less than 225 degrees of duration @ .050 should yeild in the 320HP range with good depenabilaty and fair but noticable idle.

[bobboinge]

thanks for the info...think I'll just have the 350 heads done over...had a deal going but it won't work. thanks again!!!