Your dynamic compression ratio is really what's important.
pump gas vs. compression
Thread Starter
Intermediate
Joined: Jun 2007
Posts: 29
Likes: 0
From: Crawford County MO
pump gas vs. compression
Looking for input on building a 383 with 10.4 compression vs. a 415 with 9.0 compression. My main concern is running pump gas with the 383. I've used the "search" but wasn't able to find what I'm looking for. Any input or opinions would be appreciated.
Burning Brakes
Joined: May 2007
Posts: 945
Likes: 0
From: Ventura California
I run slightly over 10/1 compression ration on mine. Here in California I can only get 91 octane from the pumps. Mine is REALLY sensitive to timing. I have to run mine with the timing backed off a bit to prevent the "rattles". We have crappy gas in California though due to all the smog stuff. I'm using an iron head though and I understand that an aluminum head will tolerate a bit more. If I were to build the engine again, given what I know now, I would knock the compression down a half a point. Another poster inquired on your cam choice. This does have a lot to due with this issue!
Race Director
Joined: Dec 1999
Posts: 19,610
Likes: 778
From: Forked River NJ
I am running a 385 with 10.4 to 1 compression. Running decent high grade fuel I don't have a problem. I am running a big solid cam which helps some. Notice I did say DECENT fuel. I have run some premium that is real crap.
Race Director
Joined: Jun 2000
Posts: 10,051
Likes: 677
From: FL
Do a google on Dynamic Compression Ratio.
Static Compression Ratio is good for nothing but bragging rights. You can (and need to) run more static compression with a big cam. Remember, the mixture will not compress till the cylinder is air tight. Than means the valves have to be closed.
Like most things in life, (valve) timing is everything.
Static Compression Ratio is good for nothing but bragging rights. You can (and need to) run more static compression with a big cam. Remember, the mixture will not compress till the cylinder is air tight. Than means the valves have to be closed.
Like most things in life, (valve) timing is everything.
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