We need more horsepower for chevy 305....I was told that you can get the 305 Vortec heads to add the HP however I can't get the straight answer on the casting numbers for these heads. I was told they are for 96 and up chevy trucks and would have around 55 cc's. If anyone knows the casting numbers for the 305 that would be great....I have also been told that you can get 305 vortec marine heads and I can't get any info on these but am interested and would welcome any numbers or a contact to purchase these.

I have had mechanic offer the 350 heads with the end casting numbers 520 but the cc's are in the 60's and I need the lesser cc's. I welcome info on these as well

i thought the only made vortec 350's

And maybe that is the case. When you search head casting numbers some list the 520 as a 350 and some list the 520 as the 305. We are getting mixed information. I'm thinking that 305 vortecs are 97 (corrected from early posting) trucks and up...This info comes off of the web. If 350 is all they make. Questions can you take 350 vortec heads and put 194 intake valves and 150 exhaust valves with a 55 cc's combustion chamber?

12552520 & 12558059 are '97-up Vortec 305 heads. I don't know what the combustion chamber looks like or how big it is, but I suspect they're smaller, since the 350 Vortec heads have chambers that are right at 4" wide, and would leave a serious ledge on a 305. Might try rousting up Berliner Bel Air if you can. I believe he used some on a 283 a couple of years ago.

hi jim, your memory is very good! I did use those 305 Vortec heads on my 283, I think they're 58 cc. They worked great! CR is about 9.1:1 on the 283, a little on the low side. I'm looking to mill the heads down a little to increase it some. The nice thing is that these heads flow so well at low lift that the motor gives good power all the way up to 6000 rpm or so with the tiny 240H comp cam I use, even though Comp Cam says the rpm range is only up to 4600. My car is just as fast as my buddy's 350 powered 57 Bel Air. But the feel is totally different, his has torque way down low whereas my power comes in much later.

not quite what you are looking for, but this article may be of some interest.

http://www.chevyhiperformance.com/t...ngine_build_ii/

Well, according to the book "Small-block Chevy Performance" by Dave Emanuel, Vortec heads were intorduced for both 305 and 350 engines on the 1996 model year of trucks. If you have a copy of the book, refer to page 49.

Maybe this will help someone...