Compression and Octane
#2573134
11/02/18 06:06 PM
11/02/18 06:06 PM
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Joined: Mar 2005
Posts: 1,550 Michigan
Kiddart
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OP
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Dumb question but I am putting together a 2004 5.7L with stock heads and I want to know what is the highest Compression I can go and still maintain using 93/94 octane gas. I want to stay away from the 110 octane due to it being $7.99 per gallon.
help and I am grateful for all answers. I am back to learning all over again.
Last edited by Kid-Dart; 11/02/18 06:07 PM.
Thank you Kiddart
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Re: Compression and Octane
[Re: Kiddart]
#2573191
11/02/18 08:14 PM
11/02/18 08:14 PM
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Joined: Jan 2005
Posts: 12,419 Kalispell Mt.
HotRodDave
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Plastic intake still?
If yes then at least 11 to 1. The 6.4 is about there with 205 thermostat and a lean emissions friendly mix and you know they put a little room to spare in it. Probably be silly to go under 11.5, these things are very octane tolerant.
Aluminum intakes heat the air a bunch and will probably take 1 to 1/2 point less compression.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Compression and Octane
[Re: Kiddart]
#2573357
11/03/18 10:38 AM
11/03/18 10:38 AM
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Joined: Mar 2005
Posts: 1,550 Michigan
Kiddart
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Hi hotrod,
I will be using the new Prefix Cascar intake. So I feel 10.1 or 11.1 I can still run premium gas? that would be awesome. it does have the stock chamber head. I will plan on getting the compression up.
anyone else like to weigh in?
Last edited by Kid-Dart; 11/03/18 10:39 AM.
Thank you Kiddart
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Re: Compression and Octane
[Re: Kiddart]
#2573486
11/03/18 03:23 PM
11/03/18 03:23 PM
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Joined: Jan 2005
Posts: 12,419 Kalispell Mt.
HotRodDave
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On my engine build I would shoot for 11 to 1 then or maybe a hair less but not more. I would focus on things like a tight quench and getting as cool air to it as possible and with an ignition curve made for the modern hemi motor instead of a 1950s design wedge it should be fine.
I am not causing global warming, I am just trying to hold off a impending Ice Age!
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Re: Compression and Octane
[Re: HotRodDave]
#2579861
11/18/18 03:06 PM
11/18/18 03:06 PM
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Joined: May 2004
Posts: 12,384 Taxes & Virus's R-US, NY
Dragula
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12:1....And maybe a little more 12.4:1 or so. Tune up has to be right on though. Hemi's can tolerate a lot more compression than other engines. And with twin plugs per cylinder, the G3 is the best.
If I find a block for my heads, I am going 13:1 with the thinnest head gaskets I can get and go from there.
Last edited by Dragula; 11/18/18 03:07 PM.
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Re: Compression and Octane
[Re: Kiddart]
#2579962
11/18/18 08:50 PM
11/18/18 08:50 PM
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Joined: Feb 2003
Posts: 18,582 Rust Belt, SW PA
Silver70
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Lots of people put the eagle heads on the earlier engines and that puts them around 12 to 1. If using a stock ecu, just need a tune.
68 Road Runner, 69 Belvedere, 71 Challenger Vert 340 barracuda, 01 Ram CTD, 95 Ram, 04 Ram, 85 Daytona turbo Z 66 GTO, 06 Magnum RT AWD. 07 Ram CTD, 07 Ram
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Re: Compression and Octane
[Re: Kiddart]
#2580107
11/19/18 09:04 AM
11/19/18 09:04 AM
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Joined: Oct 2017
Posts: 80 Australia
aus370
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Cam selection has influence on what your dynamic compression ratio ends up at : that's what a smart guy told me ; anyway It's worth looking into.
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Re: Compression and Octane
[Re: Kiddart]
#2580110
11/19/18 09:48 AM
11/19/18 09:48 AM
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Joined: Jan 2006
Posts: 1,400 Trumbauersville PA
ric3xrt
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pro stock
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FWIW, the 428 in my 2014 Ram is 12.6 to 1 static with the Eagle head and I run a comp cams"270" Duration @ .050" Intake: 222 Duration @ .050" Exhaust: 230 Valve Lift Intake: 0.615 Valve Lift Exhaust: 0.609 Lobe Sep. Angle: 115
93oct......A good tune is a must ,
Truth has no agenda, but those with an agenda make their own truth. Some of us are so open minded they only see their View
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Re: Compression and Octane
[Re: Kiddart]
#2580133
11/19/18 11:41 AM
11/19/18 11:41 AM
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Joined: Mar 2005
Posts: 1,550 Michigan
Kiddart
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this is lots of good info here. right now I have no issue filling up with 93 octane. the price of that sure beats race fuel. I really don't want to go over 11 to 1 right now because I may boost later. at that point I will change the slugs(pistons) and get right back to 9 to 1 and use some boost. that's way down the road. for now I want miles on this car to pay for the investment.
Thank you Kiddart
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Re: Compression and Octane
[Re: Kiddart]
#2598265
12/29/18 07:22 AM
12/29/18 07:22 AM
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Joined: Jun 2003
Posts: 9,225 Charleston
sixpackgut
Drag Week Mod Champion
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Drag Week Mod Champion
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Charleston
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I think about this alot and with the low spark lead on timming i am wondering if its possible to run well into the 13s with some tight lobes
Gen 3 power 6.22@110, 9.85@135 Follow @g3hemiswap on instagram
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Re: Compression and Octane
[Re: sixpackgut]
#2598315
12/29/18 12:02 PM
12/29/18 12:02 PM
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Joined: Jan 2006
Posts: 1,400 Trumbauersville PA
ric3xrt
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I think about this alot and with the low spark lead on timming i am wondering if its possible to run well into the 13s with some tight lobes I think it's possible.
Truth has no agenda, but those with an agenda make their own truth. Some of us are so open minded they only see their View
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