[Cannon13]

I have a 79 that started life with a 301, then had a 400 installed. I just finished my first ever attempt at a build - a 455 bored 60 over, summit 2802 cam, Torker 2 intake, Holley Street Avenger 770 (maybe too small?),6X-4 heads, summit long tube headers with purple hornies bolted straight to the end of the headers.

Thanks to books by Jim Hand and Rocky Rotella, a few calls to Butler performance and some youtube videos, once I got it dropped in it actually started right up.

My neighbors want me to rethink the exhaust.

Keep in mind I am a rookie, so be gentle if the question is a dumb one.

I am curious as to what my compression ratio might be. According to what I have read, it appears that standard 6X-4 heads bolted to a 455 will produce over 9:1 compression. These appear to have been cut down, because I had to get the intake cut down the equivalent of the intake manifold gaskets to bolt it on. My understanding is that this combined with the over bore will increase the compression ratio.

Any input/thoughts/advice appreciated.

 

[Terriblehondo]

Sounds like the compression will be high for iron heads. Someone like Ponyaker can probably tell you for sure. I don't know if he looks at the 2nd gen forum. If you put it in the General Engine section you will get all the expert engine guys who can let you know.

 

[Cannon13]

Thanks for the reply, hope I can squeak by with what I have. I'll post to the engine section. Forum rookie too...

 

[gdf 73]

I have 6x-4 heads on my 455. No problems running 93 octane pump gas.

 

[Terriblehondo]

I have 6x-4 heads on my 455. No problems running 93 octane pump gas.

He said his have been milled were yours also? If your heads were milled also I guess he would be good.

 

[gdf 73]

My block was zero decked(pistons flush with top of block). Both intakes I've run had to be cut to fit. He should be fine. Running 6x-4 heads on a 455 is fairly common.

 

[Terriblehondo]

My block was zero decked(pistons flush with top of block). Both intakes I've run had to be cut to fit. He should be fine. Running 6x-4 heads on a 455 is fairly common.

OK if it works it works. But what compression does that end up being? I have been out of Pontiacs for a long time. But from what I have read since coming back the -4 heads would be around 9.5 on a 455. If the engine is decked or the heads milled and having it bored out wouldn't that raise the compression even more? I also read that 9.5 to 1 is the tops for pump gas with iron heads. I was thinking of running 16's on my 400 but was told that it would be to much compression around 10 to 1. Not trying to be a jerk to you just looking for as much information as I can get. You are running 11 seconds and that is something I never did.

 

[tjs]

Again,you need to verify the CCs on the 16s and if the 400 has a over bore,deck height etc.There is really no guessing when you start to push the limit on iron heads.One person might be able to do very close tuning and get away with it where others cant and maybe drive in high heat areas or get a bad tank of gas etc,etc.Cam selection make a diff also.I did a 9.5 455 once that pumped 200 and we had to run race gas as the customer wanted too small of cam.Tom