Hey, i have a 350 (bored to 355) sbc from the yrs 77-84 and a 305 sbc HO motor from 80-84.

i cant really drop a grand right now for new heads so my question is can i use the 305 HO heads on the 355 until i can get new ones?

 

Yes you can. I've had a ride in a car equipped that very way and it went along quite well. HO heads...good, regular 305 heads...bad.

 

sweet, thanks

 

Just to be sure, the 601 castings are the HO heads. Also keep in mind that the HO heads have a smaller combustion chamber, 58cc I believe it is. Don't know what your heads are, but you're most likely going to be bumping your c.r. a bit. Make sure it isn't going to be too high to run on pump gas.

 

OK thanks, i'll check it out to make sure.

im sorry if i sound stupid lol, but what is "bumping the c.r."?

 

Compression Ratio.If it gets to high,you want be able to run pump gas.It will start knocking and pinging

 

well i definitely want to run pump gas, what all do i check for and how can i make sure i will be able to just run pump gas?

thanks

joe

 

You need to get the casting number off your current heads, then you/we can look up their cc. Then we can calculate what difference the HO heads would make. As an example, let's say you have 74 cc heads (fairly likely from the vintage they are). If your current compression ratio is 9:1, then the 58cc HO heads will give you a c.r. of 10.8:1. Determining accurate c.r. requires knowing the engines deck height, head gasket compressed thickness, head gasket bore diameter, and type of head (flat, recessed, domed). There are a lot of unknowns to be able to tell you what you have, and you can't know all of that unless you stripped down the engine. But, you can see the difference the smaller chamber size of the HO heads can make, regardless of what the other factors are.

 

well this is what i can tell you for now (until i take the #'s off of the 305) but the heads off of the 350 are #'s 462624, 76cc and the block #'s on the 305 are 14010203. dont know if that helps any? i will get the #'s off the 305 heads tomorrow.

thanks for all your time it is very appreciated

joe

 

It doesn't matter what the specs of the 305 engine are since you're putting the heads on your 355, that's where the variables are. I used "best guess" numbers for the head gasket and block deck specs to get a baseline of 9:1 c.r, which for a 355 should be somewhat realistic unless it was built differently. Based on that, my estimates (rate of change) would be pretty much what I came up with. Once your engine is apart, you can do some measuring and calculations, and if needed you can go with a thicker head gasket to lower your c.r. Changing gasket thickness also changes your "quench" area (do a Google search if you're interested in what that's about). But you don't need to get super **** since the HO heads are only temporary. All that can be determined once your engine gets opened up.