I've been trying to wrap my head around horsepower upgrades in a 455 smog engine. What is it about the smogger engines that contributes to the low horsepower output? Is it the heads/intake/compression combo? Or is the bare engine block purposely designed to produce low output? For example: If I get a bare 1970 455 block and build it from scratch with all performance parts (10:1 compression), and if I get a bare 1975 455 block and build it from scratch with the exact same performance parts (10:1 compression), Will both engines produce the same HP/TQ? If not, can you please explain why not? I would really appreciate if someone can enlighten me on this. Thank you!
Yes the same output will be seen, the difference in the smog stuff is large chamber heads and lower compression, carb jetting and timing curves were also changed that gave the lower hp output compared to the 70
Awesome, thank you so much! I was worried about buying a smogger 455, thinking I wouldn't be able to build it for high horsepower. I was killing myself to find a 1970 455. Now I can finally put my mind at ease lol.
Sorry, but it's not a clear Apples to Apples case when we are dealing with a 1970 head at 69 CCs and a 1975 head at 78CCs! The piston dome needed to get the 75 head to a 10 to 1 compression would effect the burn rate, this in turn means the Distributor timing for max power between the 2 motors will not be the same , and even the Carb jetting may need to be tweeked!
If you want to build 450 HP or more, start with good heads. The better your heads flow, the smaller the cam needs to be to achieve your goals. Save up and get a set of aluminum heads. With the entry level porting, 10:1 compression, and a cam with 230* of intake duration, you’ll make 500 easy. It doesn’t matter what year the block is if you are building it up. The 75-76 heads are open chamber and useless if you want HP.
Don't forget that the OEM's changed the way they derive dyno and correction numbers. 2 engines could have the exact same output and because of the smog years's SAE correction changes, be rated much lower.
Just in case you want to go into more detail... http://www.v8buick.com/index.php?threads/what-year-big-block-buick-to-build.120037/
I don't mean to single out the post with any negativity, but to help with the OP's question... The ability to choose various pistons and know about the castings is important to the entire process of the build. As far as emissions are concerned , there's not much different about the basic castings that can't be overcome with an intelligent plan including replacement parts selection. If talking about a mild/medium performance build, I'm sure what you have is just fine. There aren't any horrible ones making them completely impossible to work with. As mentioned, the cam specs and tuning is most of the difference, and that there aren't 150hp losses back to back like the printed ratings would suggest. They are simply rated differently.
One big factor to keep in mind with even a mild performance motor of under 10 to 1 comp is how much more there power output is tied in to having a good flowing Exh system to keep pumping losses as low as possible.
