What compression can one get away with on pump gas? June 18, 2013, 01:51:44 AM I have been wondering how much compression is too much to daily drive? My 400 sbc going into the s10 is sitting just over 11 to 1. The Big thumpr cam should bring the compression down slightly, but it'll still sit around 11 to 1. I have a set of Iron race heads. A thicker head gasket will still have the compression sitting a little high. I don't really wanna go dish pistons cause then it'll go way down, but 76cc heads would do the trick, but I just had these heads ported, polished, rebuilt and drilled steam holes into em. Does anyone have experiences in this situation. Quote Selected
What compression can one get away with on pump gas? Reply #1 – June 18, 2013, 05:23:32 AM Static compression is just a number actual sweep compression is what determines the Fuel requirements. Another words what the engine sees in sweep compression normally determines fuel requirements. Example the midnighter has a static CR of 8.6-1 and i run 26 LBS OF BOOST, But the cam is quite large. So i can use 93 R+M with no detonation. When i build engines i incorporate the cam that will be used to determine the compression i build in the motor. Cam selection is the key. Also is the cam advanced retarded how much spark advance ETC. But a basick answer in my view is around 10-1 static on 93 R+M. There are some engines running close to 12-1 on pump gas but you will need a lot of cam bleed off to accomplish this. I have an engine on the street right now running close to 12-1 on pump gas . Also you did not mention the octane of the pump you want to use and the elevation of the state you live in. I used 93 because it is readily available in my state. Quote Selected
What compression can one get away with on pump gas? Reply #2 – June 18, 2013, 04:02:24 PM Aww... The days of old 8.0 compression and lots of boost!Travis Quote Selected
What compression can one get away with on pump gas? Reply #3 – June 18, 2013, 04:52:15 PM Plenty of guys in my oldsmobile club running rocket 350/455 motors on 10.25 to 10.50 compression on regular pump gas. Many of them use 89. Quote Selected
What compression can one get away with on pump gas? Reply #4 – June 18, 2013, 05:55:38 PM I'm sure this is not an every day street car, use octane booste? Even at 11-1 93 should handle it. Quote Selected
What compression can one get away with on pump gas? Reply #5 – June 18, 2013, 07:33:41 PM I think with 68cc heads and flat top pistons the 400 sbc is closer to 12-1, but I am not sure, depends on how much the block is decked I guess.I am probably gonna go aluminum heads with 76cc chambers and thicker head gasket if possible. I'd like to get away with 89 octane. 91 octane is about tops you can find here unless you go 100miles south for 94 at Chevron. That is why I am loosing interest in my turbo cars, tired of shiznitty gas and low boost. Quote Selected
What compression can one get away with on pump gas? Reply #6 – June 18, 2013, 07:50:56 PM NO not really with a 400 and flat tops and 68 CC heads you are around 10-1. You can do the math and find out the actual number. You are no where near 12-1 Static Quote Selected
What compression can one get away with on pump gas? Reply #7 – June 18, 2013, 07:54:06 PM Just a question why cant you not get higher octane fuels. Running 89 you better start lowering that static ratio and check it totally accurately. You have flat tops so you can run an open chamber head and a thick gasket. With a 78CC head and forty thousand head gasket you are closer to app 9 -1 Static CR. Quote Selected
What compression can one get away with on pump gas? Reply #8 – June 18, 2013, 09:04:13 PM If you have compression and not much choice for octane set your timing to suit......I run 12.5s on 91 with 104 in my 289. Quote Selected
What compression can one get away with on pump gas? Reply #9 – June 18, 2013, 09:20:06 PM There's like 1 gas station in town and 1 cardlock for gas. 91 octane is the highest available. 89 octane is what is at the cardlock and that is what I use. I have tried stockpiling drums of 94 octane, but the hassle is not worth it for me, even tried running avgas (lots of float planes here), but that's too pricey. I live in a town with 1000 people and the nearest town is miles away. Thanks for that info Tom, I will see if I can calculate the exact compression right now.... Quote Selected
What compression can one get away with on pump gas? Reply #10 – June 18, 2013, 09:25:40 PM I got 11.93 to 1 4.155 bore (30thou over)3.75 stroke4.158 head gasket.021 compressed head gasket thickness68 cc chambered head.016 thou below deck clearance Quote Selected
What compression can one get away with on pump gas? Reply #11 – June 18, 2013, 09:27:49 PM 10.89 to 1 compression with 78cc heads. Quote Selected
What compression can one get away with on pump gas? Reply #12 – June 18, 2013, 09:28:27 PM Here's a link to calculate compressionhttp://www.csgnetwork.com/compcalc.html Quote Selected
What compression can one get away with on pump gas? Reply #13 – June 18, 2013, 10:15:53 PM You can calculate to your hearts content.... but it's not real world Quote Selected
What compression can one get away with on pump gas? Reply #14 – June 18, 2013, 10:53:05 PM I realize that there's a difference between static and dynamic compression. I am not sure what the dynamic compression (real world compression) would be versus the static compression (or calculated compression); I am not clear with the subject that is why I started the thread. I am also not sure how much compression a lumpy street cam bleeds off or the difference a thicker head gasket makes. Also when people are stating what compression ratios are good for what octane, is that the calculated compression or real world compression?? Quote Selected
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Topic: What compression can one get away with on pump gas? (Read 2698 times)
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