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Generation III Internal Engine
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Old 07-26-2011, 07:16 PM   #1
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Default highest compression on pump gas

Ok so what's the safest highest compression ratio you can run on pump gas?
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Old 07-26-2011, 07:25 PM   #2
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Quote:
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Ok so what's the safest highest compression ratio you can run on pump gas?
12.1 max on 93, and good 93 like exxon, sunoco, shell, mobile.......stuff like that. no like "budget" gas like wawa or sheetz....not sure if you have those where your from but in pa we do.

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Old 07-26-2011, 07:27 PM   #3
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I'm in va so we have all those except wawa but I was thinking upper 11. So u think it would be safe?
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Old 07-26-2011, 07:35 PM   #4
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11.25:1 if the engine is actually worth a **** (making good VE). If not you could go higher.
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Old 07-26-2011, 07:41 PM   #5
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Well here's what's going on. I got a rod knocking so Im about to buy a rotating assembly and make it a 383 so that's why I'm wondering so what do you guys think is safe I will be getting forged everything lol
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Old 07-26-2011, 07:51 PM   #6
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[quote=703 CAMAROSS;15199558]Well here's what's going on. I got a rod knocking so Im about to buy a rotating assembly and make it a 383 so that's why I'm wondering so what do you guys think is safe I will be getting forged everything lol[/QUOTE

play it safe go with 11-11.5....that extra .5 compressions goona do what, 10-15hp?
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Old 07-26-2011, 08:05 PM   #7
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Well my goal was 500-550whp NA
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Old 07-26-2011, 09:01 PM   #8
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I'm at 11:5:1 on 91 octane. It's all in the tune man. To get that kind of power, you better be planning a serious upgrade in cubic inches. 500whp has been done with stock cube's, but it is expensive. Check out Pat G's 500whp recipe. Great thread with killer info. Good luck!
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Old 07-26-2011, 09:21 PM   #9
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Why does everyone keep neglecting elevation?
You can run a full ratio more in Denver than you can in Death Valley.
There's also humidity, temperature, coolant temp, water / methanol injection, and octane boosters to consider.
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Old 07-26-2011, 09:35 PM   #10
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Quote:
Originally Posted by Isolde View Post
Why does everyone keep neglecting elevation?
You can run a full ratio more in Denver than you can in Death Valley.
There's also humidity, temperature, coolant temp, water / methanol injection, and octane boosters to consider.
Elevation is not the only variable not being discussed. Dynamic compression ratio is important which introduces the timing of valve events -i.e. the cam.
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Old 07-26-2011, 10:21 PM   #11
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Isolde is right. Even if you cam your 12:1 engine to run 91 octane at sea level, then that same car should be bumped to 13:1 if you move up in the high mountains. Ya gotta squeeze thinner air even more to get the same cranking compression.
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Old 07-26-2011, 10:31 PM   #12
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what is the best way to calculate dynamic compression. rather than just guessing a higher static the bigger the cam is?
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Old 07-27-2011, 01:34 AM   #13
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11:1:1 here
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Old 07-27-2011, 05:08 AM   #14
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You need to know you intake closing angle and you can use a dynamic compression calculator like Wallace racing calculators.

I'm running 12.56:1 compression and full timing on 92/93 octane pump gas because with an intake valve closing angle of 85 degrees abdc it gives me 8.25:1 dynamic compression with my 255/266 cam
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Old 07-27-2011, 05:51 AM   #15
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Wow there is allot to think about. I live about 2 hours away from tuned by frost so I will probably end up going there for a tune. So dynamic compression depends on your cam and what makes static compression?
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Old 07-27-2011, 06:16 AM   #16
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http://www.empirenet.com/pkelley2/DynamicCR.html
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Old 07-27-2011, 06:21 AM   #17
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Static compression is just your total volume difference of the cylinder and chamber at bottom dead center and top dead center. But dynamic compression adds the cam into the equation....you can't start building pressure til both intake and exhaust valves are closed
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Old 07-27-2011, 06:45 AM   #18
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It's all starting to make since now. Maybe Il just buy dynomation 5 and build my engine on the computer before I buy all the parts. I could still buy my rotating assembly because I could just change the cc on the heads if needed to raise or lower compression. So maybe Il do that. Anyone else have experience with dynomation 5?
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Old 07-27-2011, 06:52 AM   #19
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11.8 to 1 on a LS1 400ci stock block. Forged crank, rods, and mahle pistons. The bottle loves the compression. I would call up on of the sponsors and talk to them. That is what I did I am super satisfied with my out come. 93 pump gas
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Old 07-27-2011, 07:16 AM   #20
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It is more relative to your DCR than SCR. Choice of plugs, quench...etc, ya know all the little details
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Old 07-27-2011, 07:16 AM
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